A microcontroller-based quasi-balanced bridge for the measurement of L, C and R

A microcontroller-based quasi-balanced bridge for the measurement of parameters of an inductor or a capacitor is described. The unknown element (inductor or capacitor) in series with a resistor forms one-half of an ac bridge, while a multiplying digital-to-analog converter (MDAC) serves as the other half. The bridge is brought into two independent quasi-balanced conditions in succession by the microcontroller through the MDAC. The parameters of the unknown element are shown to he functions of the settings of the MDAC at the two quasi-balanced conditions. The relevant expressions for these parameters are evaluated by the microcontroller and the results displayed in appropriate display fields. The proposed scheme was implemented using an Intel 8751 microcontroller and tested. The readings obtained on the prototype were compared to those obtained with a commercial LCR meter. Employing an MDAC of basic accuracy +/- 0.2%, over the frequency range of 100-1000 Hz, an overall uncertainty in measurement of +/- 0.7% for the prototype was achieved.