accelerometer tech.information

Technical InformationTechnical Information

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PCB 716-684-0001 Vibration Division toll-free 888-684-0013 FAX 716-685-3886 E-mail [email protected] Website www.pcb.com

Typical applications for accelerometers

Introduction to accelerometers

Accelerometers sensing systems

Accelerometer mounting considerations

Driving long cable lengths

TEDS - Transducer Electronic Data Sheet

Conversions, article reprints, glossary

Information to assist with vibration analysis is readily available.Many technical papers have been published and may be found bysearching for specific topics on the worldwide web. Informationpertinent to SVS accelerometers and their operation is offeredwithin this catalog section. Additional information may beobtained through the following:

Professional OrganizationsIEST (Institute of Environmental Sciences and Technology)940 E. Northwest Hwy, Mount Prospect, IL 60056ph: (847) 255-1561 • fax: (847) 255-1699www.iest.org

SEM (Society for Experimental Mechanics, Inc.)7 School St., Bethel, CT 06801ph: (203) 790-6373 • fax: (203) 790-4472www.sem.org

SAVIAC (Shock and Vibration Information Analysis Center)3190 Fairview Park Dr., 8th Floor, Falls Church, VA 22042ph: (703) 289-5134 • fax: (703) 289-5801www.saviac.xservices.com

Vibration Institute6262 South Kingery Hwy., Ste. 212Willowbrook, IL 60514ph: (630) 654-2254 • fax: (630) 654-2271

Trade MagazinesSound and Vibration27101 E. Oviatt Rd., Bay Village, OH 44140ph: (440) 835-0101 • fax: (440) 835-9303

Sensors174 Concord St., Peterborough, NH 03458ph: (603) 924-9631 • fax: (603) 924-2076

VibrationsA Publication of the Vibration Institute(see Professional Organizations above)

P/PM TechnologyP.O. Box 2770, Minden, NV 89423ph: (702) 267-3970 • fax: (702) 267-3941

Test Engineering & Management3756 Grand Ave., Ste. 205, Oakland, CA 94610ph: (510) 839-0909 • fax: (510) 839-2950

Noise & Vibration WorldwideMulti-Science Publishing Co. Ltd.5 Wates Way, Brentwood, Essex CM15 9TBUnited Kingdomph: 44 (0) 1277 224632 • fax: 44 (0) 1277 223453

PublicationsMechanical Vibrations: Theory and ApplicationsFrancis Sing Tse, Ivan E. Morse, Rolland Theodore HinkleAllyn and BaconISBN 0-205-05940-6

Shock & Vibration HandbookCyril M. HarrisMcGraw-Hill, Inc.ISBN 0-07-026801-0

Vibration Testing: Theory and PracticeKenneth G. McConnellJohn Wiley & Sons Inc.ISBN 0-471-30435-2

On-Linewww.vibrationworld.com

PCB PIEZOTRONICS, INC. ☎ 716-684-0001

Typical Applications for AccelerometersTypical Applications for Accelerometers

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TYPICAL APPLICATIONS FOR ACCELEROMETERS

If something moves, it experiences acceleration.Measurement of this acceleration helps us gain a higherunderstanding of the nature of the motion, understandingthat increases our awareness of an event or encouragesrefinement of the engineering design of a moving device. Fora manmade object, motion is regarded as either desirable orundesirable. Desirable motion, for example, is the monitoringof performance of a controlled process, such as the action ofan intake valve on an automobile engine. Two situationsdemonstrating motion that is undesirable are the monitoringof a process undergoing an upset, such as the excessivevibration caused by a worn motor bearing, or a process inneed of control, such as the motion stabilization of asophisticated optical instrument platform. Someapplications in which PCB’s accelerometers havedemonstrated to be successful include:

Machinery Vibration Analysis — Increased vibrationlevels, detected by periodically monitoring rotatingmachinery vibration, are an indication of bearing or gearwear, imbalance, or broken mounts. Machinery like motors,pumps, compressors, turbines, paper machine rolls, andfans, engaged in critical processes, are routinely monitoredto predict failure, intelligently schedule maintenance, reducedowntime, and avoid catastrophic interruption of productionruns. Such programs have successfully proven to increaseproduction and save money by minimizing downtime.

Balancing — Performance and longevity of rotatingmachinery is improved when rotors, turbines, and shafts areproperly balanced. Measurement signals generated byaccelerometers implemented into balancing machineryprovide indication of the severity of any imbalance. Thismeasurement, in conjunction with a timing signal providedby a tachometer or key phasor, allows for propercounterweight sizing and placement to bring machinery intoacceptable balance.

Environmental Stress Screening — Latent defects, suchas inadequate solder bonds of a printed circuit board orinadequately tightened fasteners, often appear in the handsof an end user after a product is transported or subjected toits service environment. Many such defects can bediscovered by intentionally inducing vibration stress to the

product before final release. Test specimens are mounted toa vibrating shaker and instrumented with accelerometers toflag abnormal response characteristics. Such practices helpreduce the number of faulty goods reaching end users,improving customer satisfaction, the manufacturer’sreputation for quality, and the costs associated withproviding warranty repairs. Often, temperature, humidity, orother simulated conditions are combined with vibration tobetter simulate the environment in which a product is used.

Vibration Control — Desired vibration, such as thatinduced for the purpose of environmental stress screening,must be precisely controlled. Accelerometers sensegenerated vibration at the driving point of a vibration exciteror shaker. This sensor’s measurement signal is then fed intoa vibration controller, which adjusts the input parametersthat drive the shaker. This is known as a closed-loopfeedback control system and is not unlike the cruise controlfeature of an automobile.

Active Vibration Reduction — To enhance user comfortlevels of sound and motion generated by such items ashousehold appliances, aircraft, and machinery, designers arenow considering the use of active electronic techniqueswhere passive methods, such as isolation, insulation, anddamping have become insufficient or impractical.Accelerometers are used to sense the disturbing vibrationinduced, structure-borne sound, or motion. Themeasurement signal is then manipulated, typically withdigital signal processing, into one of opposing phase for usein driving an actuator or shaker to null the annoyingvibration. This closed-loop control method proves useful inapplications like helicopters, marine hulls, dishwashers, andaircraft fuselages.

Structural Testing — Accelerometers measure stimulusresponse and structural resonance characteristics of a widevariety of mechanical devices, from small computer disk drivecomponents to massive bridges, buildings, and civilstructures. Such measurements allow designers to optimizeproduct performance and life cycle by selecting constructionmaterials with proper strength and stiffness characteristics.Vibration measurements can also provide an indication ofstress, fatigue, damage, or defective assembly due to looseor missing fasteners, welds or joints on finished goods, oritems undergoing maintenance assessment.

VIBRATION DIVISION TOLL-FREE ☎ 888-684-0013

Typical Applications for AccelerometersTypical Applications for Accelerometers

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Modal Analysis — Accelerometers measure relative phaseand amplitude of structural motion, allowing operatingdeflection shape determination, which offers a virtual studyof the animated mode shapes. This computerizedrepresentation enables designers to optimize performanceand user comfort for such items as automobiles, aircraft, andsatellites.

Seismic Vibration — Accelerometers detect motion of theground, buildings, floors, foundations, bridges, and othercivil structures for purposes of earthquake detection,geological exploration, condition assessment monitoring,and impact surveys of nearby activities such as mining,construction, or heavy vehicle transportation.

Package Testing — Measuring the shock experienced by apackaged product compared to the level of actual shockexposure allows assessment of the effectiveness of a packingmaterial or package design. Package testing can also be usedto measure vibration and shock that a product mayexperience during transport.

Shock — Accelerometers measure the maximum impactacceleration levels experienced by such items as vehicles andcrash dummies. Metal-to-metal impacts, pyroshock studies,and shock exposure experienced by space vehicles and cargoduring liftoff and stage separation are also measured andanalyzed using shock accelerometers.

Motion and Attitude Detection and Stabilization —Accelerometers monitor motion and orientation of items thatrely on precise positioning for proper operation. Themeasurement signal can be used to warn of excessive motionduring upset conditions so that equipment is not operatedwhen inadequate performance is certain. Measurementsignals can also be used in a feedback-control-loop scenarioto perform active motion reduction to maintain levels withinacceptable limits. Apparatus requiring such attention tomotion includes sensitive optical instruments, satelliteantennas, lasers, surveillance cameras, and semiconductorfabrication equipment.

Ride Quality, Response, and Simulation — accelerometersplay a key role in vehicle design by measuring their responseto on- and off-road conditions. Suspension performance,chassis and frame evaluations, engine mount damping,drivetrain NVH, and rider comfort levels are among the manystudies conducted. Proving ground tests, dynamometers,electrodynamic shaker, and hydraulic motion simulators areall methods of providing input stimulus to vehicle structuresfor which accelerometers are used to measure the resultingvibration, shock, and motion of the vehicle and itscomponents.


Introduction to AccelerometersIntroduction to Accelerometers

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INTRODUCTION TOACCELEROMETERS

Accelerometers are sensing transducers that produce anelectrical output signal proportional to the accelerationaspect of motion, vibration, and shock. Someaccelerometers also measure the uniform accelerationaspect of earth’s gravitational effect. Most accelerometersgenerate an electrical output signal that is proportional to aninduced force. This force is proportional to acceleration,according to Newton’s law of motion, F=ma, where “F” is theinduced and subsequently measured force, “m” is the masscreating the force, and “a” is acceleration. Accelerationmeasurements are quite useful for a wide variety ofapplications due to this proportionality to force, one ofscience’s truly fundamental, physical measurementparameters.

