Explanation of the application scope and functional skills of clamp ammeters
Usually, when measuring current with a regular ammeter, it is necessary to cut off the circuit and stop it before connecting the ammeter for measurement. This is very troublesome, and sometimes normal running motors are not allowed to do so. At this point, using a clamp type ammeter becomes much more convenient, as it can measure current without cutting off the circuit. Clamp type ammeter
The working principle is as follows:
The tested circuit wire passing through the iron core becomes the primary coil of the current transformer, where the current is induced in the secondary coil through the current. Thus, 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 gears of the switch. However, it is not allowed to operate with power when shifting gears. The accuracy of clamp shaped 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 functions
Pithy formula
Use a clamp ammeter to measure small AC currents.
The insulation wire of the tested load is wound around the clamp iron core.
Divide the reading by turns plus one to obtain the true current value.
explain
When checking whether the three-phase current of a small three-phase motor (less than 5 amperes) is balanced, if measured with a clamp type ammeter, the minimum head of the meter is 1-10 amperes, and some meters have a grid of 2 amperes. Less than 2 amperes or a few tenths of an ampere is even more difficult to measure. In addition, ammeters typically have significant errors at low ranges, making it difficult to read when the pointer is deflected. 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. Apply the principle of current transformer to enhance the magnetic field, thereby reading 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, divide the reading 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.
