Microprocessor-Controlled Potentiometric System for Nanovolt Measurements

In order to complete an automatic system for EMF comparison of standard cells in a reference group, an automatic potentiometer at nanovolt level was implemented. However, the equipment can be dedicated for general purpose measurements of dc voltages lower than 1 V. The system reproduces the techniques of manual potentiometers opposing the unknown voltage against a compensation voltage. Starting from the unbalance signal of a galvanometric photocell amplifier, a microcomputer provides a suitable strategy of null balance, acting on the compensation source and the galvanometer sensitivity. In this way, the current in the measuring circuit is continuously kept at an almost zero value. With respect to manual potentiometers, this apparatus does not require an operator and reduces the measurement time. The period of a measurement cycle depends on the present noise level and the number of successive balances. A time of about 2 min is typical for a peak noise of 1 nV.