When measuring vibration by means of an accelerometer, it is necessary to incorporate a preamplifier between it and the measuring Amplifier The preamplifier is introduced in the measuring circuit for two reasons: 1. to transform the high output impedance of the accelerometer to a lower value and 2. to amplify the relatively weak output signal from the accelerometer. The signal from the piezoelectric accelerometer appears as a voltage across a capacitive impedance. As the capacitive output impedance of the accelerometer is very high, the associated Amplifier must be of a special design having a high input impedance. This is necessary in order to avoid loading of the accelerometer and thereby obtaining decreased sensitivity and limitation at the low end of the frequency range. The combination of a charge Amplifier and a piezoelectric accelerometer gives a sensitivity which is independent of cable length within very wide limits. This feature makes a charge Amplifier especially attractive in vibration systems where different cables are used. The Conditioning Amplifier Type 2626 may be used with cable lengths up to several thousand meters. Another advantage the 2626 Amplifier offers is the wide conditioning possibilities to different transducers and measuring requirements. It features a 3 digit sensitivity adjustment network which enables the Amplifier ensitivity to be adjusted to the particular transducer used. The network is calibrated in PC g. Output of the Amplifier can be adjusted stepwise between 1 mV/g and 10V/g, depending on the transducer sensitivity. A maximum sensitivity of 1 V PC is available. The output signal is available either directly coupled or through a transformer (switchable) for floating output. Stepwise adjustable HP and LP Filter are incorporated, by which the frequency limits can be adjusted independent of sensitivity. The Filter Scale give the 5% as well as 3 dB frequency limits. The lowest frequency limit for the Amplifier is 0.3 Hz which makes it quite suitable for measurement of impulses. Two neon indicators are connected to the output, one for overload and the other for underload which lights when the signal level is at least 1 V peak. On account of quick recovery time after overload, the Amplifier is also suitable for use in a servo-loop in exciter systems.