Height gages measure vertical dimensions from a reference surface (granite surface plate) and are used for layout, inspection, and scribing operations. Calibration verifies the accuracy of the vertical measurement system using certified gage blocks wrung to the surface plate. Height gages combine the functions of a surface plate and a caliper in one instrument.
Verify the surface plate is within its calibration period and the surface is clean and free of nicks. Record the ambient temperature. The height gage and surface plate must be thermally stabilized to the same temperature.
Inspect the height gage for damage, wear on the scriber or measuring jaw, and display function. Verify the column is straight and the slider moves smoothly without excessive play.
With the measuring jaw or probe resting on the surface plate, record the as-found zero reading. If the gage has a zero-set function, note the offset but do not zero the gage until the as-found readings are complete.
Wring gage blocks of known heights to the surface plate and measure each one. Test at a minimum of five points spanning the height gage range (e.g., 25 mm, 50 mm, 100 mm, 200 mm, and near maximum). Record the displayed reading and calculate the error at each point.
Measure a single gage block height ten times, lifting the measuring jaw between each measurement. Calculate the standard deviation to assess repeatability.
Record all as-found and as-left data, gage block IDs and certified values, surface plate ID, and environmental conditions. Issue the calibration certificate and apply the calibration label.
Error at any test point must not exceed ±(10 + L/50) µm where L is the measured height in mm, or per the manufacturer's specification. Repeatability (standard deviation of 10 readings) must not exceed one-half the display resolution.
12 months
Yes, the surface plate and the height gage are separate instruments and each must have its own calibration. The surface plate provides the reference datum for the height gage, so errors in the plate will directly affect height gage measurements.
A height gage can be used as a measurement standard only if its calibrated uncertainty is significantly better than the tolerance of the instrument being checked. For most applications, gage blocks or a CMM provide lower uncertainty than a height gage.
A height master is a fixed-length reference standard (similar to a gage block stack) used to set or verify other instruments. A height gage is a variable measuring instrument that can measure any height within its range. Height masters are sometimes used to verify height gages.
CalibrationOS tracks due dates, stores certificates, and generates audit-ready reports.
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