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Use Those Surplus Meters

Find out what's inside that meter, and how it can be used.

by J. Frank Brumbaugh KB4ZGC

Junk boxes all over the world hold panel meters with all kinds of scalcs, most of which provide no clues to the characteristics of the internal movements. If ihe capabilities of these meters could be determined easily, many would be dusted off and placed in useful service in power supplies and test gear. This article will describe some simple and easy methods thai any ham can use to identify the electrical parameters of most types of panel meters, and show how tn tailor them to his or her exact requirements.

Meter Varieties

Disregarding the oddball meters which were originally intended for use in military equipment for exotic purposes, mosi common panel meters are of two basic types: iron-vane and DArsonval. Typical of the iron-vane movement are the small, black metal-cased meters such as those manufactured by Shu rite and a few other companies. The D'Arsonval movement is a moving coil movement and is used in the more expensive, and accurate, panel meters, as well as in analog VOMs and other types of electronic equipment,

The iron-vane meter is neither very sensitive nor very accurate, and in most cases its function is clearly indicated by the scale on the meter. This meter is often used on automotive battery chargers and in AC line voltage measurement.

The d'Arsonval—moving coil—movement is usually found in meters which at least look expensive, in black or white or clear plastic cases. Occasionally the case may be metal, usually painted black, and a few may be hermetically sealed. Almost every such meter can be identified and placed in service to measure either voltage or current or both {with switching) of practically any value.

Some surplus panel meters, especially those made originally for WWII and more recent military equipment, and many more removed from commercial gear and manufactured under such well-known names as Simpson, Westinghouse, Marion, etc., contain essential information on their faces. For now, ignore the main scale and look at the very small type at the bottom of the meter face, usually on one or both sides of the movement, visible through a cutout in the center. Either the DC resistance, the full-scale DC current, or both may be printed there.

The many small square and edgewise panel meters in plastic cases now available from mail order pans dealers for about S2 are usual i y 100 [lA. 200 tlA, 500 ^lA, or 1 mA movements. However, be aware that these ratings are nominal, not exact, and these inexpensive meters may not have a linear response, regardless of any scale printed on them. These meters arc available in left- or right-handed zero and center zero. They were made originally as tuning meters in commercial AM FN- and stereo equipment for home use, and as power and S-meter service in citizen band transceivers.

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