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| The most well known electric instrument is probably the circuit tester, the instrument that is used universally to measure voltage, current and resistance. Not so long ago circuit testers were needed to assemble radios, and the instrument was widely used for do-it-yourself handicrafts and modeling. These days, another version of the circuit tester known as the digital multimeter has been adopted throughout the world.
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Circuit Testers in the Yokogawa Collection
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| There were two types of universal circuit testers: battery testers and circuit testers |
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A storage battery tester from Yuasa Battery Co., Ltd. (14 x 10 x 4 cm)
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Circuit testers become popular with the appearance of the vacuum-tube radio. Radio enthusiasts and electrical-appliance dealers started using testers to measure voltage and resistance.
The first vacuum-tube radios used dry cells or storage batteries, which meant that only the lower and higher DC voltages had to be measured. Pocket meters, which had A and B terminals, were used to measure the A power supply (the heater voltage, which was lower) and the B power supply (the plate voltage, which ran from 200 to 300 volts). When radios started using the eliminator method, which no longer required batteries that ran on the 100-V AC mains, the pocket voltmeter had to employ AC and DC ranges.
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Pocket meters (approximate width 5 cm) produced in the 1930s by companies such as Sakurai Denki, Western, and Radiometer. They were used to service radios.
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| Modern multi-range, needle-pointer circuit testers which have a switch for selecting voltage, current, or resistance are popularized versions of the testers used by telephone companies to perform maintenance. These testers were quite expensive. The first supplier was believed to be Automatic Coil Winder, Co., Ltd., which began selling the AVO meter in 1923. |
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The AVO meter from Automatic Coil Winder Co., Ltd., had five AC and five DC ranges and one OHM range. (10 x 12 x 5 cm)
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| In Japan, circuit testers were first introduced around 1935, at which time they cost more than the annual salary of a new college graduate and were for professional use only. It was not until after World War II that amateurs could afford to buy a tester. |
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The L-15 rotary-switch circuit tester with 15 ranges, manufactured by Yokogawa in 1947 (21 x 19 x 8 cm)
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Twelve-range universal tester from Weston (39 x 24 x 14 cm)
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| Eighty percent of the circuit testers currently on the market are digital. In the past, meter manufacturers produced selector switches and copper sub-oxide rectifiers as separate components; nowadays, analog-to-digital converters and computation circuits are contained on a single chip, completely changing the nature of technological competition among manufacturers. |
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The 7533-06 digital multimeter with automatic range selection, manufactured by Yokogawa in 1997 (18 x 8 x 4 cm)
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