In-house vs outsourced calibration: how to decide what to calibrate yourself

What in-house and outsourced calibration mean

In-house calibration is done by your own staff, with your own reference standards, under your own procedures. A technician checks a caliper against a set of gauge blocks, or a thermocouple against a reference thermometer in a dry block, and records the results. You own the method, the evidence and the decision.

Outsourced calibration is done by a calibration provider, either at its lab or on-site at your premises. The provider may be accredited to ISO/IEC 17025 for that calibration, or not. On-site work by an outside lab is still outsourced, because the method, the reference standards and the certificate are the provider's.

Many in-house checks are verifications rather than full calibrations. The gage is compared with a reference and judged against a tolerance. That is legitimate, as long as the procedure says which one you do.

What the standards allow

ISO 9001 does not require an outside laboratory, and it does not require accreditation. Clause 7.1.5.2 applies where measurement traceability is a requirement or is essential to confidence in the results. Measuring equipment is then calibrated or verified at specified intervals, or before use, against measurement standards traceable to international or national measurement standards. Where no such standard exists, you retain the basis you used. Clause 7.1.5.1 asks you to keep evidence that the equipment is fit for its purpose, and clause 7.2 asks you to ensure the competence of the people doing the work.

ISO/IEC 17025:2017 is the competence standard for laboratories. It applies to any organization performing laboratory activities, whatever its size, so an internal lab can work to it or be accredited to it. ISO 9001 does not ask for either. If your lab does work to it, clause 7.6.2 requires an uncertainty evaluation for all calibrations, including calibrations of its own equipment.

IATF 16949 is more specific. Clause 7.1.5.3.1 says an internal laboratory needs a defined scope, included in the quality management system documentation, that covers the inspections, tests or calibrations it performs. The lab has to specify and implement at least these requirements.

• Adequate technical procedures.
• Competent laboratory personnel.
• Testing of the product.
• The capability to perform the services correctly, traceable to the relevant process standard. Where no national or international standard exists, you define and implement a method to verify the capability of the measurement system.
• Customer requirements, if any.
• Review of the related records.

• Calibration requirements by standard

External labs, aerospace and customer requirements

For outside labs, IATF 16949 clause 7.1.5.3.2 asks for a defined laboratory scope that covers the service you buy. The lab must also be accredited to ISO/IEC 17025 or a national equivalent with that service in its scope, with the certificate carrying the mark of a national accreditation body. Sanctioned interpretation 10 allows one alternative. You may use a lab without that accreditation, such as the equipment manufacturer, if you hold evidence that it was evaluated and meets the internal laboratory requirements of clause 7.1.5.3.1.

AS9100 keeps the ISO 9001 rules and adds, among other things, a register of the equipment that needs calibration or verification. The register records the method, frequency and acceptance criteria for each item, and you need a process to recall equipment for calibration. AS9100 does not itself require an accredited lab. Aerospace customers can require one in their purchase order terms, so read your flowdowns.

Customer requirements come on top of all of these. A purchase order or quality agreement that asks for accredited calibration overrides the freedom the standard gives you.

• Approving a calibration supplier

What in-house calibration needs

Before you take a gage type in-house, make sure you can show each of these to an auditor.

• Reference standards with their own traceable calibration. Gauge blocks, master rings, reference thermometers and test weights go out to a competent lab, usually an accredited one, on their own interval. Their uncertainty has to be small enough for the tolerances you will check with them.
• A documented procedure for each instrument type. It names the reference, the test points, the method, the environment and the acceptance criteria.
• A suitable environment. Dimensional measurements are referenced to 20 °C (ISO 1). A temperature difference between the gage and the reference adds uncertainty, so let them settle together before you measure.
• Competent people, with training records and a way to show they can do the procedure, such as a supervised first calibration or a comparison with an outside result.
• An uncertainty estimate or a test uncertainty ratio for each procedure, so you know the method is good enough for the tolerance.
• A record of each calibration: the instrument, the reference standard used, the as-found and as-left readings, the result, the person, the date and the next due date.
• Status control and a process for gages found out of tolerance, so you can assess what was measured with them.

• Metrological traceability explained
• What NIST traceable means
• How to build a measurement uncertainty budget

Which instruments to keep in-house and which to send out

The split usually follows two questions. Can you buy and maintain a reference standard that is clearly better than the instrument? And is the method simple enough to write down and repeat? The table shows how that often works out. Your tolerances and your customers can move any row.

• Load cell calibration
• Flow meter calibration
• Torque wrench calibration under ISO 6789
• Pressure gauge calibration
• Thermometer and temperature probe calibration

The hybrid model

A common arrangement has three tiers. Reference standards go to an accredited lab on a fixed interval. Working gages are calibrated in-house against those standards. Complex instruments are calibrated by an outside provider, at its lab or on-site, with in-house checks between visits.

The tiers are connected. Each in-house calibration rests on a reference standard whose certificate came from outside, so a lapsed reference standard affects every gage calibrated against it. Track the due dates of your reference standards as closely as those of your gages.

Revisit the split when something changes. A customer may ask for accredited certificates, a gage type may grow in number, a tolerance may tighten or the person who ran a procedure may leave.

• Approved supplier list template

Cost factors to weigh

No price list settles this, because the answer depends on your volume, your tolerances and your people. These are the costs to put side by side.

• Reference standards for in-house work, and their own outside calibration on their interval.
• Technician time, training and competence records for the people doing in-house work.
• A written procedure and an uncertainty evaluation for each in-house method.
• A temperature-stable space, and the audit time your own lab will draw.
• For outsourced work, the provider's fee per instrument, shipping, and the admin of purchase orders, supplier approval and certificate review.
• Downtime while gages are away, which may mean buying spares, and the chance of damage in transit.

Risks on each side

The main in-house risk is an error nobody outside sees. A reference standard used past its due date, a procedure that misses a test point or an untrained technician can pass bad gages without anyone noticing. Sending the occasional gage out after an in-house calibration and comparing the two results is a practical check. Expect the auditor to read your procedures, competence records and reference standard certificates, because there is no provider's certificate to rely on.

The main outsourced risk is buying the wrong service. A lab can be accredited, but not for your parameter or range. A certificate can arrive without as-found data or without an uncertainty. Gages are also away for the turnaround time, and an adjustment made without your approval can erase the as-found evidence you need if the gage was out of tolerance.

Records you need either way

Who does the work changes the records you hold, not whether you hold them.

• An equipment list or register with each instrument's identification, location, interval, status and next due date.
• For in-house work, the procedure used, the reference standard and its certificate, the as-found and as-left readings, the result, and who did the work and when.
• For outsourced work, the provider's calibration certificate, your review of it and the supplier approval behind the order.
• For any instrument found out of tolerance, your assessment of the measurements and product it affected, and the action taken. ISO 9001 clause 7.1.5.2 asks you to determine whether earlier results were adversely affected.
• Under IATF 16949, the internal laboratory scope and, for outside labs, evidence of their accreditation scope or evidence that they were evaluated against the internal laboratory requirements.

• Calibration certificate requirements
• How to set calibration intervals

Where Axiospec fits

Axiospec is calibration management software, and it records both kinds of work. An in-house calibration records the reference standard used, the as-found and as-left readings and the certificate. An instrument sent out carries the vendor and an out-for-calibration status until it comes back, and due dates cover both. It does not make an internal lab conform or a provider qualified. Those decisions stay with you.