Reference Bar Calibration
The purpose of this procedure is to provide general instructions for the calibration
of reference bars.
This general procedure shall be used in the absence of any specific calibration
procedure for reference bars.
A reference bar is a stack of precision gage blocks permanently wrung and fastened
together. There are two sizes of gage blocks alternately used over the length of
the bar. The two sizes are 0.3 inch and 0.7 inch with the 0.3-inch protruding beyond
the 0.7-inch blocks.
Preliminary Instructions and Notes
- Read this entire procedure before beginning the calibration.
- Calibration shall be performed in an environment that conforms to Manufacturer Specifications.
- The reference bar will hereafter be referred to as the Instrument Under Test (IUT).
- Verify that the IUT is clean.
- Visually examine the IUT, including the base, for any condition that could cause
errors in the calibration.
- Apply gage block corrections where applicable.
- If any of the requirements cannot be met, refer to the applicable manufacturer manual.
- If a malfunction occurs or a defect is observed while calibration is in progress,
the calibration shall be discontinued and necessary corrective action taken; if
corrective action affects a measurement function previously calibrated, the function
shall be recalibrated before the remainder of the procedure implemented.
Applicable Manufacturers Manual or Brochures.
The specifications of the IUT are determined by the applicable manufacturer's documentation.
If the manufacturer's documentation is not available, then the specifications identified
in this procedure are used.
The following are "nominal diameters" and tolerances for all reference bars.
- Accuracy: +/- 0.000010 per inch of length.
- Gage surface to base parallelism: 0.000015
The Standards listed below should be selected on the basis of their higher accuracy
level when compared to the IUT. Equivalent Standards must be equal to or better
than the Minimum-Use-Specification.
Minimum-Use-Specifications for Standards listed are 1/4 the accuracy required by
Electronic Height Gage Comparator
+/- 0.000002 inch
+ 0.000006 -0.000005 inch
- Check parallelism of the IUT at the one-inch step and three random steps over the
- Check accuracy of the IUT at five random steps over the full range.
- Place IUT on surface plate in the vertical position.
- Position the standard comparator so the gage head contact is on the first step of
the IUT. Move the contact to the side of the block and zero the indicator.
- Move the electronic comparator contact the width of the IUT block and note the deviation
- Repeat steps 4 and 5 for the remaining parallelism checks over the range of the
- Select five gage blocks to check the accuracy of the IUT over the full range.
- Place the smallest block adjacent to the IUT.
- With the contact point of the gage head on the gage block, adjust the indicator
pointer of the standard to zero.
- Slide the standard to the IUT. When the contact point of the gage head is in the
middle of the measuring surface observe the reading on the standard.
- Recheck the standard reading on both the gage block and the IUT for repeatability.
- Repeat steps 8 through 11 for the four remaining gage block selections.
Reason for Reissue
Revision A - First Release
Download Calibration Control