transducers

Vibration Transducers

GE Measurement & Control

2

Transducers fundamentals

1. Introduction

2. Displacement

3. Velocity

4. Acceleration

5. Other transducers

3

Introduction to vibration

4

What is vibration?

Vibration is the motion of a machine or machine part in harmonic motion either side of its neutral or stationary position

Vibration is the response of a system to some internal or external excitation or force applied to the system

5

Machines vibrate differently to one another due to differing stiffness, mass and damping

These three fundamental conditions combine to determine how the machine reacts to forces which excite vibration

What is vibration?

6

Unbalance of rotating parts

Eccentric rotor

Bent shaft

Misalignment

Mechanical looseness

Rotor rubbing

What causes vibration?

7

Sleeve bearings: wear, oil whirl, oil whip

Rolling element bearings (REBs): defects

Hydraulic & aerodynamic forces

Electrical problems

Gear problems

Drive belt problems

What causes vibration?

8

UPPER

LIMIT

NEUTRAL

POSITION

LOWER

LIMIT

What is vibration?

9

Displacement

The total distance travelled by the vibrating part, from one extreme limit to the other or peak to peak

Units = microns (peak to peak)

UPPER

LIMIT

NEUTRAL

POSITION

LOWER

LIMIT

peak

acceleration

peak

velocity

phase

DIS

PL

AC

EM

EN

T

TIME

PERIOD

PEAK TO PEAK

DISPLACEMENT

Vibration features & units

10

Amplitude -

Expressed in displacement, velocity or

acceleration and is an indicator of severity, i.e. Is the machine running smoothly or roughly?

Vibration Signal Characteristics

Frequency

Used to distinguish the force causing the vibration defined as the repetition rate of a periodic vibration.

Vibration frequency measured in cycles per minute (CPM) or hertz (Hz). Sometimes expressed in multiples of rotative speed of the machine, such as one times rpm

(1X), two times rpm (2X), 43% of rpm (.43X), etc. Phase

The timing relationship, in degrees, between two (or more) signals. A means of describing the location or

shape of the rotor at a particular instant in time.

Signal Amplitude

1X Vibration 5X Vibration

12

The vibration amplitude is the primary indicator of a machines condition

The greater the amplitude, the more severe the vibration

Overall vibration amplitude (direct amplitude) is the unfiltered trending parameter

Vibration amplitude

13

AMPLITUDE

pk

0

pk

pk

rms

Peak-to-peak refers to the total amount of vibration.

Zero-to-peak refers to the total amount of vibration from the

maximum height of either the positive or negative peak to the

zero voltage axis.

Root mean square (RMS) is a function of the signal conditioning

performed in the monitor or diagnostic instrument and not the

output of the transducer.

14

Uses the raw vibration signal from the transducer

Reveals the true dynamic response of the machine

Time waveforms show short transient vibrations clearly, where amplitude meter damping often prevents responses of analysers to true peak amplitudes

Amplitude versus Time Domain Waveform Plot

15

10

12

14

16

18

20

22

24

26

28

30

32

34

0 180 360 540 720 900 1080 1260 1440

Time (seconds)

Am

pli

tud

e

Amplitude versus Time Domain Waveform Plot

16

Many machine problems can be detected using overall vibration trends

Analysis of trends is simple and basic

Preset alarm levels can be simply applied, usually double the normal vibration levels, or 25% of full scale range (FSR) above.

Overall amplitude trending

17

Overall amplitude trending

18

Velocity

The speed at which displacement occurs

Because the speed is constantly changing, the peak or RMS velocity are usually selected

Units - mm/s (peak) (RMS) D

ISP

LA

CE

ME

NT

Minimum

Velocity

Minimum

Velocity

Maximum

Velocity

TIME

Vibration features and vibration units

22

Vibration analysis relates the vibration frequencies captured with the rotational speed and characteristic fault frequencies of machine components.