Types of Accelerometers Offered by PCB

PCB designs and manufactures accelerometers that utilizeeither piezoelectric or capacitive sensing technology.Piezoelectric accelerometers rely on the self-generating,piezoelectric effect of either quartz crystals or ceramicmaterials to produce an electrical output signal proportionalto acceleration. Many such accelerometers contain built-insignal conditioning circuitry and are known as voltage mode,low-impedance, Integrated Electronic Piezoelectric (IEPE) orIntegrated Circuit - Piezoelectric (PCB’s trademarked name,“ICP®”) sensors. Piezoelectric accelerometers that do notcontain any additional circuitry are known as charge mode orhigh-impedance sensors. Piezoelectric accelerometers arecapable of measuring very fast acceleration transients suchas those encountered with machinery vibration and high-frequency shock measurements. Although they can respondto slow, low-frequency phenomenon, such as the vibration ofa bridge, piezoelectric accelerometers cannot measure trulyuniform acceleration, also known as static or DCacceleration. Capacitive accelerometers sense a change inelectrical capacitance, with respect to acceleration, to varythe output of an energized circuit. Capacitive accelerometersare capable of uniform acceleration measurements, such asthe gravitational effect of the earth. They can also respond tovarying acceleration events but with limitation to lowfrequencies of up to several hundred hertz.

Function of PiezoelectricAccelerometers

As stated above, piezoelectric accelerometers rely on theself-generating, piezoelectric effect of either quartz crystalsor ceramic materials to produce an electrical output signalproportional to acceleration. The piezoelectric effect is thatwhich causes a realignment and accumulation of positivelyand negatively charged electrical particles, or ions, at theopposed surfaces of a crystal lattice, when that latticeundergoes stress. The number of ions that accumulate isdirectly proportional to the amplitude of the imposed stressor force. The piezoelectric effect is depicted in the followingfigure of a quartz crystal lattice.

Piezoelectric Effect of a Quartz Crystal Lattice

In the creation an accelerometer, it is necessary that thestress imposed upon the piezoelectric material be the directresult of the device undergoing an acceleration. Toaccomplish this, a mass is attached to the crystal which,when accelerated, causes force to act upon the crystal. Themass, also known as a seismic mass, creates a force directlyproportional to acceleration according to Newton’s law ofmotion, F=ma. Thin metallic electrodes, typically made ofgold foil, serve to collect the accumulated ions. Small leadwires interconnect the electrodes to an electrical connectoror feed-through, to which signal transmission cabling isattached. Piezoelectric accelerometer signals generallyrequire conditioning before being connected to readout,recording, or analysis equipment. This signal conditioning iseither remotely located or built into the accelerometer.



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Piezoelectric Sensing Materials

Two categories of piezoelectric material predominantly usedin accelerometer designs are quartz and polycrystallineceramics. Quartz is a naturally occurring crystal; however, thequartz used in sensors today is produced by a process thatcreates material free from impurities. Ceramic materials, onthe other hand, are manmade. Different specific ingredientsyield ceramic materials that possess certain desired sensorproperties. Each material offers distinct benefits, andmaterial choice depends on the particular performancefeatures desired of the accelerometer.

Quartz

Quartz is widely known for its ability to perform accuratemeasurement tasks and contributes heavily in everydayapplications for time and frequency measurements, such aswrist watches, radios, computers, and home appliances.Accelerometers also benefit from several uniquecharacteristics of quartz. Since quartz is naturallypiezoelectric, it has no tendency to relax to an alternativestate and is considered the most stable of all piezoelectricmaterials. Quartz-based sensors, therefore, make consistent,repeatable measurements and continue to do so over longperiods of time. Also, quartz has no output occurring fromtemperature fluctuations, a formidable advantage whenplacing sensors in thermally active environments. Becausequartz has a low capacitance value, the voltage sensitivity isrelatively high compared to most ceramic materials, makingit ideal for use in voltage-amplified systems. Conversely, thecharge sensitivity of quartz is low, limiting its usefulness incharge-amplified systems, where low noise is an inherentfeature. The useful temperature range of quartz is limited toapproximately 600 °F (315 °C).

Ceramics

A wide variety of ceramic materials are used foraccelerometers, and which material to use depends on therequirements of the particular application. All ceramicmaterials are manmade and are forced to becomepiezoelectric by a polarization process. This process, knownas “poling,” exposes the material to a high-intensity electricalfield, which aligns the electric dipoles, causing the material tobecome piezoelectric. If ceramic is exposed to temperaturesexceeding its range or to electric fields approaching thepoling voltage, the piezoelectric properties may be drasticallyaltered or destroyed. Accumulation of high levels of staticcharge also can have this effect on the piezoelectric output.

Several classifications of ceramics exist. First, there are high-voltage-sensitivity ceramics used for accelerometers withbuilt-in, voltage-amplified circuits. There are high-charge-sensitivity ceramics used for charge mode sensors withtemperature ranges to 400 °F. (205 °C). This same type ofcrystal is used in accelerometers containing built-in, charge-amplified circuits to achieve high output signals and highresolution. Finally, there are high-temperature ceramics usedfor charge mode accelerometers with temperature ranges to600 °F (315 °C); these are useful for the monitoring of enginemanifolds and superheated turbines.

Structures for PiezoelectricAccelerometers

A variety of mechanical structures are available to performthe transduction principles required of a piezoelectricaccelerometer. These configurations are defined by thenature in which the inertial force of an accelerated mass actsupon the piezoelectric material. Such terms as compressionmode, flexural mode and shear mode describe the nature ofthe stress acting upon the piezoelectric material. Currentdesigns of PCB accelerometers utilize, almost exclusively, theshear mode of operation for their sensing elements.Therefore, the information provided herein is limited to thatpertaining to shear mode accelerometers.



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Shear Mode

Shear mode accelerometer designs feature sensing crystalsattached between a center post and a seismic mass. Acompression ring or stud applies a pre-load force to theelement assembly to insure a rigid structure and linearbehavior. Under acceleration, the mass causes a shear stressto be applied to the sensing crystals. This stress results in aproportional electrical output by the piezoelectric material.The output is collected by electrodes and transmitted bylightweight lead wires to either the built-in signalconditioning circuitry of ICP sensors, or directly to theelectrical connector for charge mode types. By having thesensing crystals isolated from the base and housing, shearmode accelerometers excel in rejecting thermal transient andbase-bending effects. Also, the shear geometry lends itself tosmall size, which promotes high frequency response whileminimizing mass loading effects on the test structure. Withthis combination of ideal characteristics, shear modeaccelerometers offer optimum performance.

Shear Mode Accelerometer

Function of Capacitive Accelerometers

Capacitive accelerometers sense a change in electricalcapacitance, with respect to acceleration, to vary the outputof an energized circuit. The sensing element consists of twoparallel plate capacitors acting in a differential mode. Thesecapacitors operate in a bridge circuit, along with two fixedcapacitors, and alter the peak voltage generated by anoscillator when the structure undergoes acceleration.Detection circuits capture the peak voltage, which is then fedto a summing amplifier that processes the final output signal.

Capacitive Accelerometer

Structure of Capacitive Accelerometers

Capacitive accelerometers sense a change in electricalcapacitance, with respect to acceleration, to vary the outputof an energized circuit. When subject to a fixed or constantacceleration, the capacitance value is also a constant,resulting in a measurement signal proportional to uniformacceleration, also referred to as DC or static acceleration.PCB’s capacitive accelerometers are structured with adiaphragm, which acts as a mass that undergoes flexure inthe presence of acceleration. Two fixed plates sandwich thediaphragm, creating two capacitors, each with an individualfixed plate and each sharing the diaphragm as a movableplate. The flexure causes a capacitance shift by altering thedistance between two parallel plates, the diaphragm itselfbeing one of the plates. The two capacitance values areutilized in a bridge circuit, the electrical output of whichvaries with input acceleration.

ACCELEROMETER SENSING SYSTEMS

Piezoelectric accelerometers can be broken down into twocategories that define their mode of operation. Internallyamplified ICP® accelerometers contain built-in microelec-tronic signal conditioning. Charge mode accelerometerscontain only the sensing element with no electronics.

ICP® AccelerometersICP®, as described earlier, is PCB's registered trademark thatstands for "Integrated Circuit - Piezoelectric" and identifiesPCB sensors that incorporate built-in, signal-conditioningelectronics. The built-in electronics convert the high-impedance charge signal that is generated by thepiezoelectric sensing element into a usable low-impedancevoltage signal that can be readily transmitted, over ordinarytwo-wire or coaxial cables, to any voltage readout orrecording device. The low-impedance signal can betransmitted over long cable distances and used in dirty fieldor factory environments with little degradation. In addition toproviding crucial impedance conversion, ICP® sensor circuitrycan also include other signal conditioning features, such asgain, filtering, and self-test features. The simplicity of use,high accuracy, broad frequency range, and low cost of ICP®

accelerometers make them the recommended type for use inmost vibration or shock applications. However, an exceptionto this assertion must be made for circumstances in which thetemperature, at the installation point, exceeds the capabilityof the built-in circuitry. The routine temperaturerange of ICP® accelerometers is 250 °F (121 °C);specialty units are available that operate to 350°F (177 °C).

The electronics within ICP® accelerometersrequire excitation power from a constant-currentregulated, DC voltage source. This power sourceis sometimes built into vibration meters, FFT analyzers, andvibration data collectors. A separate signal conditioner isrequired when none is built into the readout. In addition toproviding the required excitation, power supplies may alsoincorporate additional signal conditioning, such as gain,filtering, buffering, and overload indication. A typical systemset-up for ICP® accelerometers is shown below.

