Instrument Calibration Procedure
Internal and External Dial, Vernier and Digital
Calipers and Outside Micrometers
GPC CAL001
DATE 10/07
REV. 0
Quality Assurance Manager
Approved Date:
SECTION1
INTRODUCTION AND DESCRIPTION
1.1
This procedure describes the calibration of Internal and External Dial, Vernier and
Digital Calipers and Outside Micrometers. The instrument being calibrated is
referred to herein as the TI (Test Instrument)
1.2
This procedure includes test and essential performance parameters only. Any
malfunction noticed during calibration, whether specifically tested for or not,
should be corrected.
Table 1 Calibration Description
TI
Dial, Vernier
and Digital
Calipers
Outside
Micrometers
TI
Characteristics
Zero indication test
Performance
Specification
Test point 0 in.
Tolerance +/- .0005 in.
Outside accuracy
Range 0 to 12”
Tolerance: see Table II
Inside accuracy
Range 0 to 12”
Tolerance: see Table II
Depth gage accuracy
Range 0 to 12”
Length and Linearity
Range: 0 to 12”
Test Method
Determined by sliding
the jaws together and
reading the TI
indication.
Comparison to gage
blocks between the TI
jaws.
Comparison to gage
blocks dimensions
placing the blocks
with attached caliper
jaws outside the TI
jaws.
Comparison to gage
block dimensions,
placing the TI depth
gage block and
reading the TI outside
dimension scale.
Measured by
comparing TI
indications to gage
block dimensions
setup to test the basic
length and
micrometer head
linearity.
SECTION 2
EQUIPMENT REQUIREMENTS
Table 2 Equipment Requirements
Item
2.1 Gage Block Set
2.2 Low power magnifier
2.3 Micrometer wrench
2.4 Small jewelers screwdriver
2.5 Small clamp
2.6 Light machine oil or spray
2.7 Clean flat surface
Minimum Use
Specifications
Range .050- 4”
Tolerance .00005
To aid in reading the TL
vernier or barrel scale
Adjustment of micrometer
Adjustment of caliper
Hold gage blocks for inside
measurement comparison
Lubrication of slides or
thimble
Surface Plate or Steel Block
Calibration
Equipment
ESSM #SE0060
SECTION 3
PRELIMINARY OPERATIONS
3.1
TI INSPECTION
3.2
Ensure that the work area is clean, well illuminated, free from excessive drafts,
free from excessive humidity, and that the rate of temperature change does not
exceed 4 oF per hour.
3.3
Ensure that the gage block set (item 2.1) is clean and that the TI and the gage
blocks have been allowed to stabilize at the ambient temperature for a minimum
of 2 hours.
CALIPERS
3.4
Ensure that the TI jaws slide smoothly and freely along the full length of the TI
beam, if not take corrective action.
3.5
Inspect to ensure the jaws are free of nicks and burrs and that it is clean and free
from damage that would impair its operation.
NOTE
TI test point are basically determined by selecting 4 test point within the first inch
of range and 4 to 8 point additional test points extending over the remainder of the
TI range at approximately equal spacing.
3.6
In order top minimize the number of gage blocks needed to test calipers with
higher ranges, select test point at 25, 50, 75, and 100% of the TI range beyond the
1st inch and round to the nearest ½ inch. Use major vernier graduations or normal
electronic digital values as test points as necessary.
OUTSIDE MICROMETERS
3.7
Slowly rotate the TI micrometer thimble, and ensure that it operates smoothly its
entire range.
3.8
The TI length measurement test should be preformed at approximately 6 points
across the range of the TI. For example, 0 to 1” micrometer may have calculated
test points at .000, .200, .400, .600, .800 and 1.000 inch.
SECTION 4
CALIBRATION PROCESS
CALIPERS
NOTES
Unless otherwise specified, verify the results of each test and take corrective action
whenever the test requirement is not being met before proceeding.
Cotton gloves should be worn when handling gage blocks to prevent the transfer of body
heat, protect the gage surfaces.
4.1
ZERO TEST
4.1.1 Slide the TI jaws together, ensuring that no light is visible between the jaws
measuring surfaces. If the TI has inside measurement capability, verify that the
dial indicator or vernier indicates zero, as necessary. Adjust the dial bezel, if
necessary.
