Design and Analysis of Low Power Intrinsic Safe Direct-Digital Ohmmeter for Pyrotechnic Resistance Measurement

The design of a low power, intrinsically safe digital ohmmeter is presented in this paper. The design is based on a modified version of dual-slope integrating analog to digital converter. The proposed scheme provides a digital output that is proportional to the measured resistance, and is independent of circuit elements like line resistances, switch resistances, variation of integrating resistor and capacitor value and variation in supply voltage. The proposed ohmmeter circuit provides the advantage of direct interface to microcontroller input-output ports and hence reduces the need for additional hardware. Simulation studies have been carried out for the proposed converter and the output is linear with worst case error within 0.008%. Hardware realization has been completed for the proposed circuit. Test results using resistors in order to emulate the behavior of resistive sensors provided a linear output with worst case error within 0.2%.