- s?fÂ£c hm /sec 7141ft rÃcorbe* - hp labs · 2018-07-17 · the pen and the paper, separating...

HEWLETT-PACKARD JOURNAL

7 1 4 1 f t R Ã C O R B E *

- S?FÂ£C HM /SEC

"

1 1 1 ) 1 1 1 1 " t r i Ã I S T O F A N E '

S e e A l s o : A D V A N T A G E S O F D I R E C T - C O U P L E D D I F F E R E N T I A L DATA AMPLIF IERS; page 13 E R R O R S I N D A T A A M P L I F I E R S Y S T E M S ; p a g e 1 7

JULY 1967 © Copr. 1949-1998 Hewlett-Packard Co.

Pressurized Ink Recording on Z-Fold Str ip Charts A p ressu re -modu la ted i nk i ng sys tem and con tac t l ess pen - t i p pos i t i on f e e d b a c k a r e t w o o f m a n y i n n o v a t i o n s i n t h i s n e w e i g h t - c h a n n e l r e c o r d e r . By Robert A . Sanderson

MOST OF TODAY'S OSCILLOGRAPHIC RECORDERS pro duce good, readable traces, whether they do it

by heat, light, ink, or some other means. However, each method has special advantages. Optical recorders have the highest frequency response. Thermal recorders have low initial cost and are the least complicated. And when it comes to producing finished records with desirable properties, the champion is definitely ink.

Pressurized inking systems produce higher-quality traces than any other method; yet they use papers which are much less expensive than those needed for other methods. Capillary ink systems use the least expensive chart papers of all.

The best inked traces have high resolution. They are reproducible and permanent. The paper is durable. All other recording techniques fall short of ink's performance in one or more of these characteristics.

But ink has had problems, too. Most of them stem from the difficulty of handling ink in a recorder and not from deficiencies in the printed record â€” provided, of course, that the trace is continuous and no smudges are present.

Cover : Th i s Mode l 7848A Ink Reco rde r i s be ing sub jected to a programmed l i fe test designed to check i ts re l iab i l i t y . The tes t inc ludes s tar t -s top cyc les , speed changes, and high- and low-frequency input s ignals of several different waveforms. See also page 9.

Fig. 1. Two engineers put a new HP Ink Recording System

through its paces. This one has a roll-paper lakeiip, but it can aho use Z-fold charts. New black ink 'dries' on contact with paper and comes in easily replaced cartridges.

^ H E W L E T T - P A C K A R D C O . , 1 9 6 7 © Copr. 1949-1998 Hewlett-Packard Co.

Capillary ink systems use inks which can dry in the stylus tip in a relatively short time if the system is idle. Freeing the ink passages is a messy process involving the use of cleaning wires or solvents or both. Capillary sys tems also have a tendency to throw ink if the tip velocity of the pen is too high. This often becomes a problem, because high-performance pen-drive systems can pro duce tip velocities about ten times faster than a capillary system can cope with.

Replenishing the ink supply in either a capillary sys tem or a high pressure ink system can be troublesome, too. In most systems, recording has to be stopped while the ink reservoir is refilled. And, although more modern recorders use neater methods, some systems still require that ink be poured into the supply reservoir from a bottle.

High-pressure ink systems suffer from an inability to use Z-fold paper. Z-fold chart paper is much more con venient than rolled charts because any part of a Z-fold record can be examined easily at any time. With rolled

* ) .

Fig. 2. Unlike most pressurized ink recorders, the new re

corder can use Z-fold chart paper, which is much more

convenient than rolled paper because it allows any part of

a record to be examined easily, even while recording.

paper, there is no way to examine earlier portions of a record without first unrolling everything that came after wards. High-pressure ink systems can't use Z-fold charts because Z-fold paper is serrated across the chart to make it fold properly. When the pens pass over a fold, ink under pressure runs out through the serrations and makes a spot on the paper. The pens also lift slightly when they go over a fold and this, too, lets ink run out.

First-hand experience with one or more of the prob lems of early ink recorders has provided enough incen tive for many users to seek other recording techniques. Nonetheless, no finished record is more universally wanted or more useful than an inked record.

N e w I n k R e c o r d e r It is now possible to make inked records without

encountering the traditional problems of handling ink. A new eight-channel ink recorder (Fig. 1) embodies a number of new approaches to these old problems.

The new recorder has a pressurized ink system in which the ink pressure is modulated to maintain con tinuous, uniform traces at both high and low pen-tip velocities. The ink has been specially developed; it will not dry in the pen tips even if the recorder is idle for several months.

Replenishing the ink supply is a simple matter of replacing a disposable plug-in refill cartridge. One cart ridge serves all eight channels, and there is no need to stop the recorder to change cartridges.

Most important for the user is the new recorder's ability to use either Z-fold paper or rolls (Figs. 1 and 2). The new ink system is a low-pressure system which doesn't force out a large amount of ink when the pens pass over the folds in Z-fold charts.

Non-smudging, Non-dry ing Ink An important member of the ink- recorder engineering

group is a full-time chemist. Thus the development of the ink for the new recorder was an integral part of the design of the whole system.

Development and testing of more than 150 ink formu las produced at least 25 that would do an adequate job in most environments. The one selected continues to per form at 95% humidity and at 40Â°C (104Â°F). Further improvements are being made on a continuing basis.

Unlike the water-based inks used in capillary inking systems, the new ink has a glycol base which is very slow to evaporate (it has a low vapor pressure).

In the pens the ink stays fluid indefinitely because it is not exposed to air. Each pen is held against the paper

© Copr. 1949-1998 Hewlett-Packard Co.

Fig. 3. Replacing the ink cartridge in the new recorder can

be accomplished while the machine is operating. No mess

is involved. Each 4 oz. cartridge is good for 1000 miles of

recorded line.

Fig. 4. Chart paper used for ink recording has eight chan

nels, each 4 cm wide with 50 divisions. Recorded square

wave shows how ink-pressure modulation prevents loss of

Â¡race for step-function inputs.

with a force of about 20 grams, even when the recorder is not in use. Hence there is always a tight seal between the pen and the paper, separating the ink from the air. The pen tips are made of tungsten carbide to keep them from wearing out too quickly under the high pen force.

In use, the ink 'dries' instantly through absorption into the paper surface. It is formulated to give a high- resolution, near-black trace on glossy paper. This com bination appears to meet almost everyone's conception of the highest-quality type of record.

The ink comes in 4 oz. plug-in cartridges, each good for 1000 miles of recorded line (see Fig. 3). Cartridges can be replaced during recording, since there is a built-in reserve supply. An indicator light comes on when the cartridge in use is empty.

Z- fo ld Char t Paper Paper for the ink recorder was selected after testing

more than 100 samples from different manufacturers. Humidity proved to be the undoing of most of the

papers tested. Under 95% humidity most papers swell and their coatings soften. The soft coating can clog the pen tips. Swelling can impair accuracy if the paper's dimensions change more than the amount that can be compensated by recalibrating the system. The paper finally selected has a coating which softens little in high humidity, and its dimensions change less than any of the papers tested.

Other tests given the paper samples were microscopic examination for trace sharpness, and water immersion and charring tests to make sure that the traces wouldn't spread, wash off, or fade.

The chart paper selected is thin and strong, and has a smooth, glossy surface. The surface allows a high pen pressure with a minimum of friction forces and minimum chance of leakage. The paper comes in 500-foot rolls or 500-sheet Z-fold packs. Footage remaining on the roll is printed on the edge at one-foot intervals, and each page of the Z-fold pack is numbered. Each recording channel is four centimeters wide and has 50 divisions (see Fig. 4).

Pressure-modulated Ink System To maintain an adequate trace with varying chart

speeds and signal conditions, an entirely new pressurized inking system has been developed.

The purpose of ink pressure is to overcome changes in the ink flow rate caused by 1) changes in the pen speed and 2) accelerating forces created by the recti linear pen mechanism (more about this later).

In the new system the ink pressure is not constant,


Mani fo ld P u l s e P u m p

Fig. 5. Diagram of the pressure-modulated ink supply system.

One pen is shown, although the manifold supplies all eight.

but is a function of the chart speed and the input signal. The ink system (see Fig. 5) operates on air pressure

supplied by a small piston pump on the chart drive motor. Ink pressure is controlled by regulating the air with electrically-operated valves.

The ink system turns ON automatically when the chart is driven. Air from the pump (at about 6 psi) is connected directly to the plug-in ink cartridge to pres surize the ink. which is in a flexible sac in the cartridge. Air is also supplied to each of the eight channel shutoff valves to turn them on.

Ink from the supply cartridge enters the ink regulator where its pressure is dropped to one of three pressures, depending upon the chart speed. For chart speeds of 0.025 to 0.25 mm/s the ink pressure is 0.4 psi; for speeds of 0.5 to 2.0 mm/s, the pressure is 1.0 psi; and for speeds of 2.5 mm/s to 200 mm/s the pressure is 3.0 psi.

Pressure from the three pressure regulators is ade quate to maintain a continuous trace for most recorded signals. However, it is not adequate for recording some

step functions. Here the change in flow rate in the pen tube can be large and the acceleration forces along the tube are sometimes opposite to the direction of ink flow.

To overcome the negative 'g's' in the pen tube and maintain the flow at the tip when a step function occurs, a short pressure pulse is applied to the ink by a relay- driven pump behind the pen. The pump is electrically in series with the drive coil of the pen motor. It operates at all times, but its effect is small except when the signal being recorded has a rise time faster than 10 ms and an amplitude above 10 mm on the chart.

Under step condit ions a complete loss of t race would occur if there were no compensating pressure pulse. As the recorded square wave of Fig. 4 shows, the compensating pulse prevents this loss of trace. Under conditions of slower rise times or comparatively lower- frequency signals, the smaller pressure pulses from the pump serve to prevent thinning of the trace. There is always sufficient pressure to maintain a trace of near- constant width (about 0.009" wide) without the penalty of excess pressures which can create wider or wet traces.


Paper Chart

Prec is ion Wi re wound Res is to r

P icko f f Wi re

Rear P ivot

Pen -motor Drive Coi l

a

Fig. 6 (a). Pen drive mechanism is simple, yet very linear.

As pen motor ro ta tes , pen t ip descr ibes a l ine tha t i s

straight within 0.005" across 4 cm channel. Position-sens

ing transducer is located near pen t ip to detect l inkage

errors. Pickoff wire does not touch wirewound resistor, so

transducer wear is not a problem, (b). Transducer resistors

can be seen just below transverse rod in photograph.

Another important part of the ink system is a tiny hydraulic accumulator in the form of a rubber boot mounted on the pen near the tip. It does two things.

The pulse pump creates two pulses during pen deflec tions which occur in response to step inputs. One pulse is for the accelerating pen-motor current and one is for the decelerating current. A low-pressure point occurs approximately half way between these pulses, near the midpoint of the pen stroke. The tip accumulator length ens the duration of the first pulse so that it overlaps the second. This eliminates the dip in pressure.

Second, positive and negative pressure variations occur at the pen tip as the pen moves back and forth across the channel. To make the pen move in a straight line as the pen motor rotates, the distance from the pivot point to the pen tip must change; it must be minimum when the pen is at the center of the channel and maximum when the pen is at the edges. The result is a back and forth motion of the pen which accelerates and decelerates the ink and causes the pressure at the tip to vary. The boot reduces these pressure variations, thereby easing the problems of controlling the ink under all recording con ditions.

The ability of the new recorder to use Z-fold paper is primarily due to its only-when-needed ink pressure. The absence of excess pressure keeps the ink from making large wet spots as the pens are lifted slightly by the creases in the paper.

Servo Pen Dr ive

Complementing the new ink supply system is a com pletely new servo pen-drive system.

Fig. 6 is a diagram of the simple pen drive mechanism used in the new recorder. This mechanism converts the reciprocating rotary motion of the pen motor to a recip rocating linear motion of the pen tip across the record ing channel. With the chart stationary, the line described by the pen tip is straight within Â±0.005" across the width of the channel.

The purpose of any pen-drive system is to convert a variable electrical input signal to an accurately propor tional displacement of the pen tip. Tending to decrease the accuracy of this conversion are such things as non- linearities in the pen motor and in the linkage, twisting, bending, and vibration, especially in the stylus, and of course, friction.

