The accuracy of Digital Calipers

Compared with Vernier Caliper, reading value of Digital Calipers is pretty less than it. According to the principle of DIN862 Standard, the measuring range of 200mm with or without a vernier round scale caliper, of which the permission accuracy would be +/-0.04mm. This principle applies to such kind of caliper having scale and vernier reading of 0.1mm and 0.05mm. However, it is 0.01mm for the Digital Calipers, which is obviously less than the permission accuracy.

Features of Digital Calipers

Base on the principle of DIN862 Standard, Vernier Calipers are used to measure the inside, outside and deep range, which read by the main body and vernier scale. Currently, the most usable measuring instruments are the Vernier calipers. Comparatively, Dial caliper are less used. Nowadays, people have much interest in Digital Calipers. Thus pick up a Dial Caliper, a Vernier Caliper and a Digital Caliper for a test from three different companies.

Digital Calipers carry optical and electronic grid types. We have chose two optical grid type calipers and three electronic grid type calipers. The two optical grid type calipers can be connected with computer through RS232 port.

Digital Calipers often powered by battery, the electronic grid type calipers can continuously work for about 2,000 hours. But the optical grid type calipers have a shorter span. For save the power, there is necessary to timing. For an instant, power the calipers off at a 90 seconds or two minutes. Some of the calipers can be automatically powered off.

Another feature of Digital Calipers is the speed of the display parts is limited within 0.5 m or 1 m. If it is out of speed, it has to suspend the measuring, and zero-setting again.

Testing Accuracy of Shape and Position

For the main body of Digital Calipers, there are two series of accuracy need to be mentioned, named Straightness accuracy and Parallelism accuracy. Firstly, the Straightness accuracy we have a cylinder shaped accuracy tester, the vertical line would be the standard for measuring. Put the Digital Caliper on the table, and make sure it is paralleled with the vertical line of cylinder shaped accuracy tester. This is test shows us that the results of these two calipers are so different, and even for the two measuring mentions of the one caliper. For the nice measuring mention, its Straightness accuracy below 3 microns, otherwise, it is above 30 microns for a poor measuring mention. Secondly, the Parallelism accuracy also needs a cylinder shaped accuracy tester. The Parallelism accuracy of the main body would be a big difference sometime. Just as the Straightness accuracy, for the nice measuring mention, its Parallelism accuracy below 3 microns, otherwise, it is above 30 microns for a poor measuring mention.