Related knowledge of clamp ammeters
Overview of clamp ammeters
A clamp 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, and the iron core closes when the wrench is released.
The purpose of clamp ammeters
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 clamp ammeter
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.
Usage of clamp ammeter
When using a clamp ammeter to detect current, it is necessary to clamp one of the tested wires (wires). If two parallel wires are clamped, the current cannot be detected. In addition, when using the center (iron core) of the clamp ammeter for detection, the detection error is small. When checking the power consumption of household appliances, using a wire separator is more convenient. Some wire separators can amplify the detection current by 10 times, so 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 will display a negative number. This function can be used to detect whether the car's battery is in a charging or discharging state
Effective value detection
The clamp ammeter with the average value method detects the average value of the sine wave through AC detection, and displays the value after amplification by 1.11 times (sine wave AC) as the effective value. Waveforms and skewed waves with different waveform rates other than sine waves are also displayed after amplification by 1.11 times, which will cause indication errors. Therefore, when detecting waveforms and skewed waves other than sine waves, please choose a clamp ammeter that can directly test the true effective value
Leakage detection
Leakage detection is different from typical current detection, where two (single-phase 2-wire) or three (single-phase 3-wire, three-phase 3-wire) wires 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 means of judgment. 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 where power cannot be cut off
