multimeter_jedit

This material was developed with funding from the National Science Foundation under Grant # DUE 1601612

Multimeter

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A digital multimeter is a tool used to measure electrical values such as voltage (volts), current (amps) and resistance (ohms). Technicians use the tool for testing, diagnosing, and troubleshooting electrical circuits, components, and devices. The digital multimeter incorporates three types of meters into one device.

Click on each highlighted area.

1.10

The ammeter measures electrical amperage.

1.30

The ohmmeter measures the voltage produced by passing a small current through the component.

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Three Meters in One

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1.00

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120.00

Flexible, insulated wires called probes plug in to the ports. The black probe always plugs into the COM port which is the reference or ground port. The red probe plugs in to the V/Ω port to measure all voltage and resistance readings.

Plug the red probe into the 10A port to measure current that is more than 200mA (milliamps). Use the mA port to determine small amperage measurements. This port measures up to but not over 200 milliamps DC. Do not measure readings over 200 milliamps with this port. If you are unsure, use the 10A port first then switch to the mA port to get a more accurate measurement.

Face

View the measurement readouts on the digital display. The display is either a 3-, 4- or 5-digit display. More digits in the display means more accurate measurement readings.

Use the dial to select primary measurement values (volts, amps, or ohms).

Correct!

You will measure three devices—a 9-volt battery, a AAA battery and a DC power supply. When selecting a setting with the dial, you should always start with the highest voltage setting (especially if you are not sure of the voltage range of the item you are measuring). << First click on the area of the multimeter that you will be working with.

Measuring DC Voltage

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Drag each probe and plug it in to the appropriate port of the multimeter

Try Again!

If you set the dial to a value that is lower than the voltage of the item you are testing, the display flashes 1. This signifies that it is overloaded. Some digital multimeters display OL. Since the battery measures 9 volts, it is too much for the multimeter to handle at the setting 2. A digital multimeter can check to see if your battery is still good.

Measuring DC Voltage - 9V Battery

<< Click 600 to turn the selection knob. Click on each voltage setting and note the value displayed.

600

009.0 V

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09.00 V

200

Let’s start off by measuring the voltage on the 9-volt battery.

Drag and drop the 9V battery on to the probes.

Click Next to Continue

1.500 V

Drag and drop the AAA battery on to the probes.

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01.50 V

001.5 V

Measuring DC Voltage - AAA Battery

001.5 V

Now measure the voltage on the AAA battery.

Finally, measure the voltage on the DC power supply.

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150.0 V

If you set the dial to a value that is lower than the voltage of the item you are testing, the display flashes 1. This signifies that it is overloaded. Some digital multimeters display OL. Since the power supply measures 150 volts, it is too much for the multimeter to handle at the setting 20 or 2.

Measuring DC Voltage - DC Power Supply

Drag and drop the DC Power supply on to the probes.

150.0 V

<< Click on the area of the multimeter that you will be working with.

You can use a digital multimeter to measure the AC voltage in an outlet.

Testing an Electrical Outlet

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120.0 V

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120.0 V

Drag and drop the electrical outlet on to the probes.

Testing Resistance

Tolerance values

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A resistor allows precisely controlled amounts of resistance into electrical circuits. A resistor works by converting electrical energy into heat. That heat then dissipates. You can figure out the resistance of a resistor by looking at the pattern of colored bands. The first two bands represent the first two digits of the resistance (brown and black are 10). The third band is a decimal multiplier ( a power of 10). Red is 2 (102), so you multiply the 10 x 100 and the result is 1000 ohms (or 1 k Ω). The final band is the tolerance. A silver band is 10%. Therefore, if a 1,000-ohm resistor measures no less than 900 ohms and no more than 1000 ohms, it is considered accurate.

For each resistor, enter the correct value.

Resistor Color Codes

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Resistance values

An ohmmeter typically performs two functions:Measures the resistance of a component (resistance is a property that changes within components based on environmental conditions)Tests the continuity of a circuit or component (you can determine if a fuse is blown or if a switch contact can be closed).

Testing Resistors

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20k

.001 MΩ

1.00 KΩ

200k

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001 KΩ

<< Click 2M to turn the selection knob. Click on each voltage setting and note the value displayed.

The scale is not high enough to measure this level of resistance.

Drag and drop the resistor on to the probes.

01.0 KΩ

.OL

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.050 MΩ

50.0 KΩ

120 KΩ

.120 MΩ

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Drag and drop the resistor on to the probes.

.000 MΩ

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Use the ohmmeter to check the continuity of a switch, and two types of fuses. If you are checking continuity, make sure the device is not attached to a power source (unplug the device or remove the batteries). A beep indicates little resistance between the two points. If you do not hear a beep, that means that there is a short in the wire or that the fuse is blown.

Testing Continuity

Drag and drop each switch on to the probes.

Drag and drop each fuse on to the probes.

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Measuring DC Milliamps

Plug the red probe into the mA port to measure a low voltage DC circuit. Plug the black probe into the COM port.

The milliamp scale (blue port and setting) is typically used when measuring electronic circuits like those used in computers and common electronic devices. << First click on the area of the multimeter that you will be working with.

<< Click on the 200m to turn the selection knob. Click on each setting and note the value displayed.

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200m

20m 10A

25.0mA

You MUST make sure to turn off the power before inserting the ammeter and ensure that the proper scale is chosen before turning the circuit on. If you are unsure of which setting to choose, start with the highest setting and work your way down. It is unusual for a PC technician to measure circuit amperage. The most common use is in determining current consumption for selecting UPS or battery backup systems.

Measuring amperage requires you to open the circuit and insert the ammeter as part of the circuit (). This enables electrical current to flow through the ammeter.

Drag and drop the circuit on to the probes.

20m 10A

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Devices such as motors or lights are high voltage DC circuits. This type of measurement is usually only done by electricians. The electrician will open the circuit and insert the ammeter as part of the circuit.

Plug the red probe into the 10A port to measure a high voltage DC circuit. Plug the black probe into the COM port.

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Measuring DC Amps-Motors

5.0A

Turn the dial to the corresponding 10A setting (also in red). When you test this type of circuit, the probes are only safe up to a specific amperage level. Measuring circuits with higher amperage can result in electrocution.

20m 10A

Quiz 1 of 3 Measure the resistance of the switch to see if it is open or closed.

Drag and drop the switch on to the probes.

Choose the correct answer below.

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Take A Quiz

Closed

Open

Bad

Quiz 2 of 3 Measure the resistance of the fuse to see if it is good or bad.

Good

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Drag and drop the fuse on to the probes.

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Quiz 3 of 3 Measure the resistance of the fuse to see if it is good or bad.