The use and detection 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. The working principle is as follows:
A clamp type ammeter is a combination of a current transformer and an ammeter. The iron core of the current transformer can be opened when the wrench is tightened; The wire through which the measured current passes can pass through the open gap of the iron core without cutting it off. When the wrench is released, the iron core closes. 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.
Usage method
When using a clamp type ammeter to detect current, it is necessary to clamp one of the tested wires (wires). Clamping two parallel wires cannot detect current. In addition, when using the center (iron core) of the clamp type ammeter for detection, the detection error is small. When checking the power consumption of household appliances, using a wire separator is more convenient, and some wire separators can amplify the detection current by 10 times, Therefore, currents below 1A can be amplified before detection. When using a DC clamp ammeter to detect DC current (DCA), if the current flow is opposite, it displays a negative number. This function can be used to detect whether the car's battery is in a charging or discharging state
Detection of true effective value (RMS)
The clamp type ammeter with an average value method detects the average value of a sine wave through AC detection, and displays the value after amplification by 1.11 times (sine wave AC) as a value. Waveforms and distorted waves with different waveform rates other than sine waves are also displayed after amplification by 1.11 times, resulting in indication errors. Therefore, when detecting waveforms and distorted waves other than sine waves, please choose a clamp type ammeter that can directly test the true effective value
Leakage detection
Leakage detection is different from normal current detection, where two (single-phase 2-wire type) or three (single-phase 3-wire type, three-phase 3-wire type) need to be clamped together. It is also possible to clamp the grounding wire for testing. The insulation management method for detecting leakage current on low-voltage circuits has become the primary judgment method. Since its confirmation by the 1997 revision of electrical equipment technical standards, leakage current clamp meters have gradually been used for testing in buildings and factories that cannot be powered off