To counteract these sources of error, position feedback is used. A transducer senses the displacement of the pen so that it can be compared with the input signal and the current in the pen motor adjusted accordingly.


Cente r l i ne o f Prec is ion Wi re

W o u n d R e s i s t o r Pen T ip

Rear Pivot

Fig. 7. Transducer near pen tip is linear. Ratio of

tip motion to pickoff-wire displacement is 1.38 to I.

Ideally, an error-sensing transducer to eliminate all mechanical errors should be located at the pen tip. How ever, the tip is a difficult place to put a transducer without hiding the tip from view. What's more, the inertia of a given transducer increases as the square of the distance from the pivot. Therefore, a location about an inch from the tip was selected for the moving element of the trans ducer in the new recorder (see Fig. 6).

Advantages of this transducer location over other pos sible locations proved to be many. Rotary transducers could have been located either at the pen-motor shaft or at the rear pivot, but transducers in these locations would have to be nonlinear because the displacement of the pen tip isn't a linear function of the shaft angles. Another disadvantage of these locations is that the transducers wouldn't be able to detect position errors caused by slack in the mechanism or bending of the stylus.

The transducer near the pen tip is linear. The ratio of tip motion to transducer displacement is a constant 1.38 to 1 (see Fig. 7). Displacement errors are detected pre cisely enough to make typical recorders linear within 0.25%. Linearity is specified conservatively at 0.5%.

No-contact Error Sensing

Two elements make up each error-sensing transducer. One is a fixed wire-wound resistor whose resistance varies linearly with the distance from either end. The other element is a pickoff wire attached to the pen, but insulated from it. The wire moves over the resistor as the pen moves from side to side. The wire does not touch

the resistor. Clearance is about 0.040 in. Hence wear and drag are avoided and frequency response is improved over that of knife-edge/slide-wire transducers.

In operation. 20 kHz square waves, 180Â° out of phase with each other, are applied to opposite ends of the re sistor. When there is no input signal these square waves

Fig. 8. 20 kHz square waves. 180Â° out of phase, are ap

plied to ends of transducer resistor, creating a null which

is shifted as a function of the input signal. Servo system

senses pen position relative to Â¡he null and drives pen to

follow null.


Pickoff Wire on Pen (Capacit ively coupled to L inear Resis tor )

Fig. 9. Electrical drive circuit for one channel of ink recorder.

have equal amplitudes. Thus a zero-voltage point or null is created exactly in the center of the resistor (see Fig. 8).

For a non-zero input signal, the amplitudes of both square waves are varied as functions of the input signal. This causes the position of the null on the resistor to shift.

Capacitive coupling between the resistor and the pickoff wire (about 0. 1 pF) enables the pickoff wire to sense when the null has moved away from the pen. The 20 kHz voltage produced in the pickoff wire is transmitted to a carrier amplifier. The amplified 20 kHz signal is demod ulated by a phase-sensitive demodulator, then amplified again and applied to the pen motor to cause the pen to follow the null.

Electr ica l Dr ive Circui t

The electrical drive circuit is shown in the simplified block diagram, Fig. 9. The input signal first passes through a limiter, to establish the limits of pen move ment, and is then applied to the 20 kHz modulator which establishes an ac null position along the position-sensing

resistance. The electrode on the writing pen picks up an ac voltage which represents pen position with respect to the null. This ac voltage goes to the demodulator, which supplies a dc voltage when the pen is not at the null. The polarity of the dc voltage indicates the direction from pen to null. The driver amplifier then supplies current to the pen motor which drives the pen to follow the null.

New Pen-dr ive Motor

The design of the pen-drive motor for the ink recorder is somewhat different from others in this class of electro mechanical elements. The conventional D'Arsonval gal vanometer used in older recorders has a large external magnet and a soft-iron core (see Fig. 10). This results in a heavy, bulky unit, which has a strong external stray magnetic field. When several units are placed side-by- side these stray fields interact, so that each magnet affects the sensitivity of its neighbor. As a result, special adjust ments and shielding are required for multi-channel instal lations.


The new pen-drive motor uses a magnetized core and has an external soft-iron shell. In this way, the entire magnetic structure acts as its own magnetic shield to reduce the stray external field and to give a more com pact, lighter, and less expensive unit which requires no special adjustments or shielding in multi-channel use. The pen motor is designed for at least 10,000 hours of normal operation.

Because the pen motor is used with a servo positioning system there is no need for a torsion rod or a centering spring. Restoring force is provided by the electrical drive circuit. With power off, the pen can be moved freely from one position to another and will remain at rest wherever it is placed.

Speed-reduct ion Mechanism Simpl i f ied

The chart drive mechanism includes the chart drive motor and five step-down reduction units which provide fourteen different chart drive speeds. The mechanism is shown in Fig. 1 1 .

When the solenoids of all five reduction units are OFF. each reduction unit operates at the stepdown ratio shown in Fig. 1 1 , for an overall stepdown ratio of 8000: 1 . When the solenoids of all five reduction units are ON, each reduction unit operates 'straight-through; for an overall ratio of 1:1. (There is also a fixed speed reduction of

15:1 in the system.) Different combinations of solenoids, selected by the chart speed buttons on the front panel, provide intermediate overall ratios, to give fourteen dif ferent chart speeds betwen 0.025 and 200 mm/s. The drive motor can be turned on and off remotely, and the speeds can be selected remotely.

All five gear boxes are simple in design and of similar construction. Many of their parts are interchangeable. This contributes to economy and maintainability.

The drive system is also designed for a normal life of not less than 10,000 hours with periodic lubrication.

Life Test ing for Rel iabi l i ty

The new recording system is being subjected to rigor ous testing. A programmed life test has been designed to expose the system to many of the worst conditions it might meet in practice (see cover and p. 2). In this test, the recorder turns on and off six times per hour (except power supply); the clutches operate 12 times per hour (this is' estimated to be ten times normal use); the recorded trace is a combination of waveforms consisting of 13% signals with frequencies of 10 Hz to 200 Hz and 87% slow signals and no signal; each stylus writes about 3000 ft/hr.

It is estimated that one hour of this programmed life test is equivalent to 15 hours of normal operation for the

Fig. 10. New pen motor (r), is lighter and smaller than

older type (I), and has smaller stray external magnetic field.


Signal Conditioning Preamplifiers for Ink Recorder 8800 Series Single Channel Preamps

HP Model 8 8 0 1 A

8802A

8803A

880SA

8806B

8807A

8808A

8809A

F e a t u r e s

Low-ga in dc d i f fe rent ia l ampl i f ie r S e n s i t i v i t y 5 m V / d i v t o 5 0 0 0 r n V / d i v â € ¢ A c c u r a c y Â ± 1 % , L i n e a r i t y "0 .25 d i v â€¢ F requency range dc t o 10 kHz â€¢ Zene r - s tab i l i zed ca l i

b r a t e d z e r o s u p p r e s s i o n â € ¢ I n t e r n a l c a l i b r a t i o n s o u r c e Medium-ga in dc d i f fe rent ia l ampl i f i e r S e n s i t i v i t y 1 m V / d i v t o 1 0 0 0 m V / d i v â € ¢ O t h e r f e a t u r e s s i m i l a r t o 8801 A High-gain dc d i f ferent ia l ampl i f ier S e n s i t i v i t y 1 / i V / d i v t o 5 V / d i v â € ¢ A c c u r a c y Â ± 1 % t o Â ± 2 % , L i n e a r i t y ' - 0 . 25 d i v â€¢ F requency r ange dc t o 110 Hz â€¢ Ca l i b ra ted ze ro sup

p ress ion â€¢ F loa t i ng , gua rded i npu t , 160 dB CMR (dc ) â€¢ H igh i npu t res is tance â€¢ High stabi l i ty Carr ier ampl i f ie r Sens i t i v i t y 10 / iV /d i v t o 2 mV/d i v â€¢ Ca l i b ra ted ze ro supp ress ion â€¢ I n t e r n a l t r a n s d u c e r e x c i t a t i o n s o u r c e â € ¢ G a g e f a c t o r c o n t r o l a d j u s t s f o r t r a n s d u c e r s e n s i t i v i t y Phase-sensi t ive demodulator R e f e r e n c e f r e q u e n c y r a n g e 5 0 H z t o 4 0 k H z â € ¢ F r o n t - p a n e l p l u g - i n ca l ib ra ted phase sh i f t â€¢ H igh- impedance , t rans fo rmer - i so la ted s igna l a n d r e f e r e n c e i n p u t s a c t o d c c o n v e r t e r S e n s i t i v i t y 1 m V / d i v t o 1 0 V / d i v ( r m s ) â € ¢ F r e q u e n c y r a n g e 5 0 H z t o 1 0 0 k H z â € ¢ C a l i b r a t e d z e r o s u p p r e s s i o n â € ¢ F l o a t i n g , g u a r d e d 1 M i l i n p u t f o r U n u s u a l l y f a s t e n v e l o p e r e s p o n s e â € ¢ S c a l e e x p a n s i o n f o r 0 . 0 2 % r e s o l u t i o n Logar i thmic ac to dc conver te r Sens i t i v i t y : 100 /Â¿V /d i v = bo t t om sca le â€¢ Accu racy Â±1 dB q u e n c y r a n g e 1 0 H z t o 1 0 0 k H z â € ¢ 1 0 0 d B d y n a m i c r a n g e Signal coupler Swi t ch se lec ted i npu t impedance â€¢ Fu l l - sca le pos i t i on ing

F re-

Pr incipal Uses Genera l use i n a ma jo r i t y o f reco rd ing s i t u a t i o n s f r o m d c t o t h e m a x i m u m u s a b l e f r e q u e n c y o f t h e r e c o r d e r

Genera l (see 8801 A)

V e r s a t i l e g e n e r a l - p u r p o s e d c a m p l i f i e r . U s e d w h e r e h i g h s e n s i t i v i t y , s tab i l i t y , and opera t iona l f l ex ib i l i t y a re requ i red

M e a s u r e m e n t o f s t r a i n , d i s p l a c e m e n t , v e l o c i t y , e t c . E x c i t e s t r a n s d u c e r s a n d d e t e c t s t h e i r o u t p u t s

M o n i t o r i n g p e r f o r m a n c e o f a c s e r v o sys tems

M e a s u r i n g a c v o l t a g e s ( a n d c u r r e n t s w i t h c u r r e n t p r o b e ) . U s e d l i k e a c d i f f e r e n t i a l v o l t m e t e r f o r m o n i t o r i n g a n d r e c o r d i n g a m p l i t u d e s t a b i l i t y o f a c sources M o n i t o r i n g a c l e v e l s w i t h w i d e d y n a m i c r a n g e s , e . g . , s o u n d l e v e l r e c o r d i n g , v i b r a t i o n a n a l y s i s , e t c . Used whe re g rea t f l e x i b i l i t y and ve rsa t i l i t y a r e n o t r e q u i r e d a n d c o s t i s a c o n s i d e r a t i o n . B a s i c s e n s i t i v i t y m u s t b e s u i t e d t o a p p l i c a t i o n o r a f i x e d e x t e r n a l a t t e n u a t o r m u s t b e u s e d

Eight-Channel Preamps (all channels identical) 8 8 2 0 A A l l - s i l i c o n l o w - g a i n d c a m p l i f i e r

Sens i t i v i t y 50 mV/d i v to 5 V /d i v â€¢ 1 Mn inpu t res i s tance â€¢ Po la r i t y r e v e r s a l s w i t c h i n e a c h c h a n n e l ( m i n i m a l e f f e c t o n z e r o p o s i t i o n ) â € ¢ I n d i v i d u a l o r s i m u l t a n e o u s c a l i b r a t i o n o f a l l c h a n n e l s

8 8 2 1 A A l l - s i l i c o n m e d i u m - g a i n d c a m p l i f i e r Sens i t i v i t y 0 .5 mV/d iv to 5 V /d i v â€¢ F loa t ing , guarded inpu t on 6 mos t sens i t i ve r anges , d i f f e ren t i a l on 6 o the r r anges â€¢ 9 M i ! i npu t r es i s t - a n c e â € ¢ C M R 1 0 0 d B o n m o s t s e n s i t i v e r a n g e

T e l e m e t r y r e c o r d i n g , a n a l o g c o m p u t e r ou tpu t , o r gene ra l use .

