Trystan Casey
Multimeters are electrical tools used to measure electricity and test electrical components. They are used to check electricity-related properties such as voltage, current, resistance, and continuity. Multimeters come in digital and analog versions, with digital multimeters displaying a number and analog multimeters featuring a meter and an indicator. When testing with a multimeter, it is important to take safety precautions such as avoiding touching the metal tips with your fingers and always disconnecting the device from its power source. To test electrical equipment with a multimeter, you would typically measure voltage, resistance, and continuity by placing the probes on either side of the component and adjusting the settings on the multimeter accordingly.
| Characteristics | Values |
|---|---|
| Purpose | To test the condition of electrical equipment |
| Types | Analog and digital |
| Functions | Testing continuity, resistance, and voltage |
| Continuity Test | Determines whether two items are electrically connected; a reading of 0 means they are connected, while 1 or OL means they are not |
| Resistance Test | Determines how much current is lost during its journey through an electrical component |
| Voltage Test | Determines the amount of pressure pushing electricity through the circuit; a higher voltage means more electricity is flowing |
| Safety Precautions | Do not touch the metal tips with your fingers; always disconnect the device from its power source before testing; start with a high range and dial it down |
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What You'll Learn
Continuity testing
A continuity test is performed to determine whether two items are electrically connected, allowing an electric current to flow from one to the other. This is one of the most useful tests for electronics repair.
To perform a continuity test, first ensure no current is running through the circuit or component you want to test. Turn it off, unplug it from the wall, and remove any batteries. Place one probe at each end of the circuit or component you want to test. It doesn't matter which probe you place where, as continuity is non-directional. If your circuit is continuous, the screen will display a value of zero (or near zero), and the multimeter will beep. If the screen displays 1 or OL (open loop), there is no continuity, meaning there is no path for the electric current to flow from one probe to the other.
If your multimeter does not have a dedicated continuity mode, you can still perform a continuity test. Plug the black probe into the COM port on your multimeter and the red probe into the port labelled with a V symbol (in this case, the right port). Switch on your multimeter and set the dial to continuity mode (indicated by an icon that looks like a sound wave). The multimeter tests continuity by sending a small current through one probe and checking whether the other probe receives it. If the probes are connected, either by a continuous circuit or by touching each other directly, the test current will flow through.
When testing, always start with a high range and dial it down. A range that is too low can cause problems. Always set your multimeter to the correct unit to avoid danger and blown fuses.
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Voltage testing
Firstly, turn off the appliance and disconnect it from the power source. Then, plug the black probe into the COM port on your multimeter and the red probe into the port with the V symbol. Switch on the multimeter and set the dial to the correct voltage mode (AC or DC). If your appliance runs on electricity supplied by your house, you will need to set the dial to AC voltage mode. However, if your appliance runs on electricity supplied by batteries, you will need to set the dial to DC voltage mode.
Once you have set up your multimeter, insert a probe into each slot and read the line voltage measurement. A properly working outlet should give a reading of 110 to 120 volts. If there is no reading, check the wiring and the outlet. If you are testing an appliance, turn it back on and get the multimeter reading. Consult your appliance manual to see if the amps detected match the operating load of your unit.
If you are testing an outlet, you can determine whether the white and black wires are reversed or whether the outlet is grounded correctly. To do this, insert one probe of the multimeter into the small outlet slot and the other probe into the receptacle's centre screw. If the light fails to turn on, the outlet is not grounded correctly. You should then conduct a polarity test to determine whether the wires are correctly connected. To do this, insert one probe into the large slot and the other against the screw. If the voltage detector lights up, the wires are reversed.
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Resistance testing
Step 1: Prepare the Multimeter
Ensure your multimeter is set to the resistance setting, denoted by the Ω (Ohm) symbol. This setting may share a spot on the dial with other modes, so carefully select Ω. If using an analog multimeter, zero the device before testing for accurate results.
Step 2: Choose the Right Probes
Properly rated probes are essential for safety. Ensure the probes meet or exceed the maximum voltage of the component you're testing to prevent electrical shocks or equipment damage. Inspect your probes for any damage, such as frayed wires or cracked casing, and replace them if necessary.
Step 3: Disconnect Power and Isolate the Component
Turn off the power to the circuit you're testing. If the component is part of a circuit, either remove it or isolate it with an open switch. This step is crucial to ensuring accurate readings and preventing potential electrical hazards.
