page_title: Calipers
section_title: Digital caliper
hierarchical_section_title: Calipers / Types / Digital caliper
caption_attribution_description: Polski: Suwmiarka cyfrowa English: Digital caliper
context_page_description: A caliper is a device used to measure the distance between two opposite sides of an object. Many types of calipers permit reading out a measurement on a ruled scale, a dial, or a digital display. But a caliper can be as simple as a compass with inward or outward-facing points. The tips of the caliper are adjusted to fit across the points to be measured and then the caliper is then removed and the distance read by measuring between the tips with a measuring tool, such as a ruler.
  It is used in many fields such as mechanical engineering, metalworking, forestry, woodworking, science and medicine.
context_section_description: A popular refinement replaces the analog dial with an electronic digital display that displays the reading as a numeric value. Rather than a rack and pinion, these calipers use a linear encoder. Some digital calipers can be switched between centimeters or millimeters, and inches. All provide for zeroing the display at any point along the slide, allowing the same sort of differential measurements as with the dial caliper. Digital calipers may contain a "reading hold" feature, allowing the reading of dimensions after use in awkward locations where the display cannot be seen.
  Ordinary 6-in/150-mm digital calipers are made of stainless steel, have a rated accuracy of 0.001 in (0.02mm) and a resolution of 0.0005 in (0.01 mm).
  The same technology is used to make longer 8-in and 12-in calipers; the accuracy for longer measurements declines to 0.001 in (0.03 mm) for 100–200 mm and 0.0015 in (0.04 mm) for 200–300 mm.
  Increasingly, digital calipers offer a serial data output to allow them to be interfaced with a dedicated recorder or a personal computer. The digital interface significantly decreases the time to make and record a series of measurements, and it also improves the reliability of the records. A suitable device to convert the serial data output to common computer interfaces such as RS-232, Universal Serial Bus, or wireless can be built or purchased.  With such a converter, measurements can be directly entered into a spreadsheet, a statistical process control program, or similar software.
  The serial digital output varies among manufacturers.  Common options are
  Mitutoyo's Digimatic interface. This is the dominant name brand interface. Format is 52 bits arranged as 13 nibbles.
  Sylvac interface. This is the common protocol for inexpensive, non-name brand, calipers.  Format is 24 bit 90 kHz synchronous.
  Starrett
  Brown & Sharpe
  Federal
  Tesa
  Aldi. Format is 7 BCD digits.
  Mahr (Digimatic, RS232C, Wireless FM Radio, Infrared and USB)
  Like dial calipers, the slide of a digital caliper can usually be locked using a lever or thumb-screw.
  Some digital calipers contain a capacitive linear encoder. A pattern of bars is etched directly on the printed circuit board in the slider. Under the scale of the caliper another printed circuit board also contains an etched pattern of lines. The combination of these printed circuit boards forms two variable capacitors. The two capacitances are out of phase. As the slider moves the capacitance changes in a linear fashion and in a repeating pattern. The circuitry built into the slider counts the bars as the slider moves and does a linear interpolation based on the magnitudes of the capacitors to find the precise position of the slider. Other digital calipers contain an inductive linear encoder, which allows robust performance in the presence of contamination such as coolants. Magnetic linear encoders are used in yet other digital calipers.
caption: Digital caliper
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