G e n e r a l - p u r p o s e u s e o v e r r e c o r d e r b a n d w i d t h

Medical Preamplifiers M o d e l H P M o d e l D e s c r i p t i o n a n d U s e

350-1 OOOB

350-11 OOCM

350-1 300C 350-1 500A

350-2700C

350-3000C

350-3200A

350-3400A

350-3600A 350-3700B 350-5000B

d c p r e a m p l i f i e r f o r r e c o r d i n g o u t p u t s o f i n s t r u m e n t s u s e d f o r g a s a n a l y s i s , m o n i t o r i n g C O ; c o n c e n t r a t i o n , e t c . A l s o f o r d e n s i t o m e t e r a n d c a r d i o t a c h o m e t e r r e c o r d i n g , e t c . C a r r i e r p r e a m p l i f i e r , u s e d w i t h t r a n s d u c e r f o r r e c o r d i n g p r e s s u r e , f l o w , v e l o c i t y , d i s p l a c e m e n t , f o r c e , e t c . M e d i c a l u s e s i n c l u d e r e c o r d i n g v e n o u s , a r t e r i a l , g a s t r o i n t e s t i n a l , r e s p i r a t o r y a n d o t h e r p r e s s u r e s , o r f o r c e s i n p r o s t h e t i c a p p l i a n c e s . d c c o u p l i n g p r e a m p l i f i e r , s i m i l a r t o 3 5 0 - 1 O O O B b u t w i t h l o w e r s e n s i t i v i t y . L o w - l e v e l g a g e s , u s e d w i t h o n e o f e i g h t p l u g - i n s f o r m o n i t o r i n g t h e r m o c o u p l e s , E E G / E C G , s t r a i n g a g e s , W a t e r s g a l v a n i c W a t e r s e a r p i e c e s o r c u v e t t e s , o x y g e n c e l l s . A l s o f o r m e a s u r i n g g a l v a n i c s k i n r e s i s t a n c e o r b l o o d f l o w ( t h e r m a l d i l u t i o n m e t h o d ) . H i g h - g a i n a c p r e a m p l i f i e r f o r g e n e r a l u s e , i n c l u d i n g s i n g l e c h a n n e l E E G d u r i n g s u r g e r y , f e t a l e l e c t r o c a r d i o g - raphy , e tc . M e d i c a l c a r r i e r p r e a m p l i f i e r . U s e d l i k e 3 5 0 - 1 1 0 0 C M . H a s s w i t c h e s f o r a v e r a g i n g , p u l s a t i l e , a n d c a t h e t e r o p e r a t ion. E C G / g e n e r a l - p u r p o s e p r e a m p l i f i e r . S i m i l a r t o 3 5 0 - 2 7 0 0 C . O p e r a t e s w i t h W a t e r s N i t r o g e n M e t e r , B e c k m a n CO2 Ana lyze r , e t c . C a r d i o - t a c h p r e a m p l i f i e r . M e a s u r e s a v e r a g e h e a r t r a t e , t i m e b e t w e e n ' R ' w a v e s , e t c . A l s o f o r l o n g - t e r m m o n i to r ing . p H p r e a m p l i f i e r . F o r r e c o r d i n g p H o r p C O , i n w h o l e b l o o d , o r g e n e r a l - p u r p o s e p H r e c o r d i n g i n 3 - 1 1 p H r a n g I n t e g r a t i n g p r e a m p l i f i e r . U s e d a s i n t e g r a t o r o r s u m m a t o r . R e s p i r a t o r y p r e a m p l i f i e r . W i t h 2 c a r r i e r p r e a m p s a n d a n o s c i l l o s c o p e , m e a s u r e s m e c h a n i c a l r e s i s t a n c e a n d c o m p l i a n c e o f l u n g s .

10 © Copr. 1949-1998 Hewlett-Packard Co.

Fig. 1 1 . Simplified chart

drive mechanism gives

14 chart speeds

with relatively jew parts,

many of them

interchangeable. Different

speeds are obtained by

switchhif! solenoids to

engage or disengage

the five reduction

i>ctii:\ in different

combinations.

pen motor and stylus, 10 hours of normal operation for the chart drive train, and one hour of normal operation for the power supply and amplifiers. Normal life esti mates for the various parts of the recorder are based on this test and these estimated equivalence factors.

Preampl i f iers for Complete Recording Systems

So far this discussion has been limited to the new ink- writing recorder. However, the recorder is only one part of a recording system. Preamplifiers are needed to com plete the system, one for each of the eight channels.

The table on p. 10 shows the preamplifiers that will operate with the new recorder.

Three types of preamplifiers are available. One is a series of single-channel plug-in units which perform sev eral specialized signal-conditioning functions. Another type consists of lower-cost eight-channel units in which all channels are alike. The third is a series of single- channel units primarily for bio-medical applications.

All of the preamplifiers listed in the table are designed to drive the single-ended, ground-referenced, 5 k Q inputs of the ink recorder's amplifiers. All of the preamplifiers also have facilities for precise gain adjustments and for setting the zero position of the writing pen to any point on the 4-cm channel.

Acknowledgments

Important contributions to the ink recorder's develop ment have been made by many, many individuals during the past several years. I can only mention a few here.

Dr. Arthur Miller's ideas on pressure modulation were the beginning of the project. The servo system was de signed by J. William Sauber. George Larsen developed the new family of inks. The mechanical design was done by Ustun Germen, Richard L. Weddleton, Michael A. Feldstein, Daniel H. Dudley, and Richard E. Stanley. John C. Allen and Steven I. Zoltan designed the gearbox and the pen motor, respectively. Substantial contributions to the program were also made by Donald M. Brown, Edward W. Nork, C. Miller Ferguson, and Eugene J. Picard. â€¢

\

Robert A. Sanderson B o b S a n d e r s o n j o i n e d H P i n 1 9 6 2 . Be fo re tha t , he had spen t f i ve yea rs i n t h e e n g i n e e r i n g a n d p r o d u c t deve lopmen t o f magne t i c t ape d r i ves a n d c a r d c o l l a t o r s , a n d o n e y e a r a s p r o j e c t e n g i n e e r f o r t h e d e v e l o p m e n t o f a c o l o r - f i l m p r o c e s s o r . S i n c e 1 9 6 3 h e h a s b e e n p r o j e c t e n g i n e e r f o r t h e M o d e l 7 8 4 8 A I n k R e c o r d e r p r o j e c t . H e h o l d s a p a t e n t o n a c a r d - g u i d i n g a p p a r a t u s a n d h a s o n e p e n d i n g o n t h e i n k s u p p l y s y s t e m u s e d i n t h e n e w r e c o r d e r .

B o b r e c e i v e d a B S d e g r e e i n m a c h i n e d e s i g n f r o m t h e R h o d e I s l a n d S c h o o l o f D e s i g n i n 1 9 5 6 . B e t w e e n h i s f i r s t t w o y e a r s o f c o l l e g e a n d h i s l a s t t w o y e a r s , h e s p e n t t w o y e a r s i n t h e U . S . A r m y O r d n a n c e C o r p s . H e i s m a r r i e d , h a s f o u r c h i l d r e n , a n d e n j o y s s k i i n g , c a m p i n g , a n d f l y i n g .


S P E C I F I C A T I O N S HP

M o d e l 7 8 4 8 A R e c o r d e r

( T h e s e s p e c i f i c a t i o n s a r e l o r t h e r e c o r d e r o n l y . F o r p r e a m p l i f i e r d e s c r i p t i o n s , s e e T a b l e , p . 1 0 . )

C h a r t D r i v e S p e c i f i c a t i o n s

C H A R T S P E E D S : F o u r t e e n , s e l e c t e d b y s e v e n s p e e d b u t t o n s

a n d X 1 a n d X 1 0 0 b u t t o n s . S p e e d s a r e : 0 . 0 2 5 , 0 . 0 5 , 0 . 1 0 ,

0 . 2 5 , 0 . 5 0 , 1 . 0 . 2 . 0 , 2 . 5 . 5 , 1 0 , 2 5 , 5 0 , 1 0 0 , a n d 2 0 0 m m / s .

S p e e d a c c u r a c y Â ± 0 . 2 5 % w i t h 6 0 - c y c l e l i n e .

R E M O T E C O N T R O L : B y p r e s s i n g r e m o t e b u t t o n ; a l s o p r o

v i d e s r e m o t e i n d i c a t i o n o f s y s t e m r e a d i n e s s .

P A P E R W E A V E : L e s s t h a n 0 . 5 m m . D e f i n e d a s t o t a l l a t e r a l

m o t i o n o f a n y a m p l i t u d e l i n e o n t h e c h a r t a s p a p e r p a s s e s

t h r o u g h t h e r e c o r d e r , w i t h r e s p e c t t o a n y f i x e d r e f e r e n c e

p o i n t o n t h e r e c o r d e r .

R E C O R D I N G C H A R T : 5 0 0 - f o o t r o l l s o r 5 0 0 - s h e e t Z - f o l d p a c k .

E i g h t f o u r - c e n t i m e t e r c h a n n e l s , d i v i d e d i n t o 5 0 d i v i s i o n s .

T i m e l i n e s e v e r y 1 m m . F o o t a g e r e m a i n i n g i n d i c a t e d o n

r i g h t e d g e a t 1 - f o o t i n t e r v a l s ( r o l l s ) o r e a c h s h e e t n u m

b e r e d ( Z - f o l d p a c k s ) .

I n k S y s t e m S p e c i f i c a t i o n s

I N K S U P P L Y : P l u g - i n p l a s t i c b o t t l e , 4 - o z . c o n t e n t s . F r o n t

p a n e l i n d i c a t o r s h o w s w h e n b o t t l e i s e m p t y . R e s e r v e s u p

p l y o f 1 / z h o u r a p p r o x i m a t e l y .

B A N D W I D T H - A M P L I T U D E P R O D U C T : 6 0 H z f o r f u l l - s c a l e d e f l e c t i o n . S e e c h a r t .

I N K F E E D : P r e s s u r i z e d ,

i n e a c h c h a n n e l .

( i t h i n d i v i d u a l p r e s s u r e m o d u l a t i o n

I N K : N o n - s m u d g i n g , d r y - o n - c o n t a c t , p e r m a n e n t . D i a z o r e p r o

d u c i b l e .

Recorded Line Specif icat ions T R A C E W I D T H : N o m i n a l l y 0 . 0 1 0 " , m a y b r o a d e n t o 0 . 0 2 0 " a t

l o w e s t c h a r t d r i v e s p e e d s .

R E C T I L I N E A R A C C U R A C Y : L i n e i s s t r a i g h t w i t h i n 0 0 0 5 " o v e r

4 c m d i s p l a c e m e n t , w i t h p e n p r e s s u r e b e t w e e n 1 5 a n d 2 5

g r a m s .

M a r k e r S p e c i f i c a t i o n s L E F T - E D G E M A R K E R : P u s h - b u t t o n s e l e c t i o n o f p u l s e a t 1 - s

o r 1 - m i n i n t e r v a l s f r o m i n t e r n a l s y n c h r o n o u s m o t o r t i m e r s .

I n d i c a t i o n i s s t a t i c d i s p l a c e m e n t , a p p r o x i m a t e l y 2 m m .

M a y o p e r a t e r e m o t e l y , o r f r o m + 1 . 5 v o l t s i g n a l i n t o i n t e r

n a l a m p l i f i e r .

R I G H T - E D G E M A R K E R : P u s h - b u t t o n e v e n t m a r k e r . I n d i c a t i o n

i s s t a t i c d i s p l a c e m e n t , a p p r o x i m a t e l y 2 m m . M a y b e o p e r

a t e d r e m o t e l y b y c o n t a c t c l o s u r e , o r f r o m + 1 . 5 v o l t s i g n a l

i n t o i n t e r n a l a m p l i f i e r .

Record ing Spec i f i ca t ions S E N S I T I V I T Y : 0 . 1 v o l t i n p u t g i v e s o n e d i v i s i o n d e f l e c t i o n

Â ± 2 % .

