Practical case: Measure resistance with a multimeter

Level: Basic — Measure a resistor accurately and safely using a multimeter.

Materials

• 1x Resistor R1 (e.g., 1 kΩ, 1/4 W, ±5%)
• 1x Digital multimeter with resistance (Ω) mode
• 2x Multimeter probes (red and black, typically included)
• 1x Breadboard or two jumper wires to hold the resistor (optional)
• 1x Tweezers (optional; helpful for small parts)

Wiring guide

• Power safety:
• Ensure the resistor is NOT connected to any powered circuit. If it was, disconnect power and discharge nearby capacitors before measuring.
• Mount the resistor:
• Insert R1 into a breadboard or hold it by its insulated body so both leads are accessible.
• Multimeter setup:
• Set the multimeter to resistance (Ω) mode. If manual ranging, choose a range above the expected value.
• Abbreviations used:
  • DMM_Ω+ = red probe of the digital multimeter in ohms mode.
  • DMM_Ω− = black probe of the digital multimeter in ohms mode.
• Probe placement:
• Touch DMM_Ω+ to the upper lead of R1 and DMM_Ω− to the lower lead, exactly at the black dots shown in the schematic.
• Avoid touching the bare metal of the resistor leads with your fingers during the reading to prevent parallel resistance paths.

Schematic

+V (no se usa en esta medición)
                          ● Ω+
                          │
                        ┌─┴─┐
                        │   │   R1 = 1 kΩ (Resistor 1/4 W, ±5%)
                        │   │
                        └─┬─┘
                          │
                          ● COM
                          │
         GND (no se usa en esta medición)

Measurements and tests

• Basic measurement:

  • Set the meter to Ω mode and connect DMM_Ω+ (red) and DMM_Ω− (black) to the black dots as in the schematic.
  • Read the displayed resistance. Call this R_meas (measured resistance).

• Compare to nominal value:

  • Decode R1’s color bands (or read its marking) to get R_nom (nominal resistance) and tolerance tol%.
  • Verify R_meas is within R_nom ± tol%. Example for 1 kΩ ±5%: acceptable range is 950 Ω to 1050 Ω.

• Lead resistance compensation (for low-ohm parts):

  • Short the probes together; record R_leads (lead/probe resistance).
  • Compute R_true = R_meas − R_leads. Use R_true for comparison.

• Stability and contact check:

  • Reverse the probes (swap DMM_Ω+ and DMM_Ω−) and re-measure; ideal resistors read the same both ways.
  • If the reading jumps or drifts, clean the leads or improve probe contact pressure.

• In-circuit caution:

  • Measuring R1 while it’s soldered on a PCB can read lower due to parallel paths.
  • If R_meas is unexpectedly low, lift one lead of R1 from the circuit and remeasure isolated.

Common mistakes and safety

• Measuring resistance on a powered circuit can damage the multimeter and give false readings. Always remove power and discharge capacitors.
• Holding the metal leads with fingers during measurement can lower R_meas. Grip the body or use tweezers.
• Using the wrong range can cause “OL” or slow autoranging. Select a manual range just above the expected value if possible.
• For hot components, readings may drift; allow parts to cool to room temperature before measuring.

Improvements and extensions

• For very low resistances (<1 Ω), use a 4-wire (Kelvin) measurement DMM to eliminate lead resistance errors.
• Log multiple readings and average them to reduce noise; note ambient temperature, as resistance changes with temperature (TCR).

More Practical Cases on Prometeo.blog

Carlos Núñez Zorrilla

Electronics & Computer Engineer

Telecommunications Electronics Engineer and Computer Engineer (official degrees in Spain).

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