What is a caliper

What is a caliper?

Caliper is a kind of measuring tool, which is used to measure length, internal and external diameter and depth. It has the function of measurement and inspection.

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Measuring tools are instruments for measurement and inspection. Length measuring tools are one of its main categories, such as caliper, depth ruler, height ruler, micrometer, dial indicator, dial indicator, gauge block, step gauge, angle ruler, inclinometer, etc. Caliper is one of the most important types of length measuring tools. Common mechanical vernier calipers are shown in the composition structure.

Composition and structure of caliper

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Its measuring range includes: 0 – 150mm, 0 – 200mm, 0 – 300mm, etc. the general resolution (formerly called graduation value) is 0.02mm, also 0.1mm and 0.05mm, and the accuracy is generally ± 0.03mm, also ± 0.04mm and ± 0.05mm. It is composed of inner measuring claw, outer measuring claw, fastening screw, main ruler, traveling ruler, depth ruler, etc. some are also equipped with fine-tuning devices.

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There are two pairs of movable measuring claws on the main ruler and vernier of the vernier caliper, namely the internal measuring claw and the external measuring claw. The internal measuring claw is usually used to measure the inner diameter, and the external measuring claw is usually used to measure the length and outer diameter.

Measuring principle of caliper

The measuring principle of caliper is to use the difference between the scribed line spacing on the main ruler (referred to as line spacing) and the line spacing on the vernier ruler to read out the decimal part. For example, the line spacing on the main ruler is 1mm, and there are 10 grids on the vernier ruler, and the line spacing is 0.9mm. When the zero score lines of the two coincide, if the ruler moves by 0.1mm, its first score line coincides with the first score line of the main ruler; If the ruler moves 0.2mm, its second scribe line coincides with the second scribe line of the main ruler. By analogy, the decimal part of the measurement value can be read out from the coincidence of the scribed line on the vernier ruler and the main ruler. The difference between the line distance of the main ruler and the vernier ruler is 0.1mm, which is the minimum reading value of the vernier caliper. Similarly, if the difference between their line distances is 0.05 mm or 0.02 mm (there are 20 grids or 50 grids on the vernier ruler respectively), the minimum reading values are 0.05 mm or 0.02 mm respectively.
The vernier principle was proposed by French P. venier in 1631. It is often used in the subdivision reading mechanism of length and angle of length measuring tools. For details, please refer to national standards (GB / t21388, GB / t21389 and GB / t21390).

Main types of calipers

Calipers mainly include vernier calipers, calipers with meters and electronic digital calipers.

  • 1. Vernier caliper. A ruler shaped hand-held universal length measuring tool for subdividing readings based on the principle of vernier, which is mainly used to measure inner diameter, outer diameter, step and depth. During measurement, the integer part of the measured value is read out from the main ruler and the decimal part is read out from the vernier ruler. The principle of vernier is to use the difference between the scribed line spacing on the main ruler and the line spacing on the vernier ruler to read out the decimal part. There are three minimum reading values of 0.02mm, 0.05mm and 0.01mm.
  • 2. Caliper with watch. It is a large hand-held length measuring tool with the tooth pitch of precision rack and gear as the known length and the indicator with corresponding graduation as the amplification, subdivision and indication part. The caliper with meter can solve the problem of reading error of vernier caliper. The common minimum reading values are 0.01mm and 0.02mm.
  • 3. Electronic digital caliper. It is a length measuring tool with capacitive grid, magnetic grid and other measuring systems to digitally display the measured value. The common resolution is 0.01mm, and the allowable error is ± 0.03mm/150mm. There are also high-precision digital calipers with a resolution of 0.005mm, and the allowable error is ± 0.015mm/150mm. There is also a multi-purpose digital display micrometer caliper with a resolution of 0.001mm (this is the national patent of Anyi measuring tool, which can be produced only by them), and the allowable error is ± 0.005mm/50mm. Because the reading is intuitive and clear, the measurement efficiency is high.

In addition, there are various non-standard special calipers, such as hook depth calipers for measuring groove depth, tooth thickness calipers for measuring gear thickness, height calipers for measuring object height and weld calipers (weld gauge) for measuring welding quality.
Special purpose calipers: pointed claw type, irregular unknown size measurement offset type, depth measurement of position and size of unequal height area, depth measurement sheet type, narrow groove diameter measurement.