L I N E A R I T Y :

M e t h o d 1 : A f t e r c a l i b r a t i n g f o r z e r o e r r o r a t c e n t e r s c a l e

a n d + 2 0 d i v i s i o n s , e r r o r i s l e s s t h a n â € ¢ 0 . 2 5 d i v i s i o n a t

a n y p o i n t o n p r i n t e d c o o r d i n a t e s .

M e t h o d 2 : A f t e r c a l i b r a t i n g f o r z e r o e r r o r a t l o w e r a n d

Â ± 0 . 5 d i v i s i o n a t a n y p o i n t o n s c a l e .

N O I S E : < 0 . 1 d i v p e a k - t o - p e a k .

F R E Q U E N C Y R E S P O N S E : d c t o 1 6 0 H z . w i t h r e s p o n s e n o t

p e a k - t o - p e a k e x c u r s i o n w i t h d a m p i n g s e t f o r 4 % o v e r s h o o t

o n s q u a r e w a v e s .

R E S P O N S E T I M E : V a r i e s w i t h t o t a l d e f l e c t i o n , n o t m o r e t h a n

4 % o v e r s h o o t :

1 0 % t o 9 0 Â ° 0 s q u a r e

P e a k - t o - p e a k d e f l e c t i o n w a v e r e s p o n s e t i m e

1 0 d i v i s i o n s 3 m i l l i s e c o n d s



F R E Q U E N C Y I N H z

Prices: E I G H T - C H A N N E L S Y S T E M F O R U S E W I T H 8 8 0 0 S E R I E S

P R E A M P L I F I E R S

M o d e l 7 8 5 8 A E i g h t - C h a n n e l R e c o r d i n g S y s t e m . . . $ 9 , 6 5 0 . 0 0 c o n s i s t i n g o f :

1 ) 7 8 4 8 A E i g h t - C h a n n e l I n k R e c o r d e r 8 ) 0 7 8 5 0 - 6 1 0 0 0 D r i v e r A m p l i f i e r s 1 ) 0 8 8 0 0 - 6 3 0 0 0 o r 8 8 0 0 - 0 3 A

P r e a m p P o w e r S u p p l y 1 ) 0 7 8 5 8 - 6 9 0 0 0 C a b i n e t

O p t i o n 0 1 : l e s s C a b i n e t

O p t i o n 0 2 : P o r t a b l e C a s e s

O p t i o n 0 3 : Z F o l d P a p e r T a k e u p A d d $ 1 0 0 . 0 0

O p t i o n 0 8 : 5 0 H z O p e r a t i o n A d d $ 5 0 . 0 0

O p t i o n 0 9 : 2 3 0 V o l t s , 9 9 0 0 - 2 0 2 9 T r a n s f o r m e r i n s t a l l e d i n c a b i n e t

E I G H T - C H A N N E L P R E A M P L I F I E R S :

8 8 2 0 A L o w - g a i n d c a m p l i f i e r $ 1 , 1 5 0 . 0 0

8 8 2 1 A M e d i u m - g a i n d c a m p l i f i e r $ 2 , 4 0 0 . 0 0

E I G H T - C H A N N E L S Y S T E M F O R U S E W I T H 3 5 0 S E R I E S P R E A M P S

M o d e l 7 8 6 8 A E i g h t - C h a n n e l I n k R e c o r d i n g S y s t e m . $ 1 0 , 2 5 0 . 0 0 c o n s i s t i n g o f :

1 ) 7 8 4 8 A E i g h t - C h a n n e l I n k R e c o r d e r 8 } 0 7 8 5 0 - 6 1 0 0 0 D r i v e r A m p l i f i e r s 8 ) 3 5 0 - 5 0 0 B P r e a m p P o w e r S u p p l i e s 2 ) 0 0 3 5 0 - 6 3 0 1 0 P r e a m p R a c k s 1 ) 0 7 8 6 8 - 6 9 0 0 0 C a b i n e t

O p t i o n 0 1 : l e s s C a b i n e t D e d u c t $ 4 2 5 . 0 0

O p t i o n 0 2 : P o r t a b l e C a s e s N o c h a n g e

O p t i o n 0 3 : Z F o l d P a p e r T a k e u p A d d $ 1 0 0 . 0 0

O p t i o n 0 8 : 5 0 H z O p e r a t i o n A d d $ 5 0 . 0 0

O p t i o n 0 9 : 2 3 0 V o l t s . 9 9 0 0 - 2 0 2 9 T r a n s f o r m e r i n s t a l l e d i n c a b i n e t A d d $ 1 0 0 . 0 0

D e d u c t $ 4 2 5 . 0 0

N o C h a n g e

8 8 0 0 S E R I E S P R E C I S I O N S I G N A L C O N D I T I O N E R S :

8 8 0 1 A L o w G a i n P r e a m p l i f i e r $ 2 7 5 . 0 0 O p t i o n 0 1 : B e n c h T o p U n i t , i n c l u d e s 8 6 0 - 5 0 0 P o w e r S u p p l y a n d 8 6 0 - 1 4 0 0 P o r t a b l e C a s e A d d $ 3 1 0 . 0 0

8 8 0 2 A M e d i u m G a i n P r e a m p l i f i e r $ 3 2 5 . 0 0 O p t i o n 0 1 : B e n c h T o p U n i t , i n c l u d e s 8 6 0 - 5 0 0 P o w e r S u p p l y a n d 8 6 0 - 1 4 0 0 P o r t a b l e C a s e A d d $ 3 1 0 . 0 0

8 8 0 3 A H i g h G a i n P r e a m p l i f i e r $ 6 0 0 . 0 0 O p t i o n 0 1 : B e n c h T o p U n i t i n c l u d e s 8 6 0 - 5 0 0 A P o w e r S u p p l y a n d 8 6 0 - 1 4 0 0 P o r t a b l e C a s e A d d $ 3 2 5 . 0 0

8 8 0 5 A C a r r i e r P r e a m p l i f i e r $ 4 0 0 . 0 0 O p t i o n 0 1 : B e n c h T o p U n i t , i n c l u d e s 8 6 0 - 5 0 0 C P o w e r S u p p l y a n d 8 6 0 - 1 4 0 0 P o r t a b l e C a s e A d d $ 3 2 5 . 0 0

O p t i o n 0 2 : 4 6 2 - 2 3 7 H a r m o n i c F i l t e r K i t i n s t a l l e d f o r u s e o f 8 8 0 5 A w i t h 2 6 7 o r 2 6 8 t r a n s d u c e r s A d d $ 3 0 . 0 0

8 8 0 6 B P h a s e S e n s i t i v e D e m o d u l a t o r $ 4 9 5 . 0 0 O p t i o n 0 1 : B e n c h T o p U n i t , i n c l u d e s 8 6 0 - 5 0 0 P o w e r S u p p l y a n d 8 6 0 - 1 4 0 0 P o r t a b l e C a s e A d d $ 3 1 0 . 0 0

O p t i o n 0 2 : 8 8 0 6 - 0 1 B V a r i a b l e F r e q u e n c y P h a s e S h i f t e r P l u g - i n . 5 0 H z t o 4 0 k H z A d d $ 1 7 5 . 0 0

O p t i o n 0 3 : 8 8 0 6 - 0 2 B C a l i b r a t e d P h a s e S h i f t e r P l u g - i n , 6 0 H z A d d $ 1 2 5 . 0 0

O p t i o n 0 4 : 8 8 0 6 - 0 3 B C a l i b r a t e d P h a s e S h i f t e r P l u g - i n ,

4 0 0 H z A d d $ 1 2 5 . 0 0

O p t i o n 0 5 : 8 8 0 6 - 0 4 B C a l i b r a t e d P h a s e S h i f t e r P l u g - i n , 5 k H z A d d $ 1 2 5 . 0 0

8 8 0 7 A A C t o D C C o n v e r t e r $ 7 0 0 . 0 0 N o r m a l l y s u p p l i e d w i t h 0 8 8 0 7 - 6 0 0 4 0 . 4 0 0 H z F i l t e r f o r s i g n a l f r e q u e n c i e s f r o m 3 3 0 H z t o 1 0 0 k H z .

O p t i o n 0 1 : 0 8 8 0 7 - 6 0 0 3 0 6 0 H z F i l t e r f o r s i g n a l f r e q u e n c i e s f r o m 5 0 H z t o 1 0 0 k H z N o C h a r g e w h e n S u b s t i t u t e d

O p t i o n 0 2 : 0 8 8 0 7 - 6 0 0 5 0 D C P l u g - i n N o C h a r g e w h e n S u b s t i t u t e d

O p t i o n 0 3 : B e n c h T o p U n i t , i n c l u d e s 8 6 0 - 5 0 0 P o w e r S u p p l y a n d 8 6 0 - 1 4 0 0 P o r t a b l e C a s e A d d $ 3 1 0 . 0 0

8 8 0 8 A L o g L e v e l P r e a m p l i f i e r $ 6 2 5 . 0 0 O p t i o n 0 1 : B e n c h T o p U n i t , i n c l u d e s 8 6 0 - 5 0 0 P o w e r S u p p l y a n d 8 6 0 - 1 4 0 0 P o r t a b l e C a s e A d d $ 3 1 0 . 0 0

8 8 0 9 A S i g n a l C o u p l e r $ 1 1 0 . 0 0 O p t i o n 0 1 : B e n c h T o p U n i t , i n c l u d e s 8 6 0 - 5 0 0 P o w e r S u p p l y a n d 8 6 0 - 1 4 0 0 P o r t a b l e C a s e A d d $ 3 1 0 . 0 0

E I G H T - C H A N N E L S Y S T E M F O R U S E W I T H 8 8 2 0 A O R 8 8 2 1 A E I G H T - C H A N N E L P R E A M P B A N K

M o d e l 7 B 7 8 A E i g h t - C h a n n e l I n k R e c o r d i n g S y s t e m $ 8 . 6 0 0 . 0 0 c o n s i s t i n g o f : 1 ) 7 8 4 8 A E i g h t - C h a n n e l I n k R e c o r d e r 8 ) 0 7 8 5 0 - 6 1 0 0 0 D r i v e r A m p l i f i e r s 1 ) 0 7 8 7 8 - 6 9 0 0 0 C a b i n e t

O p t i o n 0 1 : l e s s C a b i n e t

O p t i o n 0 2 : P o r t a b l e C a s e s

O p t i o n 0 3 : Z F o l d P a p e r T a k e u p .

O p t i o n 0 8 : 5 0 H z O p e r a t i o n

O p t i o n 0 9 : 2 3 0 V o l t O p e r a t i o n . 9 9 0 0 - 2 0 2 9 T r a n s f o r m e r i n s t a l l e d i n c a b i n e t A d d $ 1 0 0 . 0 0

3 5 0 S E R I E S M E D I C A L P R E A M P L I F I E R S :

3 5 0 - 1 0 0 0 B D C P r e a m p l i f i e r $ 3 2 5 . 0 0

3 5 0 - 1 1 0 0 C M C a r r i e r P r e a m p l i f i e r w i t h h a r m o n i c f i l t e r k i t i n s t a l l e d f o r u s e w i t h 2 6 7 o r 2 6 8 T r a n s d u c e r s . . 4 2 5 . 0 0

A d d $ 1 0 0 . 0 0 3 5 0 - 1 3 0 0 C D C C o u p l i n g P r e a m p l i f i e r 2 5 0 . 0 0

3 5 0 - 1 5 0 0 A L o w L e v e l P r e a m p l i f i e r 5 2 5 . 0 0

3 5 0 - 2 B D C P l u g - i n w i t h Z e r o S u p p r e s s i o n 1 9 0 . 0 0

3 5 0 - 3 A E E G / E C G P l u g - i n 2 2 5 . 0 0

3 5 0 - 4 A D C S t r a i n G a g e P l u g - i n 1 3 0 . 0 0

3 5 0 - 8 W a t e r s O x i m e t e r P l u g - i n 1 7 5 . 0 0

3 5 0 - 9 A W a t e r s E a r p i e c e / C u v e t t e P l u g - i n 2 0 0 . 0 0

H P M o d e l 6 2 0 3 B P o w e r S u p p l y f o r u s e w i t h 3 5 0 - 9 A . 1 6 9 . 0 0

