How to Read Multimeter

To the uninitiated, the symbols on a multimeter are like a foreign language. But even those with experience in electricity sometimes need help with strange multimeters that have an unorthodox system of abbreviations. Luckily, it doesn’t take too long to understand the names of the settings and understand how to read the scale, so you can get used to it and get to work.

Table of Contents

Read knob settings

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Check for alternating current (AC) or direct current (DC). In general, V is a voltage symbol, when accompanied by a tilde-like curve, it represents alternating current (in household circuits), while when combined with a straight line or dash, it represents for direct current (in most batteries). The straight or curved stroke can be next to or above the V . ^{[1] X Trusted Source Science Buddies Go to Source}

The current in most home circuits is AC. However, some devices can convert power to DC through a transistor, so check the voltage symbol before checking something.
The setting for voltage testing in AC circuits is usually denoted V~ , ACV or VAC .
To check the voltage in a DC circuit, set the multimeter to the V– , V— , DCV or VDC setting.

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Set the multimeter to amperage mode. The unit of amperage is the ampere, abbreviated A. Depending on the circuit you need to test, choose direct or alternating current. Analog multimeters usually do not have amperage testing.

A~ , ACA and AAC are the symbols for alternating current.
A– , A— , DCA and ADC represent direct current.

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Define resistance measurement settings. Resistance measurement mode is usually denoted by the Greek letter omega: Ω . This is a unit of measurement for resistance, also known as an ohm. On older multimeters, this setting is sometimes denoted by the letter R .

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Use DC+ and DC-. If the multimeter has this setting, set it to DC+ when testing DC. If the display does not show readings and you suspect you have connected the wrong electrode to the probe, switch to DC- mode to make adjustments without rewiring. ^{[2] X Research Source}

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Learn more symbols. If you’re not sure why there are so many settings for voltage, amperage, or resistance, read the troubleshooting section to learn range information. In addition to these basic settings, most multimeters have a few extra features. If more than one of the symbols below is marked on the same setting, it is possible that the multimeter performs two functions simultaneously, or you should consult the instruction manual.

) ) ) or a series of parallel arcs representing the “continuity check” setting. When in this mode, the multimeter will “beep” if the two probes are electrically connected. ^{[3] X Trusted Source Science Buddies Go to Source}
The arrow pointing to the right with a cross through it is the “measure diode” symbol, which is a setting used to check if a DC circuit is connected. ^{[4] X Trusted Source Science Buddies Go to Source}
Hz stands for Hertz, the unit of measurement for the frequency of AC circuits. ^{[5] X Research Sources}
The symbol –|(– represents the capacitance setting.

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Read symbols on ports. Most multimeters have three ports or holes. Sometimes ports will be marked with a symbol as described above. If these symbols are not clear, see the following instructions:

Always plug the black wire into the COM port (also known as the ground port), with the probe connected to the negative terminal.
When measuring voltage or resistance, the red probe should be plugged into the port with the minimum current symbol (usually mA or milliamperes). ^{[6] X Trusted Source Science Buddies Go to Source}
When measuring current, you need to plug the red probe lead into the port with the unit’s designation for the expected current. Typically, low voltage ports have fuses rated up to 200mA , while high voltage ports go up to 10A . ^{[7] X Research Sources}

Read the result of an analog multimeter

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Determine the correct scale on an analog multimeter. Analog multimeters have a hand behind the glass, which moves to point to the result. Usually there will be three arcs printed on the background behind the needle. Here are three separate scales used for different purposes: ^{[8] X Research Sources}

The Ω scale is used to measure resistance and is usually the largest arc at the top. On this scale, the value 0 is to the right instead of the left like other scales.
The “DC” scale represents the DC voltage reading.
The “AC” scale represents the AC voltage reading.
The “dB” scale is the least used. You can see a short description of the “dB” scale at the end of this section.

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Record voltage scale readings based on range. Look closely at the DC or AC voltage scale. There will be several rows of numbers below the scale. Check the range you selected on the knob (e.g. 10V) and look for the corresponding symbol next to one of these rows. This is the row of numbers from which you will read the result.

