The potentiometer is a type of variable (adjustable) resistor. It is widely used to control the output power of electrical devices (for example the volume of a radio or amplifier, the speed of a toy or tool, lighting levels, and so on). Its main function is to resist electric current, reducing it. By turning the potentiometer you change the resistance and consequently adjust the volume of the guitar or dim the lights in the house. It's a really inexpensive tool - this article tells you how to check that it's working properly.
Steps
Step 1. Find the nominal value of the potentiometer
This is the total resistance expressed in ohms and is usually printed on the bottom or side of the device.
Step 2. Get an ohmmeter and set it to a resistance greater than the rated resistance of the potentiometer
For example, if the device has a resistance of 1,000 ohms, you can set the meter to 10,000 ohms.
Step 3. Inspect it carefully
Identify the three terminals that protrude from the body of the device; the outermost ones are the ends of the resistor, while the central one is the "slider". In most cases, the ends are arranged close together while the cursor is somewhere else.
Step 4. Get the ohmmeter probes
Connect them to both ends of the resistance of the potentiometer; the data shown on the display should be a few ohms and less than the nominal value; if you detect a very different reading, it means that one of the probes is connected to the cursor instead of at the end of the resistance. If you have trouble recognizing the function of the three terminals, try different combinations until you find a sensible measurement.
Step 5. Rotate the controller fully in the opposite direction
Make sure that the probes never detach from the terminals during this phase; the resistance detected should be constant or change slightly.
The value found may not be the real power at which the potentiometer has been calibrated. This device usually has a tolerance of 5-10%, a detail that is sometimes reported on the body of the potentiometer itself but not always. The reading should not fall outside this range (for example, a 10,000 ohm potentiometer with a 5% tolerance should report readings between 9,500 and 10,500 ohms)
Step 6. Detach one of the ohmmeter probes from the end of the resistor and connect it to the slider
Slowly turn the controller in the other direction as far as it will go while looking at the measuring tool. When you reach the end, the resistance should be a few ohms; at the other end it should be at the maximum peak of the potentiometer. The resistance should slowly and gradually increase as you turn the control knob and you shouldn't notice sudden spikes.