3 5 0 - 1 1 A O x y g e n C e l l P l u g - i n 1 4 0 . 0 0

3 5 0 - 1 2 G a l v a n i c S k i n R e s i s t a n c e P l u g - i n 2 0 5 . 0 0

3 5 0 - 1 5 T h e r m a l D i l u t i o n P l u g - i n 2 6 5 . 0 0

1 4 0 1 2 A T h e r m i s t o r P r o b e ( 1 2 5 c m l o n g } w i t h 1 0 f t . i n t e r c o n n e c t i n g c a b l e a n d c a l i b r a t i o n c h a r t s â € ” f o r

u s e w i t h 3 5 0 - 1 5 1 9 0 . 0 0

. . 3 7 5 . 0 0 3 5 0 - 2 7 0 0 C H i g h G a i n P r e a m p l i f i e r . . 3 5 0 - 3 2 0 0 C 8 E G G A c c e s s o r y K i t , i n c l u d i n g p a t i e n t

c a b l e , s t r a p s , e l e c t r o d e s a n d R e d u x 3 9 . 0 0

3 5 0 - 2 7 0 0 C 8 E E G A c c e s s o r y K i t , i n c l u d i n g n e e d l e e l e c t r o d e s , d i s k e l e c t r o d e s . R e d u x a n d 2 5 f t . c a b l e 2 4 . 0 0

3 5 0 - 3 0 0 0 C M e d i c a l C a r r i e r P r e a m p l i f i e r . 3 2 5 . 0 0

3 2 5 . 0 0 3 5 0 - 3 2 0 0 A E C G P r e a m p l i f i e r 3 5 0 - 3 2 0 0 C 8 E C G A c c e s s o r y K i t , i n c l u d i n g 5 w i r e

p a t i e n t c a b l e , s t r a p s , e l e c t r o d e s a n d R e d u x 3 9 . 0 0

4 6 1 - 1 9 0 Y C a b l e f o r t a k i n g t w o s e p a r a t e l e a d s a t o n c e w i t h t w o 3 5 0 - 3 2 0 0 ' s , u s i n g o n e 3 5 0 - 3 2 0 0 C 8 A c c e s s o r y K i t 3 3 . 0 0

3 5 0 - 3 4 0 0 A C a r d i o - T a c h P r e a m p l i f i e r 5 5 0 . 0 0 7 6 0 - 2 0 M o n i t o r M e t e r 1 1 4 . 0 0

7 6 0 - 2 0 - 1 2 0 0 - 1 0 0 b e a t s / m i n H e a r t R a t e S c a l e 6 . 5 0



7 6 0 - 2 0 - 1 4 0 B l a n k S c a l e 3 . 5 0

6 5 1 - 2 6 3 P 1 4 V S t f o o t ( 1 3 7 0 m m ) c a b l e f o r c o n n e c t i n g 3 5 0 - 3 4 0 0 A t o 7 6 0 - 2 0 M o n i t o r M e t e r 5 . 7 5

6 5 1 - 2 6 3 P 2 1 2 f o o t ( 3 6 6 0 m m ) c a b l e f o r c o n n e c t i n g 3 5 0 - 3 4 0 0 A t o 7 6 0 - 2 0 M o n i t o r M e t e r 6 . 7 5

6 5 1 - 2 6 3 P 3 2 0 f o o t ( 6 1 0 0 m m ) c a b l e f o r c o n n e c t i n g 3 5 0 - 3 4 0 0 A t o 7 6 0 - 2 0 M o n i t o r M e t e r 7 . 7 5

3 5 0 - 3 4 0 0 C 9 C a r d i o - T a c h E C G A c c e s s o r i e s K i t 2 3 . 0 0

. . . 6 5 0 . 0 0 . . 2 2 2 . 5 0

3 5 0 - 3 6 0 0 A p H P r e a m p l i f i e r , l e s s e l e c t r o d e s . P a r t N o . 4 6 1 - 2 1 2 A d a p t e r f o r p O 2 e l e c t r o d e .

P a r t N o . 4 6 1 - 2 1 5 S w i t c h B o x f o r p H . p C O 3 . a n d p O j 3 8 2 . 5 0

3 5 0 - 3 7 0 0 A I n t e g r a t i n g P r e a m p l i f i e r

3 5 0 - 5 0 0 0 B R e s p i r a t o r y P r e a m p l i f i e r . . . . . . . . . . . . . . . . . 5 5 0 . 0 0 2 6 7 B P r e s s u r e T r a n s d u c e r . . . . . . . . . . . . . . . . . . . . . . . 2 5 0 . 0 0

D e d u c t $ 4 2 5 . 0 0

N o c h a n g e

A d d $ 1 0 0 . 0 0

. A d d $ 5 0 . 0 0

2 6 8 B P r e s s u r e T r a n s d u c e r

2 7 0 B i - D i r e c t i o n a l D i f f e r e n t i a l G a s P r e s s u r e T r a n s d u c e r

250.00

295.00

M A N U F A C T U R I N G D I V I S I O N : H P S a n b o r n D i v i s i o n 1 7 5 W y m a n S t r e e t W a l t h a m , M a s s a c h u s e t t s 0 2 1 5 4


Fig. 1. Two common configurations of data amplifiers are the direct-coupled differential (a) and the carrier-coupled design (b).

Advantages of Direct-Coupled Differential Data Amplifiers By Morton H. Lev in

THE EVOLUTION OF DATA AMPLIFIERS has been domi nated by the struggle to find better ways of achieving

common mode rejection. Two general approaches have become widely used: direct-coupled 'differential' designs, and carrier-coupled configurations. The differential de signs, Fig. l(a) raise the common-mode input impedance to a very high value by means of feedback. This type of amplifier may be completely direct-coupled, using vari ous isothermal techniques to achieve low offset errors, or it may be chopper-stabilized.

The carrier-coupled designs, Fig. l(b), modulate the signal at a high frequency, passing this ac signal through a shielded transformer, 'then demodulating and filtering out the carrier. Using the carrier-coupled system in con trast with the direct-coupled approach, yields ability to reject much larger common mode voltages (up to 1 kV) and achieves slightly higher CMR, but at the expense of increased complexity, decreased linearity and accuracy (since the modulator-demodulator link must operate without overall feedback), and limited bandwidth and transient response. The maximum signal frequency is limited to about 20% of the modulation frequency.

The advantages of chopper-stabilization versus direct- coupled differential circuitry are reduced time and tem perature dependent offsets referred to input, but the disadvantages are deteriorated transient response, in creased noise, increased complexity, and the cost of the chopper.

Direct -Coupled Di f ferent ia l Ampl i f iers Differential amplifiers using transformers and chop

pers for isolation can offer higher common-mode voltage tolerance than direct-coupled amplifiers. However, direct-

coupled differential amplifiers have other important advantages.

Without choppers there is no chopper intermodulation. This is a distinct advantage where it is necessary to gather high-accuracy data in the presence of noise; with a chopper, noise components in the range of the chopping frequency produce offsets.

In addition, the absence of chopper stabilizing cir cuitry generally results in a smoother rolloff of the open loop characteristic of the amplifier. There are no defor mations due to the chopper circuitry and settling and overload recovery times are generally faster. Where it becomes necessary to multiplex several input signals into one amplifier, the sampling rates can be higher for a fixed system error. Thus it is possible to use fewer ampli fiers and reduce system costs.

Higher Bandwidth. Transformer-isolated amplifiers have been generally limited to about 20 kHz, although some newer units appear to be somewhat higher. DC differen tial amplifier bandwidths may run as high as 1 MHz. Wide bandwidths are necessary to feed a wideband tape recorder, for instance.

Better Linearity. Total feedback can be employed in a direct-coupled differential amplifier, with the feedback loop surrounding everything. There are no active ele ments not surrounded by the feedback loop. In such cases, the feedback loop is all resistive and does not depend upon diodes or transformers. Resistors are char acteristically very precise components, thus the amplifier is likely to be capable of the needed higher precision in high-accuracy data acquisition systems.


Â¡lluu*

(a)

r T h r o u g h O u t p u t \ P o w e r C o r d C o m m o n

Fig. design The new HP Model 2470A Data Amplifier (a) is a differential design consistiu!; Â«I three amplifiers, Kl, K2 anil K3 (b). Amplifiers Kl and K2 are identical. Power supplies for the common amplifiers are completely isolated from each other to preserve the common

mode rejection offered by the design.

Fewer Components. Generally, the direct-coupled am plifiers require fewer components resulting in a more compact amplifier of potentially higher reliability. Less cabinet space is needed in large scale data acquisition systems, and it is more easily possible to achieve longer mean time between failures.

Two New Data Amplifiers. Two direct-coupled, differ ential data amplifers have been designed to amplify low- level ac or dc signals encountered in such areas of testing

as pressures, temperature, stress analysis, vibration and flow sensing.

Both amplifiers, the HP Model 2470A, Fig. 2, and the HP Model 8875A, Fig. 3, will supply Â±10 volts at 100 milliamperes into a resistive or reactive load. They may be used to drive analog-to-digital converters, digital volt meters, galvanometers, oscillographs, and X-Y plotters. In addition, they have the capability of making differen tial measurements, isolating the source ground from the output ground, impedance conversion, and they apply

(a)

Fig. amplifier to HP Model 8875A Data Amplifier (a) uses a common mode amplifier (b) to provide good common mode rejection wlhout the use of a specially shielded power

transformer.


Fig. 4. Use of the bridge method of checking gain linearity o f an ampl i f ier wi th gain K is re la t ive ly inexpensive and rapid. Precision depends mainly upon the accuracy of the voltage divider and the sensitivity of the null detector.

well where good rejection of common mode noise is needed. Characteristics of the amplifiers arc detailed in the specifications that accompany this article.

Test Precaut ions

In selecting a data amplifier, the appropriate primary considerations are: (1) zero offsets versus time and tem peratures, (2) common mode rejection and maximum common-mode tolerance, (3) gain accuracy, linearity and stability, (4) bandwidth, slewing and transient response, and (5) environmental conditions and reliability. In veri fying these specs, certain precautions must be taken or the test results may be misleading.

Common Mode Rejection Ratio. It is not sufficient to merely short the input leads, connect to a source of common-mode voltage and measure amplifier perform ance, since in nearly all practical situations, the input is unbalanced. To simulate performance under the worst likely conditions, a resistor is placed first in one lead for a test, then the test repeated with the resistor in the other lead. The source resistor must be shielded along with the input leads, or leakage capacity from the re sistor to ground will introduce errors in excess of specs.

Offset and Noise. The source resistor and input leads should be shielded and the input leads should also be twisted. This will minimize the amount of 60 Hz noise picked up by the test circuit.

Linearity and Gain Accuracy. These parameters may be checked with a highly accurate standard at the source

R e g a r d i n g ' P r e c i s i o n T h i n - F i l m C o a x i a l A t t e n u a t o r s ' I n t h e e q u a t i o n s o n p a g e 1 3 o f t h e J u n e 1 9 6 7 i s s u e , t h e t e r m a i s

t h e w i d t h o f t h e c e n t e r c o n d u c t o r a n d t h e t e r m D i s t h e d i s t a n c e b e t w e e n t h e i n n e r e d g e s o f t h e o u t e r c o n d u c t o r s . T h e s e d e f i n i t i o n s w e r e i n a d v e r t e n t l y o m i t t e d f r o m t h e t e x t o f t h e a r t i c l e ' P r e c i s i o n T h i n - F i l m C o a x i a l A t t e n u a t o r s . '

and a highly accurate voltmeter at the output. A much less expensive method, the bridge method, Fig. 4, is also much more rapid. Only the precision of the input voltage divider is important as well as the sensitivity of the null detector.

Low frequency noise and zero drift can easily give apparent out-of-spec indications. Measurements made at high gain could be affected by drift and noise. For exam ple, both amplifiers have a full-scale output of 10 volts. At a gain of 1000, full scale input is 10 millivolts and linearity measurements made against a spec of 0.01% require the allowable error be within Â± 1 microvolt. In this test, great care must be taken since a noise spike greater than 1 microvolt could make the amplifier look nonlinear.

Overload Recovery and Settling Time. The system used to measure this factor must be checked to insure that it is appreciably faster than the amplifier. Some oscillo scopes have a relatively long recovery time from satura tion.

