Clamp Meters | Clamp Multimeters How to Use

This page provides an easy-to-understand explanation of the differences between different types of clamp meters as well as general instructions and a description of how to select a model. It will give you an understanding of how to use these instruments in different applications such as load current (AC current and DC current) and leakage current measurement as well as of how to choose the model that’s right for your application.

*Details are displayed when you click on the heading.


00. How to use clamp meter. Function introduction video collection.

Using a Hioki Current Clamp Meter: True RMS & MEAN values

This video introduces some key considerations in choosing a clamp-on current meter that is suited to measuring distorted current waveforms. See our full lineup of current clamp meters.

 

Using a Hioki Current Clamp Meter: the Difference in half-wave rectification measurement

This video introduces some key considerations in choosing a clamp-on current meter that is suited to measuring special types of current waveforms, for example those that have undergone half-wave rectification. See our full lineup of current clamp meters.

 

Using a Hioki Current Clamp Meter: Verifying the Difference in Current Values based on Frequency

This video describes how current values vary with the clamp-on current meter’s frequency band. See our full lineup of current clamp meters.

 

Using a Hioki Current Clamp Meter: Measuring DC current

This video introduces some key considerations in choosing a clamp-on current meter that is suited to measuring DC currents in applications such as solar panel installations. See our full lineup of current clamp meters.

 

How to Use Hioki Current Clamp Meters: Leakage Current Testing and Using the Filter

This video introduces some key considerations in choosing a clamp-on current meter that is suited to measuring leakage current. See our full lineup of current clamp meters.


 

Using a Hioki Current Clamp Meter: Measuring the Starting Current.

This video introduces some key considerations in choosing a clamp-on current meter suited to measuring the starting current of a motor or engine. Se our full lineup of current clamp meters.

 

Using a HIOKI Current Clamp Meter as a Current Sensor

This video introduces a clamp-on current meter with output functionality that can also be used as a current sensor. See our full lineup of current clamp meters.


 

01. Types of clamp meters

Types of clamp meters

There are two types of clamp meter: instruments designed to measure load current and instruments designed to measure leakage current. The former can be further subdivided as follows:

•    Models designed to measure AC current with frequency band characteristics that are centered on commercial power supply frequencies
•    Models designed to measure DC current as well as AC current at frequencies at and below commercial power supply frequencies from devices such as general-purpose inverters

Clamp meters can also be classified on the basis of the rectification method they use (either mean-value rectification or RMS rectification).

 

Rectification methods of clamp meters

There are two methods for converting current into true RMS values: the true RMS method (true RMS value indication) and the mean method (mean rectification RMS value indication).

Although both methods yield the same value for undistorted sine waves, distortion of the waveform causes the values to diverge.

Most current measurement applications involve measurement of a current waveform that is not a perfect sine wave (i.e., they require measuring a current waveform that is distorted). If you wish to view results in the form of true RMS values, it is recommended to use a true RMS clamp meter.

 

02. How to use clamp meters

How to use load current clamp meters

When measuring load current in a 1-phase 2-wire circuit as shown in the figure, the clamp meter should be applied around one (not both) of the wires.

Because the current flowing to and from the load in the two wires forms a pair of magnetic fields that are opposite one another, the two magnetic fields cancel each other out, causing the clamp meter to indicate a current value of zero if two wires are measured at the same time.

When measuring a 3-phase circuit, it is necessary to measure the current value in each of the R, S, and T wires by applying the clamp meter to each in turn.



 

How to use leakage current clamp meters

When measuring leakage current in a 1-phase/2-wire circuit as shown in the figure, the clamp meter should be applied around both wires.

Because the current flowing to and from the load in the two wires forms a pair of magnetic fields that are opposite one another, there will be a difference in the two fields if there is any leakage current. The measured current value when the clamp meter is applied around both wires at the same time is the leakage current.

When measuring a 3-phase circuit, the clamp meter should be applied around the R, S, and T wires (all three wires) at once. Leakage current can also be measured by applying the clamp meter around a grounding wire.



 

04. Clamp meter functions and how to use them

Current measurement

•    Set the rotary switch as shown in “1”.
•    Enable zero-adjustment as shown in “2”.
•    Apply the clamp meter around the wire as shown in “3”.
•    Determine the function as appropriate from auto, AC current, DC current, AC+DC current, or frequency as shown in “4”.

*This example uses the Clamp Meter CM4370 series.

 

HOLD function

MANUAL HOLD:
•    The measured value on the display can be held by pressing the HOLD key.

AUTO HOLD:
•    Press and hold the HOLD key for 1 sec. to enable the auto hold function.
•    Once the measured value stabilizes, it will be automatically held as shown in the figure.
•    The measured value will continue to be held once the clamp is removed from the wire.
•    Once you apply the clamp meter around another wire and the measured value stabilizes, it will be automatically held again.
•    This function is convenient when you need to make and record results for a series of measurements.

