In this multimeter use guide, learn how to take resistance measurements within a circuit.
Follow Along on SkillCat: "Using a Multimeter" Course!
Want to test your knowledge? Skip to the quiz!
Multimeter Basics
There are two types of multimeters: digital multimeters and clamp multimeters. Most of what is pictured in this guide is a digital multimeter.
Multimeters can be used to measure various measurements:
Measure voltage in Volts
Measure current in Amperes
Measure resistance in Ohms - this is the focus of this guide!
Measure continuity in Ohms
Measure capacitance in Farads
Measure temperature in Farenheit or Celcius
Multimeters have 2-4 ports for the provided test leads or probes to be plugged into.
Probes have one end of the wire called the plug end that plugs into the multimeter port. The other end of the wire called the probe end is used to touch the component of measurement.
Remember that black probe represents the negative probe, and red probe represents the positive probe.
Ensure that the probe ends of your probes do not touch as you measure using the multimeter, as that can short the circuit and become a safety hazard.
Instead of probes, alligator clips can also be used.
Setting Up Your Multimeter For Resistance Measurement
Resistance is the opposition to the flow of electric current within a circuit. Resistance is measured in Ohms (Ω).
To measure resistance, connect your probes into the correct ports on your multimeter. Your red lead goes into the port marked with a “Ω” while your black probe plugs into the port marked with “COM”. Before taking any measurements, set your multimeter dial to the “Ω” symbol for resistance measurement.
Turn the power of the circuit off. Treat the circuit as if it still has power until you measure the voltage. If there is 0 voltage, then you can continue. If your multimeter measures voltage, that means the circuit still has power. Afterwards, the component must be disconnected from the circuit in order to measure resistance.
The reasoning for this process is that multimeters measure resistance by running a small test voltage through the component. When the circuit has power running through it, the multimeter cannot read the test voltage. This prevents the meter from accurately reading resistance.
The Process of Measuring Resistance
Now that your multimeter is set up, you can go through the process of measuring resistance. Place the now disconnected component away from the circuit.
To measure resistance, you need to place your probes on the positive and negative terminals of the component. When your probes are touching the component, you will see a value appear on the multimeter display. This is your resistance measurement. The display will also show the units of the measurement.
Some multimeters require you to manually set the range of your measurement. If your multimeter is not auto ranging, you may need to adjust your range to get an accurate result. Do this by slowly turning the dial to a lower range setting. Stop once you have an accurate measurement. If your multimeter is auto ranging, the multimeter will automatically change the range.
The range determines the accuracy of your measurement. If you measure a 2Ω resistance at a 2000Ω range, your precision will be very bad. By decreasing the range, you will get a more accurate result and more decimal places on the measurement.
Don't stop here! Learn everything you need to know about HVAC. Click here to download SkillCat and get started!
FAQs
What is a multimeter?
A multimeter is an essential tool used to measure various electrical properties such as voltage (Volts), current (Amperes), resistance (Ohms), and more. It can be either a digital multimeter or a clamp multimeter, with the digital multimeter being more commonly used for this guide.
How do I measure resistance with a multimeter?
To measure resistance, first ensure the circuit is powered off. Then, insert the test leads into the appropriate multimeter ports: the red lead into the "Ω" port (for resistance) and the black lead into the "COM" port (for common ground). Set the multimeter dial to the "Ω" symbol. Touch the probes to the component terminals to get the resistance measurement on the multimeter display.
Why should the circuit be powered off before measuring resistance?
A multimeter measures resistance by sending a small test voltage through the component. If the circuit is still powered, the multimeter can't accurately measure the resistance, and it might interfere with the measurement due to the existing current or voltage.
What happens if I don’t turn off the power before measuring resistance?
If the circuit remains powered on, the multimeter may not properly measure resistance because the test voltage cannot be correctly applied, which will result in inaccurate or unreliable readings. This can also cause potential safety hazards.
How do I interpret the resistance value on a multimeter?
When measuring resistance, the multimeter will display a value in Ohms (Ω). The unit is important to note. For more accurate results, ensure your multimeter is set to an appropriate range. If it's not auto-ranging, manually adjust the range to the nearest setting for more precise measurements.
What should I do if my multimeter is not auto-ranging?
