July 31, 2008
In the maintenance of dimensional metrology equipment, organizations have a choice when it comes to who performs calibration: the organization itself, the gage manufacturer or a calibration laboratory. An organization needs to consider a variety of factors before making this decision.
Basic RequirementsIf an organization wants to calibrate its own instruments correctly, it must be able to verify traceability to the National Institute of Standards and Technology (NIST). Also, the organization should be able to meet a 4:1 accuracy level, meaning that the standard it is using is four times more accurate than the gage being inspected. In addition, customers may require that instruments be calibrated by accredited organizations.
The resources-equipment and knowledgeable technicians-to satisfy the aforementioned requirements are out of reach for many organizations. Very large organizations with thousands of gages to calibrate may be able to justify the cost of investing in such resources, but smaller organizations usually cannot.
“The decision basically comes down to dollars and cents,” says George Schuetz, director of precision gages for Mahr Federal Inc. (Providence, RI). “How many gages and standards need to be controlled and what is the external cost of doing this? This is then compared to the cost of buying and maintaining calibration equipment, supporting a laboratory environment, the cost of accreditation, and the training and salary costs of the calibration technicians.”
Calibration LabsIf an organization elects to outsource calibration, it usually has two choices: calibration laboratories or the gage manufacturer. Most calibration laboratories will be accredited to the internationally recognized ISO/IEC 17025: 2005 General Requirements for the Competence of Calibration and Testing Laboratories.
The use of a 17025-accredited laboratory can bring an organization both the benefits of ensured accuracy and lower overhead because the laboratory is the one investing in the capital and personnel, rather than the owner of the gage. When such a laboratory is used, it is ensured that the calibration is performed according to 17025, that the calibration is performed in a controlled environment and that proficient technicians are performing the calibration.
“Calibration is the main focus of a calibration laboratory,” says Eric Lundquist, president of A.A. Jansson (Waterford, MI). “They are performing the same types of calibrations routinely. Therefore, they are typically more efficient at the calibration. In addition, because the calibration laboratory’s only focus is calibration, they have invested in equipment that is accurate, fast and efficient.” Lundquist also points out that a calibration laboratory may be more up to date in terms of technique, methods and relevant standards than a do-it-yourself organization.
When choosing a calibration laboratory, there are typically two choices: specialized or comprehensive. As the names suggest, a specialized laboratory will have a much narrower scope than a comprehensive laboratory; however, such laboratories may be able to perform calibrations not available from larger laboratories. Because specialized laboratories only concern themselves with a limited scope, they also may have lower uncertainties than comprehensive laboratories and, therefore, more accurate calibration capabilities.
“Industries such as aerospace and medical may have very tight tolerances and thus require the most accurate masters,” says Schuetz. “For this high-end calibration, a specialized calibration facility may be the only and right choice.”
On the other hand, comprehensive laboratories offer convenience, but may not be able to match the accuracy and certain calibrations that specialized laboratories can perform.
The organization needs to decide which type of laboratory is appropriate based on criteria such as required accuracy and instrument variety.
Gage ManufacturersSome gage manufacturers also perform calibration. In many cases, a manufacturer will have a specialized laboratory used for calibrating proprietary or custom equipment. “Typically in these situations the manufacturer has protected the software or hardware in such a way that only the manufacturer will have access to the areas needed to adjust and improve accuracy,” says Lundquist.
Also, the manufacturer will have expertise in its own instruments and more than adequate repair capabilities. “When a client sends their tool to The L.S. Starrett Co., it is repaired using original parts by current craftsmen and inspected or calibrated to meet all performance and accuracy requirements of a new tool,” says Dexter Carlson, chief inspector, Starrett Calibration Laboratory (Athol, MA).
However, because a gage manufacturer puts much of its resources into making gages, it will typically have a longer turnaround time and higher costs than calibration laboratories. Also, manufacturers may not be accredited to 17025.
“The manufacturer has initially set up the parameters for their instruments,” says Bill Hangartner Sr., president of Quality Calibration Service Inc. (West Allis, WI). “However, it has never been mandated that they must meet uncertainty requirements or adhere to a specific standard.” Hangartner does concede, however, that many manufactures are becoming accredited to 17025.
The paramount concern when choosing where to have a gage calibrated- either a calibration laboratory or the gage manufacturer-should ultimately be the prospective company’s credentials, in this case its statement of scope and statement of uncertainty. The former will verify that a company is accredited and describe the extent of its scope; the latter states that a company is cognizant of its sources of error and can describe its confidence in measurement.
“You should always ask for and review these statements before making your selection, whether it be the manufacturer or a calibration laboratory,” stresses Schuetz. “They are the heart and soul of the calibration facility, and there is nothing wrong with asking for supporting documentation.”
