extended range milli/volt meter

58 extended range milli-voltmeter A multimeter, as the name implies, is a multi- purpose measuring tool, although it has its limits. For example, its range for measuring AC in the audio band is usually inadequate, and the sensitivity, internal resistance and frequency response cheaper moving-coil multi-purpose normally leaves quite a lot to be desired. The wide- range millivoltmeter described here closes that gap in a very simple and elegant way. The instrument can be used to measure alternating current of 500 kHz. When frequencies between 100 Hz and inpu t impedance using MOS-F ET input opamPs the at all measurement ranges will amount to 10 MR. of the instrument At the lowest measuring voltage of 15 mV the sensitivity is such that there is a full-scale deflection on the 100 pA meter. The opamp serves both as measurement amplifier and active rectifier. The level of amplificationRi6s. C2 100n R7 00k determined by the switched resistors With the instrument set at a particular sens...