Direct loading of a piezoelectric accelerometer’s output, even by relatively high impedance loads, can greatly reduce the accelerometer’s sensitivity as well as limit its frequency response. To minimise these effects the accelerometer output signal is fed through a preamplifier which converts to a much lower impedance, suitable for connection to the relatively low input impedance of measuring and analyzing instrumentation.
With measuring amplifiers, analyzers, and voltmeters a separate accelerometer preamplifier is used while vibration meters intended for use with piezoelectric accelerometers normally have the preamplifier built-in.
In addition to the function of impedance conversion, most preamplifiers offer additional facilities for conditioning the signal.
(1) A calibrated variable gain facility to amplify the signal to a suitable level for input to, for example a tape recorder;
(2) A secondary gain adjustment to “normalize” awkward" transducer sensitivities;
(3) Integrators to convert the acceleration proportional output from accelerometers to either velocity or displacement signals;
(4) Various filters to limit the upper and lower frequency response to avoid interference from electrical noise, or signals outside the linear portion of the accelerometer frequency range;
(5) Other facilities, such as overload indicator, reference oscillator, and battery condition indicator are also often included.