accelerometer design

8/4/2019 Accelerometer Design

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Vibration Sensing and

Accelerometer Design

Wilcoxon Research

Vibration Product Training

Vibration pp.1



Basic Measurement Considerations

Sensor Parameters! Sensitivity

! Frequency Response

! Amplitude Range

! Reliability

! Ruggedness

! Ease of Use

! Compatibility! Temperature Range

Measurement Parameters! Frequency

! Minimum Amplitudes

! Peak Amplitudes

! Machine Design

! Machine Environment

! Environmental Noise

! Accessibility

Vibration pp. 2



Vibration Amplitude

! Very Little Vibration

Amplitude in terms of

Acceleration is Produced

at Low Frequencies

! Much Larger

Amplitudes are produced

in terms of Displacement

!Very High

Acceleration Levels are

produced at High

Frequency

1,000

100

10

1.0

0.1

.01

.001

.0001.1.6

Hzcpm

160

10600

1006,000

1,00060,000

EU(mils pp)

(ips)(g)

FREQUENCY

Velocity (ips)

Acceleration (g)

Displacement (mils pp)

1607-R1

Vibration pp. 3



PiezoelectricA c c e l e r o m e t e r ElectrodynamicVe lo c ity Trans duc e rEddyProbe

1205a.cdr R.1

Basic Vibration Sensors

Vibration pp.4



Piezoelectric Accelerometers

!

Measures Acceleration! Very Sensitive

! Contacting

! Measures Absolute

Casing Motion

! Measures Very LowFrequency

! Measures Very High

Frequency

Pi ezocerami cs

Se is mic Mas s

Con n ector

2 2 08 a - R 1

Amplifier

MountingBas e

P i ezo cera m i cs

2 3 3 9 a

Se is mic Mass

Co n n ect o r

Amplifier

MountingB a s e

2339b

Amplifier

C o n n e c t o r

Moun ting Ba s e

S e is micMas s

P i e z o c e r a m i c

MountingS c r e w

Vibration pp. 5



Compression Accelerometer

! Commonly Used

! Wide Frequency

Range! Very Reliable

! Medium Turn-on

Time (8-10 sec)

Piezoceramics

2 3 3 9 a

S e is mic Mas s

Co n n e c t o r

Amplifier

MountingBa s e

Vibration pp. 6



Flexure Accelerometers

!

Very Low Frequency! Very Low Noise

! Small Size/High Output

! Long Turn-on Time

(> 30 sec)

! Fragile! Do not use with

Magnets

Pi e z oc e r am i c s

S e is m ic Mas s

C o n n e c t o r

2 20 8a - R 1

Amplifier

MountingBa s e

Vibration pp. 7



Shear Accelerometers

2339b

Amplifier

C o n n e c t o r

Mo un ting Bas e

S e i s m i cMass

Piezoceramic

MountingS c r e w

!

Latest Designs!Wide Frequency Range

!Fast Turn-on Time

( 3 sec)

!Fast Shock Recovery

!Resists ThermalTransients

Vibration pp. 8



Operational Range

Vibration pp. 9



Industrial

Accelerometer Considerations

!

High Resonance– Reduces Overload

– Shear PZT

! Low Noise– PZT required for low

frequencies

! Environmental Protection

– Mispowering Protected

– ESD shunts– Overload Reduction

2339b

Amplifier

Co n n e c t o r

Mo unting Bas e

S e i s mi cMass

Piezoceramic

MountingScrew

Piezoceramics

2339a

S e is mic Mas s

C o n n e c t o r

Amplifier

MountingB a s e

Vibration pp. 10



Frequency Response

! Resonance GovernsFrequency ResponseSmall Mass = High Frequency

Large Mass = Low Frequency

! High Frequency can be

shaped with filtering

! Low Frequency Response

governed by Filter Setting

Filter used to “cutoff” lowfrequency noise and transients

Vibration pp. 11



Electronic Sensor Noise

! Sets the Absolute

Measurement Floor

! Increases as Frequency

Decreases

! Dependant on Charge

Sensitivity

PZT Piezoceramics are very

sensitive and must be used

for Low Frequency

Measurements

Vibration pp. 12



Sensitivity

! Charge Sensitivity is setby the mechanical design

! Voltage Sensitivity is set

by the amplifier gain! Low Sensitivity reduces

overload

! High Sensitivityovercomes monitor noise

! PVTs provide very high

outputs at low frequency

2223aFreq u en cy

0. 1 Hz

0. 6 c p m

1

60

10

60 0

10 0

6k

1k

60 k

10 k

600k

30 k

1,800k

1 00 0 V

1 00 V

10 V

1 V

1 0 0 m V

1 0 m V

1 mV

0 . 1 m V

0 .0 1 m V

1 0 0 m V/ g

100 mV/in/s ec

500 mV/g

Sensitivity(re 1g input)

Vibration pp. 13



Sensor Powering

! SCP (Standard Current

Powering)

! Current Limited

Voltage Supply! Uses Bias Voltage

18 to 30 VDC

2-10mACCD

Amplifier

Bias Voltage

Supply Voltage

Crystal

Isolation Layer

+

+

Shield

Connector

22 F µ

>

500K

Readout

Equipment

#625

Vibration pp. 14

accelerometer design

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