Vernier Calipers are widely used in automotive industry for measurement of various parts. The old caliper looks like a tomahawk with the scale dawn its length. A measuring instrument consisting of an L-shaped frame with a linear scale along its longer arm and an L-shaped sliding attachment with a vernier, used to read directly the dimension of an object represented by the separation between the inner or outer edges of the two shorter arms. Likewise micrometer screw gauge, the Vernier Caliper is used to take the measurement that are accurate to within 0.001 of an inch or 0 .02 of a millimeter or in other words its used to make very accurate measurements which cannot be accurately measured from a meter scale. The Vernier Caliper is a precision instrument that can be used to measure internal and external diameters of small tubes, depth of given vessels, diameter of thick wires, etc. It has two scales, one is the vernier scale and the other is the main scale. The vernier scale is also called the sliding scale as it slides on the main scale, which is fixed.
The vernier scale on it is marked in both British Imperial and metric divisions. The length is read from the vernier scale. The movable scale on the vernier caliper is parallel to the fixed scale. The main scale of the caliper is divided into 10 parts, each equal to 0.100 inch. The area between the 0.100 marks is divided into four. Each of these divisions is equal to 0.025 inches. To read the caliper, locate the line on the main scale that lines up with the zero(0) on the vernier scale. If the zero lined up with the 1 on the main scale, the reading would be 0.100 inches. If the zero on the vernier scale does not line up exactly with a line on the main scale, then look for a line on the vernier scale that does line up with a line on the main scale.
Vernier caliper was invented in ancient China early as the Qin dynasty (9AD) as Calipers without vernier scale. The secondary scale, which contribute extra correctness, was invented in 1631 by French mathematician Pierre Vernier (1580-1637). Its use was described in detail in English in Navigatio Britannica (1750) by mathematician and historian John Barrow. While calipers are the most typical use of Vernier scales today, they were originally developed for angle-measuring instruments such as astronomical quadrants. It utilize two graduate scales: a main scale similar to that on a ruler and an especially graduate secondary scale, the vernier, that slides parallel to the main scale and enables readings to be made to a fraction of a division on the main scale.
Vernier calipers are widely used in scientific laboratories and in manufacturing for quality control measurements, and in automotive industry. In some languages the Vernier scale is called a nonius. It was also commonly called a nonius in English until the end of the 18th century. Nonius is the Latin name of the Portuguese astronomer and mathematician Pedro Nunes (1502-1578), who in 1542 invented a different system for taking fine angular measurements. Nunes' nonius was not widely adopted, being difficult to make and also difficult to read. Tycho Brahe used it on at least one instrument.
The name "vernier" was popularised by the French astronomer Jerome Lalande (1732-1807) through his Traited astronomie (1764).
In metrology, the least count of a measuring instrument is the smallest change in the measured quantity that can be resolved on the instrument's scale. A scale is a defining feature of any measuring instrument. Generally measurements are taken by placing an object on top of a scale and nothing the distance between the edges. In this case a larger number of divisions on the scale leads to a more accurate measurement and vice-versa. The technical term used to describe this parameter is known as least count, which is the smallest measurement which can be measured by a scale. Its value can be obtained by the division of one unit on the scale by the number of divisions that lies in between. The size of the smallest division on a scale. For the main scale on the common vernier caliper this is probably 0.1 cm. With the vernier scale the least count might be 0.002 cm. The scale on the larger, fixed portion of the caliper.
The correct determination of the least count of a vernier caliper is important for the measurement to be accurate, this is a common difficulty faced by the people, even engineers leads to incorrect readings while measuring heights, diameter, lengths, etc. Sometimes both metric and imperial units together on the scale may also cause confusion. The smallest measurement which can be recorded by the vernier caliper is defined as the least count. For the measurement first we need to determine the least count of the main scale which can be done as described previously. Then we need to count the number of division on vernier scale and divide the least count of the main scale by it. This will give us the least count of the vernier calipers.
The main scale is calibrated in millimeter. To get the least count of the main scale, count the number of divisions on the main scale in one cm of it. Divide 1cm into that much number of divisions, the value obtained is the least count of the main scale in cm. In most of vernier calipers, the vernier scale has 10 divisions. Count the number of divisions on the vernier scale. Use a magnifying glass if necessary.
Least count = Least count of main scale / Number of divisions on vernier scale
Least count = 0.01 / 10cm
Least count = 0.001cm
When jaws of a Vernier Caliper or Screw Gauge are closed, zero of main scale must overlap with the zero of vernier scale or circular scale in case of screw gauge. If they do not overlap then it is said that a zero error is present in the instrument. Zero error may be positive or negative. "The difference between the measured value and actual value" is known as zero error. Positive zero error refers to the fact that when the jaws of the vernier calipers are just closed, the reading is a positive reading away from the actual reading of 0.00mm. If the reading is 0.10mm, the zero error is referred to as +0.10 mm. When the vernier is closed the first mark (zero) on the main scale is allied with the first mark on the auxiliary scale. Care must be taken to assure that the vernier caliper is properly zeroed. A rectification may be either positive or negative. If the first mark on the auxiliary scale lies to the right of the main scale, then the reading is too large and the error is positive (and vice-versa). You have to subtract it from the reading to get the right value.
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