How the clamp meter works and how multimeters differ
The most prominent feature of the clamp meter is the caliper that can be opened in the front, which can be easily stuck into the wires to measure the current in the circuit, so that the original line does not need to be destroyed or altered, and it can measure a very large current. Multimeter also has a current measurement function, so what is the difference between it and the clamp meter current measurement? First of all, let's respectively understand the principle and difference between the multimeter detecting current and clamp meter detecting current.
When the multimeter measures current, it is necessary to disconnect the circuit under test and connect the multimeter in series to measure the current. Through the multimeter internal current detection circuit can be seen, the current gear in the multimeter is actually a very small resistance, the current flows through this resistance, it will produce a voltage drop on it, because the resistance value is determined, as long as the measurement of the voltage on the resistor, you can calculate the current through the resistor according to the formula, because the resistor is connected in series in the circuit, so the current flowing through it is the current of the circuit being measured.
So the current measurement circuit in the multimeter, including the current measurement circuits in many meters, is to convert the current into voltage by means of a resistor shunt to measure the current. The selection of this resistor resistance value is also required, if the resistance value is too large, the current through the resistor when the voltage drop is large, so on the one hand, it will be divided into more voltage, affecting the normal operation of the measurement load, on the other hand, the larger the resistor value, the same current, the same current, the power consumption generated on it is also the larger, which will make the resistor heat, so from the consideration of the two problems, the smaller the resistor is the better.
Disadvantages of measuring current with a multimeter
From the multimeter current detection methods and principles can be seen, the measurement of current needs to be connected in series with the multimeter in the circuit being measured, so that in some of the circuits that can not be powered off the measurement is not appropriate, another point is the measurement range of the multimeter current, usually the maximum range of the multimeter current is generally 10A or 20A, and in order to prevent the internal current detecting resistor heating, the multimeter is not allowed to measure large currents for a long time, for even larger currents, the resistance value is better. In order to prevent the internal current detecting resistor from heating up, the multimeter is not allowed to measure large current for a long time, and it is not easy to realise the measurement of large current with the general multimeter.
Principle of Clamp Meter Current Measurement
Clamp meter current measurement principle and the principle of universal pen current measurement is actually basically the same, the difference is that the clamp meter is not directly detect the voltage on the shunt resistance, but the use of current transformers. The transformer is actually an application of the transformer, which transforms the current in a certain proportion. After the current transformer into the load, its primary is equivalent to a turn, the secondary is also the number of turns inside the clamp meter is more, so the current in accordance with a certain proportion of smaller, so the current transformer is also equivalent to a step-up transformer, the clamp meter internal circuit by detecting the voltage on the secondary side of the transformer, you can calculate the measured current.
The difference between a clamp meter and a multimeter
As mentioned above, the main function of the clamp meter is used to detect the current, compared to the multimeter, the clamp meter to detect the current in the use of more convenient, the range of measurement is also much larger than the multimeter, but there is a point, the clamp meter in the measurement of smaller currents can not be displayed properly (such as hundreds of milliamps of small current), and in the measurement of the accuracy is not as good as the multimeter.
