Conductive Inclination Sensor
Original article date: May 1996
Whether it be in the fields of measurement technology, precision tools, plant machinery or control, often the most important thing is to monitor horizontal measurements or measure angles. So many engineers have a need to measure angles of inclination with absolute accuracy.
Conductive inclination sensors are based on the idea that, when electrodes are mounted in a planar position on a substrate, one of the factors influencing the measurement of the electrolytic conductivity of a fluid is the height of the surface of the liquid above the electrodes.
Electrodes are mounted parallel to the axis of the tilt of the sensor on the bottom of an electrolyte chamber, which is partially filled with an electrically conductive liquid. When an alternating voltage is passed between two electrodes, a current flows through the liquid in the form of a stray (dispersed) field.
By tilting the sensor – and thereby reducing the level of the liquid – it is possible to confine this stray fields and, given a constant specific conductivity of the electrolyte, a resistance is formed which is a function of the liquid level.
With the pairs of electrodes arranged to the left and right at the bottom of the sensor cell with respect to the axis of tilt, an angle of inclination can be derived.
The particular advantage of this recently-patented measurement technique is that, by virtue of positioning all the electrodes on a level plane, the measurement of inclination does not depend on the different degrees of wetness of the electrodes, but is a function solely of the volume. The influence of temperature can be eliminated, making it unnecessary to measure the ambient temperature.
The technique is extremely accurate and is reproducible. Modern production methods are used to manufacture the cells. Planar microstructuring techniques produce extremely precise platinum electrode geometries and this contributes to the reliability of the data. The compact, heavy-duty measuring cells are manufactured to IP65 protection. A ceramic housing for the electrolyte is hermetically sealed by a glass-solder connection, guaranteeing a seal which is proof to gas and moisture.
The system, which is manufactured by FRABA Sensorsysteme has a CAN-Bus Interface. Both CAN specifications (standard 11 bit and extended 29 bit) are supported. A 16-bit data and address bus between CAN and microcontroller provides a very fast data transfer, so that the encoder position is available for the CAN-Bus within 10aes. A flash EPROM means that software can be customised for individual applications and that the data is stored permanently in non-volatile form. The angular encoder can send or receive 15 parameters with different identifiers.
- Litton Precision Industries
- Tel: 016284 486060
- Fax: 016284 472438
- Contact: Bill Pearce
May 1996