Classification of clamp ammeter
Clamp ammeters can be divided into pointer type and digital type according to the different display forms of the measurement results; from the measurement voltage, there are high-voltage clamp ammeters and low-voltage clamp ammeters; from the function, there are AC-DC clamp meters, AC clamp meter, clamp multimeter, and leakage current clamp meter; according to the structure and working principle, they are divided into rectification system and electromagnetic system. The rectifier clamp ammeter can only be used for the measurement of AC current, while the electromagnetic clamp ammeter can realize both AC and DC measurements. The electromagnetic clamp ammeter is mainly composed of a current transformer, a magnetoelectric ammeter, a rectifier circuit, a range changeover switch and a measuring circuit. The iron core of the current transformer is a clamp-shaped structure, which is divided into a fixed part and a movable part, and is placed at the front end of the current transformer. The movable part is linked with the wrench; when the wrench is gripped, the iron core of the current transformer will It can be opened, so that the wire of the measured current can pass through the gap of the iron core without cutting off, and then relax the hand to close the iron core. At this time, the wire passing the current is equivalent to the primary coil of the current transformer, and the secondary coil will There will be an induced current, and the pointer of the ammeter connected to the secondary coil will deflect, thereby indicating the value of the measured current. The range conversion switch and the switching circuit can realize the multi-range current measurement of the clamp ammeter.
Selection Guide for Clamp Meters
(1) First of all, it should be clear whether the measured current is AC or DC. The rectifier clamp ammeter is only suitable for measuring power frequency current with low waveform distortion and little frequency change, otherwise, large measurement errors will occur. For the electromagnetic clamp ammeter, since the deflection property of the movable part of the measuring mechanism has nothing to do with the polarity of the current, it can be used to measure both AC current and DC current, but the accuracy is usually relatively low . The accuracy of the clamp ammeter mainly includes 2.5 grades, 3 grades, 5 grades, etc., and should be selected according to the measurement technical requirements and actual conditions.
(2) For digital clamp ammeters, the readings of the measurement results are intuitive and convenient, and the measurement functions have also been expanded a lot, such as being able to measure resistance, diodes, voltage, active power, reactive power, power factor, parameters such as frequency. However, the digital clamp ammeter is not perfect. When the electromagnetic interference in the measurement occasion is serious, the displayed measurement results may have discrete jumps, making it difficult to confirm the actual current value; if the pointer clamp ammeter is used, due to The damping effect of the magnetoelectric mechanical meter itself makes it relatively slow to respond to strong electromagnetic field interference. At best, the hands produce a small swing, and its indication range is relatively intuitive. Relatively speaking, reading is not too difficult. .