Charge Mode AccelerometersCharge mode sensors output a high-impedance, electricalcharge signal that is generated by the piezoelectric sensingelement. This signal is sensitive to corruption fromenvironmental influences. To conduct accuratemeasurements, it is necessary to condition this signal to alow-impedance voltage before it can be input to a readout orrecording device. A charge amplifier or in-line chargeconverter is generally used for this purpose. These devicesutilize high-input-impedance, low-output-impedanceinverting amplifiers with capacitive feedback. Adjusting thevalue of the feedback capacitor alters the transfer function orgain of the charge amplifier.

Typically, charge mode accelerometers are used when hightemperature survivability is required. If the measurementsignal must be transmitted over long distances, PCBrecommends the use of an in-line charge converter, placednear the accelerometer. This minimizes the chance of noise.In-line charge converters can be operated from the sameconstant-current excitation power source as ICP®

accelerometers for a reduced system cost.

Sophisticated laboratory-style charge amplifiers usuallyinclude adjustments for normalizing the input signal andaltering the feedback capacitor to provide the desired systemsensitivity and full-scale amplitude range. Filtering alsoconditions the high and low frequency response. Somecharge amplifiers provide dual-mode operation, which can beused to provide power for ICP® accelerometers or tocondition charge mode sensors.

Because of the high-impedance nature of the output signalgenerated by charge mode accelerometers, several importantprecautionary measures must be followed. Always use speciallow-noise coaxial cable between the accelerometer and thecharge amplifier. This cable is specially treated to reducetriboelectric (motion induced) noise effects. Also, always


Accelerometer Sensing SystemsAccelerometer Sensing Systems

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ICPAccelerometer

ICP® SensorSignal

ConditionerReadout Device

StandardSensor Cable

OutputCable

Vibration ChargeAmplifier

Readout Device

Low-NoiseSensor Cable Output

Cable

Charge ModeAccelerometer

Readout Device

Standard Sensor Cable or

Output Cable

In-Line ChargeConverter

Low-NoiseSensor Cable

OutputCable

Charge ModeAccelerometer ICP® Sensor

SignalConditioner

Continued on next page


Accelerometer Sensing SystemsAccelerometer Sensing Systems

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maintain high insulation resistance of the accelerometer,cabling, and connectors. To insure high insulation resistance,all components must be kept dry and clean.

Capacitive AccelerometersCapacitive accelerometers operate on a three-wire systemwith one wire carrying the excitation power, one wire carryingthe measurement signal, and the third wireserving as a common ground. Once energized,the capacitive accelerometer generates anoutput measurement signal directlyproportional to input acceleration, with respectto its specific acceleration sensitivity value. Theoutput signal is a low-impedance voltagecapable of being transmitted over ordinary wiresand over long distances.

The excitation voltage required of a capacitive accelerometeris a fixed, DC voltage ranging in value from 10 to 28 VDC,depending on specific model. Additional conditioning of thisvoltage, such as current limitation, is unnecessary. Anattractive feature of the capacitive accelerometer is its abilityto operate from basic power requirements; it may be used witha simple battery hookup. Some low-voltage-supply versionsmay even be operated from a 12 VDC automobile battery.

A peculiar item of concern with capacitive accelerometers istheir inherent zero-g offset voltage. This voltage is the resultof electrical component tolerances and is typically a valueless than 200 mV. This value can be nulled by the zero-adjustfeature of most common oscilloscopes; however, all PCBsignal conditioners for use with capacitive accelerometersinclude a zero-offset adjust feature to null this output. Theability to null the offset in the signal conditioner is especiallyadvantageous when utilizing readout or recordinginstruments that may not have a zero-offset feature.

CapacitiveAccelerometer

CapacitiveSensor Signal

ConditionerReadout Device

4-conductorSensor Cable

OutputCable


Accelerometer Mounting ConsiderationsAccelerometer Mounting Considerations

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ACCELEROMETER MOUNTINGCONSIDERATIONS

Frequency ResponseOne of the most important considerations in dealing withaccelerometer mounting is the effect the mountingtechnique has on the accuracy of the usable frequencyresponse. The accelerometer's operating frequency range isdetermined, in most cases, by securely stud mounting thetest sensor directly to the reference standard accelerometer.The direct, stud mounted coupling to a very smooth surface,generally yields the highest mechanical resonant frequencyand therefore, the broadest usable frequency range. Theaddition of any mass to the accelerometer, such as anadhesive or magnetic mounting base, lowers the resonantfrequency of the sensing system and may affect the accuracyand limits of the accelerometer's usable frequency range.Also, compliant materials, such as a rubber interface pad,can create a mechanical filtering effect by isolating anddamping high-frequency transmissibility.

Surface PreparationFor best measurement results, especially at high frequencies,it is important to prepare a smooth and flat machinedsurface where the accelerometer is to be attached. Inspectthe area to ensure that no metal burrs or other foreignparticles interfere with the contacting surfaces. Theapplication of a thin layer of silicone grease between theaccelerometer base and the mounting surface also assists inachieving a high degree of intimate surface contact requiredfor best high-frequency transmissibility.

Stud MountingFor permanent installations, where a very secure attachmentof the accelerometer to the test structure is preferred, studmounting is recommended. First, grind or machine on thetest object a smooth, flat area at least the size of the sensorbase, according to the manufacturer's specifications. Then,prepare a tapped hole in accordance with the suppliedinstallation drawing, ensuring that the hole is perpendicularto the mounting surface. Install accelerometers with themounting stud and make certain that the stud does notbottom in either the mounting surface or accelerometerbase. Most PCB mounting studs have depth-limitingshoulders that ensure that the stud cannot bottom-out intothe accelerometer's base. Each base incorporates acounterbore so that the accelerometer does not rest on theshoulder. Acceleration is transmitted from the structure'ssurface into the accelerometer's base. Any stud bottoming or

interfering between the accelerometer base and the structureinhibits acceleration transmission and affects measurementaccuracy. When tightening, apply only the recommendedtorque to the accelerometer. A thread-locking compoundmay be applied to the threads of the mounting stud tosafeguard against loosening.

Screw MountingWhen installing accelerometers onto thin-walled structures, acap screw passing through a hole of sufficient diameter is anacceptable means for securing the accelerometer to thestructure. The screw engagement length should always bechecked to ensure that the screw does not bottom into theaccelerometer base. A thin layer of silicone grease at themounting interface ensures high-frequency transmissibility.

Adhesive MountingOccasionally, mounting by stud or screw is impractical. Forsuch cases, adhesive mounting offers an alternativemounting method. The use of separate adhesive mountingbases is recommended to prevent the adhesive fromdamaging the accelerometer base or clogging the mountingthreads. (Miniature accelerometers are provided with theintegral stud removed to form a flat base.) Most adhesivemounting bases available from PCB also provide electricalisolation, which eliminates potential noise pick-up andground loop problems. The type of adhesive recommendeddepends on the particular application. Petro Wax (availablefrom PCB) offers a very convenient, easily removableapproach for room temperature use. Two-part epoxies offer




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stiffness, which maintains high-frequency response and apermanent mount. Other adhesives, such as dental cement,hot glues, instant glues, and duct putty are also viableoptions with a history of success.

There is no one "best" adhesive for all applications becauseof the many different structural and environmentalconsiderations, such as temporary or permanent mount,temperature, type of surface finish, and so forth.

A variety of adhesives are available from manymanufacturers, who usually provide specification charts andapplication bulletins for their adhesives. A ConsumerReport's article entitled "Which Glue for Which Job" (Jan.1988) provides rating information on adhesives. A PopularScience magazine article, "Secrets of the Superglues" (Feb.1989), provides informative data on the use of superglues.Loctite provides an adhesive "Selector Guide" for itsproducts.

For most accelerometer adhesive mounting applications,PCB Series 080 Adhesive Mounting Bases are suggested.These mounting pads keep the accelerometer base clean andfree of epoxy that may be very difficult to remove. Also,Series 080 Mounting Bases allow the accelerometer to beeasily removed from the test structure without damage toeither the sensor or the test object.

Surface flatness, adhesive stiffness, and adhesion strengthaffect the usable frequency range of an accelerometer.

Almost any mounting method at low acceleration levelsprovides the full frequency range of use if the mountingsurface is very flat and the sensor is pressed hard against thesurface to wring out all extra adhesive. Generally, as surfaceirregularities or the thickness of the adhesive increase, theusable frequency range decreases.

The less-stiff, temporary adhesives reduce anaccelerometer's usable frequency range much more than themore rigid, harder adhesives. Generally, temporary adhesivesare recommended more for low-frequency (<500 Hz)structural testing at room temperature. Petro Wax is generallysupplied with most of the accelerometers for a quick,temporary mounting method used during system set-up andcheck-out. When quick installation and removal is requiredover a wide frequency range up to 10 kHz, use a Series 080AAdhesive Mounting Base with one of the stiffer, morepermanent adhesives. Also, consider a magnetic mount,using the Series 080A27 Super Magnet with Model 080A20Steel Adhesive Mounting Pad for such measurements. Forboth, the mounting surface must be very flat to achieveaccurate high-frequency information.

Care should be exercised in selecting and testing an adhesivewhen concern exists regarding the possible discoloration ordamage to the test structure's surface finish. Test theadhesive first on a hidden location or a sample of thestructure's finish. Temporary adhesives like Petro Wax orbeeswax offer a good solution for quick installation in room-

temperature applications. When highertemperatures are involved, apply a pieceof aluminized mylar tape to the teststructure and mount the accelerometerwith adhesive base using one of the othertypes of adhesives. After the test, thetape can be easily removed with nodamage to the surface finish of thestructure.

