Design and Implementation of Highly Accurate Current Measurement Acquisition Card

Aiming at requiring accurate current measurement, an ISA bus computer card with resistor sampling method and current to frequency (I/F) conversion method is designed and implemented. Resistor sampling method minimizes error by adopting resistor network, temperature compensation, data fitting and selection of precision instrumental amplifier and AfD converter. I/F conversion method combines noise filtering with measurement. Current signal could be converted to a square wave signal whose frequency is proportional to the current's amplitude by a compensated I/F conversion circuit. Through theoretical calculation and experiments of the two methods, the maximum reference error of the acquisition card is 0.01%.