Testers | Digital Multimeters (DMMs) How to Use

This page provides an easy-to-understand explanation of how to use electrical testers and digital multimeters (DMMs). Please use it to gain an understanding of how to use these instruments, and refer to it when choosing the model that’s right for your application. Hioki digital multimeters are safe, high-quality products.

*Details are displayed when you click on the heading.


01. How to use digital multimeters (DMMs) properly and how to choose a safe multimeter

Overvoltage accidents caused by impulse voltage

The figure illustrates the waveform characterizing the type of overvoltage that occurs when a solenoid valve operates. In this example, you can see that an impulse voltage of close to 1000 V was generated on the 100 V AC line. Impulse voltages such as this one can occur in manufacturing plants with numerous inductive loads or in the event of a lightning strike near a location where a multimeter is in use.

 

Measurement categories

IEC 61010-1, an international standard on multimeter safety, sets forth the measurement categories shown in the figure. Below is a list of multimeters and other measuring instruments that deliver adequate capacity for each category. (For Hioki products, this type of information is available in product catalogs and the Hioki website.)

Card HiTester 3244-60: CAT III (300 V), CAT II (600 V)
Digital Multimeter DT4256: CAT IV (600 V), CAT III (1000 V)

For an instrument to be used in a given measurement category, it must have adequate capacity to withstand the impulse voltage (see table) that can be expected based on the location of use (CAT IV, CAT II, or CAT II) and its voltage relative to ground (circuit voltage).

For example, CAT II (300 V) multimeters are required to be able to withstand an impulse voltage of 2500 V based on a voltage to ground of 300 V. In locations (i.e., categories) such as industrial manufacturing lines where a large impulse voltage described above is possible, it’s good practice to choose a multimeters with as high a measurement category as possible. A detailed description of each category follows.

CAT II: From the power plug of a device connected to an electrical outlet to the device’s power supply circuit

CAT III: Circuits between a distribution panel and the power supply wiring and power supply circuit of a device connected directly to a power source (for example, fixed equipment) and circuits between the distribution panel and electrical outlets

CAT IV: Buildings’ lead-in circuits and circuits between the service entrance and a power meter or distribution panel


 

Voltage input to the digital multimeter’s current measurement circuit

When using a digital multimeter to measure current, the multimeter should be connected in series with the circuit being measured. To minimize instrument loss (resistance) caused by connecting the digital multimeter, the multimeter’s current measurement circuit is designed to have low impedance.

If the digital multimeter is mistakenly connected in parallel to the circuit’s power supply, the supply voltage will be applied across the multimeter’s terminals, causing an overcurrent to flow and the instrument to burn out.

To prevent such damage, most multimeters incorporate a protective fuse. Additionally, some products intentionally omit a current terminal (“A” terminal) or incorporate a mechanism linked to the rotary switch so as to prevent a test lead from being inadvertently connected to the wrong terminal.


 

Voltage input to the digital multimeter’s resistance measurement circuit

Because the digital multimeter’s resistance measurement circuit has low input impedance, application of a voltage across the test leads could burn out the instrument by causing an overcurrent to flow inside it, and the resulting short-circuit could in turn cause the distribution panel to burn out.

Hioki digital multimeters have an internal overcurrent protection circuit that minimizes any overcurrent caused by voltage input, and they are designed to withstand an overvoltage for up to 1 minute.



 

Accidents caused by shorting the test leads

Use of test leads with long metal tips can cause a short-circuit accident when measuring voltage.
All Hioki digital multimeters use capped test leads that have a shorter exposed metal area at the tip.

 

02. Using and function of digital multimeters

Digital multimeter (DMM) part names

The rotary switch is used to switch among measurement parameters (AC voltage, DC voltage, continuity check, resistance, capacitance, current, etc.) depending on the application in which the digital multimeter is being used.

The terminals into which the test leads (measurement cables) are inserted vary depending on the parameter being measured. For all parameters other than current, the red test lead is connected to the “VΩ” terminal, and the black test lead is connected to the “COM” terminal.

The operation keys are used to measure DC and AC voltage and current, to access other measurement parameters such as temperature and diode check functionality, and to utilize other functionality such as holding measured values. 

*This description uses the DT4282 for explanatory purposes. Please check the product specifications for other models as specifications and settings vary.

 

Using digital multimeters (DMMs): Measuring AC voltage

To measure an AC voltage, for example an outlet or circuit breaker’s line voltage or a piece of equipment’s supply voltage, set up the digital multimeter as follows:

1. Rotary switch position: ~V (“1” in figure)
2. Test lead connections to digital multimeter: Black (negative) to COM and red (positive) to VΩ (“2” in figure)
3. Test lead connections to outlet: “3” in figure
(When performing AC RMS measurement, there is no need to concern yourself with polarity.)