Magnetic MountingMagnetic mounting bases offer a veryconvenient, temporary attachment tomagnetic surfaces. Magnets offering highpull strengths provide best high-frequencyresponse. Wedged dual-rail magneticbases are generally used for installationson curved surfaces, such as motor andcompressor housings and pipes. However,dual-rail magnets usually significantlydecrease the operational frequency rangeof an accelerometer. For best results, themagnetic base should be attached to a

Mounting Surface Temperature AvailabilityCondition

AdhesivesFlat & Rough Room Elevated PCB

Smooth Surfaces Temp. Temp. Commercial PiezotronicsSurfaces (Casting, etc.) Only (see Mtg. Spec.) (request sample)

Temporary/Easily Removed

Petro Wax ■ ■ ■ ■

Bee’s Wax ■ ■ ■ ■

Duct Putty ■ ■ ■ ■

Two-sided Sticky Tape ■ ■ ■ ■

Semi-Permanent/Permanent

Super Glue(Thin one part quick dry)

Loctite® 430 Super Bonder ■ -65°F to +175°F ■ ■

Eastman 910 ■ -65°F to +180°F ■

Super Glue-Gap Filling(thick liquid & gel)

Pacer RX-50 “Gel” ■ -114°F to +180°F ■

Loctite® 498 Super Bonder ■ -40°F to +223°F ■

Loctite® 422 “Gap Filling” ■ -65°F to +175°F ■

Hot Glue ■ ■

Various Grades■

(apply with hot glue gun) from +150°F

Permanent

Two Part Std ■ ■ to +250°F ■

Commercial Epoxies

Loctite® 325 Speed Bonder ■ ■ -65°F to +350°F ■



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smooth, flat surface. A thin layer of silicone grease should beapplied between the sensor and magnetic base, as well asbetween the magnetic base and the structure. When surfacesare uneven or non-magnetic, steel pads can be welded orepoxied in place to accept the magnetic base. Use of such apad ensures that periodic measurements are taken from theexact same location. This is an important consideration whentrending measurement data.

Probe TipsHandheld vibration probes or probe tips on accelerometersare useful when other mounting techniques are impracticaland for evaluating the relative vibration characteristics of astructure to determine the best location for installing theaccelerometer. Probes are not recommended for generalmeasurement applications due to a variety of inconsistenciesassociated with their use. Orientation and amount of handpressure applied create variables, which affect themeasurement accuracy. This method is generally used onlyfor frequencies less than 1000 Hz.

Mass LoadingThe vibrational characteristics of a structure can be alteredby adding mass to that structure. Since most measurementsare conducted to quantify the structural vibration, anyalteration of the vibration leads to an inaccurate evaluationof the vibration. An accelerometer that is too heavy, withrespect to the test structure, may produce data that does notcorrectly represent the vibration of interest. Use care whenselecting an accelerometer and mounting hardware to avoidthe effects of mass loading.

Ground Isolation, Ground Noise, and Ground LoopsWhen installing accelerometers onto electrically conductivesurfaces, a potential exists for ground noise pick-up. Noisefrom other electrical equipment and machines that aregrounded to the structure, such as motors, pumps, andgenerators, can enter the ground path of the measurementsignal through the base of a standard accelerometer. Whenthe sensor is grounded at a different electrical potential thanthe signal conditioning and readout equipment, groundloops can occur. This phenomenon usually results in currentflow at the line power frequency (and harmonics thereof),potential erroneous data, and signal drift. Under suchconditions, it is advisable to electrically isolate or "float" theaccelerometer from the test structure. This can beaccomplished in several ways. Most accelerometers can beprovided with an integral ground isolation base. Somestandard models may already include this feature, whileothers offer it as an option. Optional ground-isolated modelsare identified by the prefix "J"; for example, Model J353B33.The use of insulating adhesive mounting bases, isolationmounting studs, isolation bases, and other insulatingmaterials, such as paper beneath a magnetic base, areeffective ground isolation techniques. Be aware that theadditional ground-isolating hardware can reduce the upperfrequency limits of the accelerometer.

Cables and ConnectionsCables should be securely fastened to the mountingstructure with a clamp, tape, or other adhesive to minimizecable whip and connector strain. Cable whip can introducenoise, especially in high-impedance signal paths. Thisphenomenon is known as the triboelectric effect. Also, cablestrain near either electrical connector can lead tointermittent or broken connections and loss of data.

To protect against potential moisture and dirtcontamination, use RTV sealant or heat-shrinkable tubing oncable connections. O-rings with heat shrink tubing haveproven to be an effective seal for protecting electricalconnections for short-term underwater use. The use of only




108108

RTV sealant is generally only used to protect the electricalconnection against chemical splash or mist.

Under high shock conditions or when cables must undergolarge amounts of motion, as with package drop testingapplications, the use of a solder connector adaptor andlightweight ribbon cables are generally recommended. Thesesolder connector adaptors provide a more durableconnection and can be installed onto the accelerometer witha thread locking compound to prevent loosening. Use oflightweight cables helps to minimize induced strain at theconnector, which can create an erroneous output signal.Electrical connection fatigue is also minimized, reducing thepossibility of intermittent or open connections and loss ofdata. Solder connector adaptors are installed onto the cablewith solder. This easy connection makes this type ofconnector user- or field-repairable in times of crisis. Normally,a flexible plastic plug is placed over the electrical connectionsfor protection, as well as to provide cable strain relief.

The solder connector adaptor provides an affordable andsimplistic method for making cables in the field. Only solderand a soldering iron are required. No special tools orequipment are necessary for installation on a cable end.Because of the reliability and strength of this connection,these connectors are recommended for use in shockapplications.

CABLE DRIVING CONSIDERATIONSAND CONSTANT CURRENT LEVEL

Operation over long cables may effect frequency responseand introduce noise and distortion when an insufficientcurrent is available to drive cable capacitance.

Unlike charge mode systems, where the system noise is afunction of cable length, ICP® sensors provide a high voltage,low impedance output well-suited for driving long cablesthrough harsh environments. While there is virtually noincrease in noise with ICP® sensors, the capacitive loading ofthe cable may distort or filter higher frequency signalsdepending on the supply current and the output impedanceof the sensor.

Generally, this signal distortion is not a problem with lowerfrequency testing within a range up to 10 000 Hz. However,for higher frequency vibration, shock, or transient testingover cables longer than 100 ft. (30 m.), the possibility ofsignal distortion exists.

The maximum frequency that can be transmitted over a givencable length is a function of both the cable capacitance andthe ratio of the peak signal voltage to the current availablefrom the signal conditioner according to:

fmax = 109

2πCV / (lc-1)

where, fmax = maximum frequency (hertz)

C = cable capacitance (picofarads)

V = maximum peak output from sensor (volts)

lc = constant current from signal conditioner (mA)

109 = scaling factor to equate units

Note that in the equation, 1 mA is subtracted from the totalcurrent supplied to the sensor (1c). This is done tocompensate for powering the internal electronics. Somespecialty sensor electronics may consume more or lesscurrent. Contact the manufacturer to determine the correctsupply current. When driving long cables, the equation above


Driving Long Cable LengthsDriving Long Cable Lengths

109109

shows that as the length of cable, peak voltage output ormaximum frequency of interest increases, a greater constantcurrent will be required to drive the signal.

The nomograph on the next page provides a simple,graphical method for obtaining the expected maximumfrequency capability of an ICP® measurement system. Themaximum peak signal voltage amplitude, cable capacitance,and supplied constant current must be known or presumed.

For example, when running a 100 ft. cable with a capacitanceof 30 pF/ft, the total capacitance is 3000 pF. This value can befound along the diagonal cable capacitance lines. Assumingthe sensor operates at a maximum output range of 5 volts andthe constant current signal conditioner is set at 2 mA, theratio on the vertical axis can be calculated to equal 5. Theintersection of the total cable capacitance and this ratioresult in a maximum frequency of approximately 10.2 kHz.

The nomograph does not indicate whether the frequencyamplitude response at a point is flat, rising, or falling. Forprecautionary reasons, it is good general practice to increasethe constant current (if possible) to the sensor (within itsmaximum limit) so that the frequency determined from thenomograph is approximately 1.5 to 2 times greater than themaximum frequency of interest.

Note that higher current levels will depletebattery-powered signal conditioners at afaster rate. Also, any current not used bythe cable goes directly to power theinternal electronics and will create heat.This may cause the sensor to exceed itsmaximum temperature specification. Forthis reason, do not supply excessivecurrent over short cable runs or whentesting at elevated temperatures.

Experimentally Testing Long CablesTo more accurately determine the effect oflong cables, it is recommended toexperimentally determine the high frequencyelectrical characteristics.

The method illustrated below involvesconnecting the output from a standard signal generator intoa unity gain, low-output impedance (<5 ohm)instrumentation amplifier in series with the ICP® sensor. Theextremely low output impedance is required to minimize theresistance change when the signal generator/amplifier isremoved from the system.

In order to check the frequency/amplitude response of thissystem, set the signal generator to supply the maximumamplitude of the expected measurement signal. Observe theratio of the amplitude from the generator to that shown onthe scope. If the ratio is 1:1, the system is adequate for yourtest. (If necessary, be certain to factor in any gain in the signalconditioner or scope.) If the output signal is rising (1:1.3 forexample), add series resistance to attenuate the signal. Useof a variable 100 ohm resistor will help set the correctresistance more conveniently. Note that this is the onlycondition that requires the addition of resistance. If thesignal is falling (1:0.75 for example), the constant currentlevel must be increased or the cable capacitance reduced.

It may be necessary to physically install the cable duringcable testing to reflect the actual conditions encounteredduring data acquisition. This will compensate for potentialinductive cable effects that are partially a function of thegeometry of the cable route.

