Principle of clamp ammeter

The clamp ammeter consists of a current transformer and an ammeter. It is a meter used to measure the current size of an operating electrical circuit and can measure AC current without power failure.

As shown in the figure, the core of the transformer is made into a movable opening and a clamp shape, and the movable part is connected to the handle 6. When the handle is tightly gripped, the core of the current transformer opens (as shown by the double-dotted line in the figure), and the measured wire 4 can be placed in the jaws, and the current-carrying wire becomes the primary winding of the current transformer. When the jaws are closed, an alternating magnetic flux passes through the core of the current transformer, and an induced current is generated in the secondary winding 5 of the transformer.) The ammeter is connected to both ends of the secondary winding, and the current indicated by its pointer is proportional to the operating current of the clamped current-carrying wire, and the measured current value can be read directly from the dial. The clamp ammeter is essentially composed of a current transformer, a clamp wrench and a rectifier-type magnetoelectric reaction force meter. As shown in the figure.

1. Preparation before the test:

First, look at the jaws. The jaws on the outside should be clean. If there is any debris or oil stain, it should be cleaned in time to ensure that the magnetic circuit is strictly closed and the measurement result is accurate.

Second, check the pointer. Check the pointer position. If it is not at zero, perform mechanical zero adjustment.

2. Measurement process:

The first step is to select the range

First estimate the size of the measured current and adjust the switch to the required measurement range. If the measured current size cannot be estimated, measure it with the highest range first, and then adjust to the appropriate range according to the measurement situation.

Step 2: Opening and threading

The operation method is to hold the handle tightly, open the jaws, and place the wire to be tested. To reduce errors, the wire to be tested should be placed at the base of the jaws.

Figure Clamp Ammeter

1—Ammeter 2—Current transformer 3—Iron core 4—Measured wire 5—Secondary winding 6—Handle

Step 3 Silent Reading

Loosen the handle, the jaws will naturally return to the tight contact state, and read the indication after the pointer stabilizes. If there is noise, check whether the jaws are in tight contact or try again.

Step 4: Open offline

Hold the handle tightly, open the jaws, and separate the clamp meter from the wire. After the measurement is completed, turn the range selection switch to the maximum range position.

3. Things to note:

1) The voltage of the circuit under test should be lower than the rated voltage of the clamp ammeter.

2) When measuring the current of a high-voltage line, wear insulating gloves, insulating shoes, and stand on an insulating mat.

3) The jaws must be tightly closed and the measuring range cannot be changed while power is on.

4) The range should be selected appropriately. When selecting the range, you should first select the larger range and then the smaller range or calculate based on the nameplate value.

5) Place the wire in the base of the jaws.

6) After the measurement is completed, place the switch at the maximum range.

4. Measurement tips:

When measuring low currents below 5A, in order to improve the measurement accuracy, if conditions permit, the measured wire can be wound a few more times before being put into the jaws for measurement. At this time, the actual current should be the surface reading divided by the number of wire turns placed in the jaws.