A voltmeter is an electrical device to measure the voltage of electricity in a circuit. Today voltmeters are usually digital, but half a century they were analogue devices that used a form of galvanometer. The galvanometer has a coil of fine wire suspended in a strong magnetic field. When an electric current is applied, the interaction of the magnetic field of the coil and of the stationary magnet creates a torque, tending to make the coil rotate. The torque is proportional to the current through the coil. The coil rotates, compressing a spring that opposes the rotation. The deflection of the coil is thus proportional to the current, which in turn is proportional to the applied voltage, which is indicated by a pointer on a scale.

Tonight we are looking at a military marked voltmeter from the late 1950s:imageThis large device was designed to be mounted on an electrical panel and has a series of screw holes around its rim to allow it to be attached. The dial itself is /|\ marked with a date of 1958:imageThe scale allows a voltage of between 0V and 20V to be measured in 1/2V increments. The rear of the voltmeter has a pair of brass contacts to allow the voltmeter to be wired into a circuit:imageAlso obvious is a large paper label attached to one of the contacts. This label dates to when the voltmeter was last tested to see if it worked. This is an RAF label, indicating that this voltmeter was from their stores, rather than the army:imageThe date on the rear indicates it was tested in September 1960:imageThe fact that this label survives on the voltmeter shows that it has never been used and is in fact what is often referred to as ‘new old stock’. Vintage military electrical gear is available to the collector very cheaply and seem to hold little interest to most militaria collectors- I on the other hand rather like these instruments as there is something very attractive and ‘retro’ about these old, chunky dials and switches that I find appealing…

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