Metrological Evaluation of Robust Relaxation-Oscillator Interface for Remote Resistive Sensors and its Application towards Realizing Few Industrial Measurement Systems

A robust relaxation-oscillator-based conditioning circuit for remotely located resistive sensors is proposed in this article. The proposed circuit uses a simple analog architecture comprising an integrator, Schmitt trigger, inverter, and novel switching logic as its core blocks. The circuit provides a linear digital indication of the sensor resistance. The output of the proposed circuit is independent of many non-idealities such as bias-current and offset voltage of Op-amps, connecting lead and switch on-resistances, and mismatch/drift in the circuit components and power-supply levels. The proposed circuit has the capability to render all these merits while interfacing with various types of resistive sensor configurations. The working mechanism and analysis of the proposed circuit are described first in this article. The performance of the circuit is verified using simulation and experimental studies. Later, the immunity of the developed circuit from the effect of various parameters is also experimentally verified. Results show that the proposed circuit possesses a linear digital output and generates a low error in the output. The maximum nonlinearity is merely 0.07 % when a typical single-element-based sensor is interfaced with the developed circuit. The performance features of the developed circuit are also compared with the prior art and are observed to be adequate for interfacing industrial resistive sensors.