Readout Device

ExtensionCable

Cable Coupler

Short Sensor Cable

OutputCable

ICP®

AccelerometerICP® Sensor

SignalConditioner

Readout Device

LongExtension

Cable

Model 073AVariableResistor

Model 401A04Sensor

Simulator

SignalGenerator

Short Sensor Cable

OutputCable

ICP® SensorSignal

Conditioner


Driving Long Cable LengthsDriving Long Cable Lengths

110110

VIc - 1

(Ratio ofMaximum Output

Voltage from Sensorto

AvailableConstant Current)

Frequency (Hz)

fmax = Maximum frequency given the following characteristics

C= Cable capacitance (pF) Ic= Constant current level from power unit (mA)V= Maximum output voltage from sensor (volts) 109= Scale factor to equate units

Cable Driving Nomograph


TEDS — Transducer Electronic Data SheetTEDS — Transducer Electronic Data Sheet

111111

SMART SENSORS PROVIDE SELF IDENTIFICATION

TEDS is a “Transducer Electronic Data Sheet” embedded in a sensorfor the purpose of maintaining critical sensor information, reducingpaperwork, providing better management of transducers, reducing usererror, and saving time and money.

Sensors incorporating Transducer Electronic Data Sheet(TEDS) are mixed-mode (analog/digital) sensors that have abuilt in read/write memory that contains relevant informationabout the sensor and its use. Also referred to as “smart”transducers or sensors, a portion of the memory is reservedfor sensor specifications as defined by the manufacturerwhile another portion is user definable. Manufacturerinformation includes manufacturer name, model number,serial number, sensor type, sensitivity, etc. The user canselect from dozens of transducer templates that includemore sensor specific information and/or test information likechannel ID, location, position, direction, tag number, etc.

The mixed-mode design allows the transducer to operate intwo different modes. The first is its traditional IEPE(Integrated Circuit Piezoelectric) measurement mode, with itswide bandwidth, wide range, and analog output signal. Thesecond mode is the digital communication mode, whichswitches the analog circuitry out of the system and passesthe transducer’s memory content over the same wires usedto access the analog output. This enables the additionalcapability of the TEDS to operate with existing cabling.

The TEDS feature was designed with a “plug-n-play” conceptin mind. By containing relevant information that can beaccessed digitally, a sensor simply needs to be “plugged into”a system which can digitally read all of the pertinentinformation about the sensor. This includes NIST traceablecalibration data that satisfies ISO 9001 and QS 9000requirements, which can eliminate the need for maintainingto printed calibration records.

Even though TEDS sensors contain digital information, thebasic sensor design and performance is unchanged. It stilloperates as a standard ICP® sensor and can be used withexisting ICP sensor signal conditioners. In order to access thedigital TEDS information however, additional circuitry isrequired in the signal conditioner or data collector. Since thebasic sensor is unchanged, not only are its wide bandwidth,dynamic range, and 2-wire system maintained but also itscost effectiveness.

The operation of TEDS sensors is defined by IEEE P1451.4.PCB Piezotronics and The Modal Shop actively participate onthe IEEE committee involved in the development of the TEDSstandard and have also delivered over 1000 fully functionalTEDS sensors. These shipments also include supportingelectronics that comply with the current proposed standard.Additionally, many leading manufacturers of tape recorders,signal conditioners, FFT analyzers, etc. are working toimplement TEDS support in their products.

Digital communication enables transducer self identification and retrieval of calibration data

Self-identification organizes multi-channel testing

Saves time and reduces errors

Automatically identify PM data collection points

Standardized for industry compatibility

Stores NIST traceable calibration data

On-board calibration data satisfies ISO & QS 9000 requirements


Conversions and Useful FormulasConversions and Useful Formulas

112112

Voltage sensitivity of a charge mode piezoelectricsensor:

V=

V = voltage sensitivityq = charge sensitivityC = capacitance of sensor

Voltage sensitivity of a charge mode piezoelectricsensor with source follower:

V =

C1 = capacitance of sensor

C2 = capacitance of interconnecting cable

C3 = input capacitance of unity gain source follower

Time constant for a first order, high pass filter:

t = RC

R = resistance in ohmsC = capacitance in faradst = time constant in seconds

Lower corner frequency (-3 dB) for an RC timeconstant:

fc =

fc = frequency at which signal is attenuated by -3 dB

Lower -5 % frequency point for an RC timeconstant:

f-5% =

f-5% = frequency at which signal is attenuated by 5 %

Approximate upper +5 % frequency point forsingle degree-of-freedom mechanical system:

f+5% =

f+5% = frequency at which signal is amplified by 5 %

fr = natural (resonant) frequency

Approximating two time constants in series foroscillating signals:

(R1C1) (R2C2)

√ (R1C1)2 + (R2C2)2

Approximating two time constants in series fortransient inputs lasting up to 10 % of the smallertime constant value:

(R1C1) (R2C2)

(R1C1) + (R2C2)

Rise time of a piezoelectric sensor:

tr =

tr = rise time

fr = natural (resonant) frequency of the sensor

Acceleration:

m=

gsec2 9.81

Temperature:

°C =(°F-32) 5

9

Weight:

gm =lb

453.59

gm =oz

28.35

qC

12 fr

fr5

qC1 + C2 + C3

12 π RC

32 π RC


Article ReprintsArticle Reprints

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To order copies of the following articles, simply request the"AR" number preceding each article; just write or call theMarketing Department at: 716-684-0001.

AR-1 Application of Integrated-Circuits to PiezoelectricTransducers, Paper P4-2 PHYMID 67ICP® transducer - basic operation and application /Cornell Aeronautical Lab, Robert Lally, 1967.

AR-2 ICP® ConceptIntegrated-circuit piezoelectric. Low impedance, voltagemode system, PCB, 1967.

AR-3 Piezoelectric AnalogiesElectrostatic vs. hydrostatic system. Piezoelectric vs.hydraulic circuit, Robert Lally, 1967.

AR-4 Guide to ICP® InstrumentationVoltage vs. charge systems. Effect of coupling and timeconstant on response. Powering ICP system, Robert Lally, 1971.

AR-6 MetrigenisisSensor behavior. Rigid body, structural, acoustic modes,Robert Lally, 1976.

AR-7 How to Balance with Your Real Time AnalyzerModel 302A04 accelerometer / measure bearingvibration, George Lang, 1977.

AR-8 Impulse Technique for Structural FrequencyResponse TestingTheory, display of frequency response; equipmentrequirements and measurement procedures, Wm. Halvorsen, D. Brown, 1977.

AR-9 Testing the Behavior of StructuresRigid body, structural, and acoustic modes of behaviortesting, Robert Lally, 1978.

AR-11 TransductionThe effect of sensor mass and/or stiffness on the quantitybeing measured, Robert Lally, 1982.

AR-14 Modal Analysis Test Set-UpFixturing, boundary conditions, transducer selection,calibration, applying excitation, and typical test, Jeff Poland, Richard Lally, 1985.

AR-15 Modal-Tuning Improves Impact TestingModally tuned® instrumented force hammers solveproblem of spurious glitches in the frequency responseduring impact testing, Rick Lally, 1985.

AR-16 Predictive & Selective Machinery MaintenanceDigital velocity meter, model 396A / U.S. Navy shipboardapplications, William Young, 1985.

AR-18 Introduction to Piezoelectric SensorsBasic accelerometer, pressure, and force sensor designconsiderations and typical applications, Jim Lally, 1985.

AR-19 Calibration of Piezo SensorsCalibration systems for dynamic pressure sensors, forcesensors, and accelerometers with typical calibrationresults, Jim Lally, 1985.

AR-20 Integrity - The Priceless Ingredient in TestingModel 305A triaxial configuration / firing of projectile,muzzle of machine gun application, Cover ApplicationPhoto, Test Magazine, 1985.

AR-27 Six-Axis Dynamic Calibration of AccelerometersCalibration technique for modal systems, A. Severyn,Richard Lally, D. Brown, R. Zimmerman, 1987.

AR-28 Accelerometer Calibration: Is It Credible?Compliance with MIL-STD-45662A, Jim Lally, 1987.

AR-32 Analyzing the Noise of a FanICP® Accelerometer with magnetic base / effect of"accelerometer's mounting location on a fan" uponvibration spectrum, George Lang, 1988.

AR-33 Diagnosing Faults in Rolling Element BearingsPCB rms vibration meter 396 / periodic machinerymonitoring, J. Berggren, 1988.

AR-35 Frequency Response Considerations for PiezoelectricSensors and Related Inst.Time constant and AC coupling or DC coupling effects onfrequency response. Time constant vs. shock pulse inputduration, Ray Limburg, 1988.

AR-39 High Frequency Calibration with the StructuralGravimetric TechniqueModel 965A system with 961A drop tester, 911A shaker /calibrate from 0.1 to 100,000 Hz (calibration capability for MIL-STD-740-2), Richard Lally,J. Lin, P. Kooyman, 1990.

AR-43 Troubles With CablesCables for voltage and charge mode systems. Cablemanagement system, J.F. Lally, 1990.

AR-47 Low Frequency Calibration With the StructuralGravimetric TechniqueModel 963A system - comparison of calibration testresults between structural gravimetric, laser, and back-to-back methods, Richard Lally, Jing Lin, DavidLally, 1991.

AR-48 Multichannel Management Concepts for ModalAnalysis and TestingUsing 496 channels - 12 force, 208 acoustic, 276accelerometer responses / aircraft structure - all testsperformed in 27 hours, Michael Lally, T. Severyn, 1991.

AR-59 Recommended Practices: Accelerometer, Wiring andConnectionsReliability of ICP® and charge mode systems based uponselection of cables and connections / long cable use withcable drive nomograph, James Lally, 1993.


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Glossary of TermsGlossary of Terms

Reprinted with permission from Application Note: AN 243-1,“Effective Machinery Measurements Using Dynamic SignalAnalyzers,” Hewlett-Packard Company, 1991. Editing and additionsperformed by PCB Piezotronics, Depew, NY, 1998.

