8.6 Verifying Calibration
Calibration should be verified periodically depending on user requirements, system usage, and should be performed at least monthly. Calibration should also be verified after the system has been serviced or moved. A chrome-on-glass calibration verification standard artifact is available from Starrett or its authorized distributors. This standard has a length of 300 millimeters and major calibration fiducials spaced every 25 millimeters.
Figure 26. X and Y Calibration Axes
To validate calibration, perform the following steps:
1. Place the calibrated standard along the X-axis. Secure the standard to the stage with a holder (available from Starrett).
2. Skew the center of the two end circles of the calibration standard. Refer to the M3 Software User Guide for proper alignment procedure.
3. Using the HDV system, measure the position of fiducials spaced every 25 millimeters. For each fiducial, take the average of multiple readings for improved accuracy.
4. Calculate the absolute measurement error for each fiducial by subtracting the calibrated position of the fiducial from the above average readings.
5. Verify that the calculated absolute X measurement errors are within the HDV system accuracy specification, which is E2 = 3.0 µm + 1 µm x L/(33 mm).
6. Repeat for the Y-axis.
7. Enter the absolute X and Y errors on an X-Y Axes Accuracy Validation Results Plot, as shown in the following figure. In this plot, the straight line defined by blue diamonds is the maximum error specified by 3.0 µm + 1 µm x L/(33 mm). The green squares ■ are the absolute X errors. The red triangles ▲ are the Y errors. The HDV system is within the factory calibration spec if all X and Y errors fall below the straight line.
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