Dial indicators (dial test indicators and plunger-type indicators) are used for comparative dimensional measurement, alignment, and runout inspection. Calibration verifies the accuracy of the displayed reading across the full travel range using gage blocks or a calibrated indicator checker. Accurate indicators are essential for machine setup and inspection.
Inspect the indicator for cracked crystal, damaged bezel, bent spindle, or loose mounting stem. Verify the pointer rotates smoothly and the revolution counter (if present) functions correctly. Check that the contact point is not worn.
Extend and retract the spindle to the same point ten times using a single gage block. Record the reading each time and calculate the repeatability. This checks for hysteresis and spindle binding.
Using gage blocks of increasing size (or an indicator checker), test the indicator at a minimum of ten equally spaced points across the full range. Record the indicator reading and the reference value at each point.
Return through the same ten points in descending order and record the readings. The difference between ascending and descending readings at the same point is the hysteresis error.
Check the accuracy within any one revolution of the pointer (typically 0.100 in or 2.5 mm) at five points. Short-range errors detect individual gear tooth errors in the indicator mechanism.
Record all data including accuracy errors, hysteresis, repeatability, and short-range errors. Issue the calibration certificate and apply the calibration label. If errors exceed limits, remove the indicator from service.
Per ASME B89.1.10 for AGD Group 2 indicators (0.001 in resolution): total range error must not exceed ±0.001 in, short-range (one revolution) error must not exceed ±0.0005 in, and repeatability must not exceed 0.0005 in. Metric indicators have proportional limits.
12 months
A dial indicator (plunger type) has a spindle that moves in and out axially, with a typical range of 0.250 in to 1 in. A dial test indicator (lever type) has a contact arm that pivots, with a shorter range (typically 0.030 in). Both are calibrated similarly but have different error specifications.
Yes, gage blocks are the primary standard for dial indicator calibration. Stack gage blocks incrementally to create known displacements across the indicator's range. An indicator checker (which holds the indicator and provides controlled displacement) makes this process easier and more repeatable.
Common causes include worn gear teeth in the mechanism, a bent or binding spindle, a worn contact point, contamination inside the case, and damage from dropping. A sudden change in calibration results usually indicates physical damage, while gradual drift suggests gear wear.
CalibrationOS tracks due dates, stores certificates, and generates audit-ready reports.
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