The A-197 displays DC or AC voltages by means of an illuminated moving coil meter with mirror scale. The display range is 0...+10V (resp. -5V...+5V in the offset mode). There are 3 different measuring methods that are selected by a toggle switch:
Full Wave Rectifier: This mode is normally used to display audio signals (AC voltages). The incoming signal is rectified and smoothed with a low pass filter. Even DC voltages can be measured in this mode. The display shows however the absolute value (i.e. positive voltages remain unchanged, negative voltages - e.g. -3V - are converted into the corresponding positive voltages - e.g. +3V). To distinguish between positive and negative input signals a LED is available that lights up in case of a negative signal.
Direct Mode: In this mode the incoming voltage is passed to the meter without additional electronic modification. This mode will display positive DC voltages (Control Voltages), or even Gate/Clock signals.
Offset Mode: In this mode +5V are added to incoming voltage before it reaches the meter. Zero volt input correspond to the middle position of the display needle (i.e. +5V read out). This mode can be used to display positive and negative voltages, e.g. a slowly swinging LFO, S&H, bipolar random voltages, joy stick or Theremin for example.
The input is available as a triple multiple so that the signal to be measured can be used in the system simultaneously.