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.
- Low cost
interface chips, that are easy to use, are available from AnderMotion Technologies LLC
Example encoder
patterns (Each sensor has two parts)
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Linear 75 mm ABSOLUTE range.
Resolution 75 micron
 
|
|
Angular 8 deg.
|
Rotational 13
mm diameter
4 wavelengths/rev 
|
Wavelength 4
mm
Resolution 4 micron
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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. The other element contains receiver electrodes for
(+) and (-) signals to the differential receiver in the electronic unit. The
ratio of the different phase signals transmitted from the transmitter to the
receiver is a function of the relative position between the two elements.
·
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 a scale with two wavelengths plus a microprocessor
for combining the outputs from the two wavelengths.
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