*This example uses the Clamp Meter CM4370 series.

 

Filter function

•    The filter can be applied based on a 100 Hz cutoff frequency.
•    This function is convenient when you wish to measure the current value near the power supply frequency without being affected by noise or other interference.

*This example uses the Clamp Meter CM4370 series.



 

MAX/MIN/AVG/PEAK

•    The MAX/MIN/AVG function records the maximum, minimum, and average values for the measured value (RMS) interval being displayed.
•    The peak max and peak min functions display the maximum and minimum values of current waveform peaks after 10 kHz sampling.

*This example uses the Clamp Meter CM4370 series.

 

DC current and DC voltage PEAK measurement

•    Apply the clamp around the wire coming from the vehicle battery’s positive terminal as shown in “1” in the figure and set the rotary switch as shown in the figure.
•    Operate the control key as shown in “2” in the figure.
•    Start the vehicle’s engine.
•    By performing the steps shown in “4” in the figure, you can read the maximum and minimum values for the instantaneous DC current when the engine is started as well as the DC voltage maximum and minimum values.

*This example uses the Clamp Meter CM4370 series. 


 

Inrush current measurement (INRUSH)

•    Disconnect the power supply of the motor or other load.
•    Determine the appropriate position for the rotary switch as shown in “2” in the figure.
•    Perform zero-adjustment as shown in “3” in the figure.
•    Apply the clamp around one of the load circuit’s wires as shown in “4” in the figure.
•    Enable the INRUSH function as shown in “5” in the figure.
•    Start the motor or other load.
•    As shown in “7” in the figure, you can read the peak (maximum peak value) and RMS value for the interval during which the inrush current (starting current) occurs.

*This example uses the Clamp Meter CM4370 series. 


 

Other measurement functions: Voltage measurement

•    Connect the measurement leads to the clamp meter.
•    Set the rotary switch to voltage measurement as shown in “1” in the figure.
•    Place the measurement leads in contact with the point you wish to measure as shown in “2” in the figure.
•    Select the desired function (auto, AC voltage, DC voltage, AC+DC voltage, or frequency) as shown in “3” in the figure.

*This example uses the Clamp Meter CM4370 series. 


 

Other measurement functions: Continuity check, Resistance, Diode

•    Set the rotary switch to the position shown in the figure.
•    Using the SHIFT key, you can check continuity or perform resistance or diode measurement.

*This example uses the Clamp Meter CM4370 series.

 

Other measurement functions: Capacitance, Temperature

•    After setting the rotary switch to TEMP, you can use the SHIFT key to perform capacitance or temperature measurement.

*This example uses the Clamp Meter CM4370 series. 


 

Other measurement functions: Electric charge detection, Simultaneous display of DC current and voltage, DC power

After determining the rotary switch position as shown in the figure, you can use the SHIFT key to detect a voltage, simultaneously display DC current and voltage, or measure the DC power being produced by a solar power system.
 
*This example uses the Clamp Meter CM4370 series. 

 

05. Clamp meter measurement principles

Clamp meter measurement principles: CT method

Clamp meters measure current by using a sensor to detect the magnetic field produced by a flowing current and then converting the result to obtain the current. The measurement method and principle used by CT-type clamp meters are described below.

Design:
Coil wound around a magnetic core

Principle:
In this application of the principle of a transformer, the primary side consists of one winding (the wire around which the clamp has been applied), and the second side consists of N windings (the wire wound around the magnetic core). This arrangement is used to measure current. Due to the principle that is applied, caution is necessary if a current flows to the primary side while the secondary side is in the open state as a high voltage may occur at the open terminal due to the tendency of a current to develop on the secondary side of the device under such conditions.

Advantages:
Linearity and broad measurement range

Disadvantages:
Inability to detect DC currents

 

Clamp meter measurement principles: Hall element method

Clamp meters measure current by using a sensor to detect the magnetic field produced by a flowing current and then converting the result to obtain the current. The measurement principle used in the Hall element method is described below.

Design:
Hall element embedded in a magnetic core

Principle:
The magnetic field produced by the wire around which the clamp has been applied is converted to a voltage by the Hall element, and the voltage is converted to a current.

Advantages:
Ability to measure both DC currents and AC currents

Disadvantages:
Significant impact of sensor enclosure, magnetic circuit, and magnetic core design on instrument performance

 

Clamp meter measurement principles: Rogowski method

Clamp meters measure current by using a sensor to detect the magnetic field produced by a flowing current and then converting the result to obtain the current. The measurement principle used in Rogowski-type clamp meters is described below.

Design:
Rogowski coil wound around a coreless, nonmagnetic material

Principle:
Differentiated voltage waveforms are output at both ends of the coil depending on the current. The waveforms are integrated to calculate the current.

Advantages:
Flexibility due to the absence of a core, broad frequency band

Disadvantages:
Limited to measurement of AC currents