Enhanced sensitivity multi-range meter - has second selector switch and differential amplifier to increase deflection for low voltages

摘要

A mutlirange meter has two input terminals (11) one of which is connected to earth and the other of which is connected to a potential divider (20). Tappings on the potential divider are selected by a range selector switch (12) to provide desired full scale deflection for a given input voltage level. The output from the selector switch passes to an amplifier (17) and by way of a resistor (21) to the inverting input of a differential amplifier, the other input of which is fed from a reference voltage source (18). Tappings of a potential divider across the latter are selected by one pole of a three-way switch, the other pole of which sets the feedback resistance to this inverting input of the differential amplifier so that the ranges of the meter may be further subdivided to provide greater reading accuracy.