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General Notes on use of Caliper 5. Moving jaw tilt error
If the moving jaw becomes tilted out of parallel with the fixed jaw, either
1. Potential causes of error through excessive force being used on the slider or lack of straightness in the
A variety of factors can cause errors when measuring with a caliper. Major reference edge of the beam, a measurement error will occur as shown in the
factors include parallax effects, excessive measuring force due to the fact that a figure. This error may be substantial due to the fact that a caliper does not
caliper does not conform to Abbe's Principle, differential thermal expansion due conform to Abbe’s Principle.
to a temperature difference between the caliper and workpiece, and the effect
of the thickness of the knife-edge jaws and the clearance between these jaws f = h = h·a/
during measurement of the diameter of a small hole. Although there are also
other error factors such as graduation accuracy, reference edge straightness, f
main scale flatness on the main blade, and squareness of the jaws, these h
factors are included within the instrumental error tolerances. Therefore, these h
factors do not cause problems as long as the caliper satisfies the instrumental a
error tolerances.
L
D Example: Assume that the error slope of the jaws due to tilt of the slider is 0.01 mm in 50 mm and
the outside measuring jaws are 40 mm deep, then the error (at the jaw tip) is calculated as
D (40/50) x 0.01 mm = 0.008 mm.
L < D
If the guide face is worn then an error may be present even using the correct measuring force.
2. Inside measurement
Insert the inside jaw as deeply as possible before measurement. 6. Relationship between measurement and temperature
Read the maximum indicated value during inside measurement. The main scale of a caliper is engraved (or mounted on) stainless steel, and
Read the minimum indicated value during groove width measurement. although the linear thermal expansion coefficient is equal to that of the most
3. Depth measurement common workpiece material, steel, i.e. (10.2 ±1) x 10-6 / K, note that other
Read the minimum indicated value during depth measurement. workpiece materials, the room temperature and the workpiece temperature
4. Parallax error when reading the scales may affect measurement accuracy.
Look straight at the vernier graduation line when checking the alignment of 7. Handling
vernier graduation lines to the main scale graduation lines. Caliper jaws are sharp, and therefore the instrument must be handled with
If you look at a vernier graduation line from an oblique direction (A), the care to avoid personal injury.
apparent alignment position is distorted by X as shown in the figure below Avoid damaging the scale of a digital caliper and do not engrave an
due to a parallax effect caused by the step height (H) between the planes of identification number or other information on it with an electric marker pen.
the vernier graduations and the main scale graduations, resulting in a reading Avoid damaging a caliper by subjecting it to impact with hard objects or by
error of the measured value. dropping it on a bench or the floor.
8. Maintenance of beam sliding surfaces and measuring faces
Wipe away dust and dirt from the sliding surfaces and measuring faces with a
dry soft cloth before using the caliper.
9. Checking and setting the origin before use
Clean the measuring surfaces by gripping a sheet of clean paper between the
outside jaws and then slowly pulling it out. Close the jaws and ensure that
the vernier scale (or display) reads zero before using the caliper. When using a
Digimatic caliper, reset the origin (ORIGIN button) after replacing the battery.
ORIGIN button sets display to zero
ORIGIN
Close jaws Battery
completely
10. Handling after use
After using the caliper, completely wipe off any water and oil. Then, lightly
apply anti-corrosion oil and let it dry before storage.
Wipe off water from a waterproof caliper as well because it may corrode the
working surfaces.
11. Notes on storage
Avoid direct sunlight, high temperatures, low temperatures, and high humidity
during storage.
If a digital caliper will not be used for more than three months, remove the
battery before storage.
Do not leave the jaws of a caliper completely closed during storage.
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