Accelerometer Selection for Vibration Testing
When you boil it down to its essentials, vibration testing is about introducing a specified level of energy into a DUT at or over a range of frequencies. We normally control and measure that energy with one or more accelerometers. Understanding the capabilities of these accelerometers is important to ensure that vibration energy is introduced into the DUT within the specified limits.
Some of the more significant accelerometer characteristics that you need to consider when selecting an accelerometer for a vibration test are sensitivity, frequency response, temperature and mass loading. An accelerometer’s sensitivity is the ratio of its output (in mV or picocoulombs) to its input in g’s. If you’re performing a test at a low level (like 0.25g rms) it’s necessary to select an accelerometer that has a high sensitivity otherwise the controller will not receive a signal higher than the background electrical noise and will be unable to control the shaker.
Accelerometers are designed to measure acceleration accurately over a range of frequencies. Some are optimized for lower frequencies, even down to DC levels, others are good at measuring at very high frequencies but can’t accurately measure below 2 hz. Because of this, it’s necessary to match the frequency response of the accelerometer to the frequency range of your test profile. The manufacturers’ specification for the accelerometer will define the acceptable frequency range for the accelerometer.
The temperature which an accelerometer is exposed to will affect its sensitivity and can significantly change the acceleration values that you’re measuring. Again, the manufacturers’ specification for the accelerometer should be consulted to ensure that your accelerometer will measure accurately at the temperature under which you’re testing.
The mass of the accelerometer that you attach to your DUT, will change the mass of the DUT itself. When you change the mass of your DUT, you also change its frequency response, so that the resonance that you measure with a 5 gram accelerometer will not be the same frequency if you’ve mounted a lightweight 0.5 gram accelerometer to your circuit board.
Choose your accelerometers carefully for the condition you want to measure and environment they will experience.