Explanation of clamp ammeter applications and features
Usually, when measuring current with a regular ammeter, it is necessary to cut off the circuit and stop the machine before connecting the ammeter for measurement, which is very troublesome. Sometimes, normally running motors are not allowed to do so. 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 the current is induced in the secondary coil through the current. So that the ammeter connected to the secondary coil has an indication - to measure the current of the tested circuit. The clamp meter can be changed to different ranges by shifting the gear of the switch. But it is not allowed to operate with electricity when shifting gears. The accuracy of clamp watches is generally not high, usually ranging from 2.5 to 5 levels. For ease of use, there are also conversion switches with different ranges in the meter for measuring different levels of current and voltage
When checking whether the three-phase current (less than 5 amps) of a small three-phase motor is balanced, if measured with a clamp ammeter, the minimum head of the meter is 1-10 amps, and some meters have a first cell of 2 amps. It is even more impossible to measure below 2 amperes or a few tenths of an ampere. In addition, ammeters often have significant errors at low ranges, making it difficult to read when the pointer deviates. To accurately measure the current value, the load insulation wire can be wound 1 to N turns on the iron core of the ammeter clamp. Applying the principle of current transformers to enhance the magnetic field, in order to read larger current values. This way, the reading is enlarged, but the true current value must be subtracted from 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 the number of turns is N, the current is increased by N+1 times, and the current value is equal to the meter reading/(N+1). In addition, to eliminate the influence of residual magnetism in the iron core of the ammeter, if a large current is measured and a small current is measured immediately, the iron core of the ammeter should be opened and closed several times to eliminate residual magnetism in the iron core.