DC Input Impedance. Input impedance is defined as the ratio of the change in input voltage to the resulting change in input current. Transistor circuits always have a small but finite input current flowing. The measuring technique must take this into account or errors will result.

Slewing. The slewing test determines how fast the ampli fier will respond to a rapidly changing input. A pure sine wave (symmetrical around zero) is fed in and the dc out put measured. If the amplifier characteristics are ideal, there will be no dc output at any frequency. In this test, the ac source must not generate error producing dc. Transformer coupling between the source and amplifier will satisfy the requirement. â€¢

o v â € ” v

Morton H. Levin

Mor t Lev in i s a g raduate o f Massachuse t t s I ns t i t u t e o f Techno logy w i th the deg ree o f Bache lo r o f Sc ience i n E lec t r i ca l Eng inee r i ng . A f t e r g radua t i on i n 1948 , he wo rked fo r t he Na t i ona l Adv i so ry Commi t t ee f o r A e r o n a u t i c s a t L a n g l e y F i e l d , V i r g i n i a o n i n s t r u m e n t a t i o n r e s e a r c h .

\ M o r t j o i n e d t h e H e w l e t t - P a c k a r d Sanborn D iv i s ion in 1953 . He has des igned seve ra l choppe r - s tab i l i zed a m p l i f i e r s f o r S a n b o r n r e c o r d i n g

sys tems and has des igned da ta amp l i f i e r s i nc lud ing the HP Mode l 8875A. He i s p resen t l y sec t ion leader fo r t he B iopo ten t i a l and Mon i t o r i ng Sec t i on .

Mor t i s a Sen io r Member o f IEEE.


S P E C I F I C A T I O N S

HP M o d e l 8 8 7 5 A

Di f fe rent ia l Ampl i f ie r

B A N D W I D T H : D C t o 7 5 k H z w i t h i n 3 d B . C a n b e c h a n g e d b y a d d i t i o n o f a c a p a c i t o r ; 3 d B p o i n t s d o w n t o 2 H z c a n b e o b t a i n e d .

G A I N : R a n g e i s f r o m 1 t o 1 0 0 0 i n s e v e n f i x e d s t e p s o f 1 , 3 . 1 0 , 3 0 , 1 0 0 , 3 0 0 . a n d 1 0 0 0 . p l u s a n O F F p o s i t i o n .

G A I N A C C U R A C Y : ' 0 1 % .

G A I N S T A B I L I T Y : â € ¢ 0 . 0 1 % a t c o n s t a n t a m b i e n t t e m p e r a t u r e f o r 3 0 d a y s , i _ 0 . 0 0 5 % / Â ° C ( f o r f i x e d g a i n s t e p s o n l y ) .

G A I N A D J U S T M E N T : G a i n c o n t r o l c o v e r s a t 3 % r a n g e w i t h s u f f i c i e n t r e s o l u t i o n f o r s e t t i n g a n y o n e g a i n t o Â ± 0 . 0 1 % . A v e r n i e r c o n t r o l c a n b e s w i t c h e d i n f o r s e t t i n g t h e g a i n t o a n y d e s i r e d v a l u e b e t w e e n t h e s t a n d a r d f i x e d s t e p s S t a b i l i t y o f t h i s c o n t r o l i s a p p r o x i m a t e l y 2 % o v e r a 0 - 5 5 Â ° C

i t i s i n i t s e x t r e m e p o s i t i o n ( g a i n c h a n g e a t m a x i m u m ) t h e b a n d w i d t h d r o p s t o 3 0 k H z ( 3 d B p o i n t ) .

I N P U T C I R C U I T : B a l a n c e d d i f f e r e n t i a l ; m a y b e u s e d s i n g l e - e n d e d . W i l l a c c e p t f l o a t i n g s i g n a l s o u r c e s w i t h o u t r e q u i r e m e n t f o r r e t u r n p a t h t o g r o u n d .

D I F F E R E N T I A L I N P U T I M P E D A N C E : 2 0 m e g o h m s i n p a r a l l e l w i t h l e s s t h a n 0 . 0 0 1 / Â ¿ f d .

C O M M O N M O D E R E J E C T I O N : A t l e a s t 1 2 0 d B f r o m d c t o 6 0 H z f o r u p t o 5 0 0 o h m s s o u r c e i m p e d a n c e i n e i t h e r s i d e o f i n p u t c i r c u i t a t g a i n o f 1 0 0 0 ; 6 6 d B m i n . a t g a i n o f 1 .

G U A R D E D C O M M O N M O D E I N P U T I M P E D A N C E : 2 0 0 0 m e g o h m s i n p a r a l l e l w i t h l e s s t h a n 2 p i c o f a r a d s .

C O M M O N M O D E T O L E R A N C E : Â ± 2 0 v o l t s .

I N P U T O V E R L O A D T O L E R A N C E : Â ± 3 0 v o l t s d i f f e r e n t i a l ; â € ¢ 7 0 v o l t s c o m m o n m o d e w i l l n o t d a m a g e t h e a m p l i f i e r .

D R I F T :

V O L T A G E D R I F T : ' 3 / t V r e f e r r e d t o i n p u t , Â ± 0 . 2 m V r e f e r r e d t o o u t p u t a t c o n s t a n t a m b i e n t t e m p e r a t u r e f o r 3 0 d a y s ; Â ± 1 M V / Â ° C r e f e r r e d t o i n p u t , Â ± 0 . 2 m V / Â ° C r e f e r r e d t o o u t p u t .

C U R R E N T F E E D T O S O U R C E ; 1 0 ' a m p m a x . a t c o n s t a n t a m b i e n t t e m p e r a t u r e , Â ± 1 0 - 9 a m p / Â ° C .

D R I F T A S A F U N C T I O N O F S O U R C E I M P E D A N C E : F o r u n b a l a n c e d s o u r c e s , e q u i v a l e n t i n p u t v o l t a g e d r i f t i s t h e s u m o f t h e v o l t a g e d r i f t p l u s c u r r e n t f e e d t o s o u r c e t i m e s s o u r c e i m p e d a n c e . F o r b a l a n c e d s o u r c e s , e q u i v a l e n t i n p u t v o l t a g e d r i f t i s a p p r o x i m a t e l y V a t h e v a l u e f o r u n b a l a n c e d s o u r c e s .

O P E R A T I N G T E M P E R A T U R E R A N G E : 0 - 5 5 C . W a r m u p t i m e

1 m i c r o v o l t p - p 3 m i c r o v o l t s p - p 6 m i c r o v o l t s p - p 3 m i c r o v o l t s r m s 4 m i c r o v o l t s r m s 5 m i c r o v o l t s r m s

N O I S E : M e a s u r e d w i t h r e s p e c t t o i n p u t w i t h 1 K s i g n a l s o u r c e i m p e d a n c e a t g a i n o f 1 0 0 0 . N o i s e m e a s u r e m e n t s w i t h r e s p e c t t o i n p u t a r e :

B A N D W I D T H d c â € ” 1 0 H z d c â € ” 1 0 0 H z d c â € ” 1 k H z d c â € ” 1 0 k H z d c â € ” 5 0 k H z d c â € ” 2 5 0 k H z

1 0 K s o u r c e â € ” n o i s e a p p r o x i m a t e l y d o u b l e 1 0 0 K s o u r c e â € ” n o i s e i n c r e a s e s b y a p p r o x i m a t e l y 5 X

O U T P U T C I R C U I T : - 1 0 v o l t s a c r o s s 1 0 0 o h m s . ( 1 0 0 m A ) a n d 0 . 2 o h m s m a x o u t p u t i m p e d a n c e a t d c . S h o r t c i r c u i t p r o o f . C u r r e n t l i m i t e d t o a p p r o x i m a t e l y 1 5 0 m A . W i l l n o t o s c i l l a t e w i t h a n y v a l u e o f c a p a c i t a n c e l o a d . M a g n i t u d e o f c a p a c i t a n c e l o a d i s g o v e r n e d o n l y b y o u t p u t c a p a b i l i t y o f a m p l i f i e r .

N O N - L I N E A R I T Y : L e s s t h a n 0 . 0 1 % o f f u l l s c a l e v a l u e . 1 0 v o l t s .

S E T T L I N G T I M E : 1 0 0 A S t o 9 9 . 9 % o f f i n a l v a l u e f o r a s t e p i n p u t .

O V E R L O A D R E C O V E R Y T I M E : R e c o v e r s t o w i t h i n 1 0 f i V r e f e r r e d t o i n p u t p l u s 1 0 m V r e f e r r e d t o o u t p u t i n 1 0 m s f o r a d i f f e r e n t i a l o v e r l o a d s i g n a l o f - 1 0 v o l t s a t g a i n s o f 3 0 0 t o 1 0 0 0 . a n d 1 m s a t g a i n s o f 1 t o 1 0 0 . F o r a 1 0 t i m e s f u l l s c a l e o v e r l o a d o f a n y d u r a t i o n ; 2 m s f o r g a i n s o f 3 0 0 t o 1 0 0 0 a n d 1 0 0 u s f o r g a i n s o f 1 - 1 0 0 .

S L E W I N G : O U T P U T C I R C U I T : W i t h r e s i s t i v e l o a d o f 1 0 0 o h m s o r

g r e a t e r 1 0 * V / s f o r 1 0 m V s h i f t i n d c o u t p u t .

I N P U T C I R C U I T : G a i n o f 1 , 2 , 5 X 1 0 * V / s f o r 1 0 m V s h i f t i n d c o u t p u t ; g a i n o f 3 , 0 . 8 3 x 1 0 * V / s f o r 1 0 m V s h i f t i n d c o u t p u t . F o r g a i n s g r e a t e r t h a n 3 . o u t p u t c i r c u i t d e t e r m i n e s s l e w i n g r a t e s .

P O W E R : 1 1 5 / 2 3 0 v o l t s Â ± 1 0 % . 5 0 - 4 0 0 H z . 6 w a t t s .

D I M E N S I O N S : 4 % " h i g h x i y 1 6 " w i d e x 1 5 " d e e p ( 1 2 1 x 4 0 x 3 8 1 m m ) .

P R I C E : M o d e l 8 8 7 5 A . $ 4 9 5 . 0 0 .

M A N U F A C T U R I N G D I V I S I O N : S A N B O R N D I V I S I O N 1 7 5 W y m a n S t r e e t W a l t h a m . M a s s a c h u s e t t s 0 2 1 5 4

HP M o d e l 2 4 7 0 A

D a t a A m pl i f i e r

D C G A I N :

S T A N D A R D : 5 f i x e d s t e p s o f X 1 0 , X 3 0 , X 1 0 0 , X 3 0 0 , X 1 0 0 0 . s e l e c t e d a t f r o n t p a n e l . A X O p o s i t i o n s h o r t s t h e o u t p u t .

O P T I O N M 1 : 4 f i x e d s t e p s o f X 1 , X 1 0 , X 1 0 0 , X 1 0 0 0 . s e l e c t e d a t f r o n t p a n e l . A X O p o s i t i o n s h o r t s t h e o u t p u t .

S P E C I A L : O n s p e c i a l o r d e r , a n y f i x e d s t e p s b e t w e e n X 1 a n d X 1 0 0 0 c a n b e p r o v i d e d , w i t h a m a x i m u m o f 6 p o s i t i o n s .

N O I S E : 0 t o 1 0 H z 0 t o 1 0 0 H z 0 t o 1 k H z 0 t o 1 0 k H z 0 t o 5 0 k H z

1 Â ¿ t V p - p r l i a n d 1 0 y V p - p r t o . 3 Â ¿ i V p - p r t i a n d 3 0 / Â ¿ V p - p r t o .

1 Â ¿ t V r m s r t i a n d 3 0 y V r m s r t o . 3 ^ V r m s r t i a n d 3 0 0 / i V r m s r t o . 5 / i V r m s r t i a n d 5 0 0 / Â ¿ V r m s r t o .

O U T P U T : - M O V m a x . 0 t o 1 0 0 m A . S e l f - l i m i t s a t a p p r c 1 1 . 5 V , 3 0 0 m A .

O U T P U T I M P E D A N C E : 0 . 1 1 . ' i n s e r i e s w i t h 1 0 Â ¿ i h m a x .

