Principle and difference of detecting current between multimeter and clamp meter
Main functions and working principle of clamp watch
The most prominent feature of the clamp meter is the clamp with an opening in the front, which can be easily clamped into the wire to measure the current in the loop, so that it is not necessary to destroy or change the original line and can measure a large current. Multimeter also has the function of measuring current, so what's the difference between it and clamp meter? First of all, let's understand the principle and difference between multimeter and clamp meter respectively.
Principle of measuring current with clamp meter
The working principle of the clamp meter for measuring current is basically the same as that of the universal pen. The difference is that the clamp meter does not directly detect the voltage on the shunt resistor, but uses a current transformer. Transformer is actually an application of transformer, which can transform the current according to a certain proportion. After the current transformer is connected to the load, its primary is equivalent to one turn, and the secondary is more turns inside the clamp meter, so the current is reduced according to a certain proportion, so the current transformer is equivalent to a step-up transformer. The circuit inside the clamp meter can calculate the measured current by detecting the voltage on the secondary side of the transformer.
Therefore, compared with the multimeter, the clamp meter does not need to change the circuit when measuring current, and can measure larger current, such as the current of inductive loads such as motors. However, because the current transformer is used in the clamp meter, according to the working principle of the transformer, it can't pass DC. So the clamp meter really can't measure DC current? In fact, the clamp meter can measure DC current, but it doesn't use a current transformer.
Principle of measuring DC current with clamp meter
Because DC can't produce the change of magnetic flux, the clamp meter can't measure DC current if it uses current transformer. A transformer is used to measure AC current, which is called electromagnetic transformer, while a clamp meter for measuring DC current uses another sensor-Hall sensor.
The principle of measuring DC current with Hall sensor is that when current flows through a wire, it will generate a magnetic field (similar to an electromagnet), and this magnetic field is proportional to the current. The clamp of the clamp-on meter collects the magnetic field generated by the wire, which is detected by the Hall element located in the clamp. The Hall element is a magnetic sensitive element, which converts the magnetic field into a voltage signal and outputs it. This voltage signal can be amplified by the circuit to show the current of the load. Nowadays, many clamp meters are AC and DC dual-purpose, including electromagnetic transformers and Hall sensors to detect AC and DC currents respectively.
