Working principal of the ZEROTRONIC sensor

The pendulum, suspended by three Archimedes helical springs, is mounted between two electrodes. Depending on the inclined position of the system, the pendulum will swing out of the zero-position and by that, change the capacity between the pendulum and the two electrodes.

These capacities will be transformed into different frequencies through the RC-oscillator. The ratio of the two frequencies available will be used as the primary signal for detecting the required angle.
 

The sensor cell is completely encapsulated and filled with nitrogen. Humidity changes therefore have no influence on the measurement. The nitrogen serves also as a damping media between the electrodes.

CALIBRATION OF DIGITAL SYSTEMS

For the calibration of the sensors an improvement of quality over other existing systems was reached by using a specific mathematical process, interpolation by “spline function“. With this function mechanical as well as electronic deviations may be compensated. The calibration data are stored in the sensor.

The temperature stability can be substantially increased by calibrating the sensor at various different temperatures. The actual temperature is detected in the sensor head and the correct angular value is computed by interpolation between the closest corresponding calibration curves.

Depending on the switched-on electrode and the resulting capacity, one RC-Oscillator is supplying the required frequency between 350‘000 and 500‘000 Hz. Because of the alternating engagement of both of the electrodes through a selector switch and always using one oscillator only, it is assured that the temperature influence is limited to a minimum. This configuration has proved to be superior in terms of long-term stability over other existing applications. The short distances between the electrodes and the oscillator and the stable connections between the critical electronic elements, further improve the system‘s capability.

The frequency difference of approx. 100‘000 Hz assures that, even when a high measuring rate is applied (numbers of measurements per second), an excellent resolution is available. Most of the existing measuring instruments have an output rate of ± 2 Volts. This output rate is equal to a possible ± 2000 digits. Certainly not enough for accurate measurements of large angles.

The implemented calibration curve, stored in the sensor’s head, allows easy calibrating and leads to excellent results even when using large angles.