Practical case: Measure capacitance with a multimeter

Materials

• 1 digital multimeter with capacitance (C) function
• 1 electrolytic capacitor C1 = 10 µF, ≥16 V (under test)
• 1 resistor R1 = 10 kΩ, 1/4 W
• 1 jumper J1 (removable link) or SPST switch
• 1 breadboard
• 4 jumper wires
• 1 DC supply, +5 V (for safe charge/discharge, not used during the measurement)

Wiring guide

• Abbreviations used in the schematic:
• MEAS+ = multimeter red probe contact point (node between R1 and C1).

• MEAS− = multimeter black probe contact point (GND).

• Steps:

• Place C1 on the breadboard: positive lead to an isolated node (this will be MEAS+), negative lead to the ground rail.
• Connect the ground rail to the supply GND.
• Place R1 vertically from the +V side (through J1) down to the MEAS+ node.
• Insert J1 between the +5 V rail and the top of R1 so that +5 V → J1 → R1 → MEAS+ → C1 → GND.
• Double-check C1 polarity: positive up (toward MEAS+), negative to GND.
• To discharge or pre-charge safely, you may close J1 briefly with the supply on; then power the supply off.
• Before measuring capacitance: remove J1 (isolate from +V) and ensure the supply is switched off.
• Connect the DMM in capacitance mode: red probe to MEAS+, black probe to MEAS−.

Schematic

              ├────● PM+───────┬──────────────
              │                │
             ┌┴┐              ┌┴┐
             │ │              │ │
             │ │              │ │
             └┬┘              └┬┘
              │                │
              │               ┌┴┐
              │               │ │
              │               │ │
              │               └┬┘
              ├──● PM−         │
              │                │
──────────────┴────────────────┴────────────────
                      GND

C1 = 100 nF (capacitor bajo prueba)
S2 = Pulsador NA (DESCARGA)
R2 = 1 kΩ (descarga a GND)

Measurements and tests

• Prepare the DMM:

  • Set the multimeter to capacitance mode (C or nF/µF symbol).
  • If available, short the probes and press REL/Zero to null stray capacitance.

• Ensure a safe, isolated capacitor:

  • Power off the +5 V supply and remove J1 so the capacitor is not connected to any source.
  • If C1 might be charged, momentarily install J1 with power off to discharge through R1, then remove J1 again.

• Measure C1 (electrolytic):

  • Connect red probe to ● MEAS+ and black probe to ● MEAS−.
  • Hold steady for 1–5 seconds; the reading should settle near 10 µF (typical electrolytic tolerance ±20%).
  • Reverse the probes only if the meter requests it; otherwise keep polarity as drawn.

• Validate the reading:

  • Compare the measured value with the capacitor’s labeled value and tolerance band.
  • If reading is unstable, clean probe tips, reseat C1 leads, and ensure no other components are connected.

• Optional cross-check (leakage hint):

  • Switch DMM to resistance mode and measure from MEAS+ to MEAS−; an initially low reading that rises indicates charging behavior. A persistent low resistance suggests leakage or a faulty capacitor.

Common mistakes and tips

• Do not measure capacitance while the capacitor is connected to a powered circuit; you can damage the DMM and get false readings.
• Always remove J1 and turn off the supply before connecting the DMM in capacitance mode.
• Observe polarity on electrolytic capacitors: positive to MEAS+, negative to GND.
• Avoid touching the leads during measurement; body capacitance and leakage will alter the reading.
• For very small capacitors (<1 nF), stray capacitance dominates—use REL/Zero and short probe adapters to minimize error.

Safety notes

• Large capacitors can store hazardous energy. Discharge through R1; never short large capacitors directly with a wire.
• Verify voltage ratings: do not pre-charge C1 above its rated voltage.
• Keep the DMM in the correct jack and mode (capacitance) to avoid blown fuses or meter damage.

Improvements and variations

• Add a small 2-pin header at MEAS+ and GND to clip probes reliably.
• Test multiple capacitors (e.g., 100 nF ceramic, 1 µF film, 10 µF electrolytic) and record their measured values and tolerances.
• For in-circuit parts, lift one lead from the board before measuring to avoid parallel paths that skew the reading.

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Carlos Núñez Zorrilla

Electronics & Computer Engineer

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

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