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Vibration Sensors
 
Piezo Velocity Transducers (PVT)

Piezo velocity transducers (PVT) are solid state piezoelectric velocity measurement devices. Since many vibration analysts prefer to examine vibration signals in terms of velocity (inches per second or ips) to amplify the signal of interest. PVT's inherently decrease high frequency signals allowing better measurement of low frequency vibration. PVT sensors are essentially accelerometers with an internal integration circuit which wil produce an output relative to velocity.

PVT can reduce signal noise in many low frequency measurements. The integration circuit amplifies low frequency signals and attenuates high frequency signals. This increases the voltage output at low frequency and filters high frequency noise. The increases in low frequency voltage output reduces the noise contribution of the data collector. The inherent filtering reduces intermodulation (washover) distortion caused when high frequency signals overload the amplifier and may reduce "ski slope" noise in many applications.

 

 

 

Key features 

- Rugged design.

- Eliminates distortion caused by high frequency signals.

- Corrosion-resistant.

- ESD protection.

- Internally integrated to velocity.

- Ultra low-noise electronics for clear signals at very low vibration levels.

- Miswiring protection.

 

Technical data 

Dynamic

Sensitivity, +/- 10%, 25 0C

100 mV/in/sec

Velocity range

50 in/sec peak

Amplitude nonlinearity

1 %

Frequency response

-10%

2.0...3,500 Hz

-3dB

1.5...7,000 Hz

Resonance freq.

15 kHz

Transverse sensitivity, max

5 % of axial

Temperature response

-50 0C

-5%

+80 0C

+3%

+120 0C

-5%

 

 

Electrical

Power req.

18...30 VDC, current regulating diode 2...10 mA

Output impedance

4mA supply, the greater of 5,000/f or 200 W

Bias output  voltage

10 VDC (noninal)

Noise

2.5 Hz to 25 kHz

100 min/sec

10 Hz

10 min/sec/vHz

100 Hz

1.0 min/sec/vHz

1000 Hz

0.2 min/sec/vHz

Temperature Range

-50...1200C.

Vibration limit

250 g peak, shock limit 5,000 g peak.

Electromagnetic sensitivity, equiv. in/sec

25 min/sec/gauss.

Sealing

Hermetic.

Base strain sensitivity

0.0005 in/sec/mstrain.

Sensing element design

PZT ceramic / compression.

Weight

145 grams.

Case material

316L stainless steel.

Mounting

1/4 - 28 tapped hole.

Output connector

2 pin. MIL-C-5015 style.

 

Wiring 

Connection pin

Function

Cable conductor color

shell

ground

shield

A

power/signal

white

B

common

black

 

Dimensions 

 

 

 
Low Frequency Accelerometers

Low frequency measurement is critical for many industries. The petrochemical, machine tool, and paper industries use low frequency for both condition monitoring and process measurements. Other applications include slow speed agitators, cooling towers, semiconductor lithography, and structural testing.

Low frequency measurements and low levels of vibration are closely related. As shown in the figure below, acceleration levels decrease at low frequencies. In order to have adequate voltage signals at the acquisition equipment, low frequency sensors have greater output sensitivity (usually 500mV/g) than general-purpose sensors. Additionally, the low-end frequency cut-off is improved (down to 0.1 Hz @ -3dB) inorder to read slow speed vibration signals.

 

 

Acceleration & Displacement Levels Relative to a Constant Velocity Level

 

Low Frequency (Seismic) Accelerometer & Power Amplifier

 

Key features 

l         Ultra high sensitivity.

l         Ultra low-noise electronics for clear signals at sub micro-g levels.

l         Low frequency capable.

l         Low pass filtered to eliminate high frequencies.

l         ESD protection.

l         Miswiring protection.

 

Technical data 

Dynamic

Acceleration sensitivity, selectable

10, 100, 1000 V/g

Velocity sensitivity, selectable

0.1, 1, 10 V/in/sec

Vibration range, max

0.5 g peak

Amplitude nonlinearity

1 %

Frequency response

Filter 

100 Hz

450 Hz

-10%

0.08...70 Hz

0.08...300 Hz

-3dB

0.05...100 Hz

0.05...450 Hz

Transverse sensitivity, max

1 % of axial

Electrical

Output impedance

2500 W, recommended load impedance > 250 kW

Maximum output Voltage

5 V peak

Noise

2 Hz

0.03 mg/vHz

10 Hz

0.01 mg/vHz

100 Hz

0.004 mg/vHz

Grounding

Case isolated

 

Output connector

Model H731A

2 pin, MIL-C-5015

HP31

BNC

Input connector

Twin axial BNC (HP 31)

Power requirements (HP 31)

Internal batteries consist of four 9 Volt alkaline, > 150 hours, or external 18...36 VDC

Environmental

Temperature range -10...65 0C, vibration limit 10 g peak, shock limit fragile, base strain sensitivity 0.0001 g/mstrain

Sensing element

PZT ceramic / flexure

Weight

670 grams (H731A), 600 grams (HP31)

 

Wiring

Output

Connector

Function

Cable

H731A

shell

ground

shield

A

power/signal

white

B

common

black

HP31

shell

common

shield

Pin

signal

center conductor

Input

Connector

Function

Cable

HP31

shell

ground

shield

Pin

power/signal

white

socket

common

black

 

 

Dimensions

H731A

 

HP31