Application range and functional skills of clamp ammeter
When measuring current with a regular ammeter, it is usually necessary to cut off the circuit and stop the machine before connecting the ammeter for measurement. This is very troublesome, and sometimes it is not allowed to do so for normally running motors. At this point, using a clamp ammeter becomes much more convenient as it can measure current without cutting off the circuit. The working principle of a clamp ammeter is as follows:
The tested circuit wire passing through the iron core becomes the primary coil of the current transformer, and current is induced in the secondary coil through the current. So that the ammeter connected to the secondary coil can indicate the current of the tested circuit. The clamp gauge can be changed to different ranges by shifting the switch. But it is not allowed to operate with electricity when shifting gears. Clamp gauges generally have low accuracy, typically ranging from 2.5 to 5 levels. For the convenience of use, there are also conversion switches with different ranges in the table for measuring different levels of current and voltage functions
Mnemonic
Use a clamp ammeter to measure small AC currents.
The tested load insulation wire is wound around the clamp iron core.
The reading divided by turns plus one gives the true current value.
explain
When checking whether the three-phase current (less than 5 amps) of a small three-phase motor is balanced, if a clamp ammeter is used for measurement, the minimum reading on the meter head is 1-10 amps, and some meters have a first grid of 2 amps. It is even more impossible to measure below 2 amperes or a few tenths of an ampere. In addition, ammeters usually have large errors at low ranges, and it is difficult to read when the pointer deviates. To accurately measure the current value, the load insulation wire can be wound around the iron core of the ammeter clamp for 1 to N turns. Applying the principle of current transformer to enhance the magnetic field, in order to read larger current values. The reading obtained in this way is enlarged, but the true current value must subtract the enlarged part. When adding one turn, the reading needs to be divided by 2; Divide by 3 when winding two turns. The rule is that with N turns, the current is increased by N+1 times, and the current value is equal to the meter reading divided by (N+1). In addition, to eliminate the influence of residual magnetism in the iron core of the ammeter, if a small current is measured immediately after measuring a large current, the iron core of the ammeter should be opened and closed several times to eliminate residual magnetism in the iron core.