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Estimate the value between the numbers. The voltage scale on an analog multimeter works similarly to a regular gauge. The resistance scale is built on the basis of the logarithmic system, which means that the same distance will show different changes in value depending on the position the needle is pointing at. Lines between two numbers represent an even division. For example, if there are three lines between “50” and “70”, these are levels 55, 60, and 65, regardless of whether the distance between them is even.

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Multiply the resistance on an analog multimeter. Look at the range setting you selected on the multimeter’s dial. This will be the factor that you need to multiply by the reading. For example, if the multimeter is in R x 100 mode and the needle shows 50 ohms, the actual resistance of the circuit is: 100 x 50 = 5000 ohms.

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Learn more about the dB scale. “dB” or decibel is usually the smallest scale at the bottom of an analog multimeter face. This scale is based on the logarithmic system and is used to measure the ratio of voltage (also known as voltage rise or fall). ^{[9] X Research Source} In the standard dBv scale in the US, 0 dBv is equivalent to 0.775 V measured at a resistance of 600 Ω, in addition to other scales such as dBu, dBm and even dBV (letter letters). V is capitalized). To use the “dB” scale, you need more in-depth insights. ^{[10] X Research Source}

Troubleshoot

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Set range. Unless you have a multimeter that sets the auto range, every basic mode (voltage, resistance, and amperage) comes with additional settings. This is the range that you need to select before connecting the probe to the circuit. Proceed by predicting a value slightly higher than the closest result. For instance, if you expect a reading to be around 12V, scale up to 25V, not 10V (assuming those are the two closest options). ^{[11] X Research Source}

If you are unsure of the measured result, choose the highest range on the first attempt to avoid damage to the meter.
The other modes rarely damage the meter, but you should default to the lowest resistance and 10 V range ^{. [12] X Research Source}

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Adjust when the metric is “out of scale”. On a digital watch face, an “OL”, “OVER” or “overload” message indicates that you need to select a higher range, while a result close to zero means the lower range is correct. On an analog watch face, if the hand remains stationary while measuring, you should lower the range. In case the needle suddenly spikes to the highest level, you need to immediately move to the higher range.

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Disconnect the power supply before performing a resistance measurement. Turn off the switch or remove the power supply battery in the circuit for accurate resistance readings. ^{[13] X Reliable Source Science Buddies Go to Source} When measuring resistance, a multimeter will transmit a current, so if other currents are flowing in the circuit, the results will be inaccurate.

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Measure the amperage in a series circuit. To measure amperage, a multimeter must be connected “in series” in the circuit with other components. For example, you can unplug the battery terminal to connect one probe, the other probe to the battery to close the circuit.

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Measure voltage in parallel circuit. Voltage is the change in electrical energy across some point in a circuit. The multimeter needs to be connected “in parallel” by connecting the two probes to two different openings on a closed circuit where current is flowing. This measurement should be carried out with caution to avoid bias.

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Calibrate the ohm scale on the needle gauge. Analog multimeters often have an additional dial with the symbol Ω used to calibrate the resistance scale. Before taking a resistance measurement, touch the two probes together. Then calibrate by turning the knob on the multimeter until the ohm scale points to 0. At this point you can start taking measurements. ^{[14] X Research Source}

Advice

If the needle on the analog dial points below zero even though the multimeter is at its lowest range, the “+” and “-” terminals may be stuck backwards. Invert the two probes and measure again.
If the analog dial is reflective, tilt the watch left or right so that the shadow is covered by the hand itself so you can get a more accurate reading.
If you have trouble reading the readings on a digital multimeter, consult the manual. By default, the device displays the results as a number, but sometimes there are settings to display a bar graph or other form of information.
When measuring AC voltage, the initial measurement will fluctuate and gradually stabilize at the correct reading. ^{[15] X Research Source}
If the multimeter doesn’t work, you should check the device itself to determine the problem.
If you have trouble remembering the difference between voltage and amperage, imagine a water pipe. Voltage is the pressure of water flowing through the pipe, and amperage is the size of the pipe. The size of the water pipe will determine the amount of water that can flow through the pipe at the same time.

Warning

If the range you select is lower than the expected output of the circuit or battery, the multimeter may be damaged. Analog multimeters are generally more susceptible to damage than digital ones, but auto-range multimeters are the most durable.

Steps

Read knob settings

Read the result of an analog multimeter

Troubleshoot

Advice

Warning

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