Device for measuring the impedance of sensors with a double-feedback phase locked loop

摘要

In inductive, capacitive and resistive sensors, the signals are usually evaluated by analog means with resonant LC circuits, measuring bridges or by 4-conductor measuring techniques. A frequency-analogous signal evaluation with a double-feedback phase locked loop (PLL), a measuring phase shifter being arranged as low-pass or high-pass filter with the sensor component in one feedback line, offers significant advantages compared with the usual methods. On the one hand, the sensitivity is much higher and, on the other hand, digitisation of the phase locked loop is possible, with the exception of the measuring phase shifter, so that the output signal can be present both in analog form and digitally in series or parallel form.