Frequencies must be considered in association with the amplitude of the frequency peak to assess the severity of the problem

Vibration frequency

27

PHASE

A

B

TIME

(DEGREES)

PHASE

TIME

(DEGREES)

A M P L I T U D E

PHASE (BETWEEN VIBRATION SIGNALS)

28

PHASE ANGLE

0 360

PHASE

LAG

VIBRATION

SIGNAL

KEYPHASOR

SIGNAL

TIME

DEGREES

OF

ROTATION

The phase angle is defined as the number of degrees from the Keyphasor pulse to the first positive peak of vibration.

37

Vibration characteristics

time

Vibration transducers produce

an electrical signal that

represents the vibration in the

sensitive axis of the transducer.

Sensitive

Axis

Vibration transducers

39 Introduction to vibration

2/14/2013

Rolling Element Bearing Fluid Film Bearing

Machine vibration


2/14/2013

Fluid film bearing machine

Rolling element bearing machine

Machine vibration


2/14/2013

The vibration transducer is responsible for accurately sensing the vibration of interest

There are numerous types of transducers; each having limitations according to their requirements


42


Motion Electrical

Signals

Any transducer converts one kind

of energy into a different kind

(into an electrical signal).

Vibration

Transducer


2/14/2013


Four types that are commonly used in condition monitoring are

Velocity Transducers

Accelerometers & Velomitors

Proximity Probes

44

Mechanical vibration is the dynamic motion of machine components. The vibration measurement is the measurement of this mechanical vibration relative to a known reference.

Rotors, Bearing, Seals, Bearing Housings and Machine Cases

Accurately measuring and monitoring the vibration of these components will describe the mechanical condition of the machine.

Four transducers to measure vibration:

Proximity Transducers Velocity Siesmoprobes Accelerometers Velomitors

Vibration Measurements

45

Displacement

Definition

Displacement is the change in distance or position of an object relative to a reference.

Typical application

Measuring rotor position within the clearance of fluid film bearings.

Used for permanent monitoring of turbines, large pumps, compressors

Capable of low frequency response (down to 0 Hz).

Units: microns (m) or thousandths of an inch (mil)

Eddy-current

proximity probe

The non-contact transducer senses relative motion between the shaft and bearing of the machine

shaft

bearing

transducer

46

Velocity

Definition

Velocity is the time rate of change of the displacement of an object.

Typical application

Measuring vibration of machine casing and other structural response characteristics.

Useful for medium frequencies (~10 Hz to 10,000 Hz).

Units: millimeters per second (mm/s) or inches per second (ips).

Moving-coil

sensor

Piezoelectric

(crystal)

sensor

47

Acceleration

Definition

Acceleration is the time rate of change of an objects velocity.

Typical application

Universally used with portable vibration analyzers

Measuring high frequency vibration of gear mesh, rolling element bearing defects, etc.

Capable of high frequency response (up to ~20 kHz).

Units: meters per second2 (m/s2), inches per second2 (in/s2), or Standard Gravity (g).

Piezoelectric

sensor

48

Machine Casing

Displacement

Velocity

Acceleration

Time

Relationships between vibration signals

Displacement, velocity and

acceleration measurements are

out of step with each other.

Displacement = maximum ( - direction ) Velocity = zero Acceleration = maximum ( + direction )

Displacement transducers

50

Position

Radial shaft position is a measurement of the shaft centerline radial position within the radial bearing.

Derived from the dc information provided by the proximity system.

Used to determine bearing wear, misalignment, external preloads and other malfunctions.

