The principle of AC current clamp

　　The principle of AC current clamp

AC current clamp can be regarded as a derivative application of current transformer. The working principle of the transformer is to wind two coils on both sides of an iron core (as shown in Figure 1). When current I1 passes through coil C1, coil C2 produces current I2. The relationship between the number of coil turns and current is: N1*I1=N2*I2. Where N1 and N2 represent the number of coil turns.

So I2=N1*I1/N2 or I1=N2*I2/N1

The principle of the current clamp is the same (shown in Figure 2). The B2 coil is installed on the “iron core” of magnetic material that is hinged together, and then clamped on the conductor of the current I1. At this time, the measured conductor clamped is equivalent to the primary coil B1 of the current transformer. The coil B2 clamped on the conductor will induce a secondary current:

I2 (current clamp output) = N1/N2*I1, where N1=1, the formula can also be written as: I2=I1/N2 (number of turns of the current clamp coil). Since the measurement current is too large for the meter to withstand, and it is impossible to break the measurement loop, it is usually difficult to obtain the measurement results of I1 directly and simply. To provide an effective output, a certain number of coils are wound around the current clamp itself.

If N2 is 1000 turns, then the transformation ratio is 1000:1, or expressed as 1mA/A (each 1mA current represents 1A measurement current). In addition, there are 500:5, 2000:2, 3000:1, 3000:5, etc. to choose from.

Current clamps and multimeters are often used together. A 1000:1 current clamp (model: C100) outputs a measured value of 1mA/A, and the current passing through the current clamp will be output according to a certain ratio.

Connect the current clamp to the digital multimeter and set the AC range control output. At this time, the measured current size is the multiplication number multiplied by the transformation ratio. (For example: a value of 150mA read on the multimeter means that 150mA*1000=150A flows through the conductor under test).

In addition, the current clamp can also be used with equipment that has input impedance requirements to measure current. (shown in Figure 3)

The current clamp can also output AC/DC voltage to adapt to the current measurement requirements of instruments that only respond to the voltage range (such as recorders, oscilloscopes, etc.). (as the picture shows)

The voltage can be obtained by adjusting the output of the current clamp (for example: Y4N, MINI09, etc.). The output voltage is proportional to the measured current.