Capacitive encoder technology

The capacitive encoder technology has over the last 20 years been applied in many Millions of Digital calipers and other instruments for dimensional measurements. It can be used in a multitude of other applications where it offers many advantages:
  • The capacitive sensor elements are very simple and inexpensive
  • The sensor elements can easily be tailored to different resolution and measuring range.
  • The sensor can be made very thin if necessary, to fit into tight spaces.
  • Sensors can be mass fabricated at very low cost using common manufacturing processes.

Example encoder patterns

PCB

Technology

The capacitive encoder utilizes the capacitive coupling between electrode pattern on two elements, that are facing each other over a small gap. One of the elements contains the transmitter pattern composed of several phases cyclically repeating with a period (wavelength) of typical1y 1 – 5 mm (linear encoder). The other element contains receiver electrodes for (+) and (-) signals to the differential receiver in the electronic unit.

The electronic unit calculates position within each wavelength from the signals received. In applications that utilize only one wavelength the ABSOLUTE position is thus determined. For applications that are utilizing a longer range, the wavelengths are accumulated for essentially incremental measurement, but it is also possible to build a long ABSOLUTE system by using dual scale with two wavelengths with an algorithm for combining the outputs from the two wavelengths.

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