Step 4: Insert Test Leads
Insert the test leads into the correct jacks. Typically, you'll insert the black test lead into the COM jack and the red lead into the Ω or VΩ jack. Ensure good contact between the leads and the circuit.
Step 5: Connect the Probes
Touch the probe tips to the component or section of the circuit you want to measure. If testing a resistor, connect one probe to each end. If testing a break in the circuit, connect the probes across the break.
Step 6: Observe the Reading
The multimeter will display the resistance reading in ohms (Ω). A reading of "0" may indicate a short circuit, while "OL" or "∞" suggests an open circuit. Compare the reading to the manufacturer's specifications to determine if resistance is an issue.
Additional Tips:
- For very low-resistance measurements, use the relative mode (REL).
- Avoid touching metal parts of the test leads to prevent errors.
- Press the "HOLD" button to capture a stable measurement for later reference.
- The human body can affect resistance readings, so avoid body contact with metal ends of the test leads.
- For sensitive electronics, consider using resistance decade boxes for precise resistance values.
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Amperage testing
Preparation:
Before you begin amperage testing, it's essential to take safety precautions. Ensure you're wearing insulated gloves and safety goggles, especially when dealing with high voltages or currents. Make sure the area you're working in is dry, as moisture can increase the risk of electric shock. Check your multimeter for any signs of damage, such as cracks, frayed wires, or exposed wires. It's crucial to use a properly calibrated and functioning multimeter to avoid inaccurate results.
Circuit Preparation:
Locate the circuit you intend to test and turn off the power supply to that circuit. This step is crucial for safety and reducing the risk of electric shock. Once the power is off, proceed to break the circuit by detaching the positive wire (usually red) from the power source. You may need to cut the wire or unscrew a cap to access the wire.
Multimeter Configuration:
Configure your multimeter by inserting the black probe into the "COM" socket and the red probe into the "A" socket. The "COM" socket is for common or negative connections, while the "A" socket is specifically for amperage measurements. Select the appropriate amperage range on the multimeter, choosing between AC (alternating current) or DC (direct current) depending on the electrical system you're testing. Ensure the range matches the amperage you're testing.
Testing:
Connect the red probe of the multimeter to the negative terminal of the power supply. Then, attach the black probe to the negative wire of the circuit. Turn on the circuit, restoring power to it. Leave the probes in place for about a minute. During this time, the multimeter will measure the amperage of the circuit.
Reading the Amperage:
After approximately one minute, you can read the amperage value from the multimeter's digital display. This number represents the amount of electric current flowing through the circuit. Ensure you turn off the circuit and remove the probes before touching any metal components to avoid electric shock.
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Safety precautions
Safety should be the top priority when testing electrical equipment with a multimeter. Here are some crucial safety precautions to follow:
- Disconnect the Power Source: Before testing any electrical equipment, it is imperative to disconnect the appliance from its power source. If the device is plugged into a wall outlet, simply unplug it. For hardwired appliances, turn off the circuit breaker. This step is crucial for your safety and prevents any accidental activation of the equipment during testing.
- Choose the Right Multimeter: Select an appropriate multimeter for the job. There are two main types: analog and digital. Digital multimeters display numerical readings, while analog multimeters have a meter and a pointer. Choose a multimeter that suits your comfort level and the complexity of the task.
- Set the Correct Range and Unit: Always set the multimeter to the correct unit and range before testing. If you are measuring voltage, select AC or DC accordingly. Ensure the voltage range is higher than the expected value of the component you plan to test. This helps ensure accurate readings and prevents equipment damage.
- Handle the Probes Carefully: Multimeters come with two probes: a black probe (negative/common) and a red probe (positive/hot wire). Avoid touching the metal tips of the probes during testing to prevent electrical shocks. Hold the probes in the same hand when testing live circuits to avoid passing a shock through your body.
- Be Mindful of Static Electricity: Static electricity can interfere with your measurements and potentially damage sensitive electronics. When working in a controlled environment, consider using electrostatic-dissipative workbenches to ground and neutralize static electricity, protecting both your equipment and your measurements.
- Turn Off After Use: When you have finished testing, remember to turn off the multimeter if it has an on/off switch. Some models have an auto-off feature to preserve battery life.
By following these safety precautions, you can confidently use a multimeter to test electrical equipment while minimizing risks to yourself and your equipment.
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