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You could have studied voltage and current measurements, but you will find resistance measurements totally different in several ways. Resistance is measured with the circuit’s power turned off. The ohmmeter sends its own present through the unknown resistance after which measures that present to provide a resistance value readout.

ROLE OF THE BATTERY

Though it reads out resistance, the ohmmeter is still a present-measuring machine at heart. The ohmmeter is created from a DC current meter by the addition of a group of resistors (called multiplier resistors) and an internal battery. The battery provides the current flow that’s finally 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 within the meter jacks. The leads are then hooked up to the ends of no matter resistance is to be measured. Since current can flow either way by way of a pure resistance, there is no polarity requirement for attaching the meter leads. The meter’s battery sends a present flow by way of the unknown resistance, the meter’s inner resistors, and the current meter.

The ohmmeter is designed in order that it will display 0 Ω when the test leads are clipped collectively (zero exterior resistance). The meter reads infinite (I) resistance or over limit (OL) resistance when the leads are left open. When a resistance is placed between the leads, the readout will increase based on how much present that resistance allows to flow.

To conserve its battery, an ohmmeter ought to never be left on the ohms perform when not in use. Since the current available from the meter is determined by the state of cost of the battery, the DMM needs to be zero adjusted to start. This may require no more than a test of touching the two probes together.

Turn off power to circuit.

Plug the black test lead into the widespread input jack. Plug the red or yellow lead into the resistance input jack.

Choose the resistance setting.

Touch the probe tips across the component or portion of the circuit.

View the reading and note the unit of measurement, ohms, kilohms, or megohms.

RESISTANCE MEASUREMENT PROCEDURES

Observe the steps beneath to measure resistance:

Before testing begins the technician ought to always know what reading to count on primarily based on the manufactures specifications, name plate rating, Ohms’s law and Kirchhoffs law. Testing blindly is harmful and counterproductive.

Turn off the power and prove the circuit to be measured is “dead” utilizing the T3 testing methodology and the voltage measuring procedures. Be sure to wear your PPE as we always assume a circuit is “live” till proven otherwise

Remove or isolate the element to be tested.

Plug the test probes into the appropriate probe jacks, Common and Ω. Note that the jacks used will be the same ones used to measure volts.

Select the ohms perform by turning the operate switch to ohms. Start with the lowest setting.

Touch the probes collectively to check the leads, connections and battery life. The meter ought to display zero or a really small amount of resistance for the test leads. With the leads apart, the meter ought to display OL or I, relying on the manufacturer.

Connect the tips of the probes throughout the break in the component or portion of the circuit for which you need to decide resistance. In the event you get an OL (over limit), switch to the next highest setting.

View the reading on the display unit. Be sure you note the unit of measurement.

Turn the meter off when testing is complete to prolengthy battery life.

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