If your multimeter is not auto-ranging, you will need to manually adjust the range. Start by selecting a higher range setting and gradually lower it until you get a clear, accurate resistance measurement. This will help you get a precise resistance value.
How does a digital multimeter work to measure resistance?
A digital multimeter measures resistance by applying a small test voltage across the component and calculating the resulting current flow. Based on this data, it displays the resistance value in Ohms (Ω).
What is the correct way to connect the probes for resistance measurement?
For resistance measurement, connect the red probe to the "Ω" port and the black probe to the "COM" port. Then, place the probe ends on the component you're measuring. Ensure the probes don’t touch each other, as it could short the circuit.
What does "Ω" stand for on the multimeter?
The "Ω" symbol on the multimeter refers to Ohms, the unit used to measure resistance. When you set the multimeter dial to this symbol, you are preparing the multimeter to measure the resistance of a component in Ohms.
Can I use a multimeter to measure other electrical properties?
Yes! A multimeter can measure not just resistance (in Ohms), but also voltage (in Volts), current (in Amperes), capacitance (in Farads), and temperature (in Celsius or Fahrenheit). Different settings and probes are used for each type of measurement.
What is the difference between measuring resistance and measuring voltage?
Resistance is the opposition to current flow in a circuit, measured in Ohms (Ω). Voltage, on the other hand, is the electrical potential difference in a circuit, measured in Volts (V). When measuring voltage, you would connect the probes across the component in question, while for resistance, you would place the probes on the terminals of the component after disconnecting it from the circuit.
Why is it important to use the correct range for measuring resistance?
The range setting determines the accuracy of your multimeter reading. If the range is set too high, the precision of your measurement will be poor, and if it's set too low, the multimeter may not be able to provide a complete reading. Adjusting the range properly ensures the most accurate resistance measurement.
What are the dangers of incorrect multimeter usage?
Incorrect usage, such as failing to disconnect the power before measuring resistance, can lead to inaccurate readings or potentially damaging your multimeter or the circuit. Additionally, shorting the probes together during measurement could lead to safety hazards.
How can I use alligator clips with a multimeter?
Instead of manually holding the probes, you can use alligator clips to connect the multimeter leads to the component being tested. This method allows for more stability and hands-free operation while taking measurements.
Can a multimeter measure the resistance of resistors in a circuit?
Yes, you can use a multimeter to measure the resistance of resistors. However, ensure the circuit is powered off before measuring to avoid incorrect readings and potential damage to the multimeter.
Why is it necessary to measure resistance in a disconnected component?
When measuring the resistance of a component, it should be disconnected from the circuit to prevent interference from other parts of the circuit, which may cause inaccurate or unreliable readings.
What does it mean when the multimeter shows “OL” while measuring resistance?
If your multimeter shows "OL" (overload) when measuring resistance, it means the resistance is too high for the selected range. You may need to adjust the range to a higher setting to get an accurate reading.
How do I know if my multimeter is working properly?
To ensure your multimeter is functioning correctly, test it on a known working component, such as a resistor with a known resistance value. If the reading matches the expected value, the multimeter is functioning properly.
What safety precautions should I follow when using a multimeter?
Always ensure the circuit is powered off before measuring resistance. Avoid shorting the probes together, and always handle the multimeter and probes with care to avoid electrical shocks or damaging the multimeter.
Can I use a multimeter to check the battery voltage?
Yes! A multimeter can also be used to measure the voltage of a battery by setting the dial to measure DC voltage (V). Place the red probe on the battery’s positive terminal and the black probe on the negative terminal.
Quiz
Question #1: True or False - “Ω” is the universal symbol for resistance on a multimeter.
True
False
Click for the answer...
Question #2: True or False - Your multimeter measures resistance by running a small test voltage through the component:
True
False
Click for the answer...
Question #3: Before measuring resistance, you must:
Disconnect the component from the circuit
Set your multimeter dial to “Ω”
Connect your leads to the “Ω” and COM ports
All of the above
Click for the answer...
Question #4: Where should you place your leads on the component:
One lead on the positive side and one lead on the negative
Both leads on the negative side
Only use one lead on the component
All of the above
Click for the answer...
Question #5: True or False - It is okay to hold a component while measuring resistance.
True
False
Click for the answer...