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Calipers

A caliper is a device used to measure the distance between two opposite sides of an object. 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

In this instrument, a small, precise rack and pinion drives a pointer on a circular dial, allowing direct reading without the need to read a vernier scale. Typically, the pointer rotates once every inch, tenth of an inch, or 1 millimeter. This measurement must be added to the coarse whole inches or centimeters read from the slide. The dial is usually arranged to be rotatable beneath the pointer, allowing for “differential” measurements (the measuring of the difference in size between two objects, or the setting of the dial using a master object and subsequently being able to read directly the plus-or-minus variance in size of subsequent objects relative to the master object).

A refinement now popular is the replacement of the analog dial with an electronic digital display on which the reading is displayed as a single value. Rather than a rack and pinion, they have 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.

Vernier caliper

Parts of a vernier caliper:

  1. Outside large jaws: used to measure external diameter or width of an object
  2. Inside small jaws: used to measure internal diameter of an object
  3. Depth probe: used to measure depths of an object or a hole
  4. Main scale: scale marked every mm
  5. Main scale: scale marked in inches and fractions
  6. Vernier scale gives interpolated measurements to 0.1 mm or better
  7. Vernier scale gives interpolated measurements in fractions of an inch
  8. Retainer: used to block movable part to allow the easy transferring of a measurement

The vernier, dial, and digital calipers give a direct reading of the distance measured with high accuracy and precision. They are functionally identical, with different ways of reading the result. These calipers comprise a calibrated scale with a fixed jaw, and another jaw, with a pointer, that slides along the scale. The distance between the jaws is then read in different ways for the three types.

The simplest method is to read the position of the pointer directly on the scale. When the pointer is between two markings, the user can mentally interpolate to improve the precision of the reading. This would be a simple calibrated caliper; but the addition of a vernier scale allows more accurate interpolation, and is the universal practice; this is the vernier caliper.

 

Calibration Standard

Thermo-Temp inc. will calibrate all equipment to meet customer requirements and national standards.