How Do You Test a Potentiometer with a Multimeter
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How do you test a potentiometer with a multimeter? Remove the part from its circuit, set the meter to ohms, and make two readings. First, read across the two outer terminals and compare the result with the marked value and its tolerance. Second, connect one probe to the middle terminal, the wiper, and the other to an outer terminal, then turn the shaft slowly and watch the reading travel from near zero to the full value without jumps. A third check compares the two halves of the track with the total.
Electrical safety first
Work on mains circuits can kill. OSHA’s fact sheet on working safely with electricity warns that if the ground path is broken, fault current may travel through a worker’s body, causing electrical burns or death. A meter’s CAT rating has to suit the circuit it is connected to, and Fluke’s guide to category ratings says test equipment with a rating that does not match the task can explode if used improperly. Panel and service work belongs to a licensed electrician. OSHA’s general-industry rule points the same way: only qualified persons may work on circuit parts that have not been de-energized. Simpson’s manual for its 260 meter adds that voltages as low as 30 volts rms can cause an electric shock.
This guide stays on the bench. It covers a loose potentiometer, or one on a board that is unplugged and disconnected from every power source, and it uses only the meter’s ohms function. It gives no steps for outlets, panels, service wiring or any powered circuit. A meter’s CAT rating comes only from its listing or manual; if the listing does not state one, do not treat the meter as suitable for household mains.
Quick answer
- Switch everything off, discharge any capacitor, and take the potentiometer out of the circuit before you measure.
- Across the two outer terminals, the reading should sit inside the marked value plus or minus its tolerance.
- From the middle terminal to either outer terminal, the reading should change steadily as you turn the shaft, with no jumps or dropouts.
- The two sections of the track should add up to the end-to-end reading, give or take small errors.
Three terminals, one resistive track
Vishay Sfernice defines a potentiometer as a mechanically actuated variable resistor with three terminals. Two terminals are linked to the ends of the resistive element, and the third connects to a moving contact that slides over the track. That contact is the wiper.
Call the outer terminals A and C and the middle terminal B. The pair A to C is the whole track, which the Vishay note calls the total resistance. A to B and B to C are the two sections either side of the wiper. If the pins are not labeled, measure all three pairs with the part isolated. By our own reasoning from this construction, the outer pair is the one whose reading stays the same as you turn the shaft, and it is the largest of the three. The remaining pin is the wiper.
Read the marking and set your pass range
Many panel potentiometers carry a three-digit code. The Bourns 3310 datasheet explains it: the first two digits are significant, and the third digit is the number of zeros to follow. A code of 103 is therefore 10 followed by three zeros, or 10,000 ohms. The same sheet gives a total resistance tolerance of plus or minus 20 percent for its linear tapers. The pass range below is our own arithmetic: nominal value × 0.80 for the low end and nominal value × 1.20 for the high end. Another series can carry a different tolerance, so the datasheet for your own part overrides this table.
| Code | Nominal (ohms) | Low end (nominal × 0.80) | High end (nominal × 1.20) |
|---|---|---|---|
| 102 | 1,000 | 800 | 1,200 |
| 502 | 5,000 | 4,000 | 6,000 |
| 103 | 10,000 | 8,000 | 12,000 |
| 503 | 50,000 | 40,000 | 60,000 |
| 104 | 100,000 | 80,000 | 120,000 |
Temperature plays a small part. The Vishay note defines total resistance at 20 degrees C plus or minus 1 degree, and the Bourns sheet quotes 1,000 ppm per degree C over its storage range, so a room 5 degrees off shifts the reading by 1,000 × 5 ÷ 1,000,000 = 0.5 percent. If the range labels on your dial are unclear, our explainer on the 200 ohms setting shows how they relate to the value you expect.
Set up the meter
Fluke’s guide to measuring resistance gives the sequence. Turn off power to the circuit, and if it includes a capacitor, discharge the capacitor before taking any resistance reading. Turn the dial to ohms. The display should show OL, because the meter starts measuring before the leads touch anything. Use the COM jack and the ohms jack.
Isolation comes next. Fluke says best results come when the component is removed from the circuit, because parts in parallel affect the reading, and its manual explains that the meter shows the total resistance through all possible paths between the probes. For resistors on a board it may be necessary to lift one lead, and the same logic applies to a potentiometer.
Then fix the range. A meter in autorange picks its own once the leads touch the part, and Fluke notes that the range button lets you set it manually. Choose the first range above the marked value and note the unit beside the digits, such as k for kilohms.
