What’s all that IEPE, CCP stuff mean?

The output of the crystal is a charge, which requires a specialised charge amplifier, with extremely high input impedance, in order to drive our measuring system. These used to be separate boxes, with specialised low-noise cabling, but nowadays, the charge amplifier is built into the accelerometer itself, and this uses a ‘phantom’ powering system known as IEPE (integrated electronic piezo-electric), also known by a variety of proprietary names such as ICP®, CCP etc. At least IEPE is standardised! This means that long cables can be driven, and as long as your instrument can provide the powering, you should be in business. But always check that you have an IEPE accelerometer rather than a charge accelerometer first!
Due to being a capacitor, such accelerometers do not have a DC response, and will roll-off at low frequencies. Make sure you select one suitable for your task, if you want to measure down to 0.5Hz for example.

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