You’ve studied voltage and present measurements, but you will discover resistance measurements different in several ways. Resistance is measured with the circuit’s power turned off. The ohmmeter sends its own current through the unknown resistance after which measures that current to provide a resistance worth readout.
ROLE OF THE BATTERY
Even though it reads out resistance, the ohmmeter is still a current-measuring device at heart. The ohmmeter is created from a DC present meter by the addition of a group of resistors (called multiplier resistors) and an internal battery. The battery supplies the present flow that is eventually measured by the meter. For this reason, use an ohmmeter only on de-energized circuits.
Within the process of measuring resistance, the test leads are inserted in the meter jacks. The leads are then hooked up to the ends of whatever resistance is to be measured. Since current can flow either way by way of a pure resistance, there is no such thing as a polarity requirement for attaching the meter leads. The meter’s battery sends a present flow by means of the unknown resistance, the meter’s inside resistors, and the current meter.
The ohmmeter is designed so that it will display zero Ω when the test leads are clipped together (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 in response to how a lot present that resistance allows to flow.
To conserve its battery, an ohmmeter should by no means be left on the ohms perform when not in use. Since the present available from the meter depends on the state of cost of the battery, the DMM must be zero adjusted to start. This could require no more than a test of touching the two probes together.
Turn off energy to circuit.
Plug the black test lead into the widespread enter jack. Plug the red or yellow lead into the resistance input jack.
Choose the resistance setting.
Touch the probe suggestions across the element or portion of the circuit.
View the reading and note the unit of measurement, ohms, kilohms, or megohms.
RESISTANCE MEASUREMENT PROCEDURES
Comply with the steps under to measure resistance:
Before testing begins the technician ought to always know what reading to expect based on the manufactures specs, name plate ranking, Ohms’s law and Kirchhoffs law. Testing blindly is harmful and counterproductive.
Turn off the ability and prove the circuit to be measured is «dead» using the T3 testing method 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 component to be tested.
Plug the test probes into the appropriate probe jacks, Common and Ω. Note that the jacks used could be the similar ones used to measure volts.
Choose the ohms function by turning the perform switch to ohms. Start with the bottom setting.
Contact the probes together to check the leads, connections and battery life. The meter should display zero or a very small quantity of resistance for the test leads. With the leads apart, the meter should display OL or I, depending on the manufacturer.
Connect the information of the probes throughout the break in the part or portion of the circuit for which you need to decide resistance. In the event you get an OL (over limit), switch to the following highest setting.
View the reading on the display unit. You should definitely note the unit of measurement.
Turn the meter off when testing is complete to prolengthy battery life.
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