Define the calibration decision first
Before calibrating a stationary profile projector, height gauge, or other measuring device in-house, determine whether the device controls product acceptance or supports production measurements. The evidence contains conflicting claims about whether an internal laboratory must be accredited: one position requires an accredited laboratory or manufacturer, while another states that internal calibration may be accredited but does not have to be. Do not resolve this conflict by assumption. Verify the applicable customer, quality-system, and accreditation requirements before authorizing internal calibration.
| Decision | Required evidence | Action if unresolved |
|---|---|---|
| May calibration be performed internally? | Applicable quality-system and customer requirements | Use an accredited laboratory or the manufacturer until the requirement is confirmed |
| Is the reference suitable? | Valid certificate and traceability to a national standard | Do not use the reference for calibration |
| Is the device used for product acceptance? | Measurement plan and device-use records | Treat loss of calibration as a potential product-impact event |
Maintain traceability of the reference standard
A gauge block, glass scale, or other reference used for calibration needs documented traceability to a national standard. Retain its valid calibration certificate and identify the reference in every device-calibration record. A reference cannot establish defensible traceability merely because it is reserved for calibration.
Material and environment also matter. The evidence identifies hardened metal and ceramic gauge blocks and notes that temperature can influence metal gauge blocks more than dimensional change over time. Control and record relevant measurement conditions instead of interpreting long-term stability as immunity to temperature effects.
Set intervals from evidence, not auditor preference
The organization sets the calibration interval; the auditor does not select it. One proposal in the evidence is annual inspection by an accredited laboratory, while another supports a longer interval when a gauge block is used only for calibration and its stability is statistically demonstrated. A reported workshop practice assigned calibration-only gauge blocks a 10-year service life, and a cited evaluation reportedly found negligible dimensional change in ceramic blocks over 5 years. These values are observations and practices, not universal requirements.
Base the interval on reference use, material, handling, environmental exposure, prior results, and measurement risk. Shorten it after damage, abnormal drift, questionable storage, or an out-of-tolerance result. Extend it only when recorded history supports the change and applicable requirements permit it.
Document each internal calibration
A simple pass/fail spreadsheet is insufficient when it cannot identify affected product or reconstruct the calibration. Use a controlled record that supports traceability, technical review, and product-impact analysis.
- Identify the measuring device and the reference standard used.
- Record the calibration date, measured results, acceptance criteria, condition, and correction or adjustment.
- Record the reference certificate status and the next scheduled review or calibration.
- Document the disposition as acceptable or not acceptable and identify the person approving the result.
- Apply a written escalation process when a result exceeds its acceptance criterion.
For a profile projector used to make production decisions, also perform measurement-system analysis. Calibration addresses comparison with a reference; measurement-system analysis evaluates whether the complete measurement process is suitable for its intended use.
Detect drift between formal calibrations
Long formal-calibration intervals can make product containment difficult because the last known-good point may be too old. For universal measuring devices used in series production, periodically measure a production-representative master part. Start with a short monitoring cycle, such as once per shift or once per day, and lengthen it only after the production and measurement process demonstrates stable behavior.
Plot deviation from the master part's assigned value over time and relate the deviation to the feature tolerance. Where several production lines or similar measuring devices are involved, compare their results; analysis of variance can help distinguish line, device, and process effects when the collected data support that analysis.
Verify control and respond to failure
Verification is complete only when records prove traceability and provide a usable last known-good point. Confirm that the device meets its acceptance criteria, the reference certificate remains valid, the monitoring result is stable, and measurement-system analysis supports the intended application.
If calibration or an intermediate master-part check fails, stop relying on the device for acceptance decisions. Follow the documented escalation process, determine when the device was last known to be acceptable, identify work measured since that point, evaluate product impact, and record correction and disposition. Recalibration alone does not close the event if potentially affected product remains unevaluated.
FAQ
Does an in-house profile projector calibration need a record?
Yes. Record the device, reference standard, certificate status, measured results, acceptance criteria, disposition, correction, date, and approval so traceability and product impact can be reconstructed.
How often should a gauge block used only for calibration be recalibrated?
The organization sets the interval from use, material, handling, environment, history, and risk. Annual inspection is one documented proposal, but a longer interval requires supporting stability data and permission under the applicable requirements.
Must an internal calibration laboratory be accredited?
The evidence contains conflicting interpretations, including both a claimed accreditation requirement and a claim that internal calibration need not be accredited. Verify the governing quality-system and customer requirements; use an accredited laboratory or the manufacturer while the requirement remains unresolved.