51

Measuring Machine Vibration

Proximity probes measure distance

Between probe and shaft

Non contacting

Magnetic energy absorbed proportional to distance

52

RADIAL MOVEMENT

AXIAL MOVEMENT

RADIAL AND AXIAL MOVEMENT

53

Eddy Current Theory

CONDUCTIVE

MATERIAL

EDDY CURRENTS

RF SIGNAL

Proximitor

Probe

54

Probe Close to Rotor

RF SIGNAL 0

55

Probe Away from Rotor

RF SIGNAL 0

56

Changing Distance Between Probe and Rotor Produces a Change in Signal Strength

RF SIGNAL 0

57

Proximity Transducer System Gap Signal

RF SIGNAL 0

RF SIGNAL 0

RF SIGNAL 0

58

Demodulator Operation

DEMODULATOR

INPUT

PROXIMITOR

OUTPUT

0

0

RF SIGNAL 0

59

Proximity Systems

- Proximitor and Probe Operation

60

CH

AN

GE

IN

VO

LTA

GE

CHANGE IN GAP

24 O

UT

PU

T IN

VO

LT

S -

DC

PROBE GAP

mils 0

0

10 20 30 40 50 60 70 80 90 100 110 120 130 140

2

4

6

8

10

12

14

16

18

20

22

PROXIMITOR CALIBRATION GRAPH

62

Proximity Transducer System

Three Components:

Probe - Installed on the machine and is referred to as the sensor.

Extension Cable - Connects to the probe's cable and allows you to reach a convenient junction box.

Proximitor - Module that contains Transducer Systems electronics (oscillator/demodulator) and is usually mounted in a junction box.

Extension Cable

Probes

Proximitor

Mounting Bases

63

Proximity Transducer System - Proximitor

Electrical Length

Probe Cable +

Extension Cable =

Total System Electrical

Length

The Total Electrical

Length must match the calibration of the

Proximitor.

Transducer Power

Signal Common

Signal Output

64

Probe Mounting

Commonly mounted directly inside the bearing

Probe views the shaft directly

65

Transducer Orientation Options

66

Probe Orientation

Y Orientation

Channel 1

X Orientation

Channel 2

67

Radial (XY) transducers

Orbit Plot

Orbit plot shows magnified view

of the movement of the shaft

centerline within the clearance

of the fluid film bearing.

X Y

Animation

68

Radial vibration Examples of internal installations

Bracket-Mounted Single Probes

Bearing-Mounted Single Probes

Bracket-Mounted

Redundant Probes

1

2

3

69

XY Probes Installed in Housings

70

Axial (Thrust) Rotor Position

71

Axial rotor loads

Nuovo Pignone, S.p.A.

Pressure differences can produce large axial forces on the machine rotor.

Axial Load

Compressor Discharge

(high-pressure end)

Compressor Suction

(low-pressure end)

Process Gas Flow

72

Probe location Thrust position measurement

Channel A Probe

Channel B Probe

Thrust Collar

Rotor Shaft

Install probes within about 30 cm

(~12 in) of thrust collar.

Thermal expansion of rotor

introduces large errors when

measurements are made too

far away from the thrust collar.

Animation

73

AXIAL (Thrust) POSITION

THRUST

BEARING

ASSEMBLY

THRUST

PADS

THRUST

COLLAR

74

THRUST POSITION

20

15

10

5

0

20 40 60 80 100 MILS

0.5 1.0 1.5 2.0 2.5

mm 0

HOT FLOAT ZONE COLD FLOAT ZONE

COUNTER

DIRECTION

NORMAL

DIRECTION

75

Example installations

Radial vibration

Keyphasor

Thrust position

This gearbox photo shows an XY radial vibration probe pair

and a Keyphasor* probe mounted in 21000 housings, and

dual axial thrust position probes mounted in a 21022 housing.

Thrust

Radial Keyphasor

Radial

77

Machine train diagram General installation guidelines

Probe designation Example: 1VD

Bearing number

Probe orientation

Measurement type

Orientation Measurement

A = Axial D = Displacement

H = Horizontal V = Velocity

V = Vertical A = Acceleration

1

VD

HD

1AD

K

DRIVER

4 2

GEAR

BOX

3

VD

HD

HD VD

4AD

HD VD

As viewed,

driver-to-driven

5AD

K

5

6VA

6

LOAD 8AD

7 8

HD VD

HD VD

HD

HD

VD

VD

78

Proximity probe installation pitfalls Inappropriate target size

Problem: Some of the electromagnetic field from the

face of the probe tip does not contact the target surface.

