The functional principle of a clamp meter and the difference between a multimeter
The main functions and working principles of clamp watches
The most prominent feature of a clamp type meter is the clamp that can be opened in the front, which can be easily inserted into the wire to measure the current in the circuit, so that there is no need to damage or modify the original circuit, and it can measure a large amount of current. A multimeter also has a current measurement function, so what is the difference between it and a clamp meter for measuring current? Firstly, let's understand the principles and differences between a multimeter detecting current and a clamp meter detecting current.
When measuring current with a multimeter, it is necessary to disconnect the measured circuit and connect the multimeter in series to measure the current. Through the internal current detection circuit of the multimeter, it can be seen that the current level inside the multimeter is actually a resistor with a very small resistance value. When current flows through this resistor, a voltage drop will occur on it because the resistance value is determined. As long as the voltage on the resistor is measured, the current passing through the resistor can be calculated according to the formula, because this resistor is connected in series in the circuit, So the current flowing through it is the current of the measured circuit.
So the current measurement circuit in the multimeter includes many current measurement circuits in the instrument, which are measured by converting current into voltage through resistance shunt. There are also requirements for selecting the resistance value of this resistor. If the resistance value is too large, the voltage drop generated when the current passes through the resistor will be large. On the one hand, this will distribute more voltage, affecting the normal operation of the measuring load. On the other hand, the larger the resistance value, the greater the power consumption generated on it at the same current, which will cause the resistor to heat up. Therefore, considering these two issues, the smaller the resistance value, the better.
However, the resistance value should not be too small. If the resistance is too small, the voltage drop generated when the current flows through will be smaller. This requires certain requirements for the subsequent measurement circuit, as low voltage needs to be amplified before it can be detected by the circuit.
Disadvantages of measuring current with a multimeter
From the method and principle of detecting current with a multimeter, it can be seen that when measuring current, it is necessary to connect the multimeter in series in the circuit being tested. This is not suitable in some circuits that cannot be powered off for measurement. Another point is the measurement range of the multimeter's current, usually the maximum measurement range of the multimeter's current is 10A or 20A. In order to prevent the internal current detection resistor from heating up, the multimeter is also not allowed to measure large currents for a long time, For measuring even larger currents, it is not easy to achieve with a typical multimeter.
The principle of measuring current with a clamp meter
The working principle of a clamp meter for measuring current is essentially the same as that of a multimeter for measuring current. The difference is that the clamp meter does not directly detect the voltage on the shunt resistor, but rather 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 stage is equivalent to one turn, and the secondary stage has more turns inside the clamp meter, which reduces the current in a certain proportion. Therefore, the current transformer is also 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.
So compared to a multimeter, a clamp meter does not need to change the circuit when measuring current, and can measure larger currents, such as the current of inductive loads such as motors. However, due to the use of a current transformer inside the clamp meter, according to the working principle of the transformer, it cannot pass through direct current. So can't a clamp meter really measure DC current? In fact, a clamp meter can measure DC current, but it does not use a current transformer.
Principle of measuring DC current with a clamp meter
Due to the inability of direct current to produce changes in magnetic flux, a clamp meter cannot measure direct current using a current transformer. The use of a transformer to measure AC current is called an electromagnetic transformer, while the clamp meter for measuring DC current uses another type of sensor - Hall sensor.
The principle of using a Hall sensor to measure DC current is that when the current flows through a wire, a magnetic field (similar to an electromagnet) is generated, and this magnetic field is proportional to the magnitude of the current. The clamp of the clamp type meter gathers the magnetic field generated by the wires and is detected by a Hall element located inside the clamp. The Hall element is a magnetic sensing element that converts the magnetic field into a voltage signal for output. This voltage signal is amplified by the circuit to display the current of the load. Many clamp shaped meters nowadays use both AC and DC, including electromagnetic transformers and Hall sensors to detect AC and DC currents.
The difference between a clamp meter and a multimeter
As mentioned above, the main function of a clamp meter is to detect current. Compared to a multimeter, a clamp meter is more convenient to use and has a much larger measurement range. However, one thing is that when measuring small currents (such as a few hundred milliamperes), a clamp meter cannot display it normally, and its measurement accuracy is not as good as a multimeter.
The second difference is that because the main function of a clamp meter is to detect current, it is not as good as a multimeter in other functions. Although many clamp meters now integrate many functions of a multimeter, such as voltage measurement, resistance measurement, frequency measurement, temperature measurement, and so on, overall, these functions other than current measurement cannot be compared to a multimeter, and the accuracy of these measurement gears is generally lower than that of a multimeter.
In summary, the focus and usage environment of clamp meters and multimeters are different. If the focus is on measuring current, especially high current, clamp meters are preferred; If it is used for measuring voltage resistance or electronic component parameters in daily use and has certain requirements for measurement accuracy, a multimeter needs to be selected. So these two types of instruments can be selected based on actual needs or simultaneously according to the usage environment.
