Position indicator for carrier-operated level controllers - uses operational amplifier unit with linear network and bias source

摘要

The level control indication circuit comprises an operational amplifier (24) which acts as the source for the controlled variable, is connected via a linear network of resistors (25) to the indicating instrument (23). One terminal of the meter is connected via one resistor (9) to the amplifier, the other is connected to a bias voltage produced by means of a potential divider (5, 7, 8) and a zener diode (6). The bias voltage source resistance and separate values are chosen so that the display voltage fed to the instrument is, at two points within the indicating range, equal to the controlled variable measured logarithmically. The internal resistance of the voltage source and the ohmic resistance provide the required relationship between indicated voltage and regulated voltage.