A differential-voltmeter using a temperature-limited diode
V. H. Attree · Journal of Scientific Instruments · 1952
A temperature-limited diode in a bridge circuit is used to measure true r.m.s. voltage. The nominal voltage is at the zero position of a centre-zero meter and voltage variations are indicated by deflexions to the left or right. Long-term stability is to ± 0.2% of the nominal voltage and short-term variations of 0.1% may be detected. The effect of changes in ambient temperature is negligible. A typical instrument for the 230 V mains has a range of 215-245 V and consumes 10 W.