Main functions of caliper

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Outer diameter measurement (lower / outer measuring claw)

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Inner diameter measurement (upper / inner measuring claw)
Step measurement (left head)

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Depth measurement (tail depth needle)

Accuracy classification of calipers

Vernier calipers commonly used vernier calipers can be divided into three types according to their accuracy: 0.1mm, 0.05mm and 0.02mm. Their working principle and application method are the same as the vernier caliper with an accuracy of 0.1mm introduced in this paper. The vernier caliper with an accuracy of 0.05 mm has 20 equal divisions on the vernier, with a total length of 19 mm. During measurement, if the 11th scale line on the vernier is aligned with the main ruler, the reading of the decimal part is 11 / 20mm = 0.55mm; if the 12th scale line is aligned with the main ruler, the reading of the decimal part is 12 / 20mm = 0.60mm.
Generally speaking, there are n equal divisions on the vernier, and their total length is equal to the total length of (n-1) equal divisions on the ruler. If the minimum scale length on the vernier is x and the minimum scale length on the main ruler is y, then:

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The difference between the minimum scale of the main ruler and the vernier Δ X is:

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Y / N is called the accuracy of the vernier caliper, which determines the number of digits of the reading result.
It can be seen from the formula that the improvement of the measurement accuracy of the vernier caliper lies in increasing the number of notches on the vernier or reducing the minimum scale value on the main ruler. Generally, y is 1mm, and N takes 10, 20 and 50, and the corresponding accuracy is 0.1, 0.05mm and 0.02mm. The mechanical vernier caliper with an accuracy of 0.02mm can not be improved due to the limitations of its own structural accuracy and the resolution of human eyes to the alignment of the two scribed lines.

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Usage of caliper

Measuring method of caliper
When measuring, hold the ruler body with your right hand, move the cursor with your thumb, and hold the object with the outer diameter (or inner diameter) to be measured with your left hand, so that the object to be measured is located between the outer measuring claws. When it is tightly attached to the measuring claw, you can read. There are scales on the ruler body and vernier ruler. Take the vernier caliper accurate to 0.1 mm as an example. The minimum division on the ruler is 1 mm. There are 10 small equal divisions on the vernier ruler, with a total length of 9 mm. Each division is 0.9 mm, which is 0.1 mm different from the minimum division on the main ruler. When the measuring claws are close together, the scale body is aligned with the zero scale line of the vernier. The difference between their first scale line is 0.1mm, the difference between the second scale line is 0.2mm,…, and the difference between the 10th scale line is 1mm, that is, the 10th scale line of the vernier is just aligned with the 9mm scale line of the main ruler. When the linearity of the measured object between equivalent claws is 0.1mm, the vernier ruler shall move 0.1mm to the right. At this time, its first scale line is just aligned with the 1mm scale line of the ruler body. Similarly, when the fifth scale line of the cursor is aligned with the 5mm scale line of the ruler body, it indicates that there is a width of 0.5mm between the two measuring claws,…, and so on. When measuring the length greater than 1mm, the whole millimeter number shall be read out from the scale line opposite to the vernier “0” line and the ruler body.

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Reading method of caliper

When reading, first take the zero scale line of the vernier as the standard, and read the integer of mm on the ruler, that is, the integer part in mm. Then, see which scale line on the cursor is aligned with the scale line on the ruler body. If the 6th scale line is aligned with the scale line on the ruler body, the decimal part is 0.6mm (if there is no line aligned exactly, take the line closest to the alignment for reading). If there is zero error, the zero error shall be subtracted from the above results (zero error is negative, which is equivalent to adding zero error of the same size). The reading result is: l = integer part + decimal part – zero error.
To judge which scale line on the cursor is aligned with the scale line of the ruler body, the following methods can be used: select three adjacent lines. For example, the line on the left is around the corresponding line of the ruler body, the line on the right is left of the corresponding line of the ruler body, and the middle line can be considered as aligned. If you need to measure several times to take the average value, you don’t need to subtract zero error every time, just subtract zero error from the final result.

Precautions for caliper

  • 1. Vernier caliper is a relatively precise measuring tool, which shall be handled with care and shall not collide or fall underground. Do not use it to measure rough objects to avoid damage to the measuring claw. When not in use, it should be placed in a dry place to prevent corrosion.
  • 2. During measurement, the fastening screw shall be loosened first, and the cursor shall not be moved too hard. The contact between the two measuring claws and the object to be measured should not be too tight. The clamped object cannot be moved in the measuring claw.
  • 3. When reading, the line of sight shall be perpendicular to the ruler surface. If the reading needs to be fixed, the vernier can be fixed on the ruler body with fastening screws to prevent sliding.
  • 4. During actual measurement, the same length shall be measured several times, and its average value shall be taken to eliminate accidental.

Caliper has many advantages such as multiple measurement modes, easy operation, durability, strong universality and low cost. It can be said that it is the most common measuring tool in the toolbox. However, there are still many matters needing attention to use the caliper correctly. Let’s start with the error factors affecting the measurement results.

