Digital Caliper Buying Guide

Things to Consider when Purchasing a Digital Caliper

A digital caliper is a tool used for precision measuring and is commonly used in mechanical engineering, carpentry, metalworking and medicine. Regular calipers have been used for a long time to measure the distance between two opposite sides of something and will have a scale of measurement which can look a little like a ruler, but with jaws attached on one end.

Measurements are usually Metric and English with high resolution precision. The digital element has kicked in when the analog dial of the Dial Caliper was replaced by an LCD screen. The small digital screen shows easy to read measurements as a single value. The digital aspect has served to make an already precise measuring instrument, even easier to use.

What to look for When Buying Digital Calipers

Digital calipers are the easiest of all the different types of calipers to use because reading and adding measurements from a very small scale is not required. No estimating is required because the finished reading is displayed on an LCD screen. Readings are quick and easy. While these things are definitely an advantage over other Mitutoyo in boxtypes of calipers, it also serves to indicate a few of the things you need to keep an eye on before you buy one.

Measurements

You should look for digital calipers which have a feature which allows you to switch between millimeters and centimeters and/or inches. If you are going for ultimate precision measurements, you should make sure this feature is included so you have flexibility in unit measurements.

Reading Hold

This is definitely a feature you want to have. If you are measuring in an awkward position, you might not be able to read the LCD. A reading hold will allow for the reading of measurements for those times when you cannot see the screen. This is really just an extension of the same function as occurs on the dial caliper where the display can be ‘zeroed’ at any point along the slide, so that you can read it when you are out of the awkward position.

Sizes and Accuracy

Depending on the level of accuracy you want to work with, the rule of thumb is that the larger the measurement, the accuracy declines. This is best shown in the following table.

SizeRated AccuracyResolution
6 inch/150mm0.001 in 0.02mm0.0005 in 0.01mm
8 inch0.001 in 0.03mm100-200mm
12 inch0.0015 in 0.04200-300mm

Cheap Digital Calipers

These generally come from China and are said to do a reasonable job. The thing to look out for with these is that they keep drawing power when he switch is turned to the off position. The display might be off, but the calipers continue to draw current, sometimes as much as 20 microamperes. This is a lot higher than more expensive established brands. Another issue to watch for with cheap calipers is that if the voltage drops, even just a little, the calipers may not work properly. Silver cell batteries (SR44) tend to have a more constant voltage and also last longer than alkaline button cells (LR44).

Good Quality Digital Calipers

The most accurate digital calipers are always going to be those of good quality. Some of the best brands are Brown & Sharpe and Mitutoyo. Cool Tools is a non-commercial site that provides consumers with product information so you should go and check out the rank of some of the various brands of digital calipers. The Mitutoyo brand is the best and they were one of the first manufacturers to make digital calipers. There are many who copy their design, but quality is questionable.

A good digital caliper for DIY casual users is the Neiko brand. They have a good reputation for quality and their 6 inch digital caliper comes with an extra-large display screen, a depth gauge, and will also allow you to switch from standard to metric.

Serial Data Output

This is coming to be a standard feature on digital calipers, but it is always a good idea to check that your calipers of choice have it. This feature will allow you to interface the digital readings from the calipers, to a personal computer. Depending on what measurements you are recording and why, this is a very useful feature because of the small time it takes to make and record the data. Record reliability also improves if you can store the data in a spreadsheet for example after converting serial data to a computer interface. Serial digital output varies but some common ones are Mitutoyo Digimatic interface, the Sylvac interface, Starrett, Brown & Sharpe, Federal, Mahr, Tesa and Aldi.

Encoders

Some digital calipers contain a capacitive linear encoder which is basically a pattern of bars which are etched directly on the printed circuit board in the slider. Underneath the scale of the caliper there is another printed circuit board which also contains an etched pattern of lines. The combination of these printed circuit boards forms two variable capacitors which are out of phase. As the slider moves the capacitance changes in a linear motion and in a repeating pattern.

The circuitry in the slider counts the bars as the slider moves and does a linear interpolation based on the magnitudes of the capacitors. In this way, it finds the precise position of the slider. Other digital calipers contain an inductive linear encoder, which allows robust performance in the presence of contamination such as coolants Magnetic linear encoders are also used in other digital calipers.

Conclusion

All digital calipers are not equal in their ability to provide precision measurements. This being so, it is always good to be aware of the features which can differ between brands, but at the same time are adequate to the task you need them for. If you want very accurate digital calipers, the best advice is to go with a known brand which has a reputation for quality. A professional would do well to get a more expensive, durable, and precise tool, while casual users can manage with the less expensive models, like Neiko and lower-end Mitutoyo. Keep these things in mind as you shop and you will find the best digital caliper to suit your needs.

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