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TEMPERATURE_TO_FREQUENCY_CONVERTER

2014-11-05 14:24  
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TEMPERATURE_TO_FREQUENCY_CONVERTER
A1's positive input is biased by the thermocouple. A1's output drives a crude V → F converter, comprised of the 74C04 inverters and associated components. Each V→F output pulse cduses a fixed quantity of charge to be dispensed into the 1 μF capacitor from the 100 pF capacitor via the LT1043 switch. The larger capacitor integrates the packets of charge, producing a dc voltage at A1's negative input. A1's output forces the V→F converter to run at whatever frequency is required to balance the amplifier's inputs. This feedback action eliminates drift and nonlinearities in the V→F converter as an error item and the output frequency is solely a function of the dc conditions at A1's inputs. The 3300 pF capacitor forms a dominant response pole at A1, stabilizing the loop.