Precision Amplifier for Applications in Electrical Metrology

Abstract: This master's thesis addresses two main problems. The first is how to suppress a common mode voltage that appears for current shunts, and the second how to let a voltage divider work under an unloaded condition to prevent loading errors and thereby a decreased measurement accuracy. Both these problems occurs during calibration of power meters, and verification of current shunts and voltage dividers. To the first problem three alternative solutions are presented; prototype a proposed instrumentation amplifier circuit, evaluate the commercial available instrumentation amplifier Analog Devices AD8130 or let the voltage measuring device suppress the common mode voltage. It is up to the researchers at SP to choose a solution. To address the second problem, a prototype buffer amplifier is built and verified. Measurements of the buffer amplifier show that it performs very well. At 100 kHz, the amplitude error is less than 20 μV/V, the phase error is less than 20 μrad, and the input Rp is over 10 MΩ. This is performance in line with the required to make accurate measurements possible at 100 kHz and over that.