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Accelerometers (App Note)

This application note is about selecting and using accelerometers and vibration sensors.

Power Supply:  The ideal sensor runs off 5 volts DC so you can power it from the LabJack, but if a sensor needs 12 or 24 volts DC that is easy to provide with an external power supply.

Signal:  The ideal signal is a voltage signal that matches the analog input range of the LabJack.  With the ±10 volt inputs found on most LabJacks, the typical signal ranges of 0.5-4.5, 0-5, 0-10, or ±10 volts are all excellent options.

MEMs:

These are usually the best option.  MEMs sensors often have the ideal characteristics of accepting a 5 volt power supply and providing an easy-to-use voltage output signal such as 0-5 volts.  We have used some MEMs sensors like this from Analog Devices and Measurement Specialties among others.  Digikey is a source for Analog Devices and other brands.

Raw Bridge:

If the output is specified as something like 2 mV/V, that is a raw bridge sensor.  Another thing to look for is 4 wires labeled something like Excitation+, Excitation-, Signal+ and Signal-.  A raw bridge sensor can be handled, but is certainly more demanding than a signal-conditioned sensor.  For more information see classic forum topic #4376, especially post #13.

ICP or IEPE:

One common type of accelerometer is the ICP or IEPE type.  This provide a decent high level voltage signal, but the problem with these is they need a special constant current excitation source typically providing 2 mA to 10 mA at 18-30V.  We do not provide such an excitation source so that will have to be sourced along with the sensor. 

As for the signal from these sensors, often it can be measured directly, but sometimes you need to AC-couple to get rid of DC offset and then might need the LJTick-InBuff.

It is suggested that if using an ICP or IEPE sensor a signal conditioner also be acquired to go with it.  Look for a signal conditioner that provides the special current source excitation and also conditions the output signal if needed.