Manfred Weber
Metra Mess- und Frequenztechnik in Radebeul e.K.
Accelerometer Selection
In order to achieve optimum measurement conditions the following questions should be answered:
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Can you make at the selected location unadulterated measurements of the vibration and derive the needed information?
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Does the selected location provide a short and rigid path to the vibration source?
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Is it allowable (considering warranty restrictions) and possible in technical respects to prepare a flat, smooth, and clean surface with mounting thread for the accelerometer?
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Can the accelerometer be mounted without altering the vibration characteristics of the test object?
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Which environmental influences (heat, humidity, EMI, bending etc.) may occur?
The following table shows a summary of the most important criteria for selecting an accelerometer:
Criteria
Accelerometer Properties
Amplitude Range
Choose appropriate sensitivity and maximum acceleration.
Use seismic accelerometers for lowest vibration.
Selection chart for acceleration:
<10 g
10 - 200 g
200 - 1000 g
1000 - 10000 g
Frequency Range
Choose resonant frequency and linear frequency range
Selection chart for upper 3 dB frequency limit:
<200 Hz
0.2 - 10 kHz
10 - 15 kHz
15 - 25 kHz
>25 kHz
Weight of Test Object
Accelerometer weight <1/10 the weight of test object.
Test method for accelerometer weight to ISO 2954: Double de co-vibrating mass of the sensor by an additional mass. If the new indication shows a deviation from the original reading of more than 12%, the mass of the accelerometer is too great.
Choose miniature accelerometers for light objects.
Selection chart for sensor weight:
<3 g
3 - 20 g
20 - 50 g
50 - 100 g
> 100 g
High temperature
Temperature Transients, Base Strain, Magnetic Fields, Extreme Acoustic Noise
Assess influence, choose sensor according to characteristics,
choose shear type accelerometers when temperature transients or base strain may occur, stainless steel versions for strong magnetic fields
Humidity and Dust
Industrial accelerometers with protection grade IP67
Measurement of Vibration Velocity and Displacement
Single and double integration, below 20 Hz use shear type accelerometers
Mounting
- Quick measurement below 1 kHz with low accuracy
- For temporary measurement without altering the test object
Use magnetic clamp, wax or adhesives
- Long-term measurement
Use stud mounting or insulating flange
Grounding problems, potential differences
Long distance between sensor and instrument
Use IEPE accelerometers
Measurement in two or three axes
Sensor telemetry and battery-powered equipment
Use charge accelerometers or Low Power IEPE accelerometers
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Last update: 05.02.10
Jan
Burgemeister
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