Caution: Do not connect either test lead to the “A” terminal. Some models have a shutter function designed to prevent the inadvertent connection of a test lead to the “A” terminal, while other models lack an “A” terminal entirely. Hioki digital multimeters also have an internal fuse designed to protect against the possibility of a test lead being inadvertently connected to the “A” terminal. For more information, please check the product specifications for each product. Verify that the voltage of the circuit being measured falls within the digital multimeter’s input specifications.

*This description uses the DT4282 for explanatory purposes. Please check the product specifications for other models as specifications and settings vary.

 

Using digital multimeters (DMMs): Measuring DC voltage

To measure a DC voltage, for example the output voltage of a solar panel, an instrumentation board’s 24 V DC signal, or a battery’s voltage, set up the digital multimeter as follows:

1. Rotary switch position: :::V (“1” in figure)
2. Test lead connections to digital multimeter: Black (negative) to COM and red (positive) to VΩ (“2” in figure)
3. Test lead connections to DC voltage source: Black to negative side and red to positive side (“3” in figure)

Caution: Do not connect either test lead to the “A” terminal. Some models have a shutter function designed to prevent the inadvertent connection of a test lead to the “A” terminal, while other models lack an “A” terminal entirely. Hioki digital multimeters also have an internal fuse designed to protect against the possibility of a test lead being inadvertently connected to the “A” terminal. For more information, please check the product specifications for each product. Verify that the voltage of the circuit being measured falls within the digital multimeter’s input specifications.

*This description uses the DT4282 for explanatory purposes. Please check the product specifications for other models as specifications and settings vary.

 

Using digital multimeters (DMMs): Checking continuity

To investigate a wire break or check a wire harness cable, set up the digital multimeter as follows:

1. Rotary switch position: (“1” in figure)
2. Test lead connections to digital multimeter: Black (negative) to COM to red (positive) to VΩ (“2” in figure)
3. Test lead connections to object under measurement: “3” in figure (no polarity)

If continuity is detected, the digital multimeter will indicate that fact on its display and beep. If continuity is not detected, for example due to a wiring break, no value will be indicated, and no beep will sound.

Caution: Shut off the supply of power to the circuit being measured before measurement.

*This description uses the DT4282 for explanatory purposes. Please check the product specifications for other models as specifications and settings vary.

 

Using digital multimeters (DMMs): Checking a diode

To diagnose a diode failure, set up the digital multimeter as follows:

1. Rotary switch position: “1” in figure
2. Control key operation: “2” in figure
3. Test lead connections to digital multimeter: Black (negative) to COM and red (positive) to VΩ (“3” in figure)
4. Test lead connections to diode under measurement: Black to cathode side (side with the bar mark) and red to anode side (side without the bar mark) (“4” in figure)

The digital multimeter will show the diode’s forward voltage if connected in the forward direction and “OVER” if connected in the reverse direction.

Caution: Shut off the supply of power to the circuit being measured before measurement.

*This description uses the DT4282 for explanatory purposes. Please check the product specifications for other models as specifications and settings vary.

 

Using digital multimeters (DMMs): Resistance measurement

To measure resistance, set up the digital multimeter as follows:

1. Rotary switch position: “1” in figure
2. Test lead connections to digital multimeter: Black (negative) to COM and red (positive) to VΩ (“2” in figure)
3. Test lead connections to resistor: “3” in figure (no polarity)

Caution: Shut off the supply of power to the circuit being measured before measurement.


 

Using digital multimeters (DMMs): Measuring temperature

To measure temperature, for example the discharge temperature of an air conditioner, set up the digital multimeter as follows:

1. Rotary switch position: “1” in figure
2. Control key operation: “2” in figure
3. Test lead connections to digital multimeter: Using DT4910 Thermocouples (K) (option) (“3” in figure)
*Other K thermocouple sensors may also be used.

*This description uses the DT4282 for explanatory purposes. Please check the product specifications for other models as specifications and settings vary.

 

Using the digital multimeter (DMM): Measuring capacitance

To measure a capacitor, set up the digital multimeter as follows:

1. Rotary switch position: “1” in figure
2. Test lead connections to digital multimeter: Black (negative) to COM and red (positive) to VΩ (“2” in figure)
3. Test lead connections to capacitor: For a polar capacitor, red lead to positive terminal and black lead to negative terminal (“3” in figure)

Capacitor capacitance display: F, μF, nF, pF

*This description uses the DT4282 for explanatory purposes. Please check the product specifications for other models as specifications and settings vary.


