Digital calipers contain Grid-Capacitance Linear Synchronous Sensors which are comprised of a set of grid-capacitances and signal processing circuit.The set of grid-capacitances consist of stator grid-capacitance and sliding grid-capacitance. A pattern of grids is etched directly on the top copper layer of a standard glass-epoxy laminate of the printed circuit board stator. In the slider another printed circuit board contains 48 etched separate grids which are called emitters. The combination of these printed circuit boards forms two variable Capacitors. As the slider moves the capacitance changes in a linear fashion and in a repeating pattern. The two capacitances are out of phase. The signal processing circuit built into the slider counts the grids as the slider moves and does a linear interpolation based on the magnitudes of the capacitors to find the precise position of the slider.
|