Value 17025-Accredited LabsBesides the fact that customers may mandate it, it may be beneficial to use a 17025-accredited laboratory because such facilities will have competent, highly trained technicians and will operate under standardized procedures and polices. “17025 accreditation ensures that the lab has stated, quantified and understands its measurement uncertainties,” says Scott Sokolik, technical supervisor, Edmunds Gages (Farmington, CT). “It also ensures that the accredited laboratory has a control on its measurement process and that it must go through annual proficiency tests to ensure that it is still competent in measuring.”
In the United States, 17025-accredited labs are awarded accreditation and then periodically assessed by accreditation bodies such as A2LA, NVLAP, ACLASS, IAS and L-A-B. These accreditation bodies are recognized by the International Laboratory Accreditation Cooperation (ILAC) and signatories to the ILAC mutual recognition arrangement (MRA). Calibration laboratories that are accredited by such bodies possess international credence because their accreditation body has signed onto the ILAC MRA, which is a vehicle that promotes international acceptance of accredited calibration results.
17025-accredited laboratories also have to participate in calibration studies with NIST and other laboratories to compare accuracy capabilities. Furthermore, an accredited laboratory must have its measurement uncertainties and entire scope published for prospective clients to see.
All accredited laboratories, however, are not created equally, and a laboratory that offers a low price may also be offering a low-quality calibration. To be sure of a laboratory’s competence, an organization should evaluate its uncertainty budgets. “Laboratories with questionably low uncertainties may have overlooked some sources of uncertainties,” says Jack Gaughan, sales manager for custom gaging, Edmunds Gages. “Uncertainties are usually proven in proficiency tests. Performing a personal audit of a laboratory is a sure-fire method for understanding its strengths, weaknesses and uncertainties.”
Also, the competency of laboratory personnel should be checked by acquiring about internal quality training and educational programs. “There is a shortage of qualified PMEL (precision measurement equipment laboratory)-trained technicians,” says Mark Dillard, director of sales, marketing and new business programs for Sypris Test & Measurement (Orlando). “Less competent calibration technicians are calibrating customers’ equipment.”
In addition, if an organization wants to use an accredited laboratory, it needs to be sure that the prospective laboratory is, in fact, accredited-a laboratory may say it is 17025 compliant, meaning that it adheres to the standard, but has never been assessed and validated by a qualified third party.
Understanding industry requirements and calibration options will help an organization get the most out of its dimensional metrology instruments-not to mention its budget. While cost is important, gage accuracy should not be compromised. A thorough examination of options will ensure that money spent will result in value. Q
Sidebar: IS0 9001: The Catch-22When looking for an accredited laboratory to handle dimensional metrology instrument calibration, an organization should be cognizant of the differences between the general ISO 9001: 2000 Quality Management Systems - Requirements and the industry-specific ISO/IEC 17025: 2005 General Requirements for the Competence of Calibration and Testing Laboratories.
First and foremost, while both standards are used to create management systems and also have areas that have been aligned, demonstrating compliance to the one does not equate with compliance to the other. 9001 can be applied to any and all organizations for the creation of a management system.
While 17025 contains much of the same content as 9001 on management system requirements, its fifth section, Technical Requirements, is not included in 9001. As the name suggests, this section states the technical requirements specific to test and calibration laboratories.
Secondly, organizations are certified to 9001 and accredited to 17025. This means that certification bodies grant 9001 certification, while accreditation bodies grant 17025 accreditation. Calibration laboratories-as well as organizations that use them-need to be wary of certification bodies claiming to be able to assess for 17025 accreditation; the resultant accreditation would not be valid because certification bodies have not been granted the authority to assess the technical content of 17025’s Section 5.
Because much confusion persists in industry as to the purpose of each standard, some calibration laboratories spend the time and money to ensure compliance to both standards, as not doing so could result in lost business. Quality Calibration Service Inc. (West Allis, WI) is one such laboratory, as President Bill Hangartner Sr. explains, “We do it strictly as a marketing tool because a lot of people don’t understand what’s going on-and I’m talking manufacturing sector.”
Though dual compliance can be leveraged as a marketing tool, it is not necessary and in reality a redundancy. “It’s a major catch-22. Do we or do we not? We would have some fallout so we’ve elected, from a management standpoint, to continue with the 9001: 2000,” says Hangartner.
Tech TipsIf an organization wants to calibrate its own instruments correctly:
- It must be able to verify traceability to the National Institute of Standards and Technology (NIST).
- It should be able to meet a 4:1 accuracy level.
- It needs to learn whether customers require instruments to be calibrated by an accredited organization.
For more information about the companies mentioned in this article, visit their Web sites:
- A.A. Jansson, www.aajansson.com
- Edmunds Gages, www.edmundsgages.com
- Mahr Federal Inc., www.mahr.com
- Quality Calibration Service Inc., www.qualitycalibration.com
- Starrett Co., The L.S., www.starrett.com
- Sypris Test & Measurement, www.sypris.com
Qualtiy OnlineFor more information on dimensional measurement equipment, visit www.qualitymag.com to read these articles:
- “Changes Come to Gage Blocks”
- “Get Answers for CMM Calibration Uncertainty”