Circuit analysis of current probe

The current probe is a magnetic ring designed according to Faraday principle , It is used to measure the interference current signal in the conductor . The current probe can be used to measure the current flowing through the wire . The current probe is divided into AC/DC Current probe and AC Current probe . The former can measure the magnitude of DC and AC current , The latter can only measure the magnitude of AC current

In order to analyze the working principle of the current probe , According to the figure 1 Extract the equivalent circuit model of the current probe （ Pictured 3 Shown ）：M It refers to the mutual inductance between the current probe and the measured conductor ;L1 It refers to the self inductance of the measured wire passing through the current probe ;L Self inductance for winding current probe ;C Is the distributed capacitance ;r Is the winding resistance ;R Is the internal resistance of the instrument （ It's usually 50Ω）;V0 Is the output voltage ;Z Is the total resistance in the dotted line .

Slave mode （5） It can be seen that ,Zt And M,L,C,r, Have a relationship , It is difficult to draw a conclusion from the formula alone , Therefore, it is difficult to guide the design of current probe .

In order to analyze the influencing factors of transmission impedance more simply , Ignore distributed capacitance , Winding resistance , At this time, a low-pass filter is formed . Assuming that the amplitude of the primary current is constant, scan according to the frequency , Then the mutual inductance voltage shall be as per 20dB Increase every ten times the frequency , Pictured 4 The curve of Ⅰ Shown . At low frequencies , Self feeling L The inductive resistance is very small , As the frequency increases , The inductive reactance increases gradually , When frequency point f0 When the inductive reactance is equal to the load impedance , The voltage drop caused by inductive reactance also begins to press 20dB Increase every ten times the frequency , Pictured 4 The curve of Ⅲ Shown . The whole synthetic voltage is like a curve Ⅱ Shown .

From the picture 4 The curve of Ⅱ It can be seen that , Past the frequency point f0 after , The output voltage becomes flat , It is an ideal working area for current probe . Within this operating frequency range , Transmission impedance Zt Is a constant .