A clamp multimeter is composed of a current transformer and a current meter. The core of the current transformer can open when the lever is squeezed; the wire carrying the current to be measured can pass through the gap of the opened core without being cut. When the lever is released, the core closes.
A clamp multimeter is composed of a current transformer and a current meter. The core of the current transformer can open when the lever is squeezed; the wire carrying the current to be measured can pass through the gap of the opened core without being cut. When the lever 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 as a clamp meter). A clamp multimeter is an instrument used to measure the current in electrical circuits while they are in operation and is a commonly used tool by electricians. Clamp multimeters can be divided into two main categories: clamp AC ammeters and clamp AC/DC ammeters, some of which can also measure AC voltage.
Structure:
The clamp AC ammeter is essentially composed of a current transformer and a rectifying instrument. The wire carrying the current to be measured acts as the primary winding of the current transformer, while the secondary winding of the current transformer is on the core and 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, where the wire being measured is placed within the clamp jaws and acts as an excitation coil, forming a circuit of magnetic flux within the core. The electromagnetic measuring mechanism is located in the middle of the core’s gap and is deflected by 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 method of using a clamp multimeter is simple. As shown in the image above, to measure current, simply clamp the wire that is currently running into the jaws 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, 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), and different functions can be selected using the knob, making the usage method very similar to a regular digital multimeter. For specific function buttons, refer to the corresponding manual.
Phase Sequence Testing:
(1) Turn the dial to the phase sequence detection setting;
(2) Insert the yellow, black, and red probes into the C, COMb, and VΩa sockets respectively;
(3) Connect the red, black, and yellow probes to A, B, C (or L1, L2, L3) respectively. When the red and black probes are connected, the indicator light will glow dimly. When the yellow probe is connected, the indicator light will be bright, indicating positive phase sequence; if the indicator light goes out, it indicates reverse phase sequence;
(4) The phase sequence setting can also measure phase-to-phase voltage.
AC Voltage Measurement:
(1) Turn the dial to the AC voltage setting;
(2) Insert the red and black probes into the VΩa and COMb sockets respectively;
(3) Connect the other end of the red and black probes to the point to be measured, and read the value.
AC Current Measurement:
(1) Select the appropriate current range;
(2) Fully clamp the wire to be measured with the jaws, and read the data;
Note: The maximum test 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 and COMb sockets respectively;
(3) Connect the other end of the red and black probes to the point to be measured, and read the value.
Resistance Measurement:
(1) Turn the dial to the 2kΩ resistance range;
(2) Insert the red and black probes into the VΩa and COMb sockets respectively;
(3) Connect the other end of the red and black probes to the point to be measured, and read the value;
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 and COMb sockets respectively;
(3) Connect the other end of the red and black probes to the point to be measured, and read the value. If the value is very small and the multimeter emits a “beep” sound, it indicates continuity; conversely, if the value shows “1” and the multimeter does not sound, it indicates an open circuit or 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 operating manual to familiarize yourself with the function of the power switch, range switch, input sockets, probes, and various function keys, knobs, and accessories. Additionally, understand the multimeter’s limit parameters, and the characteristics of overload display, polarity display, low voltage display, and other indicator displays and alarms, as well as the rules for the position of the decimal point. Before measuring, check for cracks in the probes, damage to the insulation of the leads, and whether the probes are correctly inserted to ensure the operator’s safety.
(2) Before each measurement, double-check the measurement project and range switch to ensure they are set correctly, and that the input sockets (or dedicated sockets) are selected correctly.
(3) When measuring, the instrument may display jumping numbers; wait for the displayed value to stabilize before reading.
(4) Although digital multimeters have relatively complete protection circuits, avoid operational errors such as measuring voltage with the current range, measuring voltage or current with the resistance range, or measuring a charged capacitor with the capacitance range to prevent damage to the instrument.
(5) If only the highest position shows the number “1” while other positions are off, it indicates that the instrument has overloaded, and a higher range should be selected.
(6) Do not change the range switch when measuring voltages above 10V or currents above 0.5A to avoid arcing and burning the contacts of the range switch.
(7) The numbers marked with a danger sign next to the input sockets represent the limit values for voltage or current input. Exceeding these limits may damage the instrument and even endanger the safety of the operator.
(8) Clamp multimeters should not be used to measure currents in high-voltage lines, and the voltage of the measured line should not exceed the voltage level specified for the clamp meter (generally not exceeding 500 volts) to prevent insulation breakdown and electric shock.
(9) Estimate the magnitude of the current to be measured and select the appropriate range; do not use a small range to measure large currents.
(10) Before measuring, ensure the range switch is set to the appropriate AC current range; do not use the voltage or resistance range to measure current.
Remember! Never use the resistance range or current range to measure voltage, as doing so may destroy the meter.
(11) During each measurement, only one wire can be clamped. When measuring, ensure the wire to be measured is positioned in the center of the clamp jaws to improve measurement accuracy. It is best to hold the meter body level with your hand, ensuring that the wire does not touch the clamp jaws and meter body.
(12) After measuring, the range switch must be turned to the maximum voltage range position before turning off the power switch to ensure safe usage next time.
Source: Power Partners
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