What is a clamp meter? The clamp meter (clamp meter) is a meter that combines a current transformer and an ammeter. It is an important branch of the digital multimeter; it is a portable meter that can directly measure the AC current of the circuit without disconnecting the circuit.
Clamp meter structure and principle The clamp meter consists essentially of a current transformer, a clamp wrench and a rectifying magnetoelectric system with a reaction force meter.
The clamp meter works like a transformer. The primary coil is the wire that passes through the clamp core, which is equivalent to the primary coil of a 1-turn transformer, which is a step-up transformer. The secondary coil and the ammeter for measurement constitute a secondary circuit. When the wire has an alternating current, it is that the coil generates an alternating magnetic field, and an induced current is generated in the secondary circuit. The magnitude of the current and the ratio of the primary current are equivalent to the inverse of the number of turns of the primary and secondary coils. . Clamp-type ammeters are used to measure large currents. If the current is not large enough, you can increase the number of turns of the primary wire through the clamp meter and divide the measured current by the number of turns.
The secondary winding of the through-current current transformer of the clamp ammeter is wound around the iron core and connected to the alternating current ammeter, and its primary winding is the conductor to be tested passing through the center of the transformer. The knob is actually a range selection switch. The function of the wrench is to open and close the movable part of the core of the core-type transformer so that it can clamp the wire to be tested.
When measuring the current, press the wrench to open the jaws, and place the measured current carrying wire in the middle of the through-current current transformer. When there is alternating current in the tested wire, the magnetic flux of the alternating current is in the transformer pair. A current is induced in the side winding, which passes through the coil of the electromagnetic ammeter, deflecting the pointer, and indicating the measured current value on the dial scale.
After placing the wire to be tested into the window through the iron button, it should be noted that the two faces of the jaw have a good fit, and no other objects can be placed in the middle;
The minimum range of the clamp meter is 5A, and the display error will be larger when measuring a smaller current. This is the result of measuring the energized wire around the clamp meter for a few weeks and dividing the resulting reading by the number of turns.
Clamp table use points (1) Mechanical zeroing before measurement
(2) Select the appropriate range, first select the large, then select the small range or look at the nameplate value estimate.
(3) When the minimum range measurement is used and the reading is not obvious, the measured wire can be wound a few turns, and the number of turns should be based on the number of turns in the center of the jaw. Then the reading = indicating value & TImes; range / full bias & TImes Number of turns
(4) After the measurement is completed, the transfer switch should be placed at the maximum range.
(5) When measuring, the conductor to be tested should be in the center of the jaws and the jaws should be closed tightly to reduce the error.
Diagram of the use of the clamp meter The use of the clamp multimeter's gear position, jack use, and range selection are all important. We take FLUKE337 as an example to give a detailed introduction to the method of testing AC current using a clamp ammeter.
1) Correctly select the gear position of the clamp meter, as shown in the figure, select AC AC current file
2) Open the clamp meter jaw and connect the clamp meter to the circuit under test.
The access method shown in the figure below is wrong, so that the current consumption of the circuit cannot be measured, but the leakage current of the circuit is normally zero.
3) Open the clamp-shaped table jaws and correctly connect the clamp meter to the circuit under test. At this point, the actual current of the household appliance can be measured.
The access method shown in the figure below is correct. Only the single power cable of the circuit under test can pass through the jaws. Two wires can be tested separately. The measured values should be equal in theory, otherwise the line is not normal. The leakage current is large. The measured current value of the test circuit shown in the figure is 4.5A.