4.1.2 Tighten the TI sliding jaw set screw, if applicable
4.1.3 If the TI has a digital readout, depress the zero set and verify that the digital
indication reads 0.000.
4.1.4 If the TI is a vernier type, verify that the TI zero marks are aligned, as applicable.
4.2
OUTSIDE ACCURACY TEST
4.2.1 Determine the gage blocks required to obtain test points at a minimum of 4 point
throughout the first inch of the TI as follows .125, .300, .650, and 1.000 inch.
4.2.2. Open the TI to beyond the first test point. Insert the gage blocks and close the
jaws until they are firmly in contact with the gage block. Repeat each reading 3-5
times and verify that each indication does not exceed +/- ¼ of the least dial
graduation.
4.2.3 Verify that the first inch test points are within +/- .001 inch for 0-6” range and +/.002 for 0-12”calipers.
4.2.4 Repeat steps 4.2.2 and 4.2.3 for the remaining test points of 25%, 50%, 75% and
full range (100%).
4.3
INSIDE ACCURACY TEST
4.3.1 Determine the gage blocks required to obtain test points at a minimum of 4 point
throughout the first inch of the TI as follows .125, .300, .650, and 1.000 inch.
4.3.2. Using a three gage block set-up. Place the test gage block between two other
blocks and secure with a thumb screw type clamp (Figure 1). Open the TI to
the approximately the first test point. Insert the TI and open the jaws until they are
firmly in contact with the inside of the gage blocks. Repeat each reading 3-5 times
and verify that each indication does not exceed +/-¼ of the least dial graduation.
4.3.3 Verify that the first inch test points are within +/- .001 inch for 0-6” range and +/.002 for 0-12”calipers.
4.3.4 Repeat steps 4.2.2 and 4.2.3 for the remaining test points of 25%, 50%, 75% and
full range (100%).
Test Point Gage Block
Gage Block
Gage Block
Clamp
Figure 1
Inside Measurement Set-up
4.4
DEPTH ACCURACY
4.4.1 Position the end of the TI beam against a 1.0 inch gage block surface with the end
of the rod against the surface plate or steel gage block.
4.4.2 Ensure that the TI gage measuring surfaces are squarely placed against the surface
of the gage block and the surface plate.
4.4.3 Make any necessary final adjustments and note the scale indication.
4.4.4 Verify that the value(s) noted in the preceding step is within +/- .001 for 0-6”
range and +/- .002 for 0-12”calipers.
4.4.5 Perform steps 4.4.1 through 4.4.4 for each additional inch of depth gage range,
changing gage blocks, as necessary.
SECTION 5
CALIBRATION PROCESS
OUTSIDE MICROMETERS
5.1
Determine the gage blocks required to obtain test points at a minimum of 5 point.
(Lowest TI indication, 20%, 40%, 60%, 80% and full range.)
5.1.1 Adjust the spindle several tenths of an inch from zero, based on the TI basic
length. Starting with the gage block equal to the lowest TI range, slide the gage
block(s) between the anvil and spindle.
5.1.2 Adjust the TI as applicable to contact the gage block(s). Repeat each reading 2-3
times and verify each indication. Refer to Table 3 Micrometer Calibration
Tolerance.
5.1.3 Repeat step 5.1.1 & 5.1.2 through the complete range of the TI.
5.2
If the TI is the interchangeable anvil type, attach the each anvil in range and
verify as outlined in paragraph 5.1-5.1.3.
Table 3 Micrometer Calibration Tolerance
Micrometer Size Range
Calibration Tolerance
Calibration Tolerance
w/vernier
Without vernier
0-1”
+/- .0001
+/- .001
1”-2” through 9”-10”
+/- .0002
+/- .001
10”-11” and greater
+/- .0003
+/- .002
SECTION 6
LABELING AND RECORDS
6.1
Complete a Measuring and Test Calibration Record (QA-4) for each item
calibrated. Utilize additional QA-4 form as continuation sheet as needed.
6.2
Affix a calibration label to the TI with the date calibrated, date of next calibration
and who performed the calibration.
6.2.1
6.3
Special calibration label shall be applied to any item that has not been
calibrated to it’s fully range of capability.
All completed calibration records shall be file and maintained.