Detecting the impedance and impedance of the coil normalized
1. Detect the impedance of the coil
Set the self-impedance of the detection coil (primary coil) with alternating current to ignore the capacitive reactance.
When the primary coil and the secondary coil (the object to be inspected) are coupled to each other, an induced current is generated in the closed secondary coil due to the mutual inductance, which in turn affects the voltage and current in the primary coil. This effect can be reflected by the impedance of the secondary coil reflected by the mutual inductance M to the folded impedance of the primary coil circuit.
The sum of the folded impedance of the secondary coil and the impedance of the primary coil itself is called the apparent impedance Zs of the primary coil.
Impedance normalization Although the impedance plan as shown is relatively straightforward, the position of the semicircular curve on the impedance plan is related to the impedance of the primary coil itself and the inductance and mutual inductance of the two coils themselves. In addition, the radius of the semicircle is not only affected by the above factors, but also varies with frequency. Thus, if an apparent impedance is to be made for the apparent impedance of each primary coil having a different impedance value, or for the apparent impedance of a primary coil having a different frequency, or the apparent impedance of a primary coil having a different coupling coefficient between the two coils, Many semicircular curves with different radii and different positions are obtained, which not only causes inconvenience to the drawing, but also makes it difficult to compare curves in different situations. In order to eliminate the influence of the primary coil impedance and the excitation frequency on the position of the curve, it is convenient to compare the curves in different cases, and the impedance is usually normalized.
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