 

Using the digital multimeter (DMM): Measuring DC current

To measure current in a DC circuit, set up the digital multimeter as described below. The digital multimeter should be connected in series between the load side and the power supply side of the circuit by cutting the wire indicated with an “X” in the figure.

1. Rotary switch position: “1” in figure
2. Control key operation: “2” in figure
3. Test lead connections to digital multimeter: Black (negative) to COM and red (positive) to A (“3” in figure)
4. Test lead connections to circuit: Black to negative side of power supply and red to load side (so that the digital multimeter is in series with the power supply and load) (“4” in figure)

Caution: Shut off the supply of power to the circuit being measured before measurement and then turn it back on after connecting the digital multimeter. Exercise care not to apply a voltage (i.e., not to connect the digital multimeter in parallel with the power supply). Check the maximum current value that the digital multimeter can measure and only use it to measure circuits with currents that are less than or equal to that value.

*This description uses the DT4282 for explanatory purposes. Please check the product specifications for other models as specifications and settings vary.

 

Using digital multimeters (DMMs): Measuring DC current (4 to 20 mA)

To measure current in a DC circuit, set up the digital multimeter as described below. The digital multimeter should be connected in series between the load side and the power supply side of the circuit by cutting the wire indicated with an “X” in the figure.

1. Rotary switch position: “1” in figure
2. Control key operation: “2” in figure
3. Test lead connections to digital multimeter: Black (negative) to COM and red (positive) to μA mA (“3” in figure)
4. Test lead connections to circuit: Black to sensor side and red to power supply side (distributor side) (“4” in figure)

Caution: Shut off the supply of power to the circuit being measured before measurement and then turn it back on after connecting the digital multimeter. Exercise care not to apply a voltage (i.e., not to connect the digital multimeter in parallel with the power supply). Check the maximum current value that the digital multimeter can measure and only use it to measure circuits with currents that are less than or equal to that value.

*This description uses the DT4282 for explanatory purposes. Please check the product specifications for other models as specifications and settings vary.

 

Using digital multimeters (DMMs): Measuring AC current with a clamp-style sensor

To measure current in an AC circuit using the digital multimeter with a clamp-style sensor, set up the digital multimeter as follows and clamp the sensor around the wire being measured:

1. Rotary switch position: “1” in figure
2. Control key operation: “2” in figure
3. Conversion adapter connections to clamp-style sensor: “3” in figure
Conversion adapter connections to digital multimeter: Black (negative) to COM and red (positive) to VΩ
4. Clamp-style sensor current range setting: “4” in figure
5. Digital multimeter range setting: “5” in figure (Set with the RANGE key to reflect the clamp-style sensor’s range.)
6. Clamp sensor connections: “6” in figure

Caution: If the clamp-style sensor’s range changes during measurement, the digital multimeter’s range must be changed to reflect the new value.

*This description uses the DT4282 for explanatory purposes. Please check the product specifications for other models as specifications and settings vary.

 

Using digital multimeters (DMMs): Convenient functions

Auto hold function: This function automatically stops updating the measured value after the leads have been placed in contact with the circuit under test so that you can write down the measured value. Then it automatically resumes updating the measured value after the test leads have been placed in contact with another measurement point, before once again stopping updating the measured value. (Press and hold the HOLD key for at least 1 sec.)

Recording function: This function records the maximum and minimum measured values. (Press the MAX/MIN key.)

Relative value function: This function measures the amount of variation from a reference value. (Press and hold the MAX/MIN key for at least 1 sec.)

 

Using digital multimeters (DMMs): Zero-adjustment

For voltage, current, or resistance measurement, set up the digital multimeter as follows:

1. Rotary switch position: Set to the function for which you wish to perform zero-adjustment (“1” in figure).
2. Test lead connections to digital multimeter: Black (negative) to COM and red (positive) to VΩ (for measurement other than current) or black (negative) to COM and red (positive) to A or μA/mA (for current measurement)  (“2” in figure)
3. Test lead status: Shorted (“3” in figure)
4. Zero-adjustment: Press and hold the MAX/MIN key for at least 1 sec. (“4” in figure).

For capacitance measurement, set up the digital multimeter as follows:
1. Rotary switch position: (“1” in figure)
2. Test lead connections to digital multimeter: Black (negative) to COM and red (positive) to VΩ (“2” in figure)
3. Test lead status: Open (“3” in figure)
4. Zero-adjustment: Press and hold the MAX/MIN key for at least 1 sec. (“4” in figure)