Key points of measurement operation for clamp ammeter
1. Safety 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 devices, the distance between the wires arranged in the low-voltage busbars is generally not large enough. Some clamp type ammeters have larger body sizes, and opening the jaws during measurement may cause phase to phase short circuits or grounding. If the measuring personnel's posture is unstable or their arms shake, accidents are more likely to occur.
Therefore, it is necessary to use qualified insulation materials to isolate the busbar and electrical components from each other based on the actual on-site conditions before measurement, while also taking care 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 generally not allowed to measure the current of bare wires using a clamp type ammeter. If measurement is necessary, safety preparations for insulation isolation of bare wires should be made to prevent unexpected situations from occurring.
3) For multi-purpose clamp ammeters, 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 in an orderly manner, and sufficient distance must be maintained between each part 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 approaches their waist, and special attention should be paid to the safe distance between the limbs, especially the head and the live parts.
2. Accuracy requirements
1) When measuring current, the selection of the gear position of the clamp type ammeter should be appropriate. It is best to place the needle on the scale of more than 1/3 of the scale, as the deflection angle of the needle is too small and the scale value is difficult to distinguish, which affects the accuracy of the measurement.
2) The measured wire should be placed in the center position inside 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 a significant change, directly affecting the accuracy of the measurement. Generally, the measurement error caused by the improper position of the measured wire in the clamp can reach 2% -5%.
3) To ensure accurate readings, the two faces of the iron core pliers should be tightly closed. If you hear electromagnetic noise from the jaw or feel slight vibration from the hand holding the clamp ammeter, it indicates that the end face of the jaw is not tightly connected. At this time, the jaw should be re opened and closed; If the noise still exists, the end face of the jaw should be checked for dirt or rust. If there is any, it should be cleaned until the jaw is well combined.
4) For digital clamp ammeters, although the battery level has been checked before use, attention should also be paid to the battery level 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 at the measurement site, it will inevitably interfere with the normal operation of the measurement, so efforts should be made to eliminate the interference. Whether the measurement data can be read correctly also directly affects the accuracy of the measurement.
5) For the head of a pointer clamp watch, first identify the selected gear, and then identify which scale is used. When observing the scale value indicated by the watch needle, the eye should be facing the watch needle and scale to avoid strabismus and reduce parallax. Although the display of digital meters is relatively intuitive, the effective viewing angle of LCD screens is very limited. When the eyes are too tilted, it is easy to read wrong numbers. It is also important to pay attention to the decimal point and its position, which should not be ignored.
6) Abnormal or drastic temperature changes in the measurement site will affect the accuracy of the measurement. Because changes in temperature can increase the error of the meter, thereby reducing its accuracy. The main reason why clamp ammeters are affected by temperature is that temperature changes alter the material properties of key structural components that make up the instrument.
After changes in environmental temperature, the elasticity of the hairspring that often produces reaction torque in the instrument changes, resulting in changes in the instrument value. It can also change the magnetism of the permanent magnetic field that forms the magnetic field, causing changes in the magnitude of the action torque of the instrument.
In addition, due to changes in environmental temperature, the resistance of the circuits that make up the instrument, as well as the parameters of various electronic components and semiconductor devices, will change, and the final results will affect the accuracy of the measurement.
7) During the measurement process, it is not possible to clamp two or more wires simultaneously. When measuring currents below 5A, in order to obtain more accurate readings, if conditions permit, the wire can be wound several more times and placed in the clamp for measurement. However, the actual current value should be the reading divided by the number of wire turns placed in the clamp.
3. Storage and placement requirements
1) After each measurement is completed, the adjustment switch must be placed in the position of the maximum current range to prevent damage to the instrument due to unselected range in the next use.
2) It should be kept by a dedicated person. When not in use, it should be stored on indoor shelves or cabinets with a dry environment, suitable temperature, good ventilation, no strong vibration, no corrosive or harmful components for proper storage.
