Imagine that you oversee the quality control department for a small lug nut manufacturer that supplies the major U.S. automakers. One night, as you're watching the news, the station features a story about a car that lost one of its wheels while traveling more than 55 miles per hour. The car hit a guard rail, and all persons in the vehicle were badly injured. The ensuing investigation determines that the wheel failed because its lug nuts sheered off.

The problem ultimately is traced to a torque wrench, used during the lug nut manufacturer's final inspection, that hadn't been calibrated in more than 10 years. Consequently, it displayed incorrect torque values. You can't understand how this could have happened because your company is registered to ISO 9000 and recently achieved QS-9000 compliance. Upon reflection, however, you realize that the wrench never was entered into the calibration system and therefore never addressed during the audit.

Unfortunately, the foregoing isn't an unrealistic situation. If the lug nut manufacturer had established a more effective calibration system, then the fastener failure would never have occurred. No one wants to be part of a situation like this, which is one reason why companies are tightening down on calibration system requirements for themselves and their vendors.

Ever since specific quality systems became an integral part of manufacturing in the United States, explicit requirements for calibration have represented major issues for companies both large and small. Well-known quality systems such as ISO 9000 and QS-9000 enforce these calibration requirements within their assessments, but it's impossible to assess everything during an audit. Organizations themselves must ensure that their calibration equipment is accurate and effective. This article lays out the basics for establishing a reliable calibration system or improving upon an existing one.

Start simply

Constructing a system from scratch requires long-term planning and good organization. A calibration system is complicated enough, so the simpler the system, the easier it will be for everyone to maintain it. And maintenance is the key to a successful calibration system once you've created it.

As a first step, you must control all your gauges, which includes any measurement device. To do this effectively, each gauge must be identified separately. You can do this by using an internal gauge identification system. Simply assign each gauge an ID number and display it on the gauge by means of a sticker or tag, engraving, etching or even bar coding. How you identify your gauges depends on the type and number of gauges in the system. If your company uses many gauges, the ID process will take some time but is very necessary.

After identification, determine the gauges' status as active, inactive or reference. Active gauges are used frequently and directly affect a product's quality. Inactive gauges, commonly spares or replacements, comprise part of the calibration system but await active status. Additionally, once an inactive gauge becomes active, it must have a valid calibration record before it's used. Finally, reference gauges are identified within the system but don't affect product quality. gauges used in reference applications should be labeled as such.

 Once all gauges have been assigned a status, devise a calibration schedule for every active and inactive gauge. The schedule, usually every year for most industries, should be based on working conditions and how frequently a gauge is used. The harsher the conditions and the more it's used, the more often the gauge should be calibrated.

Documenting each gauge's limitations and location represents another important detail of an efficient calibration system. gauges aren't perfect, so tolerances must be identified. Also, maintaining full control over every gauge is critical. Therefore, you must track and document every gauge's location in your working environment. This includes all employee-owned gauges.

Assess potential laboratories

After you've determined the identification, status, calibration schedules, tolerances and locations for all gauges, establish who will perform the actual calibration. Will it be done internally by a qualified technician or by an independent calibration laboratory? You must base this decision upon the following criteria:

• Do you have the proper equipment as well as standards traceable to an international or national organization such as the National Institute of Standards and Technology?

• Do you have the proper environment to perform valid calibration?

• Do you have qualified personnel to perform calibration?

• Do you have valid resources and standards?

If you are lacking any of the above, you may want to consider sending your gauges to an independent calibration laboratory. The American Association for Laboratory Accreditation provides a list of accredited labs; check them out on A2LA's Web site at www.a2la.org. Other resources include trade publication lists such as Quality Digest's Testing Laboratory Guide in its August issue.

When choosing a laboratory, keep in mind the following steps. First, contact the lab and set up an appointment to tour the facility. Sometimes, however, the closest laboratory is in another state. If you choose not to travel, then conduct an extensive phone interview and follow it up with a written quality survey. Sample questions that you could ask either on-site or over the telephone include:

• Is there a laboratory on the premises, or do you subcontract?

• Are there written procedures, and could we view them?

• Are you registered to an established quality system such as ISO 9002?

• Are all calibration methods and standards traceable to NIST?

• Do you have additional laboratory accreditation from organizations such as A2LA or the National Voluntary Laboratory Accreditation Program?

• What do you include on your calibration certifications, and can you send me a sample?

• What are your turnaround times?

• How long do you keep customer calibration records on file?

• When gauges come due for calibration, do you automatically remind your customers?

These aren't unusual questions or requests, and any laboratory unwilling to provide objective evidence that they can satisfy your requirements shouldn't be considered. Remember, the laboratory will be calibrating your gauges that affect your product. Don't take shortcuts about calibration issues with a vendor. If you do, you may set yourself up for unnecessary problems.

Should you choose to calibrate your own gauges, keep in mind that eventually you'll have to use a calibration laboratory to certify and lend traceability to your own standards. When you successfully choose one or more laboratories, you should inform them of all your specific requirements in advance. Assume nothing. Your requirements or a reference page should appear on your purchase order.

Take care of details

After you establish the sources for your gauges' physical calibration, organize all the details outlined in this article. The easiest way to get and stay organized is to invest in gauge tracking software. You should look for a user-friendly application that automatically flags gauges due for calibration. If you use only a handful of gauges or choose not to invest additional money, then a simple database or spreadsheet also will work. Whatever organizational method you use, don't let any gauges exceed their set calibration due dates.

The last phase of creating a calibration system involves determining the type of calibration certification or records you'll keep on file. Independent laboratories offer two different certifications. Generally, the most popular is known as a long form certification. For most labs, this certification includes data for each test performed. Furthermore, it's the most commonly accepted form by recognized quality systems. The other certification option is the short form or compliance certification. This type merely attests that the gauge tested has been calibrated with standards traceable to an international or national organization.

Building a calibration system from scratch takes time. Planning and patience are the main prerequisites in establishing a successful system, so don't rush into it. Details like identification, status, calibration sources, organizational system, calibration schedule, tolerances and certification type sometimes get overlooked but are vital to a working system.

Improvement tips

The same steps for establishing a working calibration system should be followed when evaluating a system for improvements. Details such as calibration due dates, new gauge ID numbers and certification requirements sometimes fall through the cracks. When this happens, a system can't function properly or efficiently. The person responsible for maintaining the calibration system represents another contributing factor to this problem. Often, this individual has other responsibilities within a company and must spend time on other projects. In such cases, once again, good organization is a must.

When evaluating an existing system, first determine what types of problems, if any, are occurring. Then see where the system can improve in gauge control, status, calibration documents, calibration procedures, vendors, calibration schedules, gauge location and overall organization. If any of these aspects are missing from the system, implement them.

Keep your calibration system as simple as possible. When creating or improving a system, do it in a universal fashion. The turnover rate is high for quality department personnel. If the calibration system director leaves the position, his or her successor shouldn't run into problems keeping the system maintained. Many different details make up a successful calibration system. If you stay organized, you can count on having a trouble-free, mature system.