You could have studied voltage and current measurements, however you will find resistance measurements completely different in several ways. Resistance is measured with the circuit’s energy turned off. The ohmmeter sends its own present by way of the unknown resistance and then measures that present to provide a resistance worth readout.
ROLE OF THE BATTERY
Although it reads out resistance, the ohmmeter is still a present-measuring system at heart. The ohmmeter is created from a DC present meter by the addition of a bunch of resistors (called multiplier resistors) and an inside battery. The battery provides the current 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 connected to the ends of whatever resistance is to be measured. Since present can flow either way by means 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 way of the unknown resistance, the meter’s internal resistors, and the present meter.
The ohmmeter is designed in order that it will display 0 Ω when the test leads are clipped together (zero external 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 current that resistance allows to flow.
To preserve its battery, an ohmmeter ought to never be left on the ohms function when not in use. Because the present available from the meter depends on the state of cost of the battery, the DMM needs to 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 common enter jack. Plug the red or yellow lead into the resistance enter jack.
Choose the resistance setting.
Touch the probe tips throughout the component or portion of the circuit.
View the reading and note the unit of measurement, ohms, kilohms, or megohms.
RESISTANCE MEASUREMENT PROCEDURES
Follow the steps below to measure resistance:
Earlier than testing begins the technician should always know what reading to count on based mostly on the manufactures specifications, name plate score, Ohms’s law and Kirchhoffs law. Testing blindly is dangerous and counterproductive.
Turn off the facility and prove the circuit to be measured is „dead“ using the T3 testing method and the voltage measuring procedures. Make sure you wear your PPE as we always assume a circuit is „live“ till proven in any other case
Remove or isolate the part to be tested.
Plug the test probes into the appropriate probe jacks, Widespread and Ω. Note that the jacks used will be the similar ones used to measure volts.
Choose the ohms function by turning the perform switch to ohms. Start with the lowest setting.
Contact the probes collectively to check the leads, connections and battery life. The meter should display zero or a really small quantity of resistance for the test leads. With the leads apart, the meter ought to display OL or I, relying on the manufacturer.
Join the ideas of the probes throughout the break within the component or portion of the circuit for which you wish to determine resistance. If you happen to get an OL (over limit), switch to the next highest setting.
View the reading on the display unit. Make sure to note the unit of measurement.
Turn the meter off when testing is complete to prolengthy battery life.
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