Acceleration — The time rate of change of velocity. Typical units areft/s2, meters/s2, and G’s (1G = 32.17 ft/s2 = 9.81 m/s2).Acceleration measurements are usually made withaccelerometers.

Accelerometer — Transducer whose output is directly proportionalto acceleration. Most commonly use piezoelectric crystals toproduce output.

Aliasing — A phenomenon which can occur whenever a signal isnot sampled at greater than twice the maximum bandwidth ofthe signal. Causes high frequency signals to appear at lowfrequencies. Aliasing is minimized by filtering the signal to abandwidth less than ½ the sample rate. When the signal startsat 0 Hz (baseband signals), bandwidth can be exchanged tomaximum frequency in the definition above.

Alignment — A condition whereby the axes of machine componentsare either coincident, parallel, or perpendicular, according todesign requirements.

Amplification Factor (Synchronous) — A measure of thesusceptibility of a rotor to vibration amplitude when rotationalspeed is equal to the rotor natural frequency (implies a flexiblerotor). For imbalance type excitation, synchronous amplificationfactor is calculated by dividing the amplitude value at theresonant peak by the amplitude value at a speed well aboveresonance (as determined from a plot of synchronousresponse vs. rpm).

Amplitude — The magnitude of dynamic motion or vibration.Amplitude is expressed in terms of peak-to-peak, zero-to-peak,or rms. For pure sine waves only, these are related as follows:rms = 0.707 times zero-to-peak; peak-to-peak = 2 times zero-to-peak. DSAs generally read rms for spectral components, andpeak for time domain components.

Anti-Aliasing Filter — Most commonly a low-pass filter designed tofilter out frequencies higher than ½ the sample rate in order tominimize aliasing.

Anti-Friction Bearing — See Rolling Element Bearing.

Asymmetrical Support — Rotor support system that does notprovide uniform restraint in all radial directions. This is typicalfor most heavy industrial machinery where stiffness in oneplane may be substantially different than stiffness in theperpendicular plane. Occurs in bearings by design, or frompreloads such as gravity or misalignment.

Asynchronous — Vibration components that are not related torotating speed (also referred to as nonsynchronous).

Attitude Angle (Steady-State) — The angle between the directionof steady-state preload through the bearing centerline, and aline drawn between the shaft centerline and the bearingcenterline. (Applies to fluid-film bearings.)

Auto Spectrum (Power Spectrum) — DSA spectrum displaywhose magnitude represents the power at each frequency, andwhich has no phase.

Averaging — In a DSA, digitally averaging several measurements toimprove accuracy or to reduce the level of asynchronouscomponents. Refer to definitions of rms, time, and peak-holdaveraging.

Axial — In the same direction as the shaft centerline.

Axial Position — The average position, or change in position, of arotor in the axial direction with respect to some fixed referenceposition. Ideally the reference is a known position within thethrust bearing axial clearance or float zone, and themeasurement is made with a displacement transducerobserving the thrust collar.

Balancing Resonance Speed(s) — A rotative speed thatcorresponds to a natural resonance frequency.

Balanced Condition — For rotating machinery, a condition wherethe shaft geometric centerline coincides with the masscenterline.

Balancing — A procedure for adjusting the radial mass distributionof a rotor so that the mass centerline approaches the rotorgeometric centerline.

Band-Pass Filter — A filter with a single transmission bandextending from lower to upper cutoff frequencies. The width ofthe band is normally determined by the separation offrequencies at which amplitude is attenuated by 3 dB (a factor0.707 ).

Bandwidth — The distance between frequency limits at which aband-pass filter attenuates the signal by 3 dB. In a DSA, themeasurement bandwidth is equal to [(frequency span)/(numberof filters) x (window factor)]. Window factors are: 1 for uniform,1.5 for Hanning, and 3.4 for flat top (P301) and 3.6 for flat top(P401). See flat top for more information.

Baseline Spectrum — A vibration spectrum taken when a machineis in good operating condition; used as a reference formonitoring and analysis.

Blade Passing Frequency — A potential vibration frequency onany bladed machine (turbine, axial compressor, fan, etc.). It isrepresented by the number of blades times shaft-rotatingfrequency.

Block Size — The number of samples used in a DSA to computethe Fast Fourier Transform. Also the number of samples in aDSA time display. Most DSAs use a block size of 1024. Smallerblock size reduces frequency resolution.

Bode — Rectangular coordinate plot of 1x component amplitudeand phase (relative to a keyphasor) vs. running speed.

BPFO, BPFI — Common abbreviations for ball pass frequency ofdefects on outer and inner bearing races, respectively.

Bow — A shaft condition such that the geometric centerline of theshaft is not straight.

Brinneling (False) — Impressions made by bearing rollingelements on the bearing race; typically caused by externalvibration when the shaft is stationary.

Calibration — A test during which known values of the measuredvariable are applied to the transducer or readout instrument,and output readings varied or adjusted.



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Campbell Diagram — A mathematically constructed diagram usedto check for coincidence of vibration sources (i.e. 1 ximbalance, 2 x misalignment) with rotor natural resonances.The form of the diagram is like a spectral map (frequencyversus rpm), but the amplitude is represented by a rectangularplot, the larger the amplitude the larger the rectangle. Alsoknown as an interference diagram.

Cascade Plot — See Spectral Map.

Cavitation — A condition which can occur in liquid-handlingmachinery (e.g. centrifugal pumps) where a system pressuredecrease in the suction line and pump inlet lowers fluidpressure and vaporization occurs. The result is mixed flowwhich may produce vibration.

Center Frequency — For a bandpass filter, the center of thetransmission band, measured in a linear scale.

Charge Amplifier — Amplifier used to convert accelerometer outputimpedance from high to low, making calibration much lessdependent on cable capacitance.

Coherence — Measures how much of the output signal isdependent on the input signal in a linear and time-invariant way.It is an effective means of determining the similarity of vibrationat two locations, giving insight into the possibility of cause andeffect relationships.

Constant Bandwidth Filter — A band-pass filter whose bandwidthis independent of center frequency. The filters simulateddigitally by the FFT in a DSA are constant bandwidth.

Constant Percentage Bandwidth — A band-pass filter whosebandwidth is a constant percentage of center frequency. 1/3octave filters, including those synthesized in DSAs, areconstant percentage bandwidth.

Critical Machinery — Machines which are critical to a major part ofthe plant process. These machines are usually unspared.

Critical Speeds — In general, any rotating speed which isassociated with high vibration amplitude. Often, the rotorspeeds which correspond to natural frequencies of the system.

Critical Speed Map — A rectangular plot of system naturalfrequency (y-axis) versus bearing or support stiffness (x-axis).

Cross Axis Sensitivity — A measure of off-axis response ofvelocity and acceleration transducers.

Cycle — One complete sequence of values of a periodic quantity.

Damping — The quality of a mechanical system that restrains theamplitude of motion with each successive cycle. Damping ofshaft motion is provided by oil in bearings, seals, etc. Thedamping process converts mechanical energy to other forms,usually heat.

Damping, Critical — The smallest amount of damping required toreturn the system to its equilibrium position without oscillation.

Decibels (dB) — A logarithmic representation of amplitude ratio,defined as 10 times the base ten logarithm of the ratio of themeasured power to a reference. dBV readings, for example, arereferenced to 1 volt rms. dB amplitude scales are required todisplay the full dynamic range of a DSA. dB values for power orvoltage measurements yields the same result.

Degrees of Freedom — A phrase used in mechanical vibration todescribe the complexity of the system. The number of degreesof freedom is the number of independent variables describingthe state of a vibrating system.

Digital Filter — A filter which acts on the data after it has beensampled and digitized. Often used in DSAs to provide anti-aliasing protection before internal re-sampling.

Differentiation — Representation in terms of time rate of change.For example, differentiating velocity yields acceleration. In aDSA, differentiation is performed by multiplication by jw in thefrequency domain, where w is frequency multiplied by 2p.(Differentiation can also be used to convert displacement tovelocity.)

Discrete Fourier Transform — A procedure for calculating discretefrequency components (filters or lines) from sampled time data.Since the frequency domain result is complex (i.e., real andimaginary components), the number of frequency points isequal to half the number of time samples (for a real FFT). Whenusing zoom analysis, the FFT uses complex time data and thenthe number of frequency lines is equal to the number of timesamples.

Displacement — The change in distance or position of an objectrelative to a reference.

Displacement Transducer — A transducer whose output isproportional to the distance between it and the measuredobject (usually the shaft).

DSA — See Dynamic Signal Analyzer.

Dual Probe — A transducer set consisting of displacement andvelocity transducers. Combines measurement of shaft motionrelative to the displacement transducer with velocity of thedisplacement transducer to produce absolute motion of theshaft.

Dual Voting — Concept where two independent inputs are requiredbefore action (usually machine shutdown) is taken. Most oftenused with axial position measurements, where failure of asingle transducer might lead to an unnecessary shutdown.

Dynamic Motion — Vibratory motion of a rotor system caused bymechanisms that are active only when the rotor is turning atspeeds above slow roll speed.

Dynamic Signal Analyzer (DSA) — Vibration analyzer that usesdigital signal processing and the Fast Fourier Transform todisplay vibration frequency components. DSAs also display thetime domain and phase spectrum, and can usually beinterfaced to a computer.

Eccentricity, Mechanical — The variation of the outer diameter ofa shaft surface when referenced to the true geometriccenterline of the shaft. Out-of-roundness.

Eccentricity Ratio — The vector difference between the bearingcenterline and the average steady-state journal centerline.

