Step-by-Step Guide to Measuring Resistance with a Digital Multimeter

EIN FLUKE LOGO

July 28, 2022

Measuring resistance determines the condition of a circuit or component. High resistance means lower current flow, lower resistance means higher current flow.

The resistance of control circuit components (switches or relay contacts for example) will begin at a low level and increase over time due to wear or dirt build up. Motor and solenoid loads decrease in resistance over time because of moisture or insulation breakdown.

Fluke Resistance 1

Measuring resistance:

  1. First have power to circuit OFF.

If a circuit includes a capacitor, discharge the capacitor before taking any resistance reading.

  1. Next make sure the digital multimeterdial is set to resistance, or ohms. Often, there will be multiple modes (continuity, capacitance or diode) for one setting as shown in the image below.
  • The display should show OLΩ. With Resistance mode, a digital multimeter automatically begins measuring resistance before the leads are connected.
  • You may see the MΩ symbol because the resistance of unattached test leads is high.
  • When the leads are connected to a component a digital multimeter will use the Autorange mode to find the best range.
  • You can manually set the range with the Range button.
  • Removing the component being tested from the circuit for best results. When connected to the circuit you may pick up parallel components.

Fluke Resistance 2

  1. The next step is to insert the black test lead into the COM jack.
  2. Then insert the red lead into the VΩ jack. When finished, remove the leads in reverse order: red first, then black.
  3. Connect the test leads across the component being tested. Make sure that contact between the test leads and circuit is good.

For very low-resistance measurements, use the relative mode (REL: see below). It may also be referred to as zero or Delta (Δ) mode. This automatically subtracts test lead resistance—typically 0.2 Ω to 0.5 Ω. If test leads touch (are shorted together), the display should show 0 Ω.

Foreign substances (dirt, solder flux, oil), body contact with the metal ends of the test leads, or parallel circuit paths may impact readings. The human body can be a parallel resistance path, reducing total circuit resistance. Avoid touching metal parts of test leads to avoid errors.

  1. Read the measurement on the display
  2. Turn the multimeter OFF to prevent battery drain.

Options for advanced digital multimeters

  1. When using the RANGE button to select a specific fixed measurement range, note the annunciator (K or M) after the measurement in the display.
  2. You can use the HOLD button to save a stable measurement to be viewed later.
  3. The MIN/MAX button captures the lowest and highest measurement The multimeter will beep each time you record a new reading.
  1. The relative (REL) button to set the multimeter to a specific reference value. It will display measurements above and below the reference value.

Analyzing Resistance Measurements

The component being tested determines the significance of a resistance reading. Resistance of component varies over time and component type. Subtle changes in resistance are not critical, typically. Although they may indicate a pattern, which should be noted.

Slight resistance changes are usually not critical but may indicate a pattern that should be noted. For example: as the resistance of a heating element rises, the current passing through the element decreases, and vice versa, which is displayed in the diagram:

Fluke Resistance 3

For circuit boards you may need to lift one of the resistor leads from the board to get the correct resistance of the resistor measurement.

The resistance measurement displayed by a digital multimeter is the total resistance through all possible paths between the test lead probes.

Use caution when measuring resistance across a component that is part of a circuit.

Always check the circuit schematic for parallel paths. The resistance read is usually lowered by components connected in parallel.

This article was featured in our Tools, Equipment, & Technology Digital Handbook released last month, go HERE for the full issue

Related Articles


Latest Articles


Changing Scene

  • Electrozad Welcomes Jason McFarland as Windsor Branch Account Representative

    Electrozad Welcomes Jason McFarland as Windsor Branch Account Representative

    December 2, 2022 Jason McFarland joins Electrozad as an Account Representative at their #Windsor branch and will be a key point in developing relationships and accounts focused on Industrial Manufacturing/OEM’s. Jason studied advertising at St. Clair College and holds several Sales Certifications. He brings with him several years experience as a marketing coordinator and sales account manager. “My… Read More…

  • Southwire’s Latest Copper Rod Plant in Carrollton, Ga. Nears Completion, Production to Boost by Roughly 10% Annually

    Southwire’s Latest Copper Rod Plant in Carrollton, Ga. Nears Completion, Production to Boost by Roughly 10% Annually

    December 2, 2022 As part of more than a billion-dollar modernization commitment across its footprint, Southwire is nearing the completion of construction on a new, state-of-the art copper rod plant in Carrollton, Ga. The new plant replaces an aging, 40-year-old facility and will increase copper rod production by at least 10 percent annually. “Our goal… Read More…

  • Ontario Finalizes Electrification and Energy Transition Panel

    Ontario Finalizes Electrification and Energy Transition Panel

    December 2, 2022 Ontario is planning for the long-term reliability and affordability of the province’s clean energy supply by appointing the remaining members of the Electrification and Energy Transition Panel. Recently, the province appointed Dr. Monica Gattinger and Chief Emeritus Emily Whetung, former Chief of Curve Lake First Nation, to the Panel, where they join… Read More…

  • Skills Ontario’s Jennifer Green Win’s Apprenticeship Award

    Skills Ontario’s Jennifer Green Win’s Apprenticeship Award

    December 2, 2022 Skills Ontario is pleased to support the Colleges Ontario Premier’s Awards and congratulate Jennifer Green for winning the Apprenticeship Award at the annual Higher Education Summit in Toronto on Monday. There were 126 nominees in total across seven categories. As the only woman in her Industrial Mechanic Millwright program at Conestoga College,… Read More…