Introduction to Resistance Measurements

You have actually stupassed away voltage and current dimensions, yet you will certainly find resistance dimensions various in several ways. Resistance is measured through the circuit’s power turned off. The ohmmeter sends out its very own current via the unrecognized resistance and also then procedures that existing to carry out a resistance value readout.

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Role of the Battery

Even though it reads out resistance, the ohmmeter is still a current-measuring gadget at heart. The ohmmeter is produced from a DC present meter by the enhancement of a team of resistors (called multiplier resistors) and also an interior battery. The battery offers the present circulation that is eventually measured by the meter. For this reason, use an ohmmeter only on de-energized circuits.

In the process of measuring resistance, the test leads are inserted in the meter jacks. The leads are then attached to the ends of whatever before resistance is to be measured. Since existing can circulation either means via a pure resistance, there is no polarity necessity for attaching the meter leads. The meter’s battery sends a present circulation via the unknown resistance, the meter’s internal resistors, and also the present meter.

The ohmmeter is designed so that it will certainly display 0 Ω as soon as the test leads are clipped together (zero external resistance). The meter reads unlimited (I) resistance or over limit (OL) resistance once the leads are left open. When a resistance is put between the leads, the readout boosts according to exactly how much current that resistance enables to circulation.

To conserve its battery, an ohmmeter have to never before be left on the ohms feature as soon as not in usage. Due to the fact that the present obtainable from the meter relies on the state of charge of the battery, the DMM have to be zero readjusted to begin. This may call for no even more than a test of poignant the 2 probes together.

Figure 8 mirrors exactly how resistance dimensions are taken.


Note: 1000 Ω = 1 kΩ 1 000 000 Ω = 1 MΩ

Figure 8: Using a DMM to Meacertain Resistance


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Turn off power to circuit.Plug the babsence test lead into the common input jack. Plug the red or yellow lead right into the resistance input jack.Select the resistance establishing.Touch the probe tips across the component or percent of the circuit.View the reading and note the unit of measurement, ohms, kilohms, or megohms.

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Resistance Measurement Procedures

Follow the measures listed below to meacertain resistance:

Before experimentation starts the technician should constantly know what reading to expect based on the manufactures specifications, name plate rating, Ohms’s legislation and Kirchhoffs regulation. Testing thoughtlessly is dangerous and counterfertile.Turn off the power and also prove the circuit to be measured is “dead” making use of the T3 testing strategy and also the voltage measuring steps. Be sure to wear your PPE as we always assume a circuit is “live” till prstove otherwiseRemove or isolate the component to be tested.Plug the test probes into the correct probe jacks, Usual and Ω. Keep in mind that the jacks offered may be the same ones supplied to meacertain volts.Select the ohms feature by turning the attribute switch to ohms. Start through the lowest setting.Touch the probes together to check the leads, relationships and also battery life. The meter have to display screen zero or a very little amount of resistance for the test leads. With the leads acomponent, the meter should display OL or I, relying on the manufacturer.Connect the tips of the probes across the break in the component or percentage of the circuit for which you desire to determine resistance. If you acquire an OL (over limit), switch to the following highest establishing.View the reading on the display screen unit. Be sure to note the unit of measurement.Turn the meter off once experimentation is finish to extend battery life.

Video: Measuring Resistance


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