Test Instruments & Measuring Devices OHM METERSOHM METERSThe resistance of a wire or a circuit is measured by an ohm meter. An ohm meteraids the troubleshooter in determining if a ground or a short exists in a circuit.EO 1.2 STATE the electrical parameters measured by each ofthe following in-place measuring devices:c. Ohm meterEO 1.3 EXPLAIN how the following electrical test equipmentand measuring devices are connected to a circuit:c. Ohm meterOhmMeterThe ohm meter is an instrumentFigure 9 Simple Ohm Meter Circuitused to determine resistance. Asimple ohm meter (Figure 9)consists of a battery, a metermovement calibrated in ohms, anda variable resistor.Ohm meters are connected to acomponent which is removed fromthe circuit as illustrated in Figure9. The reason for removing thecomponent is that measurement ofcurrent through the componentdetermines the resistance. If thecomponent remains in the circuit,and a parallel path exists in thecircuit, the current will flow in the path of least resistance and give an erroneous reading.Ro, in Figure 9, is an adjustable resistor whose purpose is to zero the ohm meter and correct forbattery aging. It is also a current-limiting resistor which includes the meter resistance Rm.Zeroing the ohm meter is accomplished by shorting the ohm meter terminals ab and adjustingRo to give full-scale deflection.Rev. 0 Page 15 ES-14
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