L O A D C A P A B I L I T Y : 1 0 0 ' . . ' o r 0 . 0 1 / t f f o r f u l l o u t p u t . A m p l i f i e r r e m a i n s s t a b l e a n d i s u n d a m a g e d b y s h o r t c i r c u i t o r c a - p a c i t i v e l o a d u p t o 0 . 5 p f l u m p e d c a p a c i t y .

S L E W I N G : 1 0 * V / s r t i , 1 0 ' V / s r t o ( i n p u t s o f b o t h p o l a r i t i e s ) w i t h d c o f f s e t c a u s e d b y s l e w l i m i t i n g l e s s t h a n 0 . 1 % o f p e a k a c , p r o v i d e d f u l l s c a l e i n p u t i s n o t e x c e e d e d .

T h i s a s s u r e s f u l l s c a l e o u t p u t o v e r t h e e n t i r e b a n d p a s s , e x c e p t w i t h 2 4 7 0 A - M 1 a t g a i n o f 1 , w h i c h s l e w l i m i t s a b o v e 1 6 k H z .

B A N D W I D T H : ( F o r a n y g a i n s t e p / )

0 t o 5 0 k H z Â ± 3 d B 0 t o 1 5 k H z Â ± 1 d B 0 t o 5 k H z Â ± 1 % O t o 1 . 5 k H z Â ± 0 . 1 % O t o 5 0 0 H z Â ± 0 . 0 1 %

( ' W i t h o p t i o n a l v e r n i e r , 3 d B b a n d w i d t h i s 2 0 k H z a t X 3 . 5 g a i n s e t t i n g . )

N O T E : O t h e r f i x e d 3 d B b a n d w i d t h s b e t w e e n 1 0 H z a n d 5 0 k H z a v a i l a b l e o n s p e c i a l o r d e r .

S E T T L I N G T I M E : 1 0 0 ^ s t o w i t h i n 0 . 0 1 % o f f i n a l v a l u e .

O V E R L O A D R E C O V E R Y : S e t t l i n g t i m e p l u s 1 0 0 Â ¿ s f o r s i g n a l o f 1 0 t i m e s f u l l s c a l e , b u t l e s s t h a n 1 0 V . L e s s t h a n 5 m s f o r s i g n a l p l u s c o m m o n m o d e u p t o 2 0 V .

D U A L O U T P U T : S e c o n d , b u f f e r e d c

V E R N I E R ( O p t i o n M 3 ) ; 1 0 - t u r n p o t e n t i o m e t e r ( f r o n t p a n e l ) e x t e n d s g a i n u p t o X 3 . 5 , f o r a n y g a i n s e t t i n g .

D C G A I N A C C U R A C Y :

C A L I B R A T E D G A I N : 0 . 0 1 % ( r e s o l u t i o n o f g a i n t r i m a d j u s t m e n t ) . ( F a c t o r y c a l i b r a t e s g a i n o f 1 0 . )

O T H E R G A I N S : 0 . 0 3 % . c o n s i s t i n g o f 0 . 0 2 % g a i n - t o - g a i n a c c u r a c y a n d 0 . 0 1 % g a i n t r i m r e s o l u t i o n .

V E R N I E R ( O p t i o n M 3 ) : D i a l A c c u r a c y : Â ± 3 % . R e s o l u t i o n : Â ± 0 . 0 5 % . R e s e t t a b i l i t y : Â ± 0 . 0 6 % .

G A I N S T A B I L I T Y :

D C : : . 0 . 0 0 5 % p e r m o n t h . A C : Â ± 0 . 1 % p e r m o n t h , f o r d c t o 2 k H z . T E M P . C O E F F . : ^ . . 0 . 0 0 1 % p e r Â ° C .

L I N E A R I T Y :

D C : Â ± 0 . 0 0 2 % o f f u l l s c a l e , r e f e r r e d t o s t r a i g h t l i n e t h r o u g h z e r o a n d f u l l s c a l e o u t p u t . A p p l i e s f o r a l l g a i n s e t t i n g s a n d i n p u t s o f b o t h p o l a r i t i e s .

A C : Â ± 0 . 0 1 % o f f u l l s c a l e r e f e r r e d t o s t r a i g h t l i n e t h r o u g h

Z E R O D R I F T ( O F F S E T ) : F i g u r e s b e l o w a p p l y t o a n y g a i n s e t t i n g ; t h e r e i s n o n e e d t o a d j u s t z e r o o n c h a n g i n g g a i n s e t t i n g .

P E R D A Y : Â ± 5 i i V r t i * - 5 0 / i V r t o P E R M O N T H : Â ± 2 5 / i V r t i Â ± 2 5 0 / i V r t o T E M P . C O E F F . : Â ± 1 Â ¿ i V Â ± 0 . 5 n a m p r t i Â ± 1 0 j i V r t o p e r Â ° C .

M A X I M U M I N P U T S I G N A L : Â ± 1 1 V . d i f f e r e n t i a l p l u s c o m m o n m o d e . C o m b i n e d i n p u t u p t o Â ± 2 0 V w i l l n o t d a m a g e i n s t r u m e n t .

D I F F E R E N T I A L I N P U T I M P E D A N C E : 1 0 0 0 M s h u n t e d b y 0 . 0 0 1

C O M M O N M O D E R E J E C T I O N : 1 2 0 d B a t 6 0 H z , f o r g a i n s e t t i n g s o f X 3 0 a n d h i g h e r . ( 6 0 H z C M R d e c r e a s e s t o 1 1 0 d B a t X 1 0 . 9 0 d B a t X 1 . ) C M R a t d c i s 1 2 0 d B f o r a l l g a i n s e t t i n g s .

C O M M O N M O D E R E T U R N : F r o m i n p u t c o m m o n t o o u t p u t c o m m o n : 1 m e g o h m , m a x . ( P r o v i d e d i n t e r n a l l y w h e n i n p u t l e a d s h i e l d s a r e c o n n e c t e d t o e i t h e r s i d e o f i n p u t . )

p h a s e a s s t a n d a r d o u t p u t , a v a i l a b l e a s O p t i o n M 5 .

D C G A I N : X 1 ( r e f e r r e d t o m a i n o u t p u t ) .

D C G A I N A C C U R A C Y : Â ± 0 . 0 1 % .

D C G A I N S T A B I L I T Y ; Â ± 0 . 0 2 % p e r m o n t h . ( T e m p , c o e f f . - 0 . 0 0 5 % p e r Â ° C . )

D C L I N E A R I T Y : : * : 0 . 0 2 % o f f u l l s c a l e .

Z E R O D R I F T : Â ± 0 . 0 0 5 % o f f u l l s c a l e r t o p e r d a y . ( T e m p . c o e f f . Â ± 0 . 0 0 1 % o f f u l l s c a l e p e r Â ° C , r t o . )

O U T P U T : Â ± 1 0 V m a x . 0 t o 1 0 m A . S e l f - l i m i t s a t a p p r o x . 1 1 . 5 V , 3 5 m A .

O U T P U T I M P E D A N C E : 0 . 5 ' . . ' i n s e r i e s w i t h 1 0 / i h m a x .

L O A D C A P A B I L I T Y : 1 K o r 0 . 0 0 1 / Â ¿ f f o r f u l l o u t p u t . A m p l i f i e r r e m a i n s s t a b l e a n d i s u n d a m a g e d b y s h o r t c i r c u i t o r a n y c a p a c i t i v e l o a d , a n d m a i n o u t p u t i s a f f e c t e d l e s s t h a n Â ± 0 . 0 0 5 % .

S L E W I N G : F u l l o u t p u t a v a i l a b l e a t s p e c i f i e d 3 d B b a n d w i d t h ( 3 x 1 0 * V / s m a x . a t 5 0 k H z ) .

B A N D W I D T H : A n y f i x e d 3 d B b a n d w i d t h b e t w e e n 1 0 0 H z a n d 5 0 k H z , s p e c i f i e d b y c u s t o m e r . M u s t b e l e s s t h a n o r e q u a l t o 3 d B b a n d w i d t h o f m a i n o u t p u t . 1 2 d B / o c t a v e s l o p e .

S E T T L I N G T I M E : D e t e r m i n e d b y b a n d w i d t h s p e c i f i e d .

O V E R L O A D R E C O V E R Y : C a n n o t b e o v e r l o a d e d b y m a i n o u t p u t . R e c o v e r s f r o m a s h o r t o n i t s o u t p u t i n 2 X s e t t l i n g t i m e .

E N V I R O N M E N T A L C O N D I T I O N S :

O P E R A T I N G : A m b i e n t t e m p e r a t u r e s f r o m 0 t o 5 5 C C . R e l a t i v e h u m i d i t y u p t o 9 5 % a t 4 0 Â ° C . W h e n u s e d i n d i v i d u a l l y , i n s t r u m e n t s a r e s e l f - c o o l e d b y c o n v e c t i o n . A c c e s s o r y C o m b i n i n g C a s e i n c l u d e s f a n f o r a d d i t i o n a l c o o l i n g .

S T O R A G E : - 4 0 t o + 7 5 Â ° C .

R E L I A B I L I T Y : P r e d i c t e d m e a n t i m e b e t w e e n f a i l u r e s ( w i t h 9 0 % c o n f i d e n c e ) i s 2 0 , 0 0 0 h o u r s â € ” w h e n o p e r a t e d a t 2 5 Â ° C a m b i e n t .

P O W E R R E Q U I R E D : 1 1 5 / 2 3 0 V â € ” 1 0 % . 5 0 t o 4 0 0 H z . 8 W w i t h n o l o a d . 1 0 W a t f u l l l o a d . F u s e . 1 1 5 / 2 3 0 V a n d o n / o f f s w i t c h e s o n r e a r p a n e l . F a n i n c o m b i n i n g c a s e o p e r a t e s f r o m 5 0 t o 6 0 H z o n l y .

P R I C E : M o d e l 2 4 7 0 A , $ 5 8 5 . 0 0 .

M A N U F A C T U R I N G D I V I S I O N : D Y M E C D I V I S I O N 3 9 5 P a g e M i l l R o a d P a l o A l t o . C a l i f o r n i a 9 4 3 0 6


Errors in Data Amplif ier Systems Poss ib le e r ro r sou rces i n a da ta amp l i f i e r sys tem and how they a f f ec t t he cho i ce o f an amp l i f i e r . By Richard Y . Moss I I

DATA AMPLIFIER SYSTEMS acquire information repre senting physical phenomena such as temperature,

pressure, displacement, velocity and acceleration. The system translates this information into an electrical sig nal by means of a transducer, performs a conditioning operation upon the electrical signal such as amplification, bandwidth modification, or other changes necessary to make the information more useable. The information of interest is displayed or recorded on output devices of various types..

Errors may be introduced into the data by the ampli fier itself or by other parts of the system. Before discuss ing errors, an overall look at a data amplifier system is helpful. A system typically is three major blocks: (1) Sig nal source, (2) Data amplifier and (3) Output device.

Signal Sources. Most transducers are passive elements whose resistance, capacitance, or inductance varies in proportion to some environmental stimulus. Such trans ducers are electrically excited by an appropriate power source to yield a signal. There are several exceptions to this generalization, however, so it is worthwhile to ex amine some of the more popular transducer types accord ing to their primary electrical characteristics:

(1) Voltage sources: thermocouples, and signal sources such as batteries, and electronic circuits are examples, Fig. l(a). Typical potentials are from microvolts to volts, at impedance levels from ohms to thousands of ohms.

(2) Current sources: photomultiplier tubes, and PIN photodiodes are very nearly ideal current generators with outputs in the microampere region. Piezoelectric crystals are ac charge-generating devices and may also be con sidered in this class represented in Figs. l(b), (c) and (d).

(3) Resistance devices: strain gages and strain gage bridges, resistance thermometers (both metal and semi conductor), and potentiometers are among the more pop ular members of this extensive class of devices, Figs. l(e) and (f). The signals produced are similar to those in the voltage source class, except that the bridge-connected devices have no output terminal in common with their source of excitation voltage, and hence are sources of common-mode voltage as well as signal voltage.

(4) Inductance devices: variable inductors, and vari able ratio transformers are included in this class, Figs. l(g) (h). These transducers must be excited by ac to pro duce constant level signals, but produce transient signals with a dc pulse.

