Structure principle of clamp Ammeter Use of clamp Ammeter
Clamp Ammeter is one of the commonly used portable instruments for electricians. It is an instrument that measures the current value by covering the magnetic circuit that can be opened and closed on the conductor carrying the measured current. It is composed of current transformer and Ammeter, which is easy to use. It can directly measure the working current of electrical equipment in operation without disconnecting the power supply and line, so as to know the working condition of equipment in time.
Structure principle of clamp Ammeter
Clamp Ammeter consists of current transformer and Ammeter.
The iron core of the transformer is made into a movable opening and in the shape of a clamp. The movable part is connected to the handle 6. When the handle is tightly grasped, the iron core of the current transformer opens, and the measured cutoff wire 4 can be placed in the clamp, making the cutoff wire the primary coil of the current transformer. Close the clamp, and alternating magnetic flux passes through the iron core of the current transformer, generating induced current in the secondary winding 5 of the transformer. The Ammeter is connected to both ends of the secondary winding. The current value indicated by its pointer is in direct proportion to the working current of the clamped cut-off wire, and the measured current value can be read directly from the dial.
Use of clamp Ammeter
Before measurement
Firstly, the clamp Ammeter should be correctly selected according to the type and voltage level of the current to be measured. The voltage of the line to be measured should be lower than the rated voltage of the clamp. When measuring the current of high-voltage lines, the high-voltage clamp Ammeter corresponding to its voltage level shall be selected. Clamp on Ammeter of low voltage level can only measure the current in low-voltage system, but cannot measure the current in high-voltage system.
Secondly, the appearance of the clamp Ammeter should be checked correctly before use. The insulation of the ammeter must be checked to see if it is in good condition. The shell should be free of damage and the handle should be clean and dry. If the pointer is not in the zero position, mechanical zero adjustment should be performed. The jaw of the clamp type Ammeter should be tightly connected. If the pointer shakes, the jaw can be opened and closed again. If the shaking still exists, it should be carefully checked, and attention should be paid to removing debris and dirt from the jaw, and then measurement should be carried out.
The clamp Ammeter cannot measure the current of bare conductor because the clamp Ammeter must contact the measured line. When using a high-voltage clamp meter for measurement, it should be operated by two people. During measurement, insulated gloves should be worn, standing on an insulated pad, and other equipment should not be touched to prevent short circuits or grounding.
During measurement
Firstly, when using, the wrench should be tightened to open the jaws. Place the measured wire in the center of the jaws, then loosen the wrench and close the jaws tightly. If there is any noise on the joint surface of the pliers, it should be reopened and closed again. If there is still noise, the joint surface should be treated to ensure accurate readings. Additionally, it is not allowed to clamp two wires simultaneously. After reading, open the jaws, exit the measured wire, and set the gear to the highest current or OFF gear.
Secondly, select the appropriate range of clamp type Ammeter according to the measured current. The selected range should be slightly larger than the measured current value. If it cannot be estimated, to prevent damage to the clamp Ammeter, the measurement should start from the maximum range and gradually change the gear until the range is appropriate. It is strictly prohibited to switch the gear of clamp Ammeter during the measurement. When shifting, the measured wire shall be withdrawn from the jaw before changing the gear.
When measuring currents below 5 amperes, in order to make the reading more accurate, if conditions permit, the measured current carrying wire can be wound several times and placed in a clamp for measurement. At this point, the actual current value of the measured wire should be equal to the reading value of the instrument divided by the number of wire turns placed in the clamp.
When measuring, attention should be paid to maintaining a safe distance between all parts of the body and the charged body. The safe distance for low-voltage systems is 0.1-0.3 meters. When measuring the current of each phase of high-voltage cables, the distance between the cable heads should be at least 300 millimeters, and the insulation should be good. Only when the measurement is considered convenient can it be carried out. When observing the timing of the watch, special attention should be paid to maintaining a safe distance between the head and the charged part. The distance between any part of the human body and the charged part should not be less than the entire length of the clamp watch.
When measuring the current of low-voltage fusible fuses or horizontally arranged low-voltage busbars, each phase of fusible fuses or busbars should be protected and isolated with insulation materials before measurement to avoid causing phase to phase short circuits. When one phase of the cable is grounded, it is strictly prohibited to measure to prevent ground breakdown and explosion caused by low insulation level of the cable head, which may endanger personal safety.
After measurement
After the measurement, if the clamp Ammeter of the clamp Ammeter is used for measurement, the indicated value will be greatly different from the measured actual value, or even there will be no indication. The reason is that the head of the clamp Ammeter of the magnetoelectric system is connected to the secondary coil of the transformer, and the head voltage is obtained from the secondary coil. According to the principle of electromagnetic induction, the mutual inductance electromotive force is E2=4.44fW Ф m. It is not difficult to see from the public notice that the magnitude of the mutual inductance electromotive force is directly proportional to the frequency. When using this type of clamp meter to measure rotor current, due to the low frequency on the rotor, the voltage obtained on the meter head will be much smaller than when measuring the same power frequency current (because this type of meter head is designed for AC 50Hz power frequency). Sometimes the current is very small and cannot even make the rectifier element in the meter head conductive, so the clamp meter does not indicate or the indicated value differs significantly from the actual value.