Error factors of caliper

When using caliper to measure, there are many factors causing errors, such as parallax, error caused by structure non-compliance with Abbe principle, thermal expansion caused by temperature difference between caliper and workpiece, etc.
In addition, because the caliper has no constant pressure device, it is difficult to grasp the suitable and uniform force during measurement, which is also another factor causing error.

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The structure of the caliper does not conform to Abbe’s principle

The reading axis and measuring axis of the caliper do not comply with the Abbe principle due to different axes. Therefore, when using the caliper, there is a risk of increasing the measurement error by measuring the root or tip of the measuring claw. During measurement, pay attention to the measured workpiece as close as possible to the ruler body (reading axis).

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Read the parallax of the scale

When checking whether the vernier scale line is aligned with the main scale dividing line, look directly at the vernier scale line.
There is a step height difference between the vernier ruler and the scale surface of the main ruler, which is easy to cause reading error. As shown in the figure below, if the cursor scale line is viewed from an oblique direction, the results in the figure will be generated Δ Error shown in X. In order to avoid the influence of this factor, the step height (H) specified in JIS specification shall not be greater than 0.3mm.

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Bending of datum end face

If the ruler surface guiding the ruler sliding is bent, it will lead to the error shown in the figure below. This error can be expressed by the same calculation formula as the error that does not conform to Abbe’s principle.

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For example, assuming that the deformation caused by the bending of the guide ruler surface is 0.01mm/50mm and the tip of the outer diameter measuring claw is 40mm, f = 40mm × 0.01÷50=0.008mm

Relationship between measurement and temperature

The caliper body is generally made of stainless steel and has the same thermal expansion coefficient (10.2 ± 1) as iron series metals × 10-6 / K, the influence of the material of the measured object, room temperature and workpiece temperature on the measurement shall be considered.

Precautions for operation

The caliper measuring claw is very sharp, so the instrument must be operated carefully to avoid personal injury.
Avoid damaging the scale of the digital caliper, and do not engrave the identification number or leave other information with an electric pen.
Avoid colliding with hard objects or falling on the stool or floor to damage the caliper.

Maintenance of sliding surfaces and measuring surfaces

Before using the caliper, wipe off the dust and dirt on the sliding surface and measuring surface with a soft dry cloth.

Check and calibrate the origin before use

Clamp a piece of clean paper between the outer claws and slowly pull it out. Before using the caliper, close the measuring claw and ensure that the vernier scale (or display) is set to zero. When the digital caliper is used, please reset (reset button) after replacing the battery.

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Operation after use

After using the caliper, wipe off the water and oil thoroughly. Then, apply it gently with antirust oil, dry it and store it.
For waterproof caliper, in order to prevent rusting after use, it is also necessary to wipe off the moisture of the caliper.

Storage precautions

Avoid direct sunlight, high temperature, low temperature and high humidity.
If the digital caliper is not used for more than three months, remove the battery before storage.
During storage, do not completely close the external measuring claw of the caliper.

Use and maintenance of caliper

  • 1. Operation inspection before daily use, check whether the zero scale of the vernier caliper is aligned, whether the scale is clearly visible and whether the movement is smooth. If yes, the caliper can be used normally. Otherwise, the caliper needs to be repaired or replaced with a new effective caliper, and the treatment method for instrument failure in the operation inspection regulations shall be followed.
  • 2. Precautions: after using the vernier caliper, wipe it with cotton yarn. When it is not used for a long time, wipe it with butter or engine oil, close the two measuring claws, tighten the fastening screws, put it into the caliper box, cover it, and avoid placing it in the environment of dust, humidity, supercooling, overheating and acid-base steam.

Industrial application of caliper

The general caliper will be used together with the data acquisition instrument. The data acquisition instrument can be directly connected with the caliper for automatic data acquisition without manual data recording by the operator, saving labor cost; Many calipers are connected to qsmart data acquisition instrument for automatic data acquisition and data analysis. Connect caliper to realize efficient mobile data acquisition.
Application background: the current method of factory internal quality inspection is that after measuring a data, it is manually recorded in the paper by the measuring personnel, or it is measured by one person and recorded by another person. When analysis is needed, the operator enters it into the EXCEL form of the computer; The problems caused by this way are low efficiency and easy to remember wrong data. At the same time, some operators can’t take measures in time when the product exceeds the specification because they don’t know the measurement specification of the product. Moreover, when data analysis is needed, they need to input it into the computer repeatedly.
Main objective: to realize paperless measurement, improve measurement accuracy and detection efficiency, and timely remind when exceeding the specification.

Source: China Flange Manufacturer – Yaang Pipe Industry (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@steeljrv.com

what is a caliper - What is a caliper
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What is a caliper
Caliper is a kind of measuring tool, which is used to measure length, internal and external diameter and depth. It has the function of measurement and inspection.
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