What is Projected Capacitance Technology ?
Projected Capacitance Technology is a method of detecting an object at a distance ( proximity sensing ) , either though air, or through
other slightly conductive, or non-conductive materials.
The object to be detected, may be conductive, such as a metal, or non-conductive, such as a person.
It is often used
to detect a finger operating a touchscreen or keypad, through thick glass.
The technology is very similar to capacitive technology but with three major differences:
1) More than one capacitance measurement is
Only changes in capacitace are
used. Absolute values may effectively be ignored.
relatively high degree of data manipulation may be used to compare, and
discriminate between, these different capacitance measurements.
This enables a technology, that is readily influenced by a multitude of environmental variables, to be used to
accurately detect much smaller changes in one selected variable, such as
proximity of a finger.
How do these three factors enable
Projected Capacitance to work so well ?
Many factors, such as ambient
temperature and humidity, affect all capacitance sensing elements in a
A person standing close to the keypad will affect its
capacitance, as will a passing bus. These effects, however, will be
A finger, on the other hand, affects
one key more than it affects others.
The touch action of a finger also
has a certain profile - touch happens within a few seconds, and will usually be
gone after a few more seconds.
Environmental effects usually happen more
slowly and affect more than one key.
Parts of a keypad/touchscreen may change with time by
natural ageing processes, or through external factors, such as damage, or dirt
These changes will greatly alter the
capacitance environment, either globally, or
Projected Capacitance, continually tracks
By taking all these
variables into account,
it is possible for a finger to be detected with great sensitivity
and accuracy, over very long periods of time , with no false triggering
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