Target size is adequate for probe being used.

Target size is too small for the probe.

79

Problem: Electromagnetic fields from closely-spaced probe

tips interfere with each other, producing false vibration signals.

Proximity probe installation pitfalls Crosstalk

80

Problem: Electromagnetic field is attenuated by conductive

materials that are too close to the sides of the probe tip.

Proximity probe installation pitfalls Sideview

81

Proximity probe installation pitfalls Run-out

Problem: Another common problem is called run out you can find more information going to the link below

http://www.ge-energy.com/prod_serv/products/oc/en/bently_nevada/proxprobes.htm

82

Phase Reference Signal

0

0

-V

-V ONE

REVOLUTION

ONE

REVOLUTION

0

0

83

Timebase Waveform with Phase Reference

More useful information provided with Phase Reference

Balancing

Phase reference signal creates blank-bright on waveform

Called a Keyphasor by Bently Nevada

84

Keyphasor transducer Phase angle measurement

Keyway Notch or Projection Typical Probe Installation

* Trademark of General Electric Company Animation

85

Proximity transducer used as a ONCE PER REVOLUTION marker on a machine shaft KEYPHASOR.

Transducer mounted to observe a "notch" or a "projection" on the shaft and produces a voltage pulse once each revolution.

Voltage pulse is much more significant than normal vibration or distance measurements. Significant difference in voltage discriminates between a ONCE PER REVOLUTION signal, and background noise or vibration.

The Keyphasor is a very useful tool when diagnosing machinery problems. At a

minimum, the generated pulse can be used to measure machine speed.

Keyphasor Applications

87

Phase measurement

0 360

PHASE

LAG

VIBRATION

SIGNAL

KEYPHASOR

SIGNAL

TIME

DEGREES

OF

ROTATION

The phase angle is defined as the number of

degrees from the Keyphasor pulse to the first

positive peak of vibration.

88

Vibration amplitude relative phase

pk

0

pk

pk

rms

pk

0

pk

pk

rms

X Probe

Y Probe

89

Radial Position

Proximity Probes are used in the X-Y configuration to measure radial vibration, the dc signal from the transducer can be used to indicate the radial position of the rotor within the bearing

90

Orbit plot

92

Transducer system components

Example: 3300 XL 5 Metre Proximity Transducer System

Probe

Extension

Cable

Proximitor*

Sensor

93

Proximity transducers

http://www.ge-energy.com/prod_serv/products/oc/en/bently_nevada/proxprobes.htm

94

Accessories & related products

http://www.ge-energy.com/prod_serv/products/oc/en/bently_nevada/prox_probe_acc.htm

Velocity transducers

96

Velocity transducer basics

Velocity sensors

Design: Either a moving coil sensor or an accelerometer with onboard integrating circuit.

Operation: Moving-coil design is self-powered, but piezoelectric design requires a power source.

Various examples of Bently Nevada* seismic transducers

97

Typical frequency ranges Seismic transducer basics

Accelerometer: Highest frequency response. Used for gear mesh, impulse and other high frequency applications.

Piezovelocity Sensor: Lower high frequency response, but less noise than using an external integrating amplifier with an accelerometer.

Moving Coil Sensor: More limited frequency response, but has no requirement for an external power supply. Moving Coil Sensor

Piezovelocity Sensor

Accelerometer

98

Velocity sensor specifics

(click to play animation)

magnet

moving coil

case

mass

mounting stud

crystal

charge amp. &

integration circuit

preload band

Velomitor* Piezo-Velocity Sensor

Sensitive

Axis

Traditional Moving-Coil Sensor

99

330500 typical frequency response Velocity sensor specifics

Transducer sensitivity

is specified at 100 Hz.

