The clamp ammeter is referred to as a clamp meter. The working part of the clamp meter is mainly composed of an electromagnetic ammeter and a through-current current transformer. The core-type current transformer core is made into a movable opening and is clamped, so it is called a clamp-type ammeter. It is a portable instrument that can directly measure the AC current of the circuit without disconnecting the circuit. It is very convenient to use in electrical maintenance and has a wide range of applications. The clamp meter can measure the current under continuous power. It is an electrical instrument that specializes in measuring AC current. Of course, there are new products that can test AC and DC current values.
The clamp meter is actually a current transformer. The stuck wire is equivalent to the primary coil of the transformer. When there is current in the wire, the magnetic flux will be generated in the iron core of the watch, and then the secondary coil is in the table. Inductive current, this current is equal to the current in the primary coil (ie the current in the wire) multiplied by the number of turns of the primary coil (actually a wire, so it is a åŒ) divided by the number of turns of the secondary coil, then According to this relationship, it is possible to convert the current in one time (ie, the wire).
First, how to measure current in the clamp meter
Before using the clamp ammeter, you should read the instructions carefully to find out whether it is an AC or AC-DC clamp meter. You should select the correct measurement position.
Moreover, the current of the measured current should be estimated before measuring the clamp meter, and then which range is used. If you can't estimate it, you can use the maximum range and then change it to make an accurate reading. Small current files cannot be used to measure large currents to prevent damage to the meter.
Clamp meter current measurement steps:
(1) Before measuring the line to be tested, the data of the clamp meter should be zeroed to prevent errors in subsequent measurements.
(2) After determining the voltage of the line to be tested, select the appropriate range.
(3) Press the wrench on the side of the clamp meter to open the jaws, place the line to be tested in the center of the jaws, and close the jaws.
(4) Get the data.
(5) After the measurement is completed, adjust the range adjustment knob to the maximum range to prevent accidental overcurrent during the next use.
Two: How does the clamp meter measure current? -----How to use the clamp ammeter
1. Firstly, correctly select the voltage level of the clamp-type ammeter, check whether the appearance of the insulation is good, whether there is damage, whether the pointer is swinging flexibly, whether the jaws are rusted, etc. The rated current is estimated based on the motor power to select the range of the meter.
2. Read the instructions carefully before using the clamp-type ammeter to find out whether it is an AC or AC-DC clamp meter.
3. Since the clamp-type ammeter itself has low precision, when measuring small current, the following method can be used: firstly, the wire of the circuit to be tested is wound a few times, and then placed in the jaw of the clamp meter for measurement. At this time, the current value indicated by the clamp meter is not the actual value to be measured. The actual current should be the reading of the clamp meter divided by the number of turns of the wire winding.
4. The clamp-type table jaws should be closed tightly during measurement. If there is noise after closing, the jaws can be opened once again. If the noise can not be eliminated, check whether the joint surfaces on the magnetic circuit are smooth and clean. Wipe clean.
5. The clamp meter can only measure the current of one phase conductor at a time. The conductor to be tested should be placed in the center of the clamp window. It is not allowed to clamp the multiphase conductor into the window for measurement.
6. The voltage of the circuit under test shall not exceed the value indicated on the clamp meter. Otherwise, it may cause grounding accident or cause electric shock.
7. Measure the working current of the cage asynchronous motor in operation. According to the current, it can be checked whether the motor is working properly to ensure safe operation of the motor and prolong its service life.
8. When measuring, it can be measured once per phase or once in three phases. At this time, the number on the table should be zero, (because the phase current of the three-phase current is zero), when there are two phase lines in the jaw, the table The value of the current value of the third phase is displayed. By measuring the current of each phase, it can be judged whether the motor has an overload phenomenon (the measured current exceeds the rated current value), and the motor is internally or (other devices that can be converted into electric energy are called power sources) Is there a problem with the Power Supply voltage, that is, whether the three-phase current imbalance exceeds the limit of 10%.
Third, the analysis of the current principle of the clamp meter
The clamp meter consists essentially of a current transformer, a clamp wrench and a rectifying magnetoelectric system with a reaction force meter.
The clamp meter works like a transformer. The primary coil is the wire that passes through the clamp core, which is equivalent to the primary coil of a 1-turn transformer, which is a step-up transformer. The secondary coil and the ammeter for measurement constitute a secondary circuit. When the wire has an alternating current, it is that the coil generates an alternating magnetic field, and an induced current is generated in the secondary circuit. The magnitude of the current and the ratio of the primary current are equivalent to the inverse of the number of turns of the primary and secondary coils. . Clamp-type ammeters are used to measure large currents. If the current is not large enough, you can increase the number of turns of the primary wire through the clamp meter and divide the measured current by the number of turns.
The secondary winding of the through-current current transformer of the clamp ammeter is wound around the iron core and connected to the alternating current ammeter, and its primary winding is the conductor to be tested passing through the center of the transformer. The knob is actually a range selection switch. The function of the wrench is to open and close the movable part of the core of the core transformer so that it can be clamped into the wire under test.
When measuring the current, press the wrench to open the jaws, and place the measured current carrying wire in the middle of the through-current current transformer. When there is alternating current in the tested wire, the magnetic flux of the alternating current is in the transformer pair. A current is induced in the side winding, which passes through the coil of the electromagnetic ammeter, deflecting the pointer, and indicating the measured current value on the dial scale.
After placing the wire to be tested into the window through the iron button, it should be noted that the two faces of the jaw have a good fit, and the other objects cannot be placed in the middle; the minimum range of the clamp meter is 5A, and the error is displayed when measuring a small current. Will be bigger. This is the result of measuring the energized wire around the clamp meter for a few weeks and dividing the resulting reading by the number of turns.
How does the clamp meter measure current? -----Precautions for the use of clamp meter
The clamp ammeter is divided into two types: high and low voltage, which are used to directly measure the current in the line without breaking the line. Its use is as follows:
(1) When using a high voltage clamp meter, pay attention to the voltage level of the clamp ammeter. It is strictly forbidden to measure the current of the high voltage circuit with a low voltage clamp meter. When measuring with a high-pressure clamp meter, it should be operated by two people. The non-on-duty personnel should also fill in the second work ticket. Wear insulated gloves when standing, and stand on the insulation mat. Do not touch other equipment to prevent short circuit or grounding.
(2) Observe the timing of the watch. Pay special attention to keep the safety distance between the head and the live part. The distance between any part of the human body and the charged body shall not be less than the entire length of the clamp meter.
(3) When measuring on a high voltage circuit, it is forbidden to use a wire to measure from the clamp ammeter. When measuring the current of each phase of the high-voltage cable, the distance between the cable head lines should be above 300mm, and the insulation is good. It can be considered when the measurement is convenient.
(4) When measuring the low-voltage fuse fuse or horizontally arranging the low-voltage bus current, the fuse fuses or busbars of each phase should be protected and insulated by the insulating material before the measurement to avoid phase-to-phase short circuit.
(5) When the cable has a phase connection, measurement is strictly prohibited. Preventing the breakdown of the ground due to the low insulation level of the cable head and endangering personal safety.
(6) After the measurement of the clamp ammeter is completed, pull the switch to the maximum range to avoid accidental overcurrent during the next use; it should be stored in a dry room.
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