Eddy Current — Electrical current which is generated (anddissipated) in a conductive material in the presence of anelectromagnetic field.


116116


Electrical Runout — An error signal that occurs in eddy currentdisplacement measurements when shaft surface conductivityvaries.

Engineering Units — In a DSA, refers to units that are calibrated bythe user (e.g., in/s, g’s).

External Sampling — In a DSA, refers to control of data samplingby a multiplied tachometer signal. Provides a stationary displayof rpm-related peaks with changing speed.

Fast Fourier Transform (FFT) — A computer (or microprocessor)procedure for calculating discrete frequency components fromsampled time data. A special case of the Discrete FourierTransform, DFT, where the number of samples is constrained toa power of 2 for speed.

Filter — Electronic circuitry designed to pass or reject a specificfrequency band.

Finite Element Modeling — A computer aided design technique forpredicting the dynamic behavior of a mechanical system priorto construction. Modeling can be used, for example, to predictthe natural frequencies of a flexible rotor.

Flat Top Filter — FFT window function which provides the bestamplitude accuracy for measuring discrete frequencycomponents. Note: there are several different flat top windows.The HP proprietary P401 is the “best” flat top window. P301 isthe most common.

Fluid-Film Bearing — A bearing which supports the shaft on a thinfilm of oil. The fluid-film layer may be generated by journalrotation (hydrodynamic bearing), or by externally appliedpressure (hydrostatic bearing).

Forced Vibration — The oscillation of a system under the action ofa forcing function. Typically forced vibration occurs at thefrequency of the exciting force.

Free Vibration — Vibration of a mechanical system following aninitial force - typically at one or more natural frequencies.

Frequency — The repetition rate of a periodic event, usuallyexpressed in cycles per second (Hz), revolutions per minute(rpm), or multiples of a rotational speed (orders). Compare toorders that are commonly referred to as 1x for rotational speed,2x for twice rotational speed, etc.

Frequency Response Function — The amplitude and phaseresponse characteristics of a system.

G — The value of acceleration produced by the force of gravity.

Gear Mesh Frequency — A potential vibration frequency on anymachine that contains gears; equal to the number of teethmultiplied by the rotational frequency of the gear.

Hanning Window — FFT window function that normally providesbetter frequency resolution than the flat top window, but withreduced amplitude accuracy.

Harmonic — Frequency component at a frequency that is an integermultiple of the fundamental frequency.

Heavy Spot — The angular location of the imbalance vector at aspecific lateral location on a shaft. The heavy spot typicallydoes not change with rotational speed.

Hertz (Hz) — The unit of frequency represented by cycles persecond.

High Spot — The angular location on the shaft directly under thevibration transducer at the point of closest proximity. The highspot can move with changes in shaft dynamics (e.g., fromchanges in speed).

High-Pass Filter — A filter with a transmission band starting at alower cutoff frequency and extending to (theoretically) infinitefrequency.

Hysteresis — Non-uniqueness in the relationship between twovariables as a parameter increases or decreases. Also calleddeadband, or that portion of a system’s response where achange in input does not produce a change in output.

Imbalance — Unequal radial weight distribution on a rotor system;a shaft condition such that the mass and shaft geometric centerlines do not coincide.

Impact Test — Response test where the broad frequency rangeproduced by an impact is used as the stimulus. Sometimesreferred to as a bump test. See impulse response for moreinformation.

Impedance, Mechanical — The mechanical properties of amachine system (mass, stiffness, damping) that determine theresponse to periodic forcing functions.

Impulse Response — The response of a system to an impulse asinput signal. The output then produces the impulse responsethat is the time domain equivalent to the Frequency ResponseFunction, FRF.

Influence Coefficients — Mathematical coefficients that describethe influence of system loading on system deflection.

Integration — A process producing a result that, whendifferentiated, yields the original quantity. Integration ofacceleration, for example, yields velocity. Integration isperformed in a DSA by dividing the frequency lines by jw, wherew is frequency multiplied by 2p. (Integration is also used toconvert velocity to displacement.)

Journal — Specific portions of the shaft surface from which rotorapplied loads are transmitted to bearing supports.

Keyphasor — A signal used in rotating machinery measurements,generated by a transducer observing a once-per-revolutionevent.The keyphasor signal is used in phase measurements foranalysis and balancing. (Keyphasor is a Bently Nevada tradename.)

Lateral Location — The definition of various points along the shaftaxis of rotation.

Lateral Vibration — See Radial Vibration.

Leakage — In DSAs, a result of finite time record length that resultsin smearing of frequency components. Its effects are greatlyreduced by the use of weighted time functions such as Flat topor Hanning windows.



117117

Linearity — The response characteristics of a linear system remainconstant with input level and/or excitation signal type. That is, ifthe response to input a is k·a, and the response to input b isk·b, then the response of a linear system to input (a + b) will be(k·a + k·b), independent of the function k. An example of a non-linear system is one whose response is limited by mechanicalstop, such as occurs when a bearing mount is loose.

Lines — Common term used to describe the filters of a DSAproduced by the FFT (e.g., 400 line analyzer).

Linear Averaging — See Time Averaging.

Low-Pass Filter — A filter whose transmission band extends fromdc to an upper cutoff frequency.

Mechanical Runout — An error in measuring the position of theshaft centerline with a displacement probe that is caused byout-of-roundness and surface imperfections.

Micrometer (MICRON) — One millionth (.000001) of a meter. (1micron = 1 x E-6 meters @ 0.04 mils.)

MIL — One thousandth (0.001) of an inch. (1 mil = 25.4 microns)

Modal Analysis — The process of breaking complex vibration intoits component modes of vibration, very much like frequencydomain analysis breaks vibration down to componentfrequencies.

Mode Shape — The resultant deflected shape of a rotor at a specificrotational speed to an applied forcing function. A three-dimensional presentation of rotor lateral deflection along theshaft axis.

Modulation, Amplitude (AM) — The process where the amplitudeof a signal is varied as a function of the instantaneous value ofa another signal. The first signal is called the carrier, and thesecond signal is called the modulating signal. Amplitudemodulation always produces a component at the carrierfrequency, with components (sidebands) at the frequency of thecarrier frequency plus minus the modulating signal.

Modulation, Frequency (FM) — The process where the frequencyof the carrier is determined by the amplitude of the modulatingsignal. Frequency modulation produces a component at thecarrier frequency, with adjacent components (sidebands) atfrequencies around the carrier frequency related to themodulating signal. The carrier and sidebands are described byBessel functions.

Natural Frequency — The frequency of free vibration of a system.The frequency at which an undamped system with a singledegree of freedom will oscillate upon momentary displacementfrom its rest position.

Nodal Point — A point of minimum shaft deflection in a specificmode shape. May readily change location along the shaft axisdue to changes in residual imbalance or other forcing function,or change in restraint such as increased bearing clearance.

Noise — Any component of a transducer output signal that does notrepresent the variable intended to be measured.

Nyquist Criterion — Requirement that a sampled system needs tobe sampled at a frequency greater than twice the bandwidth ofthe signal to be sampled.

Nyquist Plot — A plot of real versus imaginary spectral componentsthat is often used in servo analysis. Should not be confusedwith a polar plot of amplitude and phase of 1x vibration.

Octave — The interval between two frequencies with a ratio of 2 to 1.

Oil Whirl/Whip — An unstable free vibration whereby a fluid-filmbearing has insufficient unit loading. Under this condition, theshaft centerline dynamic motion is usually circular in thedirection of rotation. Oil whirl occurs at the oil flow velocitywithin the bearing, usually 40 to 49% of shaft speed. Oil whipoccurs when the whirl frequency coincides with (and becomeslocked to) a shaft resonant frequency. (Oil whirl and whip canoccur in any case where fluid is between two cylindricalsurfaces.)

Orbit — The path of the shaft centerline motion during rotation. Theorbit is observed with an oscilloscope connected to x and y-axisdisplacement transducers. Some dual-channel DSAs also havethe ability to display orbits.

Oscillator-Demodulator — A signal conditioning device that sendsa radio frequency signal to an eddy-current displacementprobe, demodulates the probe output, and provides outputsignals proportional to both the average and dynamic gapdistances. (Also referred to as Proximitor, a Bently Nevadatrade name.)

Peak Hold — In a DSA, a type of averaging that holds the peaksignal level for each frequency component.

Period — The time required for a complete oscillation or for a singlecycle of events. The reciprocal of frequency.

Phase — A measurement of the timing relationship between twosignals, or between a specific vibration event and a keyphasorpulse. Phase is often measured as a function of frequency.

Piezoelectric — Any material which provides a conversion betweenmechanical and electrical energy. For a piezoelectric crystal, ifmechanical stresses are applied on two opposite faces,electrical charges appear on some other pair of faces.

Polar Plot — Polar coordinate representation of the locus of the 1xvector at a specific lateral shaft location with the shaft rotationalspeed as a parameter.

Power Spectrum — See Auto Spectrum.

Preload, Bearing — The dimensionless quantity that is typicallyexpressed as a number from zero to one where a preload ofzero indicates no bearing load upon the shaft, and oneindicates the maximum preload (i.e., line contact between shaftand bearing).

Preload, External — Any of several mechanisms that can externallyload a bearing. This includes “soft” preloads such as processfluids or gravitational forces as well as “hard” preloads fromgear contact forces, misalignment, rubs, etc.

Proximitor — See Oscillator/Demodulator.

Radial — Direction perpendicular to the shaft centerline.

Radial Position — The average location, relative to the radialbearing centerline, of the shaft dynamic motion.



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Radial Vibration — Shaft dynamic motion or casing vibration whichis in a direction perpendicular to the shaft centerline.

Real-Time Analyzer — See Dynamic Signal Analyzer.

