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Introduction to Resistance Measurements

 

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

 

 

ROLE OF THE BATTERY

 

Although it reads out resistance, the ohmmeter is still a current-measuring system at heart. The ohmmeter is created from a DC present meter by the addition of a group of resistors (called multiplier resistors) and an inner battery. The battery supplies the present flow that's ultimately 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 within the meter jacks. The leads are then connected to the ends of whatever resistance is to be measured. Since current 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 via the unknown resistance, the meter’s inside 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 exterior resistance). The meter reads infinite (I) resistance or over limit (OL) resistance when the leads are left open. When a resistance is positioned between the leads, the readout increases in response to how much current that resistance permits to flow.

 

 

To preserve its battery, an ohmmeter should never be left on the ohms operate when not in use. Since the current available from the meter depends upon the state of charge of the battery, the DMM ought to be zero adjusted to start. This might 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 input jack. Plug the red or yellow lead into the resistance input jack.

 

Choose the resistance setting.

 

Contact 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

 

Observe the steps under to measure resistance:

 

 

Before testing begins the technician ought to always know what reading to expect based on the manufactures specifications, 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 technique and the voltage measuring procedures. Be sure to wear your PPE as we always assume a circuit is "live" until proven in any other case

 

Remove or isolate the component to be tested.

 

Plug the test probes into the appropriate probe jacks, Widespread and Ω. Note that the jacks used stands out as the same ones used to measure volts.

 

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

 

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

 

Connect the information of the probes across the break in the part or portion of the circuit for which you wish to determine resistance. In the event you get an OL (over limit), switch to the subsequent highest setting.

 

View the reading on the display unit. You should definitely note the unit of measurement.

 

Turn the meter off when testing is full to prolong battery life.

 

 

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