Introduction to the use of current clamps

　　Introduction to the use of current clamps

An ammeter is an instrument used to measure the current in AC and DC circuits. In the circuit diagram, the symbol for the ammeter is “circle A”. The current value is in “A” or “A” as the standard unit.

The ammeter is made based on the effect of the magnetic field force on the energized conductor in the magnetic field. There is a permanent magnet inside the ammeter, which generates a magnetic field between the poles. There is a coil in the magnetic field. There is a hairspring spring at both ends of the coil. Each spring is connected to a terminal of the ammeter. A rotating shaft is connected between the spring and the coil. The rotating shaft is opposite. On the front end of the ammeter, there is a pointer. When there is current passing through, the current passes through the magnetic field along the spring and the rotating shaft, and the current cuts the magnetic induction lines, so the coil is deflected by the force of the magnetic field, which drives the rotating shaft and pointer to deflect. Since the magnitude of the magnetic field force increases with the increase of the current, the magnitude of the current can be observed through the deflection of the pointer. This is called a magnetoelectric ammeter.

Clamp-type ammeter is a type of ammeter, used to measure the current value in a circuit, referred to as current clamp.

In electrical and electronic engineering, a current clamp (or current probe) has two openable clamp-type probes that are used to clamp electrical conductors around electrical equipment without the need for the probes to come into contact with conductive parts of the equipment, that is, without disconnection Device wires are used for probe insertion to measure the properties of electrical current in a conductor. Current clamps are commonly used to measure sine wave current (alternating current (AC)). With more advanced testing instruments, phase and waveform can also be tested. Generally speaking, very high AC current (above 1000A) is easy to measure, while DC current and very low AC current (milliamp level) are difficult to measure accurately.

Usually when measuring current with an ordinary ammeter, the circuit needs to be cut off before the ammeter can be connected for measurement. This is very troublesome, and sometimes a normally operating motor does not allow this. At this time, it is much more convenient to use a clamp-type ammeter, which can measure the current without cutting off the circuit.

The conductor of the circuit under test passing through the iron core becomes the primary coil of the current transformer, in which the current is induced in the secondary coil. As a result, the ammeter connected to the secondary coil will have an indication to measure the current of the circuit under test. The clamp meter can be changed to different measuring ranges by turning the switch. However, power-on operation is not allowed when shifting gears.

Clamp meters generally have low accuracy, usually level 2.5 to level 5. For ease of use, the meter also has switches of different ranges to provide the functions of measuring current and voltage at different levels.