A temperature compensated linear inductive distance sensor assisted by added noise is demonstrated. The mixed signal processing algorithm performs an effective interpolation over a low-resolution two-dimensional calibration table addressed directly by the digitized noise-affected signals of distance and temperature sensing modules without further arithmetic operations. The table entries are directly passed to the output digital-to-analog converter. The output noise will be cancelled by the intrinsic low-pass behavior of the power output stage. The operation distance, the linearity parameters, as well as the performance of the sensor exceed the standard of the respective industrial products.

Purpose - The purpose of this paper is to study the optimization of a pulsed-excitation gradiometric inductive sensing system. Design/methodology/approach - The authors applied numerical finite-element modeling for the simulation of the step responses of different target materials to identify the particular contribution of the magnetic permeability and the electric conductivity. Four materials of technical importance (aluminum, copper, constructional steel and stainless steel) and four fictive test materials were modeled for the comparison of different materials possessing a wide range of combinations of material parameters. A microcontroller-based measurement setup was implemented for the qualitative validation of the simulation results. A simple signal processing chain was also applied for the time-domain conversion of the direct step response signals to increase the time scale of the signals to be processed by common mixed-signal components. Findings - The step response signals contain relevant information of the target material quality and the sensor-to-target distance. The target materials can be distinguished and the sensor-target distance can be determined by the evaluation of the step response signals with an appropriate algorithm based on the measurement of the time and voltage of an extreme of the time dependent measurement signals. Both direct and time-domain converted signals can be used for material independent proximity sensing. Originality/value - In order to design an inductive proximity switch, an evaluation method of the response signals has been proposed by using an analog RLC circuit. With the presented method, a target material invariant inductive proximity switch can be realized.