Introduction to transformer type clamp ammeter
Structure and principle
The clamp meter is essentially composed of a current transformer, a clamp wrench and a rectifier magnetoelectric system with reaction force instrument.
A clamp meter works on the same principle as a transformer. The primary coil is a wire passing through the clamp-type iron core, which is equivalent to the primary coil of a 1-turn transformer. This is a step-up transformer. The secondary coil and the ammeter used for measurement form a secondary circuit. When an alternating current flows through the wire, it is this turn of the coil that generates an alternating magnetic field and an induced current in the secondary circuit. The ratio of the size of the current to the primary current is equivalent to the inverse ratio of the number of turns of the primary and secondary coils. . The 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 through the clamp meter and divide the measured current number by the number of turns.
The secondary winding of the core-type current transformer of the clamp ammeter is wound on the iron core and connected to the AC ammeter. Its primary winding is the conductor under test that passes through the center of the transformer. The knob is actually a range selection switch, and the function of the wrench is to open and close the movable part of the core of the through-core transformer so that it can clamp the wire under test.
When measuring current, press the wrench, open the jaws, and place the current-carrying wire to be measured in the middle of the core-type current transformer. When an alternating current passes through the wire to be measured, the magnetic flux of the alternating current flows through the transformer. A current is induced in the side winding, and this current 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 under test into the window through the iron core button, pay attention to the good fit between the two surfaces of the jaws, and do not allow other objects to be in the middle;
The minimum range of the clamp meter is 5A, and the display error will be larger when measuring smaller currents. This is done by winding the energized wire around the clamp meter for several weeks and then measuring it. The reading obtained divided by the number of turns is the required result.
Instructions
(1) Mechanical zero adjustment is required before measurement.
(2) Select the appropriate range, first select the large range, then select the small range or estimate based on the nameplate value.
(3) When measuring with a small range and the reading is not obvious, you can wind the wire under test a few turns. The number of turns should be based on the number of turns in the center of the jaw, then the reading = indicated value × range / full deviation × Number of turns
(4) After the measurement is completed, place the transfer switch at the maximum range.
(5) When measuring, the conductor under test should be in the center of the jaws and the jaws should be closed tightly to reduce errors.
