Vernier caliper is a commonly used instrument for measuring length in the industry. It consists of a ruler body and a vernier that can slide on the ruler body, as shown in Figure 2.3-1. If viewed from the back, the cursor is a whole. There is a spring sheet between the vernier and the ruler body (not shown in the figure), and the elastic force of the spring sheet is used to make the vernier and the ruler body close. There is a fastening screw on the upper part of the vernier, which can fix the vernier on any position on the ruler. Both the ruler body and the vernier have measuring claws. The inner measuring claw can be used to measure the width of the groove and the inner diameter of the tube, and the outer measuring claw can be used to measure the thickness of the part and the outer diameter of the tube. The depth gauge is connected with the vernier gauge to measure the depth of the groove and the barrel.
There are scales on the ruler body and the vernier ruler. Take a vernier caliper accurate to 0.1 mm as an example. The smallest division on the ruler is 1 mm. There are 10 small division scales on the vernier. The total length is 9 mm. Each division is 0.9 mm, which is the smallest than the main ruler. The division difference is 0.1 mm. When the measuring jaws are close together, the ruler body and the zero scale line of the vernier are aligned. The first scale line is 0.1 mm apart, the second scale line is 0.2 mm apart,..., the tenth scale line is 1 mm apart, that is, the first scale line of the vernier. The 10 scale lines are exactly aligned with the 9 mm scale line of the main ruler, as shown in Figure 2.3-2.
When the linearity of the object measured between the equivalent claws is 0.1 mm, the vernier should move 0.1 mm to the right. At this time, its first scale line is exactly aligned with the 1 mm scale line on the ruler body. Similarly, when the fifth scale line of the vernier is aligned with the 5 mm scale line of the ruler body, it means that there is a width of 0.5 mm between the two measuring jaws, ..., and so on.
When measuring the length greater than 1 mm, the whole millimeter should be read from the scale line where the vernier "0" line is opposite to the ruler body.
The use of vernier calipers
Wipe the measuring claws clean with a soft cloth, make them close together, and check whether the vernier is aligned with the zero mark of the main ruler. If it is aligned, the measurement can be performed: if it is not aligned, the zero error should be recorded: the zero scale line of the vernier on the right side of the zero scale line on the ruler body is called positive zero error, and the one on the left side of the zero scale line on the ruler body is called negative zero error (this The method of specifying the file is consistent with the number axis, the origin is positive on the right, and the origin is negative on the left).
When measuring, hold the ruler with your right hand, move the vernier with your thumb, and hold the object with the outer diameter (or inner diameter) to be measured in your left hand, so that the object to be measured is located between the outer measuring claws. Reading, as shown in Figure 2.3-3.
Vernier caliper reading
When reading, first read the whole number of millimeters on the ruler based on the zero scale line of the vernier, that is, the integer part in millimeters. Then see which scale line on the vernier is aligned with the scale line of the ruler body. If the sixth scale line is aligned with the scale line of the ruler body, the decimal part is 0.6 mm (if there is no exactly aligned line, take the closest alignment Line for reading). If there is zero error, the above result is used to subtract zero error (zero error is negative, which is equivalent to adding zero error of the same size), and the reading result is:
L = integer part + decimal part-zero error
To determine which scale line on the vernier is aligned with the scale line on the ruler body, you can use the following method: select three adjacent lines, such as the left line on the left and right of the corresponding line on the ruler body, and the right line on the corresponding line of the ruler body. The left and middle line can be considered to be aligned, as shown in Figure 2.3-4.
If you need to measure several times to get the average value, you don’t need to subtract the zero error every time, just subtract the zero error from the final result.
The accuracy of the vernier caliper
Vernier calipers with an accuracy of 0.05 mm and 0.02 mm are commonly used in actual work. Their working principle and method of use are the same as the vernier calipers with an accuracy of 0.1 mm introduced in this book. The vernier caliper with an accuracy of 0.05 mm has 20 equal divisions on the vernier, and the total length is 19 mm. When measuring, if the 11th scale line on the vernier is aligned with the main ruler, the reading of the decimal part is 11/20 mm = 0.55 mm. If the 12th scale line is aligned with the main ruler, the reading of the decimal part is 12/20 mm = 0.60 mm.
Generally speaking, there are n equal divisions on the vernier, and their total length is equal to the total length of the (n-1) equal divisions on the ruler. If the minimum scale length on the vernier is x, the minimum scale length on the main ruler is y
The difference between the minimum scale of the main ruler and the cursor is
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 improving the measurement accuracy of the vernier caliper lies in increasing the number of scales on the vernier or reducing the minimum scale value on the main ruler. In general, y is 1 mm, and n takes 10, 20, and 50, and the corresponding accuracy is 0.1, 0.05 mm, and 0.02 mm. The mechanical vernier caliper with an accuracy of 0.02 mm is limited by its structural accuracy and the resolution of the human eye on the alignment of the two scribe lines, so its accuracy cannot be improved.
Custody of vernier calipers
After using the vernier caliper, wipe it clean with cotton yarn. When it is not used for a long time, wipe it with butter or engine oil, close the two measuring jaws, tighten the fastening screws, and put it in the caliper box and cover it.