Inspec Insights

Establishing Calibration Intervals, How Often Should One Calibrate?

By James R. Lakin, Inspec, Inc. Vice President

As a calibration service provider, Inspec committed to delivering superior value to our customers through timely and efficient calibration.  As experts in the field of calibration, we are also committed to assisting our customers manage their verification and calibration program.  This includes helping them to eliminate measurement errors, while minimizing program costs, which in this situation, really means optimizing calibration intervals.  So the questions becomes, how frequently should one calibrate?

Before we can discuss frequency, we must first agree on what we mean by “calibration”.  Calibration is defined as the comparison of readings from the instrument being tested with validated reading(s) observed on a measurement standard, typically a NIST traceable standard.  In a manufacturing setting, calibration is tool used to minimize the risk of producing out of tolerance parts that might be rejected by a customer.  It’s effectively a low-cost insurance policy; generally a $100 calibration can save $1,000,000 in rejected product.  Calibration is just one of many tools used by quality professionals to minimize all sorts of risk, tangible (primarily financial) and intangible (reputation or brand integrity); they may also use interim verification (between calibrations) and SPC to monitor trends and drift in both the instruments and processes in real-time. 

Most calibrations are routinely performed per the manufacturer’s recommended frequency, which is a good starting point.  However, depending on handling, operating and storage environments, as well as the tool’s performance (which can be dynamic), this frequency may be too long or too short.  To properly set the calibration frequency for a specific tool, you’ll need data.  The more data you have on the performance of a tool, the better you’ll be able to set a proper calibration frequency that will protect against the risk of measurement errors, while minimizing program costs. 

Any accredited calibration service provider, in conformance with ISO 17025 will issue “as-found” readings for a calibration, allowing examination of the tools condition at time of calibration.  It’s a common practice to reduce the calibration interval by one half if a tool is found to be out of tolerance at time of calibration.  Likewise, if a tool is found to be in tolerance at the time of calibration, requiring no adjustment, and you have an adequate interim verification program in place to alert you to changes in the tools performance, it’s common practice to increase the calibration interval by one half.  There are also more rigorous statistical tools available to optimize your calibration intervals; you should consult your calibrations service provider for recommendations.  If Inspec is your calibration service provider, you already have access to our “InspecGAGE Management” database, which contains the entire history of our calibration work on your tools.  This is a great starting place for evaluating your tools performance and optimizing its calibration interval. 

At the end of the day, calibration is still a low cost insurance policy.  Like any insurance policy you don’t want to be caught without it, when you need it.  So whether you calibrate per the manufacturer’s recommended interval or some other interval, it’s still about managing the risk of being out of tolerance and the associated consequences to your company’s bottom-line and reputation. 

Inspec would be happy to talk with you about your calibration program, give us a call at 800-264-7194 or email sales@inspec-inc.com

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  • amandeep singh | Nov 12, 2015
    Can we have tolerance in calibration intervals?? Like can we defined that calibration can  be performed within +/- 7 days of due date??Is it complies with ISO standards.I am writing up a Calibration policy. So, pls advice

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