Abstract: A multimeter is provided with two slide switches, one switch providing a selection of four functions, i.e. "OFF", "AC", "DC/JUNCTION" and "RESISTANCE/CONTINUITY" and the other switch providing a selection of six range settings and a "JUNCTION/CONTINUITY" setting. The multimeter also has three input sockets for insertion of test leads. At least two of the combinations of the switches and sockets are incompatible, i.e. "AC" and "JUNCTION/CONTINUITY", and a current input socket and "RESISTANCE/CONTINUITY". An internal buzzer is incorporated in the multimeter to provide an audible indication to a user that an incompatible combination has been selected. The buzzer is preferably also used in junction and continuity test modes.

Abstract: An instrument for measuring electrical resistance or reactance comprises a sine wave generator which generates an a.c. signal and reference signals for a phase sensitive detector. The a.c. signal is applied to a decade attenuator which adjusts its amplitude in dependence on a range switching. The signal is passed to a bridge section, wherein it is applied to a component to measure the value thereof. A voltage output, indicative of the value, is fed to a gain block, wherein its amplitude is re-adjusted in dependence on an input from the range switching. The voltage output is operated on by a phase sensitive detector and passes to a digital display. In the reactance mode, set by a function switching, the a.c. signal is phase shifted before being applied to the component, so that the voltage output is in phase with the reference signals.

Abstract: A low charge detector, for a measuring instrument incorporating a meter for indicating measurement readings, includes a "low battery detector" circuit which causes a first output to be released from a 1 Hz oscillator, when a battery pack supplying power to the instrument discharges to a predetermined level. The first output is then applied to a pointer on the meter, thus causing the pointer to execute oscillations of a relatively small amplitude.When the battery pack is substantially dead, a "dead battery detector" circuit causes a second output to be released from the oscillator and to combine with the first output. The combined output is then applied to the pointer, thus causing the pointer to execute oscillations of a substantially greater amplitude, thereby indicating that recharging of the battery pack is required.

Abstract: A switch actuator mechanism including a slider which can execute movement in steps along a linear track, the step-wise movement being governed by the interaction of a pair of cam-followers, carried by the slider, with respective cam-surfaces disposed alongside the track, one to either side thereof. The cam-followers are resiliently urged into contact with their respective cam surfaces and permit the slider to assume, alternately, stable and unstable conditions at locations disposed in series along the track.