Principle of construction of clamp-on ammeter
The core of the transformer is made into a movable opening, and into a clamp, and the movable part is connected to the handle 6, and when the handle is held tightly, the core of the current transformer is opened, and the measured intercept current 4 can be placed in the jaws, and the intercept current conductor becomes the primary side coil of the current transformer. Close the jaws, in the core of the current transformer there is an alternating magnetic flux through the secondary winding of the transformer 5 to produce induced current. Ammeter connected to both ends of the secondary winding, the current value indicated by its pointer is proportional to the operating current of the interceptor wire clamped into the current value can be read directly from the dial to be measured.
Clamp ammeter use
Before measurement
First of all, according to the type of current to be measured voltage level of the correct choice of clamp ammeter, the measured line voltage should be lower than the rated voltage of the clamp meter. Measurement of high-voltage line current, should be used with its voltage level in line with the high-voltage clamp ammeter. Low voltage clamp ammeter can only measure the current in the low-voltage system, can not measure the current in the high-voltage system.
Secondly, the appearance of the clamp-on ammeter should be properly checked before use, and the insulation of the meter must be checked to see if it is good, the shell should be free of damage, and the handle should be clean and dry. If the pointer is not in the zero position, it should be mechanically zeroed. Clamp ammeter jaws should be tightly engaged, if the pointer shaking, can re-open and close the jaws once, if the shaking still exists, should be carefully checked, pay attention to clear the jaws of debris, dirt, and then measured.
As the clamp ammeter to contact the measured line, so the clamp ammeter can not measure the current of the bare conductor. When measuring with a high-voltage clamp meter, it should be operated by two people, wearing insulated gloves, standing on insulated mats and not touching other equipment to prevent short-circuiting or grounding when measuring.
Measurement
First of all, when using the wrench should be pressed tightly, so that the jaws open, the measured wire into the center of the jaws, and then loosen the wrench and make the jaws close tightly. If there is any noise on the bonding surface of the jaws, it should be reopened and closed once, and if there is still noise, the bonding surface should be dealt with to make the reading accurate. In addition, do not clamp two wires at the same time. After reading, open the jaws, withdraw the measured wire, and place the block in the highest current block or OFF block.
Secondly, according to the size of the measured current to choose the appropriate range of the clamp-type ammeter. The selected range should be slightly larger than the measured current value, if it is impossible to estimate, in order to prevent damage to the clamp ammeter, it should be measured from the maximum range, and gradually change the gear until the range is appropriate. It is strictly prohibited to switch the stops of the clamp-on ammeter during the measurement, and the measured wire should be withdrawn from the jaws before changing the stops when changing the stops.
When Measurement of current less than 5 amps or less, in order to make the reading more accurate, when conditions permit, the measured current-carrying wire can be placed into the jaws of the measurement after winding a few turns. At this time the actual current value of the measured wire should be equal to the meter reading divided by the number of turns of the wire into the jaws.
Measurement should pay attention to all parts of the body and the electrified body to maintain a safe distance, low-voltage system safety distance of 0.1 ~ 0.3 meters. Measurement of high-voltage cable current in each phase, the distance between the cable head line should be more than 300 mm, and good insulation, to be considered convenient to measure before. Observe the meter time, pay special attention to maintain a safe distance between the head and the energized part, the distance between any part of the human body and the energized body shall not be less than the entire length of the clamp meter.
When measuring the current of low-voltage fusible fuse or horizontally arranged low-voltage busbar, each phase of the fusible fuse or busbar shall be protected and isolated with insulating material before measurement so as not to cause a short-circuit between phases. Measurement is strictly prohibited when one phase of the cable is connected to ground, to prevent the occurrence of ground-breaking explosion due to the low insulation level of the cable head and jeopardize personal safety.
After measurement
Measurement after the end of the clamp-on ammeter of the clamp-on ammeter, if the general common magneto-electric system clamp-on meter measurement, the indication value and the actual value of the measured will have a great discrepancy, or even no indication, the reason is that the magneto-electric system clamp-on meter of the meter head and the secondary coil of the transformer is connected to the meter head voltage is obtained from the secondary coil. According to the principle of electromagnetic induction can be seen, the mutual inductance electric potential of E2 = 4.44fWФm, by the public display is not difficult to see, the size of the mutual inductance electric potential is proportional to the frequency. When using this clamp meter to measure the rotor current, due to the rotor on the lower frequency, the voltage obtained on the meter head will be much smaller than the voltage when measuring the same industrial frequency current (because this meter head is designed according to the industrial frequency of AC 50Hz). Sometimes the current is so small that it does not even allow the rectifier element in the head to conduct, so the clamp meter does not indicate, or the indicated value is very different from the actual value.
