Variable resistor testing for beginners (2024)

Variable resistor which is also known as a potentiometer or rheostat, allows the adjustment of resistance value. To maintain the integrity and functionality of the circuit the testing of the variable resistors is essential.

To test a variable resistor with a multimeter, connect the probes to the two outer terminals to check total resistance. Then, connect one probe to the center (wiper) terminal and adjust the knob—this should change the resistance reading, confirming the resistor’s functionality.

In this article, we’ll learn about the steps that are needed for variable resistor testing.

Variable resistor testing importance

Before going into the details of the variable resistor testing process let’s discuss why we need to test variable resistors.

The following are the reasons:

1. Verification of resistance value

Verifying the resistance value of the variable resistors is crucial for circuit functionality and performance. The variable resistors come in various resistance ranges.

It’s important to check whether the resistor range matches our application requirements. If the resistance value significantly differs from the specified range, it can lead to incorrect circuit operation or affect the device’s performance.

Variable resistor testing helps us to identify the resistance range.

2. Detection of faulty resistors

Electronic components become faulty with time, the same is true with variable resistors their performance may deteriorate over time.

They may suffer from issues such as worn-out resistive elements, broken connections, or mechanical damage. You can find any flaws or imperfections that might impair the resistor’s performance by testing it.

Resistors that aren’t working properly can inject noise into the circuit, behave erratically, or result in improper voltage or current management.

3. Troubleshooting circuit issues

Sometimes the circuit performance is not according to what we expected. In the case we have to troubleshoot the circuit, a variable resistor may be one of the components under scrutiny.

You can test the resistor to see if it is contributing to the circuit issue or is operating appropriately.

To rule out the variable resistor as a possible source of the problem, it can be replaced if it turns out to be defective.

4. Calibration and adjustments

There are various functions of variable resistors but specifically, they are used for calibration and adjustment purposes in electronic devices, and variable resistors are more often used.

For example, in volume controls or temperature controls, the variable resistor is responsible for setting the desired level or value.

By testing the variable resistor, we can confirm if the resistor provides accurate and precise adjustment capabilities.

This is particularly important in applications where fine-tuning or calibration is necessary for optimal performance.

5. Maintenance

Electronic circuits need monitoring and maintenance so the testing of various electronic components becomes crucial.

As part of preventive maintenance, testing variable resistors regularly can assist in identifying any possible problems before they become serious.

Early detection and replacement of faulty resistors can save downtime, avoid circuit faults, and increase the lifespan of the electronic device.

Variable resistor testing

A good and precise multimeter will be needed for testing variable resistors. The variable resistor has two fixed terminals and the resistance value between these two doesn’t change.

1. Testing using a multimeter

Variable resistor testing can done through a multimeter, you can follow these step-by-step instructions.

a. Disconnect the Power

It is essential to disconnect the power before testing any electronic component if the component is connected to the circuit.

Turn off the device or disconnect it from the power supply to avoid any electric hazards.

This step can be skipped if the variable resistor is not connected to any circuit board.

b. Visual examination

The next step is visual inspection or examination. Look for any visible damage or signs of wear by examining variable resistors.

Physical damage, such as cracks, broken connections, or burn marks can also be identified.

In this step, if any of these damages are noticed, it may indicate that the resistor needs to be replaced.

c. Resistance measurement

To measure the resistance of the variable resistor, a good-quality multimeter will be required. Take a multimeter and set the meter to the resistance mode.

I will suggest this multimeter.

Kelin Multimeter

variable resistor testing using multimeter

d. Identify the terminals

Now it’s time to identify the terminal of the variable resistor. The variable resistor has three terminals, two fixed terminals, and a movable wiper terminal.

The fixed terminals are located at the end, while the movable terminal is at the middle.

e. Connect the multimeter

The Next step is to connect the probes of the multimeter to the fixed terminal of the variable resistor. It doesn’t matter which probe is connected to which terminal.

By connecting the multimeter to the resistor’s minimum or maximum position, we can find the range of resistance.

f. Check the display

When you connect a multimeter to the fixed terminal of a variable resistor. Read the resistance value display on the multimeter screen.

The display value should correspond to the resistance range of the selected variable resistor.

If the resistor has a range of 22k it will display the value nearer to it.

If the resistance reading deviates noticeably from the predicted range or if the multimeter displays OL (open circuit), it may indicate the resistor is open across the fixed terminal and the resistor is defective.

g. Wiper functionality

While measuring the resistance, you can also check whether the resistance value is changing smoothly by checking the wiper functionality.

Connect the probe of the multimeter to one of the outer terminals and the wiper terminal.

Now gently move the wiper terminal along the resistive element and check if the resistance value changes smoothly and continuously.

If the resistance jumps abruptly or shows erratic behavior, it may indicate a problem with the wiper or the resistive element.

h. Interpret the Results

It’s time to compare the measurement resistance value with the expected range which is given by the manufacturer.

If the resistance value falls within the specified range and the wiper functions smoothly, it means that the variable resistor functions correctly.

However, if the resistance is significantly off or if there are irregularities in the wiper movement, it suggests a faulty resistor that may need to be replaced.

2. Testing using component tester

The component tester tells you directly if the component is bad or good. Leaving the guesswork.

Following is the m328 component tester.

variable resistor testing using component tester

To use this tester for variable resistor testing, follow the following steps.

Take your variable resistor and the m328 tester
Turn on the tester and put the resistor in the socket
Press test button
See the resistance value if the resistor is fine
Else the tester will show a message on the screen saying that the variable resistor is bad

It can not be simpler than this.

Conclusion

A Variable resistor is the type of resistor in which the resistance value can be changed, it is used where variable resistance is required such as fine-tuning, etc.

The testing of variable resistors is essential before using or over time because the performance of the resistor may affected with time.

Testing helps us verify resistance value, detect any fault in the resistor, and also provides preventive maintenance which will enhance the circuit performance.

For testing you will need a multimeter and can also use a component tester. The multimeter should be set on resistor mode.

After gathering the tool identify the resistor terminals and connect the multimeter probe to the outer terminals and the resistance value will be displayed on the screen.

This was all about testing variable resistors, I’m hoping it will be useful.

Thank you…

Enjoyed the article?

Great! If you’re ready to take the next step, you’ll love the ‘Measurements and Testing’ chapter from my book, Make Your First Electronic Circuit. It’s packed with step-by-step guidance on measuring and testing all the essential electronic components—perfect for beginners.