Measuring Resistance With Digital Multimeters

Measuring Resistance With Digital Multimeters

Introduction

Electrical Resistance is a property which is shown (to varying extents) in all materials. It provides a way of quantifying the energy lost by forcing a current through a material. Resistance is measured in ohms; the symbol for ohms is Ω. A low value of resistance means that current can flow easily from one point to another (little voltage difference is necessary to move charge); a high resistance means that it is difficult to move charge from one point to another (a high voltage difference is necessary to move charge).

Measuring resistance using a DMM is, in some ways, similar to measuring voltage. The DMM leads are plugged into the V-Ω and COM ports, but the function dial on the DMM should be pointing to the Ω setting. The physical appearance of the DMM should be as shown in Fig. 1.

Figure 1. DMM configured to measure resistance.

As with the measurement of voltage, when measuring resistance the DMM probes are placed across the terminals of the component whose resistance is to be measured, as shown in Fig. 2. However, when measuring resistance of a component, you should remove the component from any circuit to which it is connected. If you leave the component in the circuit while measuring its resistance, the resistance measurement may include effects from other components to which it is connected!

Figure 2. DMM used to measure resistance.

Important Points

When measuring resistance using a DMM:

  • The DMM function selection should be set at Ω.
  • The V-Ω and COM ports are used.
  • Probes are connected across the component whose resistance is to be measured. Resistance doesn't have a “sign” (it is always a positive number) so it doesn't matter which probe is connected to which terminal of the component.
  • The component whose resistance is being measured should not be placed in a circuit while measuring resistance.


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