Charge Amplifiers

Accelerometers with charge output generate an output signal in the order of a few Picocoulomb (10^-12 C) with a very high output impedance. In order to use standard measurement equipment for further processing, it has to be converted into a low-frequent signal. Charge amplifiers are used for this purpose. These generate a voltage proportional to the charge input. In our User Guide Sensors the functionality of charge amplifiers is presented.

Charge amplifiers show to advantage particularly if vibration measurements shall be carried out with very high temperatures (> 250 °C). Since almost only piezoelectric accelerometers with charge output still work in this temperature range, these are prefered. The sensor signal is transmitted via the high-temperature-resistant cable to the charge amplifier and is conditioned appropriately (e.g. acc. to IEPE standard). Thus, the sensor signals can be evaluated at a distance from the high-temperature zone.

Furthermore, the output voltage of the charge amplifier is independent of input and cable capacities.

Therefore, different cables can be used for contacting of the accelerometer.

Typical charge amplifiers are e.g. the devices of the M72 series, which include further amplifying stages, filtering and integrators. Accelerometers with charge output can also be integrated into the VibroMatrix measurement system. For that purpose a charge amplifier (e.g. IEPE100) is integrated into the measuring line and generates an IEPE compatible signal that can be evaluated by the InnoBeamer.