Dynamic measuring of inductivity changes by adaptive controlling and lock-in technique

Magnetic materials in combination with a coil for signal establishment are often used as sensor elements. The assessment of inductivity changes δL of the coil inductivity L=L₀-δL with high dynamics and high resolution is an important issue. Here L₀ represents the constant base level of L while δL results from the changing physical parameter to be measured. Especially, a wide operation range of L and δL is of high interest in order to apply different coils, cores and sensor elements without any manual adjustment. The above problems are effectively addressed within the here introduced compact procedure. The output of the procedure is proportional to δL and does not depend on the amplitude of the excitation current. For almost all practical cases, the output signal also does not depend on the excitation frequency and the resistance of the coil as far as resonances do not arise. The offset due to L₀ is automatically eliminated. The concept is very attractive for magnetic sensor applications since no manual adjustment is necessary for different coils and cores due to wide range of L in order to achieve the maximum sensitivity in signal establishment.