Finally, check the leads. Fluke’s guide puts lead resistance at typically 0.2 to 0.5 ohms and describes a relative mode that subtracts it. The Fluke 87 manual gives 0.1 to 0.2 ohms and says to short the leads together to find the error. The two documents differ, so trust your own short-circuit reading. On a 10,000 ohm part, 0.5 ohm is 0.005 percent; on a 1,000 ohm part it is 0.05 percent. Keep your fingers off the metal tips: Fluke says the human body becomes a parallel resistance path. Our guide to resistance meters covers the basics.
Test 1: end-to-end resistance
- Place one probe on terminal A and the other on terminal C.
- Let the reading settle, then write it down.
- Turn the shaft partway and read again. In an unloaded part it should not move, because the wiper is not part of this path.
- Compare the value with the pass range in the table above.
The Fluke 87 manual defines OL as the overload indication shown when the input is too large to display. On the outer pair that points to an open track, a wrong pair of pins, or a range that is too low.
Test 2: sweep the wiper
- Keep one probe on terminal A and move the other to the wiper, terminal B.
- Turn the shaft slowly from one stop to the other while you watch the display.
- Repeat with the probe on terminal C instead of A. The readings should now move the opposite way.
With the probe on A and the wiper moving away from it, the reading should climb from a small value toward the total. With the probe on C it should fall. The Vishay note defines end resistance as the resistance between an outer terminal and the wiper when the wiper sits at the matching end of mechanical travel, and the Bourns 3310 datasheet limits it to 2 percent or 2 ohms, whichever is greater. We apply the percentage to the nominal value, which is our reading because the sheet does not say what the percentage refers to.
| Code | Nominal (ohms) | 2 percent of nominal | Limit used (greater of 2 percent or 2 ohms) |
|---|---|---|---|
| 102 | 1,000 | 20 | 20 ohms |
| 103 | 10,000 | 200 | 200 ohms |
| 104 | 100,000 | 2,000 | 2,000 ohms |
The same Bourns sheet lists contact resistance variation of 1 percent or 1 ohm, whichever is greater, but its footnote says the electrical specifications were tested at 60 RPM at about 25 degrees C. A hand-turned sweep is not that test, so use the figure for scale, not as a pass mark. The Vishay note describes continuity as the maintenance of continuous electrical contact between the wiper and the element over the whole travel, so a reading that jumps to OL or to a far higher value and then returns is a break in that contact. The Fluke 87 manual lists dirt, oil and solder flux as things that seriously affect resistance.
Do not force the shaft: Vishay recommends axial efforts below 10 newtons and no radial effort. On a multi-turn trimmer with a stop clutch, the note recommends not exceeding 10 screw turns at the clutch position.
One detail can save a false alarm. The Bourns 3310 datasheet lists an effective electrical angle of 270 degrees plus or minus 15 and a mechanical angle of 295 degrees plus or minus 10. Using the nominal figures, 295 − 270 = 25 degrees of travel do not follow the taper, so a reading that sits still near each end can be normal.
Test 3: do the two sections add up?
With the wiper left anywhere along the track, measure A to B, then B to C, then A to C. Add the first two readings and compare the sum with the third. This check follows from the construction in the Vishay note: two sections of one track either side of the wiper. The sources publish no pass limit for the gap, so repeat the check at three or four shaft positions. A healthy part should give a gap that stays small and steady.
For example, take readings we assume for a 10,000 ohm part, not figures from a source: A to C reads 9,840, A to B reads 3,910 and B to C reads 5,905. The gap is 9,840 − (3,910 + 5,905) = 25 ohms, or 0.25 percent. A gap of several hundred ohms at another position deserves a closer look.
What the mid-travel reading says about taper
Taper is the relationship between shaft position and resistance. In the Vishay note, code A is a linear taper and code L is a clockwise logarithmic, or audio, taper. Other makers use other letters, so check the datasheet. For the audio taper the note defines a checkpoint, measured from the counter-clockwise end, which is its default reference: at 50 percent of electrical travel the output ratio is 10 percent, give or take 3 percent. For a linear taper the midpoint is half the total, by proportion.
| Taper (10,000 ohm part) | Reading at 50% of electrical travel | Basis |
|---|---|---|
| Linear (code A) | 10,000 × 0.50 = 5,000 ohms | Proportion; our arithmetic |
| Clockwise logarithmic, audio (code L) | 10,000 × 0.10 = 1,000 ohms, within 700 to 1,300 ohms | Vishay Sfernice taper table |
Finding 50 percent of electrical travel by eye is imprecise, so use this to tell a linear part from an audio part, not as a precision check.