Real-Time Rate — For a DSA, the broadest frequency span atwhich data is sampled continuously. Real-time rate is mostlydependent on FFT processing speed. If the definition of real-time rate is “not miss any data”, the real-time rate will bewindow dependent.The real-time rate will decrease when usingany other window than uniform.

Rectangular Window — See Uniform Window.

Relative Motion — Vibration measured relative to a chosenreference. Displacement transducers generally measure shaftmotion relative to the transducer mounting.

Repeatability — The ability of a transducer or readout instrument toreproduce readings when the same input is applied repeatedly.

Resolution — The smallest change in stimulus that will produce adetectable change in the instrument output.

Resonance — The condition of vibration amplitude and phasechange response caused by a corresponding system sensitivityto a particular forcing frequency. A resonance is typicallyidentified by a substantial amplitude increase, and relatedphase shift.

Rolling Element Bearing — Bearing whose low friction qualitiesderive from rolling elements (balls or rollers), with littlelubrication.

Root Mean Square (rms) — Square root of the arithmetical averageof a set of squared instantaneous values. DSAs perform rmsaveraging digitally on successive vibration spectra, frequencyline by frequency line.

Rotor, Flexible — A rotor which operates close enough to, orbeyond its first bending critical speed for dynamic effects toinfluence rotor deformations. Rotors which cannot be classifiedas rigid rotors are considered to be flexible rotors.

Rotor, Rigid — A rotor which operates substantially below its firstbending critical speed. A rigid rotor can be brought into, and willremain in, a state of satisfactory balance at all operatingspeeds when balanced on any two arbitrarily selectedcorrection planes.

Runout Compensation — Electronic correction of a transduceroutput signal for the error resulting from slow roll runout.

Seismic — Refers to an inertially referenced measurement or ameasurement relative to free space.

Seismic Transducer — A transducer that is mounted on the case orhousing of a machine and measures casing vibration relative tofree space. Accelerometers and velocity transducers are seismic.

Signal Conditioner — A device placed between a signal sourceand a readout instrument to change the signal and/orbandwidth. Examples: attenuators, preamplifiers, chargeamplifiers, filters.

Signature — Term usually applied to the vibration frequencyspectrum which is distinctive and special to a machine orcomponent, system or subsystem at a specific point in time,

under specific machine operating conditions, etc. Used forhistorical comparison of mechanical condition over theoperating life of the machine.

Slow Roll Speed — Low rotative speed at which dynamic motioneffects from forces such as imbalance are negligible.

Spectral Map — A three-dimensional plot of the vibration amplitudespectrum versus another variable, usually time or rpm.

Spectrum Analyzer — An instrument which displays the frequencyspectrum of an input signal.

Stiffness — The spring-like quality of mechanical and hydraulicelements to elasticity deform under load.

Strain — The physical deformation, deflection, or change in lengthresulting from stress (force per unit area).

Subharmonic — Sinusoidal quantity of a frequency that is anintegral submultiple of a fundamental frequency.

Subsynchronous — Component(s) of a vibration signal which hasa frequency less than shaft rotative frequency.

Synchronous Sampling — In a DSA, it refers to the control of theeffective sampling rate of data; which includes the processes ofexternal sampling and computed resampling used in ordertracking.

Time Averaging — In a DSA, averaging of time records that resultsin reduction of asynchronous components with reference to thetrigger.

Time Record — In a DSA, the sampled time data converted to thefrequency domain by the FFT. Most DSAs use a time record of1024 samples.

Torsional Vibration — Amplitude modulation of torque measured indegrees peak-to-peak referenced to the axis of shaft rotation.

Tracking Filter — A low-pass or band-pass filter whichautomatically tracks the input signal versus the rpm. A trackingfilter is usually required for aliasing protection when datasampling is controlled externally.

Transducer — A device for translating the magnitude of onequantity into another quantity.

Transient Vibration — Temporarily sustained vibration of amechanical system. It may consist of forced or free vibration orboth. Typically this is associated with changes in machineoperating condition such as speed, load, etc.

Transverse Sensitivity — See Cross-Axis Sensitivity.

Trigger — Any event which can be used as a timing reference. In aDSA, a trigger can be used to initiate a measurement.

Unbalance — See Imbalance.

Uniform Window — In a DSA, a window function with uniformweighting across the time record. This window does not protectagainst leakage, and should be used only with transient signalscontained completely within the time record.

Vector — A quantity which has both magnitude and direction (phase).

Waterfall Plot — See Spectral Map.


Vibration Application Inquiry FormVibration Application Inquiry Form

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The vibration sensors listed in this catalog represent our most popular sensors, which are only a fraction of the sensors we offer. In additionto our standard sensors, PCB can customize sensors to meet your specific needs. Please fill out this inquiry form with any informationavailable to you, so that we may help you with your dynamic measurement application. If you would like to discuss your application, or if it isnot listed, please call, fax, E-mail, or write to PCB for suggestions.

Name: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Date: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Company:_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Phone: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Ext.: _ _ _ _ _ _ _ _ _ _ _ _ _

Dept.: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Fax: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Address: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ City/State: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Zip _ _ _ _ _ _ _ _ _ _ _ _ _ _

1. NATURE OF REQUEST

❑ Inquiry ❑ Order ❑ Quotation ❑ Delivery Information ❑ Complaint ❑ Trouble with Equipment

❑ Service or Repair ❑ Equipment Operation ❑ Visit required from PCB or Sales Representative in your area

2. DESCRIBE THE APPLICATION (check all that apply)

INDUSTRY MEASUREMENT TYPE

❑ Aerospace ❑ Laboratory Research ❑ Balancing ❑ Predictive Maintenance

❑ Pulp and Paper ❑ Microelectronics ❑ ESS ❑ Modal Analysis

❑ Power Plant ❑ Civil Engineering ❑ Shock ❑ High Frequency Testing

❑ Military ❑ Other ❑ Diagnostic Testing ❑ Vibration Control

❑ Automotive ❑ Seismic ❑ Vibration Isolation

❑ Trend Analysis ❑ Other

3. PHYSICAL

Physical Design: ❑ Single-Axis Accelerometer ❑ Triaxial Accelerometer ❑ Thru-Hole or Ring-Type Accelerometer

Desired Characteristics:

Sensitivity ____________ mV/g or ____________ pC/g

Frequency Range ____________ to ____________ Hz (within ± ____________ %) or (± ____________ dB)

Resonance Frequency ____________ kHz

Maximum Weight ____________ grams

Size Limitation H ____________, L ____________, W ____________; or ____________ Diameter

4. DYNAMIC

What is the approximate vibration amplitude level to be measured? ____________ g peak, ____________ m/s2 peak

What is the maximum vibration amplitude expected to be present? ____________ g peak, ____________ m/s2 peak

What is the desired resolution? ____________ g peak or rms ____________

What is the maximum frequency of interest? ____________ Hz or ____________ CPM

What is the minimum frequency of interest? ____________ Hz or ____________ CPM

5. MECHANICAL AND ENVIRONMENTAL

Continuous operating temperature range (min. to max.): ____________ to ____________ °C, to ____________ °F

Will the temperature be cycling? ____________ If yes, at what cycling profile? _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

What is the storage temperature? ____________ °C, ____________ °F

Are high amplitude mechanical signals present? _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

What is the highest shock level expected to be present? ____________ g peak

Describe in detail, operating environment _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _


Vibration Application Inquiry FormVibration Application Inquiry Form

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6. CABLING AND MOUNTING

Electrical Connection Location: ❑ Axial (Top) Exit ❑ Radial (Side) Exit

Connector Type: ❑ Military Style ❑ 10-32 ❑ 5-44 ❑ Integral Cable ❑ Four-Pin ❑ Other _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Cable Type: ❑ Coaxial Cable ❑ Two-Conductor Shielded ❑ Twisted Pair ❑ Other_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Other Cable Requirements _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Mounting Type: ❑ Removable Stud ❑ Integral Stud ❑ Captive Bolt ❑ Adhesive ❑ Magnetic Base ❑ Other _ _ _ _ _ _ _ _ _ _ _ _ _ _

Thread Size: ❑ 5-40 ❑ 10-32 UNF ❑ 1/4 -28 UNF ❑ Other _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

7. ELECTRICAL

What is the readout device? ❑ A to D ❑ Scope ❑ Other (specify) _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

What is the input impedance of the readout device (if applicable)?_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Can the readout device supply 24 to 27 VDC and 2 to 20 mA excitation to sensor? _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

What kind of signal conditioner would you like? Single channel __________ Multiple channel __________ How many?_ _ _ _ _ _ _ _ _ _ _ _

What cable lengths will be driven? Cable length _____ ft, _____ m Cable Capacitance _____ pF/ft, _____ pF/m

Will the cable be near electromagnetic interference sources (i.e., AC power lines, radio equipment, motors, and generators)?

Describe: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Is the sensor or cable located near areas prone to electrostatic discharges? _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Should the sensor be: ❑ Ground-Isolated ❑ Case-Isolated

8. OTHER SPECIFIC REQUESTS OR REQUIREMENTS

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For Shock Applications, Please complete the following:

9. SHOCK ACCELEROMETERS APPLICATION SPECIFICS

What is the pulse duration? _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

What is the pulse shape? ❑ Half sine ❑ Square ❑ Other (specify) _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Is the event repetitive? ❑ Yes ❑ No

If yes, time between events _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Is the shock caused by ❑ Pyro ❑ Metal to metal ❑ Other (specify) _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

PCB Piezotronics, Inc. Vibration Division • Shock and Vibration Sensors for Precision Testing Applications

3425 Walden Avenue • Depew, NY 14043 • 716-684-0001 • SVS Fax: 716-685-3886

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