(5) Capacitance devices: semiconductor voltage- variable and mechanically-variable capacitors operate in a manner analogous to the inductance devices, and are represented by Fig. l(i). The capacitance transducer for displacement measurement is an example.

Condit ioning Operat ions Among the operations which may be performed by a

data amplifier are impedance changing and voltage gain. Certain sources, such as a standard cell, should not be loaded, and a high amplifier input impedance is desirable to avoid drawing current from the cell. The amplifier out put usually represents a source impedance of less than an ohm to its load.

In some cases, such as a resistance strain gage, the source impedance may be varying. Here the amplifier as a buffer, provides a constant impedance to its load.

Bandwidth shaping nearly always takes the form of a low pass filter in data amplifiers, usually with a steep slope in the cutoff region, and usually with variable upper cutoff frequency, although occasionally ac-coupled am plifiers with variable lower cutoff frequency are required. A common need for filtering arises because the input signal contains noise components, perhaps as a result of sampling, which can be separated from the information components. The price paid in this case for low pass fil tering is loss of high frequency information, which may be needed in dealing with transients.

Ground potential translation includes two phenomena: common mode rejection (CMR), wherein it is desired to amplify a small difference between two large signals; and control of circulating currents between signal source ground and output load ground, whether caused by ac tual ground potential difference in the environment or by injected ground currents from the instrumentation. Ground current control is often the most important func-


Fig. 1. Classes of signal sources generally f omul in use with data amplifiers include voltage sources (a), current sources (b), as charge

sources (Â«â€¢) and (d), resistance bridges (<â€¢), po tentiometer (f), inductance bridge (g), variable transformer (h), and capacitance bridges (i).

tion performed by a data amplifier, because ground po tential differences between signal source and amplifier are often larger than the desired signal.

Output Dev ices

The output of the data amplifier may be monitored by a visual display instrument such as a meter or oscillo scope, in which case the use of the amplifier is similar to that of a laboratory measuring instrument, i.e. is as an instrument whose readings are observed in real time rather than being recorded. Often the load is a galva nometer, stripchart recorder, X-Y plotter, or FM tape recorder, so that the output signal may be recorded for future reference.

The amplifier output signal may be converted to a digital code by an analog-to digital converter or digital voltmeter, and the subsequent coded signal stored by any of a variety of devices including magnetic tape, punched tape, punched cards, or computer memory device. Such digital systems are capable of storing vast quantities of data with high resolution, and consequently make more severe demands upon amplifier noise, accuracy, linear ity, and reliability characteristics.

Often there will be feedback from the computing ele ment to a production process which is being monitored by the signal source transducers. Also, it is common for signal scanning devices to be interposed between the signal source and the amplifier, as well as between the

amplifier and the load, so discontinuities in the signal and load are imposed on the amplifier. To assure settling to the required accuracy and to be sure that unanticipated overloads will not cause errors in a subsequent signal, transient response must be properly specified.

Types of Errors

To specify a data amplifier for a system, the possible sources of error must first be examined and understood. Sources of error contributed by the amplifier are listed in the specifications of the instrument. In a direct-coupled low frequency system, the dc errors will usually domi nate. In a wideband system, there are analogous ac con siderations which contribute additional errors-. There are also system errors which arise because input signal am plitudes are not completely predictable or because of the increased number of components due to the size of the system increases likelihood of failures.

DC Error Sources. In the case of a low frequency system, such as the typical analog recording system or an amplifier-per-channel digital system, the dominant error sources are of two types: offset errors, and slope errors. To accurately specify offset (or zero offset, as it is more commonly called), one must distinguish the portion of the offset which is gain-dependent, and hence must be quoted 'referred-to-input' (RTI). from the constant por tion, which is not gain-dependent, and hence is quoted 'referred-to-outpuf (RTO). Fig. 2(a). The RTI offset further subdivides into a source resistance dependent term and a constant term, so that it is necessaiy to quote


Fig. 2. are voltage and offset current (a), both referred-to-input because tlie\ are dependent, and the voltage rejerred-to-output whlcli is not gain-dependent, are the major parameters in determining total offset. Insufficient common-mode-rejection is another

source to offset error (b). The common mode signal at the output is equal to <vv( """ } \CMRl

both offset voltage RTI and offset current RTI, as well as offset voltage RTO. These three specifications com pletely determine the amplifier offset error for a given gain setting and source resistance. All three parameters must be known as functions of time and temperature to predict the possible error in the system environment.

Another source of offset error is insufficient common mode rejection (CMR). When the amplifier input ter minals are both at the same potential but not at ampli fier ground, Fig. 2(b), some fraction of this common mode voltage may be amplified and appear at the output terminals of the amplifier, indistinguishable now from the expected output signal. The ratio of the common mode voltage to the equivalent differential signal which would have produced the same output is called the common mode rejection (CMR). Another way of stating this is that CMR is the ratio of differential gain to common mode gain. To preserve system accuracy, the CMR should remain high at all gain settings, and with worst- case source impedance unbalance conditions.

Errors in the slope of the input-output curve of the amplifier may be due to gain inaccuracy, loading, or

linearity problems. The accuracy of the gain is deter mined by the precision of the attenuator or feedback re sistors, and errors caused by finite gain inside the loop. The resulting errors are expressed as a function of the signal amplitude, time and temperature. Insufficient feed back can also contribute to linearity errors; that is, the departure of the input-output curve from a straight line. The only useful specification is 'terminal' linearity, where the straight line is drawn exactly through zero and full scale. Fig. 3(a). A 'best straight line; Fig. 3(b), approach makes normal zero and full scale calibration procedures meaningless since the 'best' line usually does not run through the full-scale point, but runs instead through other points on the input-output curve whose location is chosen to produce the smal les t numbers for the specification. However, they are unrelated to conditions of real use.

Loading errors, resulting from the loading of the sig nal source by the amplifier input circuits, or reduction of the amplifier output signal by load circuits, may be con sidered as gain slope errors, since the effect is the same. Certain types of reactive loads or sources, however, may

Fig. 3. Comparing the 'terminal linearity' method of specifying .vain accitracv (u) M-///Ã the 'best straight line' method (b) shows that while the 'best straight line' method results in better numbers on specifications, the 'terminal linearity' method results in a more

accurate statement of real usefulness.


Fig. 4. Sources of additional offset error are due to injected current, iÂ¡, source resistance and capacitance.

result in nonlinearity, slew limiting, or even oscillation, and must be avoided. For example, a pure sine wave which has been distorted by slew limiting will acquire a dc component, as well as harmonics, and hence can cause low-frequency error.

AC Error Sources. In the case of a wideband system, such as a high speed digital system, there are error sources in addition to those in the lower frequency case. Additional 'offset' errors are due to noise, Fig. 4, which should be specified as a voltage and current RTI and a voltage RTO, but are also a function of the bandwidth. Excess noise in the low frequency region, due primarily to the characteristic semiconductor noise that is inverse to frequency, distorts the otherwise uniform spectrum of the predominantly thermal noise. AC common mode signals produce an output signal in the same manner as the dc common mode case, except that stray capaci tances are usually causative elements rather than stray resistances. Another mechanism, which may cause noise in electronic instrumentation not properly shielded or grounded, is 'injected' current such as ac power line leak age into circuits with floating power supplies. This results in a common mode current circulating in a manner anal ogous to a system with poor CMR.

The similarity to the dc case carries over into the area of slope errors: AC gain errors are generally specified under the heading of 'frequency response'; loading errors

* T h e l i m i t ' s l e w l i m i t i n g ' d e s e r v e s s o m e e x p l a n a t i o n : t h e s l e w l i m i t o f a n a m p l i f i e r i s t h e m a x i m u m r a t e o f c h a n g e o f s i g n a l ( d V / d T ) ^ w h i c h t h e a m p l i f i e r c a n f o l l o w l i n e a r l y . S l e w l i m i t i n g o c c u r s w h e n t h e c u r r e n t r e q u i r e d t o p r o d u c e a v o l t a g e a c r o s s

a c a p a c i t o r ( i = C ~ 7 p ) e x c e e d s t h e m a x i m u m c u r r e n t a v a i l a b l e a t t h a t s t a g e w i t h i n t h e a m p l i f i e r c i r c u i t r y . I t i s a l s o p o s s i b l e f o r t h e c u r r e n t r e q u i r e m e n t s o f t h e l o a d , e s p e c i a l l y w h e n i t i s c a p a c i t i v e , t o i m p o s e a s l e w l i m i t u p o n t h e s y s t e m w h i c h i s l e s s t h a n t h e a m p l i f i e r n o - l o a d s l e w l i m i t . F o r e x a m p l e : A 2 0 - v o l t p e a k - t o - p e a k s i n e w a v e a t a k H z r e q u i r e s 3 X 1 0 * v o l t s / s s l e w i n g c a p a b i l i t y t o r e p r o d u c e i t , a n d a 0 . 0 3 i i f d l o a d c a p a c i t o r w o u l d r e q u i r e 1 0 0 m A p e a k o u t p u t c u r r e n t t o d e v e l o p t h i s s ignal . For a s ine wave

\ U L /

w h e r e = k = p e a k v o l t a g e , e m ( = r m s v o l t a g e o f t h e s i n e w a v e , a n d f = f r e q u e n c y .

must consider impedance rather than just resistance, and linearity errors result in the generation of distortion com ponents such as harmonics, intermodulation, and even dc offsets.

System Error Sources. Two additional types of errors should be considered when specifying an amplifier for systems use. The first is transient response, not only to signals with short rise times, but also in the case where the input connection is switched, as with a scanner, or where the amplifier has been overloaded in some way. Rapid recovery in all these cases is necessary to prevent blocking the proper operation of the system long after the input signal has returned to proper limits, and to pre vent damage to the amplifier.

The second consideration is reliability, a factor which becomes especially significant where several hundred sig nals are to be amplified in a test which is costly or even impossible to repeat. Unfortunately, specifying reliability in impressive statistical terms is not valid unless the goal was designed into the entire system. Inspecting does not guarantee reliability, but rather attempts to discover in formation which will indicate whether the goal was achieved. A valid specification must include three ele ments: a measure of the predicted reliability (such as mean time between failures), the environmental condi tions under which this prediction was assumed (such as temperature, humidity, vibration, etc.), and a measure of the confidence of the prediction (which indicates the extent of sample testing necessary). â€¢

Richard Y . Moss I I Af te r r ece i v i ng h i s Bache lo r o f Sc ience in E lec t r i ca l Eng inee r ing f rom Pr ince ton Un ive rs i t y in 1958 , D ick Moss w o r k e d a s a d e v e l o p m e n t e n g i n e e r i n m i ss i l e gu idance e l ec t r on i cs equ ipment . He rece ived h is MS in EE f rom S tan fo rd Un i ve rs i t y i n 1960 and jo ined the Dymec D iv i s ion o f H e w l e t t - P a c k a r d a s a d e v e l o p m e n t eng ineer .

A t Dymec , D i ck des i gned t he f r equency coun te r and con t ro l l og i c o f t he HP

Mode l 2401 A In tegra t ing D ig i ta l Vo l tmete r . He has been p ro jec t eng inee r on the HP Mode l 2460A Opera t i ona l Amp l i f i e r , and was p ro jec t manager f o r t he HP Mode l 221 2A Vo l tage to F requency Conver te r . He became p ro jec t manage r on t he HP Mode l 2470A D i f fe ren t ia l Da ta Ampl i f i e r i n 1964 .

D ick i s respons ib le fo r two pa ten t app l i ca t i ons re la t i ng to d i f fe ren t ia l amp l i f i e rs . He i s a lso the au thor o f two a r t i c les in ma jo r e lec t ron ics magaz ines in recen t years .

HEWLETT-PACKARD JOURNAL Â£JUL Y Volume 18 â€¢ Number 11

T E C H N I C A L C A L I F O R N I A F R O M T H E L A B O R A T O R I E S O F T H E H E W L E T T - P A C K A R D C O M P A N Y P U B L I S H E D A T 1 5 0 1 P A G E M I L L R O A D P A L O A L T O C A L I F O R N I A 9 * 3 0 4


- s?fÂ£c hm /sec 7141ft rÃcorbe* - hp labs · 2018-07-17 · the pen and the paper, separating...

Documents