Linear Position Sensing through Conductive Wall without Permanent Magnet

A linear position sensor for pneumatic actuators is presented. Position of the piston rod made of ferromagnetic material is detected by low frequency magnetic field which penetrates the aluminum wall of the cylinder. The sensor consists of an array of integrated fluxgate sensors and two excitation saddle coils mounted outside the actuator. The method does not need a permanent magnet attached to the piston as required by common magnetic position sensors

Improved 3-Phase Current Transducer

We propose improved contactless DC/AC current transducer for 3-phase current lines based on 8 integrated fluxgate sensors. Using proper processing we ideally achieve a complete suppression of external homogeneous fields, and field gradients up to the 4th order. The sensitivity to external currents (crosstalk) is improved 15-times compared to [1]. The usage of micro fluxgate sensors instead of magnetoresistive sensors improves the temperature stability: the sensitivity temperature coefficient was reduced from 0.3%/K to 50 ppm/K and offset drift was reduced from 50 mA/K to 1 mA/K

Inductance position sensor for pneumatic cylinder

The position of the piston in pneumatic cylinder with aluminum wall can be measured by external inductance sensor without modifications of the aluminum piston and massive iron piston rod. For frequencies below 20 Hz the inductance is increasing with inserting rod due to the rod permeability. This mode has disadvantage of slow response to piston movement and also high temperature sensitivity. At the frequency of 45 Hz the inductance is position independent, as the permeability effect is compensated by the eddy current effect. At higher frequencies eddy current effects in the rod prevail, the inductance is decreasing with inserting rod. In this mode the sensitivity is smaller but the sensor response is fast and temperature stability is better. We show that FEM simulation of this sensor using measured material properties gives accurate results, which is important for the sensor optimization such as designing the winding geometry for the best linearity