Calibration services: how to prepare for an on-site visit.

Manufacturers are turning to on-site calibration services with increasing frequency. This is occurring for several reasons, including fulfilling ISO requirements, minimizing downtime on the shopfloor, and improved record keeping. Preparing properly for an on-site visit can save time and money and optimize the benefits received from the metrology service provider.

Choosing a provider

The first and most important step is choosing the right on-site gage calibration service. Here are some guidelines to follow that will help make this important decision easier.

Your on-site calibration provider should:

* Have a good foundation, reputation, and history in the field of gage calibration and be staffed with at least two well-trained, on-site technicians. You should ask to contact current customers that use this service and ask questions about on-time scheduling, reporting, ISO audit support, and documentation.

* Utilize the latest revisions of current standards: ANSI/NCSL Z540-1 or ISO Guide 25, not Mil-Std-45662A which was canceled some years ago.

* Show "steps of traceability" to NIST. The more steps, the more uncertainty.

* Help set up proper recalibration schedules pertaining to the usage of the gaging being calibrated. No gaging in continuous use should exceed 1 year for recalibration; while most hand held gaging in use should be calibrated every 3 to 6 months.

* Consider becoming accredited to either A2LA (American Association for Laboratory Accreditation) or NVLAP (National Voluntary Laboratory Accreditation Program). This shows through auditing and testing that the laboratory/calibration service is competent in its scope of calibration. It is important to verify what your provider's "scope" of calibration includes. Note that ISO 9002 does not apply to metrology labs and services. It only states that paper-work was in order at the time of the most current audit and says nothing about proficiency.

It is preferable to have off-site calibration performed before the onsite calibration. Not all measuring instruments can be calibrated onsite for two primary reasons:

1. Some need strict environmental conditions, such as those found in most metrology labs.

2. The equipment needed to perform these types of calibrations is delicate.

Gages to be calibrated off-site include gage blocks; cylindrical gages such as rings, plugs, and discs; thread gages; taper gages; and other close tolerance pieces generally used as masters or high magnification indicating devices.

If these types of gages can be shipped or delivered to the lab prior to the on-site visit, the lab team can usually return them when they arrive to calibrate the others. This pre-on-site calibration minimizes total gage downtime during the on-site by staggering the periods of gage/hand tool inactivity. Larger equipment such as optical comparators, super mics, hardness testers, and other big bench measuring equipment can usually be calibrated on-site, saving the expense and anxiety of sending units of this type out for calibration.

What the on-site team will expect from you before they visit. Organization and pre-visit preparation will provide substantial benefits. Prepare a detailed inventory of your gages and request a cost estimate of the service before committing. This inventory can also serve as a database for an ongoing certification program. Retrieving and identifying all measurement equipment requiring calibration - before the visit - will help the work go quickly and efficiently, reducing the time that the tools will be out of service, and the time that the technicians must spend at the facility. Having the calibration technicians standing by waiting while you search and transport gages may add costs above and beyond the quoted calibration estimates.

Having an area set up for the calibration technicians to work in is also a good idea. A clean, dry, empty worktable with electrical outlets close by, in an area where the air temperature stays fairly constant throughout the day would be ideal for most on-site crews. However, they have been known to live with less.

What you should expect from the on-site calibration team. When the calibration technicians arrive, and after they set up, the procedure for each gage should go something like this: Each gage is initially inspected and its condition is noted for overall functionality of its intended use before cleaning and adjusting. This fulfills requirements for both ISO and ANSI for reporting "as found" condition of the gage. Next, the gage is cleaned, observed for missing and/or worn parts, contact points, etc, and then checked for performance. Identification data, such as serial number, description, and gage type, are then entered into the computer system via dedicated calibration software. Then the actual calibration begins. Technicians will follow proper, written procedures. Each calibration will use certified master gages, and the data obtained will be entered into calibration software. Upon completion of the reporting, a calibration sticker is applied to the gage and a long form certification report is printed, signed, and issued. At the conclusion of the onsite visit, computerized printouts or disks are provided for inventory listings including serial numbers, gage types, locations, and recalibration dates for all gaging equipment. Some calibration services will notify their customers with a call or letter 45 days prior to becoming due, triggering scheduling of the next visit.

After the initial on-site visit, subsequent calibration sessions should be simpler to prepare for and conduct. Although it requires some up-front preparation and organization costs, the total program pays off over the long run in several ways:

* Increased control with a standardized database that will make your "ISO life" easier,

* Gage calibration and procedures are no longer an internal worry,

* Gaging maintenance has been improved, meaning your gages will function better and last longer, and

* Up-to-date inventory lists tend to keep gages around the shop, where you can find them.