A clamp multimeter is composed of a current transformer and a multimeter. The core of the current transformer can open when the clamp is squeezed; the wire through which the measured current flows can pass through the gap in the opened core without needing to be cut. When the clamp is released, the core closes.

A clamp multimeter is composed of a current transformer and a multimeter. The core of the current transformer can open when the clamp is squeezed; the wire through which the measured current flows can pass through the gap in the opened core without needing to be cut. When the clamp is released, the core closes.

When we need to measure current without breaking the circuit, we need to use a clamp multimeter (sometimes referred to simply as a clamp meter). A clamp multimeter is a device used to measure the magnitude of current in an electrical circuit that is currently operating, and it is a commonly used measuring tool by electricians. Clamp multimeters are divided into two major categories: clamp AC ammeters and clamp AC/DC ammeters; some can also measure AC voltage.

Structure:

The clamp AC ammeter is essentially composed of a current transformer and a rectifying instrument. The current-carrying wire being measured acts as the primary winding of the current transformer, while the secondary winding of the current transformer is on the core, which is connected to the rectifying instrument. Based on a certain proportional relationship between the primary and secondary windings of the current transformer, the rectifying instrument can display the current value of the measured circuit.

The clamp AC/DC meter is an electromagnetic instrument. The wire being measured placed in the clamp acts as an excitation coil, forming a magnetic circuit in the core. The electromagnetic measuring mechanism is located in the gap of the core and is deflected under the influence of the magnetic field to obtain a reading. Since its deflection is not affected by the measured current, it can measure both AC and DC currents.

Usage Method:

The usage method of the clamp multimeter is simple. As shown in the above image, to measure current, you only need to clamp the wire being measured into the core of the clamp multimeter and then read the value on the digital display or dial.

It’s quite simple, right? Just clamp the measuring wire! However, with the widespread use of digital clamp multimeters, many multimeter functions have been added to the clamp meter, such as voltage, temperature, resistance, etc. (sometimes referred to as multifunction clamp meters, as shown in the image above, the instrument has two probe sockets). You can select different functions using the knob, and the usage method is similar to that of a general digital multimeter. For some specific function buttons, refer to the corresponding manual.

Phase Sequence Testing:

(1) Turn the dial to the phase sequence detection setting;

(2) Insert the probes yellow, black, and red into the C, COMb, VΩa sockets in order;

(3) Connect the red, black, and yellow probes correspondingly to A, B, C (or L1, L2, L3). When the red and black probes are connected, the indicator light glows slightly, and when the yellow probe is connected, the indicator light lights up, indicating a positive phase sequence; if the light goes out, it indicates a negative phase sequence;

(4) The phase sequence setting can also measure inter-phase voltage.

AC Voltage Measurement:

(1) Turn the dial to the AC voltage setting;

(2) Insert the red and black probes into the VΩa, COMb sockets;

(3) Connect the other ends of the red and black probes to the points to be measured and read the values.

AC Current Measurement:

(1) Select the appropriate current range;

(2) Fully clamp the single wire being measured with the jaws and read the data;

Note that the maximum testing current for this instrument is only 600A; do not test currents exceeding 600A.

DC Voltage Measurement:

(1) Select the appropriate DC voltage range;

(2) Insert the red and black probes into the VΩa, COMb sockets;

(3) Connect the other ends of the red and black probes to the points to be measured and read the values.

Resistance Measurement:

(1) Turn the dial to the 2kΩ resistance setting;

(2) Insert the red and black probes into the VΩa, COMb sockets;

(3) Connect the other ends of the red and black probes to the points to be measured and read the values;

Note: Resistance can only be tested when the circuit is powered off.

Continuity Measurement:

(1) Turn the dial to the diode setting;

(2) Insert the red and black probes into the VΩa, COMb sockets;

(3) Connect the other ends of the red and black probes to the points to be measured and read the values. If the value is very small and the multimeter emits a “beep,” the circuit is closed; conversely, if the value shows “1” and the multimeter does not beep, the circuit is open or has a very high resistance.

Note: Continuity can only be tested when the circuit is powered off.

(1) Before using a digital multimeter, carefully read the user manual to familiarize yourself with the power switch functions, range switch, input sockets, various function keys, knobs, and the role of accessories. Additionally, understand the multimeter’s limit parameters, including overload display, polarity display, low voltage display, and other indicator displays and alarms. Before measuring, carefully check the probes for cracks, the insulation of the leads for damage, and whether the probes are correctly inserted to ensure the operator’s safety.

(2) Before each measurement, double-check the measurement item and range switch position, as well as whether the input socket (or dedicated socket) is correctly selected.

(3) When first measuring, the instrument may exhibit jumping values; wait for the displayed value to stabilize before reading.

(4) Although the digital multimeter has a relatively complete protection circuit, try to avoid operational errors, such as using the current range to measure voltage, using the resistance range to measure voltage or current, or using the capacitance range to measure a charged capacitor, to avoid damaging the instrument.

(5) If only the highest position shows the number “1” and the other positions are blank, it indicates that the instrument has overloaded; switch to a higher range.

(6) Do not switch the range switch while measuring voltages above 10OV or currents above 0.5A, to avoid generating an arc and burning out the contact points of the switch.

(7) The numbers marked with danger next to the input sockets represent the limit values of the voltage or current that can be input to that socket. Exceeding these values may damage the instrument and even endanger the operator’s safety.

(8) Clamp multimeters should not be used to measure high voltage lines; the voltage of the measured line must not exceed the voltage rating specified for the clamp meter (generally not exceeding 500 volts) to prevent insulation breakdown and electric shock.

(9) Estimate the size of the current to be measured and select the appropriate range; do not use a small range setting to measure large currents.

(10) Before measuring, ensure that the range switch is set to the correct AC current range; do not use the voltage or resistance ranges to measure current.

Remember! Never use the resistance range and current range to measure voltage; doing so will damage the meter.

(11) Only one wire can be clamped during each measurement. During measurement, the wire being measured should be placed in the center of the clamp jaws to improve measurement accuracy. It is best to hold the meter body level to avoid the wire touching the jaws and the meter body.

(12) After measurement, the range switch must be turned to the maximum voltage range position before turning off the power switch to ensure safe use next time.