100

Interconnect cable Velocity sensor specifics

Part Number 9571-AXX

101

High temp & low frequency sensors Velocity & acceleration transducers

330750 (4-bolt sensor) & 330752 (threaded stud sensor) high temperature velocity transducers.

For surface temperature up to 400C (752F).

190501 CT low frequency transducer is designed for monitoring cooling tower fans.

1.5 Hz to 1000 Hz response accommodates machine speeds as low as 90 rpm.

Sensor

Signal

Conditioning

Electronics

(330750 version is shown here)

102

Moving coil velocity sensors

330505 low frequency velocity transducer

Hydroelectric turbine generators

0.5 Hz to 1000 Hz response

20 mV/mm/s (500 mV/ips)

Specific mounting orientation

9200 & 74712 Seismoprobe velocity transducer

General purpose monitoring



Specific mounting orientation

103

Velomitor piezo-velocity sensors

350900 High-Temp Velocity and Acceleration Sensor (HTVAS).

Gas turbine monitoring

25 Hz to 2000 Hz (velocity)


10 Hz to 10 kHz (acceleration)

1.02 mV/m/s2 (10 mV/g)

330500 velocity transducer

General purpose monitoring



Signal

Conditioning

Electronics

Sensor

104

Housings Installation guidelines

Velocity transducer housing:

Part number 21128

105

Transducer positioning examples Installation guidelines

Horizontal machines

Axial Horizontal

Vertical

Vertical machines

East

South

Acceleration transducers

107

Accelerometer specifics

Sensitive

axis

case

mass

element

mounting stud

preload screw

charge amplifier

compression type sensor

case

mass

mounting stud

element

charge amplifier

preload band

shear type sensor

Piezoelectric accelerometer

108

Typical frequency ranges Seismic transducer basics

Accelerometer: Highest frequency response. Used for gear mesh, impulse and other high frequency applications.

Piezovelocity Sensor: Lower high frequency response, but less noise than using an external integrating amplifier with an accelerometer.

Moving Coil Sensor: More limited frequency response, but has no requirement for an external power supply. Moving Coil Sensor

Piezovelocity Sensor

Accelerometer

109

330400 typical frequency response Accelerometer Specifics

Transducer sensitivity

is specified at 100 Hz.

111

Accelerometers Acceleration transducers

330400 general purpose accelerometer.

10 Hz to 15 kHz response

API 670 compliant

50 g peak amplitude range

100 mV/g sensitivity

330450 High Temperature Acceleration Sensor (HTAS)

Mounting up to 400C (752F)

113

Velocity & acceleration transducers

http://www.ge-energy.com/prod_serv/products/oc/en/bently_nevada/acc_vel.htm

114

Adaptors Installation guidelines

Example: Various mounting adaptors for

Bently Nevada* seismic transducers.

115

Transducer mounting Installation guidelines

1. Ensure ambient conditions are acceptable.

2. Verify mounting surface is adequately prepared.

3. Drill and tap mounting hole.

4. Apply acoustic couplant.

5. Tighten transducer to specified torque.

Detailed information is included in the appropriate product manuals.

116

Machinery application Seismic transducer basics

Accelerometer installed to measure gear mesh

vibration on a speed increasing gearbox.

Close-up view of accelerometer

and junction box.

117

Transducer positioning example Installation guidelines

Horizontal Machines

Axial Horizontal

Vertical

Vertical Machines

East

South

119

Axial

X Y

X YX Y

T19-20

X YX Y

Gearbox

KO

Accel

T17-18 T23-24

T21-22

T25-28

LP

Compressor

X Y

T29-30 T31-32

Axial

T33-36

X Y

LP

Compressor

X Y

T39-40

T41-44

Axial

X Y X Y

Axial

T11-12T9-10

LM2500

T13-16

KO

AccelT1-T8

Accels

T37-38

Typical Transducer Configuration Rotating Machinery

Transducer selection


2/14/2013

Rolling Element Bearings Fluid Film Bearings

Machine vibration


2/14/2013

1. To protect a 600 rpm fin fan with rolling element bearings.

2. To protect a steam turbine generator operating at 3000 rpm

3. To Monitor a 7500 rpm precision gearbox with 57 teeth (gear mesh ~ 7.5 kHz)

What transducer should you use?

