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The amplifiers have very low offsets for accurate tracking of programming instructions and exceptionally stable output in fixed applications. Voltage may be operationally controlled using the built-in stable reference and summing resistance together with an external voltage feedback rheostat.
The ratio of reference voltage to summing resistance gives a control current of approximately 1 milliampere through the external voltage feedback rheostat, for a control ratio of 1000 ohms/V. (A built-in calibrating trimmer can be used to calibrate this value).
PAT models have a built-in current sensing and feedback arrangement for protective limiting, controlled by an internal trimmer over the range 10% to 105% Io. Terminals are provided on the barrier strip for external control of the current limit function, using either a 3-terminal potentiometer or a 0-1V control voltage.
For a wider current control range, the main channel of the PAT may be connected so as to sample the drop across an external current-sensing resistor in the plus output lead. An external rheostat with careful zeroing of the built-in zeroing potentiometer will control current from 1µA to 100% Io. (Note: the range of currents controlled by any single current-sensing resistor should be limited to a 50:1 ratio).
Operationally, the PATs are 3-terminal, unipolar, inverting d-c amplifiers in which the plus output sensing terminal serves as common between the output and an external programming signal. For isolated digital control, see Kepco SN and SNR Series.
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