Reading the results
| What you see | What it may mean | Basis |
|---|---|---|
| OL across the outer pair | Open track, wrong pair or low range | Fluke 87 manual, overload indication |
| Outer pair far below the marked value | Wrong pins, parallel paths or finger contact | Fluke guide, parallel paths and the body |
| Jump or dropout during the sweep | Loss of wiper contact; dirt or flux can contribute | Vishay continuity definition; Fluke 87 manual |
| Flat reading near each stop | Can be normal ineffective travel | Bourns angle figures |
Mistakes to avoid
- Measuring with power on. The Fluke 87 manual says an external voltage makes an accurate resistance measurement impossible.
- Leaving the part in the circuit. The meter reports the total through every path between the probes.
- Trusting the continuity beeper. The Fluke 87 manual says resistances below a table threshold produce a continuous tone, so a beep says only that the value is under that limit. Our guide to the continuity tester shows when that mode fits.
- Expecting the outer pair to change. The whole track does not move with the wiper, so a steady outer reading is normal.
How we chose
This procedure draws on documents opened on 2026-10-21: a Vishay Sfernice application note, a Bourns panel-control datasheet, a Fluke guide to measuring resistance, the Fluke 87 manual, two OSHA pages, a Fluke page on category ratings and a Simpson manual. A statement stays in only when one of those pages makes it, or when arithmetic shown on the page produces it. Tolerance, end resistance and angle figures come from one Bourns series. The licensed-electrician advice is a site rule, since OSHA speaks of qualified persons rather than licenses.
What we could not verify
What the sources do not say is worth listing. None gives a pass or fail number for wiper noise during a hand sweep, a failure threshold for a worn track, or a limit for the gap in the sum check. The end resistance and contact resistance figures come from a single Bourns series, tied by its footnote to a 60 RPM test at room temperature, so they are scale guides for other parts. The pages opened here do not state the test voltage or current of any particular multimeter; your meter’s manual is the place to look.
Frequently asked questions
What should a potentiometer read across its outer terminals?
The marked value within the part’s tolerance. For one Bourns panel series the datasheet gives plus or minus 20 percent for linear tapers, so a 10,000 ohm part should land between 8,000 and 12,000 ohms. Check the datasheet for your own part, because other series differ.
Do I have to take the potentiometer out of the circuit?
Yes, or at least lift one lead, because parts in parallel change the result. Do this only on a board that is unpowered and disconnected from every power source.
Why does my reading jump while I turn the shaft?
The wiper may be losing contact with the track, and dirt, oil or solder flux can distort a resistance reading. The sources give no limit for acceptable jitter, so compare with a known-good part of the same type.
Can I use continuity mode instead of ohms?
Continuity mode only tells you whether the resistance is below the meter’s threshold, so a beep proves very little. Ohms mode shows the value and lets you follow the taper.
Is a reading outside the tolerance always a bad part?
No. A wrong pair of pins, finger contact, a low range and parallel paths can all produce the same symptom. If an isolated part still reads outside its band on the outer pair, the part is the likely cause.
Bottom line
Read the outer pair against the marked value and its tolerance, sweep the wiper slowly on a fixed range, and treat any jump or dropout as the sign to look closer.
Sources
- Vishay Sfernice, Potentiometers and Trimmers application note: https://www.farnell.com/datasheets/2884008.pdf (opened 2026-10-21)
- Bourns, 3310 9 mm square sealed panel control datasheet: https://www.bourns.com/docs/Product-Datasheets/3310.pdf (opened 2026-10-21)
- Fluke, How to Measure Resistance with a Digital Multimeter: https://www.fluke.com/en-us/learn/blog/digital-multimeters/how-to-measure-resistance (opened 2026-10-21)
- Fluke, 87 True RMS Multimeter Users Manual: https://assets.fluke.com/manuals/87______umeng0800.pdf (opened 2026-10-21)
- OSHA, Working Safely with Electricity fact sheet: https://www.osha.gov/sites/default/files/publications/OSHA3942.pdf (opened 2026-10-21)
- OSHA, 29 CFR 1910.333 selection and use of work practices: https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.333 (opened 2026-10-21)
- Fluke, IEC Category Ratings: Use the Right Tools for the Job: https://www.fluke.com/en-us/learn/blog/safety/iec-category-ratings-use-the-right-tools-for-the-job (opened 2026-10-21)
- Simpson Electric, 260 Series 6XLM operator’s manual: https://www.instrumentation2000.com//media/pdf/simpson-260-6xlm-manual.pdf (opened 2026-10-21)
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