Key Points for Measuring Operations with a Clamp Meter
1. Security requirements
1) In practical work, it is often necessary to measure the current value of low-voltage wires or equipment. In the measurement of the current of low-voltage busbars and their electrical components in power distribution equipment, the distance between the wires of the low-voltage busbar layout is generally not large enough, and some clamp current meters have large body sizes. Opening the clamp during measurement may cause phase to phase short circuits or grounding. If the posture of the measuring personnel is unstable or their arms shake, accidents are more likely to occur.
Therefore, according to the actual conditions on site, qualified insulation materials must be used to isolate the busbar and electrical components from each other before measurement, and attention should be paid not to touch other live parts.
2) When measuring the current of bare wires, if the distance between different phase wires and between wires and ground is small, and if the insulation of the clamp is poor or the insulation sleeve is damaged, it is easy to cause short circuit accidents between phases and between phases and ground.
Therefore, it is usually not allowed to measure the current of bare wires with clamp ammeters. If it is necessary to measure, safety preparations for insulation isolation of bare wires should be made to prevent accidents from occurring.
3) For a multi-purpose clamp ammeter, all functions must not be used simultaneously. For example, when measuring current, voltage cannot be measured simultaneously. For safety reasons, the test wire must be unplugged from the clamp ammeter.
4) At the measurement site, all equipment should be orderly arranged, and a sufficient distance must be maintained between the various parts of the measuring personnel's body and the charged body, at least not less than the safe distance (the safe distance for low-voltage systems is 0.1m-0.3m). When reading, one often involuntarily lowers their head or waist, and special attention should be paid to the safety distance between their limbs, especially the head, and the live parts.
2. Accuracy requirements
1) When measuring current, the selection of the gear level of the clamp ammeter should be appropriate. It is best to place the pointer on more than one-third of the scale because the deflection angle of the pointer is too small, making it difficult to distinguish the scale value and affecting the accuracy of the measurement.
2) The measured wire should be placed in the center position of the clamp as much as possible. If the measured wire is too skewed, the magnetic induction intensity generated by the measured current in the clamp iron core will undergo significant changes, directly affecting the accuracy of the measurement. Generally, measurement errors caused by improper positioning of the measured wire in the clamp can reach 2% -5%.
3) To ensure accurate readings, the two sides of the iron core clamp should be tightly closed. If you hear electromagnetic noise from the jaws or feel a slight vibration in the hand holding the clamp shaped ammeter, it indicates that the end face of the jaws is not tightly connected. At this time, the jaws should be opened and closed again; If the noise still exists, check whether there is dirt or rust on the end face of the jaws. If there is, clean it thoroughly until the jaws are well connected.
4) For digital clamp current meters, although the battery level has been checked before use, the battery level should also be monitored at all times during the measurement process. If the battery voltage is found to be insufficient (such as a low voltage prompt symbol), the measurement must be continued after replacing the battery; If there is electromagnetic interference on the measurement site, it will inevitably interfere with the normal progress of the measurement, so efforts should be made to eliminate the interference. The ability to correctly read measurement data is also directly related to the accuracy of the measurement.
5) For the header of a pointer type caliper, the first step is to identify the selected gear, and then identify which scale is being used. When observing the scale value pointed by the pointer, the eyes should be directly facing the pointer and scale to avoid strabismus and reduce parallax. Although the display of digital meter heads is relatively intuitive, the effective viewing angle of LCD screens is very limited. When the eyes are too skewed, it is easy to read the wrong numbers. Attention should also be paid to the decimal point and its position, which must not be ignored.
