Application and skill description of clamp Ammeter
Usually, when measuring the current with an ordinary Ammeter, the Ammeter can be connected for measurement only after the circuit is cut off and shut down, which is very troublesome, and sometimes it is not allowed to do so for a normal running motor. At this time, it is much more convenient to use the clamp Ammeter, which can measure the current without cutting off the circuit. The working principle of clamp Ammeter 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 with the secondary coil will have an indication ----- measuring the current of the line under test. 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 clamp Ammeter to measure small AC current.
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 (less than 5 A) of a small three-phase motor is balanced, if the clamp type Ammeter is used for measurement, its head * is 1~10 A, and some meter * * is 2 A. Less than 2 amperes or a few tenths of an ampere is even more difficult to measure. In addition, the error of Ammeter is usually large at low range, and it is difficult to read when the pointer is deflected. In order to measure the accurate current value, the load insulated wire can be wound 1~N turns on the iron core of the Ammeter jaw. 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, eliminate the influence of residual magnetism in the iron core of Ammeter. After measuring a large current, if a small current is measured immediately, open and close the iron core of Ammeter several times to eliminate the residual magnetism in the iron core.
