Clamp-on ammeter use and technique description
Usually when measuring current with an ordinary ammeter, you need to cut off the circuit to stop before the ammeter can be accessed for measurement, which is very troublesome, and sometimes the normal operation of the motor does not allow this to be done. At this time, the use of clamp ammeter is much more convenient, you can not cut off the circuit to measure the current. The principle of operation of the clamp-on ammeter is as follows:
Through the core of the measured circuit wire becomes the primary coil of the current transformer, which passes through the current will be induced in the secondary coil of the current. Thus, the secondary coil is connected to the ammeter will have an indication ----- measure the current of the circuit under test. Clamp meter can be through the switch gear, change different ranges. However, the dialling is not allowed to be operated with electricity. Clamp meter general accuracy is not high, usually 2.5 ~ 5 level. In order to facilitate the use of the meter, there are also different ranges of the conversion switch for measuring different levels of current and voltage measurement function.
Check the small three-phase motor three-phase current (less than 5 amps) is balanced, if the clamp-on ammeter measurements, the minimum head is 1 ~ 10 amps, while some table calculations are qualified is 2 amps. 2 amps or zero a few amps below the even more can not be measured. In addition, the ammeter usually has a large error at low ranges, and it is difficult to read when the pointer is deflected. In order to measure the current value, the load insulated wire in the ammeter jaw core around 1 to N turns. Application of the principle of current transformer to enhance the magnetic field, so as to read a larger current value. So that the reading is expanded, but the real current value must be subtracted from the expanded part. That is, when adding a turn, the readings need to be divided by 2; around two turns divided by 3. The rule is that the number of turns N turns, the current was expanded by N +1 times, the current value = meter readings / (N + 1). In addition, to eliminate the effect of residual magnetism in the core of the ammeter, in the measurement of larger currents, such as immediately after the measurement of small currents, the ammeter core should be opened and closed several times to eliminate residual magnetism in the core.
