Calibration, certification and verification: A quick primer

08/29/2016 16:52:40

What are the differences between these three important industry terms?

ARTICLE CONTENT

Inspectors should be able to tell the difference between important industry terms, especially when they can impact getting the job done right. While it's easy to get confused about the differences, there are some key features to help you tell these different processes apart: calibration, certification and verification.

Before we get into what makes each of them unique, let's start with what they have in common. All three have to do with the state of equipment: Though they apply to many other industries, we're interested in the way they pertain to inspection equipment.

Let's look at the specifics of each process and how they can come together for a better test.

Calibration

ASTM D7091 defines calibration as “the high-level, controlled and documented process of obtaining measurements on traceable calibration standards over the full operating range of the gage, then making the necessary gage adjustments (as required) to correct any out-of-tolerance conditions.” It goes on to point out that calibration, “is performed by the equipment manufacturer, their authorized agent or by an accredited calibration laboratory in a controlled environment using a documented process.”

Calibration Adjustment is the act of adjusting a tool, generally with the use of a standard, to adjust it to work properly in for your current project. Most equipment comes with a factory calibration, however; the factory calibration is generally not the one you should use on your current project.

Not all instruments can be calibrated in the field. Electronic Dry Film Thickness gauges, Surface Profile Gauges, UT gauges, conductivity and pH meters are all made to be user calibrated along with some Dew point meters. Other meters have fixed calibrations and cannot be calibrated in the field or by the user. These include Banana gauges, many Dew Point Meter gauges, adhesion and holiday testers.

"When you calibrate a tool, you're adjusting it to maximize accuracy."

Every instrument has its own unique calibration method and you should always defer to the product's manufacturer and their directions for proper calibration. Most manufactures make their own standards to calibrate their instruments and they are normally certified to NIST (National Institute of Standards and Technology).

Some standards are made by NIST and can be used for calibration. There are exceptions, so check with the instrument manufacturer. Most standards can be used with any manufacturer's instruments.

Make sure that the standard you choose is compatible with your chosen equipment and matches the appropriate substrate. Standards will also vary in terms of how accurate they are, so understand this before selecting the standard for your next project.

Verification
As previously stated, not all instruments can be calibrated in the field. This does not relieve the inspector from verifying that the instrument being used is accurate. A prime example is using a Banana Gage (Type 1 DFT gage). Inspectors should not change the factory calibration but need to verify the accuracy of the instrument prior to using it. In addition, while calibration cannot be done, accuracy of the gauge can be increased by taking a magnetic base reading prior to use. See the coating Inspection Manual for more on this.

Certification

Certification is a separate process from calibration and verification and is often a project requirement. It does not relieve the inspector from calibration adjustments or verification but is a step above them.

"Certification is a separate process from calibration and verification and is often a project requirement."

Generally calibration is required to be provided by a third party and is done in accordance with a given standard using a calibration standard, usually traceable to NIST. NIST does not provide an interval to recertify and leaves the time between certification up to the user and their quality control program. Most Manufacturers recommend certification annually.

Traceability is the ability to follow the result of a measurement through an unbroken chain of comparisons, all the way back to a fixed international or national standard that is commonly accepted as correct. The chain typically consists of several appropriate measurement standards, the value of each having greater accuracy and less uncertainty than its subsequent standards.

Certification is verification by a third party to make sure the instrument reads the standards properly and in accordance with the manufactures recommended procedure for those instrument. This process may or may not require calibration to certify the meter.

Equipment can be calibrated by the manufacturer, or a qualified third party. MTest certifies most of the instruments that we sell and provides a one-day turnaround. Some instruments do need to be sent out for certification. Check out the M-Test store for all of the equipment an inspector needs. For more information on calibration, verification and other important practices, download and read our Coating Inspectors Handbook.

CATEGORIES

Testing Tips

SOURCE

http://www.qualitymag.com/articles/84014-calibration-vs-certification http://www.defelsko.com/standards/coating-thickness-standards.htm http://www.alicat.com/alicat-blog/solutions/verification-validation-calibration/ http://www.paintsquare.com/library/articles/metalfin_measurement_terms2.pdf http://www.defelsko.com/standards/coating-thickness-standards.htm http://www.defelsko.com/applications/galvanizing/app-galvanizing.htm

KEYWORDS

painting thickness gauge