Fabrication and Use of a Transformer Clamp Ammeter
Structure and principle
The clamp meter is essentially composed of a current transformer, a clamp wrench and a rectifying magnetoelectric system with a reaction force instrument.
A clamp meter works on the same principle as a transformer. The primary coil is the wire that passes through the clamp-type iron 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 the secondary loop. When the wire has an alternating current passing through it, it is this turn of the coil that generates an alternating magnetic field, and an induced current is generated in the secondary circuit. The ratio of the magnitude of the current to the primary current is equivalent to the inverse ratio of the turns of the primary and secondary coils. . The clamp ammeter is used to measure large currents. If the current is not large enough, the primary wire can be passed through the clamp meter to increase the number of turns, and at the same time divide the measured current by the number of turns.
The secondary winding of the feedthrough current transformer of the clamp ammeter is wound on the iron core and connected to the AC ammeter, and its primary winding is the measured wire passing 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-type 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 under test in the middle of the feed-through current transformer. A current is induced in the side winding, and the current passes through the coil of the electromagnetic ammeter, causing the pointer to deflect, and the measured current value is indicated on the dial scale.
After putting the wire under test into the window through the core button, pay attention to the good fit of the two sides of the jaws, and do not let other objects in the middle;
The minimum range of the clamp meter is 5A, and the display error will be larger when measuring a small current. This is the result that can be measured after winding the energized wire on the clamp meter for several weeks, and dividing the obtained reading value by the number of turns.
