Clamp Meter

What is Clamp Meter

Clamp meter as one of the necessary test tools in the daily maintenance work, mainly used to test the voltage, current, frequency and other related parameters, which requires it to have a high test resolution, test accuracy and more test functions.

Clamp Meter Principle

Clamp meter is essentially composed of a current transformer, clamp wrench and a rectified magneto-electric system has a reaction force meter.

A clamp meter works on the same principle as a transformer. The primary coil is the wire through the clamp core, equivalent to 1 turn of the primary coil of the transformer, which is a step-up transformer. The secondary coil and the ammeter used for measurement form the secondary circuit. When the wire has an alternating current through, it is this turn of the coil produces an alternating magnetic field, in the secondary circuit produces an induced current, the size of the current and the ratio of the primary current, which is equivalent to the inverse ratio of the number of turns of the primary and secondary coils. Clamp ammeter is used to measure large currents, if the current is not large enough, you can increase the number of turns of the primary conductor in through the clamp meter, at the same time the number of measured current divided by the number of turns.

Clamp ammeter through the core of the current transformer vice-side winding wound on the core and connected to the AC ammeter, its primary side winding that is through the center of the transformer is measured wire. Knob is actually a range selector switch, the role of the wrench is to open and close the core of the wear-center type transformer core of the movable part, in order to make it clamp the measured wire.

Measurement of current, press the wrench, open the jaws, the measured current-carrying conductor placed in the middle of the through-core current transformer, when the measured conductor has an alternating current through the alternating current flux in the transformer vice-side winding induced current, which passes through the coil of the electromagnetic ammeter, so that the pointer is deflected, in the dial scale pointed out that the measured current value.

After placing the measured wire into the window through the core button, it is important to note that the two faces of the jaws have a good fit and that no other objects can be allowed to be in the center; the minimum range of the ammeter should not be too high.

The minimum range of the clamp tester is 5A, the display error will be larger when measuring smaller current. This can be energized wire in the clamp meter around a few weeks and then measured, the resulting reading divided by the number of turns is the required results.

How to use

1. Before use, carefully read the manual to determine whether the meter is for AC or both AC and DC.
2. The voltage of the circuit under test should not exceed the value indicated on the clamp meter; otherwise, it may cause grounding accidents or electrical shock hazards.
3. Only one phase conductor can be measured at a time. The conductor being measured should be positioned centrally within the clamp window. Do not clamp multiple phase conductors simultaneously.
4. Before measuring, estimate the current size to select the appropriate range. If the current size cannot be estimated, start with the maximum range and then switch to a lower range as needed for accurate readings. Avoid using a small current range to measure large currents to prevent damage to the meter.
5. Ensure the clamp jaws are tightly closed during measurement. If there is any noise after closing, reopen the jaws and close them again. If the noise persists, check whether the contact surfaces of the magnetic circuit are clean. Clean any dust or dirt if necessary.
6. Due to the lower accuracy of clamp meters, for measuring small currents, you can use the following method: wrap the conductor of the circuit under test around several times, and then place it within the clamp jaws for measurement. The indicated current value on the meter will not be the actual current; the actual current should be the meter reading divided by the number of wire turns.
7. Do not perform maintenance with power on to avoid electrical shock.

Precautions

1. When using a high-voltage clamp meter, ensure that the meter’s voltage rating is appropriate. Never use a low-voltage clamp meter to measure high-voltage circuits. When measuring with a high-voltage clamp meter, it should be operated by two people. During measurement, wear insulating gloves, stand on an insulating mat, and avoid touching other equipment to prevent short circuits or grounding.
2. When observing the meter, maintain a safe distance between your head and any live parts. No part of your body should be closer to the live components than the length of the clamp meter.
3. When measuring high-voltage circuits, do not use additional wires to connect the meter to the circuit. When measuring the current in high-voltage cables, ensure that the distance between cable ends is at least 300 mm and that the insulation is in good condition. Perform the measurement only when it is safe and convenient.
4. When measuring current in low-voltage fuses or horizontally arranged low-voltage busbars, protect and isolate each phase fuse or busbar with insulating material before measurement to prevent inter-phase short circuits.
5. Do not measure when there is a ground fault in the cable. This prevents the risk of insulation breakdown and explosion at the cable ends, which could endanger personal safety.
6. After measurement, set the clamp meter to the maximum range to prevent accidental overcurrent in future use and store it in a dry indoor environment.