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Performance Characteristics of Accelerometers

Thorough knowledge of the performance characteristics of the sensor to obtain high fidelity test data

To consider before start the measurement:

Sensitivity is defined as a normalized sensor output signal change per acceleration unit change to reference signal:

where ∂θ is the change of the output signal due to the applied acceleration ∂a.

Output signal

The higher is the sensitivity, the greater is the system signal-to noise ratio.

Case of standard sized accelerometers

Sensitivity is proportional to the seismic mass
The higher the sensitivity for a specific design is, the greater the weight and the lower is the resonance frequency
Sensitivity selection may therefore be limited by weight and frequency response constraints

Mass Loading - criterion that must be regarded related to the measured structure

Vibratory motion will be appreciably attenuated
if the dynamic mass of the accelerometer approaches the dynamic mass of the structure on which it is mounted
In order to obtain accurate data, light-weight accelerometers must be used when the measurement is done
on small printed circuit boards, on thin panels, and on low mass elements of large test objects
Accelerometer may reduce the resonance frequency of test objects exhibiting a single-degree-of-freedom response
Miniature accelerometers must be used for all modal testing

Frequency range is a range in which the sensitivity has a value specified by a given tolerance

Typical frequency response of an accelerometer is following figure:

Frequency range is limited on one side by low frequency response
Iin the case of PE accelerometers is usually fixed to 2 to 5 Hz to reject pyroelectric output of these transducers
Highly isolated designs can be used to much lower frequencies
Piezoresistive accelerometers are capable of dc response.
High frequency response is a function of the mechanical characteristics of the accelerometer
and its method of attachment to the test object.
Most accelerometers exhibit an undamped single-degree-of-freedom response when securely mounted
Response will be flat +- 5% to about 1/5 of the mounted resonance frequency
Useful data can be obtained at higher frequencies if appropriate correction factors are applied
The resonant frequency reach typically values of few hundreds of Hz to some tens of kHz
(resonant frequency of 1.2 MHz was reported)

Transverse sensitivity is a sensitivity to transverse vibrations.

Important characteristics for single axis measurements,
Transverse sensitivity varies between 0 and 1 to 5% of main axis sensitivity
depending upon orientation to the transverse vibration

Amplitude range and linearity

PE accelerometers tend to have a very predictable non-linearity
expressed as a percentage increase in sensitivity with applied acceleration,
e.g. 1% per 500 g up to 2000 g for some models
PR accelerometers are explicitly linear
C accelerometers are inherently non-linear - can be compensated by added electronics

Temperature sensitivity can help the user to orient the choice of accelerometer working principle.

The most commonly used PE accelerometers are rated from sub-zero temperatures to 177 oC or 260 oC
Special versions can be used from near absolute zero to as high as 760 oC
Some designs are optimized for the most stable charge sensitivity
Other designs have voltage sensitivity more constant with temperature
Pyroelectric effect - transient temperature effects manifested by an output while temperature is changing
PR accelerometers have an operating range of typically -18 oC to +93 oC
The temperature limitation of C accelerometers is mostly done by limitations of associated electronics

Base strain effect - effect of dynamic flexing, stretching or bending of a test specimen at the mounting location of the accelerometer