Oscillator-Based Active Bridge Circuit for Resistance Measurement

This work deals with the designing of an oscillator based bridge set-up that can be used for in-circuit resistance measurement for a wide range of values. The circuit utilizes op-amp based active bridge in integration with relaxation oscillator to convert the resistance change into time period or duty cycle. The addition of an oscillator makes the bridge self-sustaining in nature. A novel, low cost, and highly sensitive active bridge is given for direct measurements of resistance of networks of arbitrary configuration. It can, in addition be used for the measurement of discrete resistors and resistance of the resistive sensor. The proposed circuit that we are studying is found to give accurate results for discrete resistance values in the lower range of 20 Ω - 900Ω. Also, the circuit has been interfaced with RTD (a resistive sensor) to confirm its effectiveness for small resistance measurement.