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How Do Digital Calipers Work?
The addition of a digital display to Vernier calipers makes reading measurements easier and more convenient. It uses capacitive plates that send impulses to a digital counter when you move the caliper jaws back and forth.
Digital calipers have a thin strip of etched circuit board material glued along the main body of the instrument, called the stator. The circuit board carries a linear electrode array that alters signals given off by another array on the slider.
Inside the slider, another electrode array faces the one on the stator, but does not physically touch it. Two sets of electrodes make up the slider array, one that carries a sine signal and another carrying a cosine signal.
Electronics in the slider produce a 100kHz signal in the sine and cosine electrode arrays. The stator electrodes interfere with the sine and cosine signals. A pair of detectors in the slider pick up the altered signal and produce accurate position and direction information.
A computer decodes the position and direction information into relative movement readings. It converts position into either millimeters or inches and displays the result.
Chicago native John Papiewski has a physics degree and has been writing since 1991. He has contributed to "Foresight Update," a nanotechnology newsletter from the Foresight Institute. He also contributed to the book, "Nanotechnology: Molecular Speculations on Global Abundance."