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 halt'. 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 be 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. © 1996 IEEE.

V. Jagadeesh Kumar

Vempati G.K. Murti

Bridge circuits

Capacitance measurement

Capacitors

Digital to analog conversion

Electric inductors

Electric resistance measurement

Inductance measurement

Microcomputers

resistors

Microcontroller

QUASI BALANCED BRIDGE

ELECTRIC MEASURING BRIDGES

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

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

IEEE Transactions on Instrumentation and Measurement

This paper presents a simple digitizer suitable for differential variable inductive/reluctance sensors. The proposed scheme uses two digital I/O pins, a counter and a comparator of a microcontroller and obtains a digital output directly proportional to the measurand which is sensed using a differential variable inductive/reluctance sensor possessing either a linear or an inverse transfer characteristic. The scheme uses a ratio-metric approach in the computation and hence the output is less sensitive to variation in the parameters such as excitation voltage, reference voltage, offset of the comparator, etc. A prototype of the proposed system has been built and tested using standard variable inductors that emulated a differential inductive sensor following an inverse characteristic. The output recorded was linear across the full range and worst-case error noted was less than 0.3 %. For the prototype developed, the time taken to complete a measurement was 200 μs. The prototype digitizer has been interfaced with a commercially available LVDT and tested. The worst-case error observed in this test was 0.77%. Also, the same digitizer has been employed to get a digital readout from a differential variable reluctance based displacement sensor. The worst-case error was less than 0.83%. The test results establish the efficacy of, the simple and cost effective, scheme developed. © 2015 IEEE.

Journal	IEEE Transactions on Instrumentation and Measurement
ISSN	00189456
Open Access	No