Vibration plots critical machines

124

Whats in the vibration signal?

Seismic transducer

Amplitude

Frequency

Proximity transducer

Amplitude

Phase

Frequency

Form

Position

125

pk

0

pk

pk

rms

Bar Graph

Current Value Live Data

Amplitude

126

Trend Plots

Multi Variable Trend Plots

Bode Plots

Amplitude monitoring

127

X v/s Y Plots


128

Software Alarms


129

0 360

PHASE

LAG

VIBRATION

SIGNAL

KEYPHASOR

SIGNAL

TIME

DEGREES

OF

ROTATION

Phase

130

Synchronous Spectrum Asynchronous Spectrum

Half Spectrum Full Spectrum

Frequency

131

Bently Nevada monitors record the waveform data through two separate sampling paths:

Synchronous data is linked to the rotating speed of the machine (fixed number of samples per revolution).

High sample rate = good resolution on Orbit and waveform plots, but poor frequency resolution

Asynchronous data has a fixed sampling rate

Slower sample rate = Good frequency resolution . Ideal for fault analysis with accelerometers and velomitors.

Other manufactures need to trade off data quality, usually with poorer resolution of waveforms and orbits

Synchronous & Asynchronous data

132

Full Spectrum

Frequency

133

Waterfall Plots

Cascade Plots

Frequency

134

Spectral Band

Frequency

135

Form

136

Orbit Overlays

Form

137

Axial Position

Radial Position

Position

138

Average Shaft Centerline Plots

SW alarms Gap Reference Voltage

Position

139

Amplitude and Phase displayed together

Slow roll runout vector

Heavy/high spot location

Rotor and structural resonances

Rotor mode shape 1st critical

Bode and Polar plots

Transient vibration data

140

Bode plot

141

Polar plot

Typical synchronous rotor response Phase lag angle increases with machine speed Amplitude increases to a maximum value at critical speed and then reduces

142

Transient Data Formats

**

**

*

*

**

*

*

*

3.0

2.0

1.0

0.0 -1.0 0.0 1.0

9500

9400

9200

8700

8000

7600

5500

4500

1200

500

300

4000

3000

2000

1000

00 1000 2000 3000 4000 5000 6000 7000 8000

1X

2X

3X

**

*

**

**

***

**

******** *

0

90

180

270

22052250

2280

23702385

2400

2415

2310

2430

2445

2460

2475

25052685

277529853615

300

1845

2145

2610

0 500 1000 1500 2000 2500 3000 3500 4000

4

3

2

1

0

180

240

300

360

60

120

180

240

180

Bode Plot

rpm

mil

s p

p

P

ha

se

La

g (

de

g)

Polar Plot

4.0 mils pp Full Scale CCW Rotation

Frequency (kcpm) Hanning Window

Cascade Plot

Ma

ch

ine

Sp

ee

d (

rpm

)

Average Shaft Centerline Postion (not orbit or polar plot)

Amplitude 0.20 mils/div CCW Rotation

Average Shaft Centerline Plot

143

Steady State Data Formats

0.2 2.0

0

-5

-10

-15

-20

0 5 10 15 20 25

20.0

15.0

10.0

5.0

0120 240 360 480 600

Timebase Display Orbit Display

Scheduled

Shutdown

Bearing

Backing

Ve

rtic

al P

os

itio

n (

mil

s)

Vertical Position Trend Plot

Time (days)

Half Spectrum Display kcpm

Gear Mesh Frequency

7X C

as

ing

Ac

ce

lera

tio

n -

g p

k

transducers

Documents

x vibration

vibration frequency

periodic vibration

raw vibration signal

stationary position

peak units

signal amplitude

negative peak