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articles:optimizing_calibration_intervals [2023/02/01 18:35] – [Initial Calibration Intervals] rrandallarticles:optimizing_calibration_intervals [2025/02/20 10:40] (current) – [Methodologies for the Determination of Calibration Intervals] rrandall
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 Most M&TE are on arbitrary 12 month calibration intervals... as if “one size” fits all. These are typical “manufacturer-recommended intervals” - which are often extremely conservative because the manufacturer wants their calibration labs to stay busy. And most companies happily pay them to do so. Yes… over-calibrating M&TE reduces risk… but only to a degree((A MUCH better way to reduce risk is to increase the minimum "Accuracy Ratio" between the M&TE and the tolerance of the characteristic being measured, but that's a topic for a separate article.)). Is it efficient or cost-effective? No. Does the reduction in risk justify workers being without M&TE or the company paying excessive amounts for this “over calibration”? In most situations, the answer is a resounding NO! Most M&TE are on arbitrary 12 month calibration intervals... as if “one size” fits all. These are typical “manufacturer-recommended intervals” - which are often extremely conservative because the manufacturer wants their calibration labs to stay busy. And most companies happily pay them to do so. Yes… over-calibrating M&TE reduces risk… but only to a degree((A MUCH better way to reduce risk is to increase the minimum "Accuracy Ratio" between the M&TE and the tolerance of the characteristic being measured, but that's a topic for a separate article.)). Is it efficient or cost-effective? No. Does the reduction in risk justify workers being without M&TE or the company paying excessive amounts for this “over calibration”? In most situations, the answer is a resounding NO!
  
 +[[https://openclipart.org/detail/544/balance-scale|{{ :articles:gerald-g-balance-scale.png?direct&160|}}]]
 If M&TE calibration intervals were optimized based upon performance, optimal calibration intervals for some instruments might be 18 months, 24 months, or even longer. This results in immediate tangible cost savings. And while a few instruments may require shorter calibration intervals (e.g., 9-month intervals), immediate intangible savings are realized through the increased confidence in the reliability of the M&TE. If M&TE calibration intervals were optimized based upon performance, optimal calibration intervals for some instruments might be 18 months, 24 months, or even longer. This results in immediate tangible cost savings. And while a few instruments may require shorter calibration intervals (e.g., 9-month intervals), immediate intangible savings are realized through the increased confidence in the reliability of the M&TE.
  
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 Methodologies for the determination of calibration intervals are defined in documents such as: Methodologies for the determination of calibration intervals are defined in documents such as:
-  * [[https://ilac.org/?ddownload=818|ILAC G24:2007, "Guidelines for the determination of calibration intervals of measuring instruments"]] (free)+  * [[https://ilac.org/publications-and-resources/ilac-guidance-series/|ILAC G24:2022, "Guidelines for the determination of calibration intervals of measuring instruments"]] (free)
   * [[http://www.ncsli.org/i/ItemDetail?iProductCode=RP_01|NCSLI "RP-1: Establishment and Adjustment of Calibration Intervals"]] ($80)   * [[http://www.ncsli.org/i/ItemDetail?iProductCode=RP_01|NCSLI "RP-1: Establishment and Adjustment of Calibration Intervals"]] ($80)
 There are many methods and theories to calculate calibration intervals, such as those found in NCSL RP-1, Method S1 (Classical Method), Method S2 (Binomial Method), and Method S3 (Renewal time Method). As a result, it can be difficult to choose the best method to determine the interval (Ref. [[https://www.researchgate.net/publication/268400268_A_QUANTITATIVE_COMPARISON_OF_CALIBRATION_INTERVAL_ADJUSTMENT_METHODS|"A Quantitative Comparison of Calibration Interval Adjustment Methods"]]). There are many methods and theories to calculate calibration intervals, such as those found in NCSL RP-1, Method S1 (Classical Method), Method S2 (Binomial Method), and Method S3 (Renewal time Method). As a result, it can be difficult to choose the best method to determine the interval (Ref. [[https://www.researchgate.net/publication/268400268_A_QUANTITATIVE_COMPARISON_OF_CALIBRATION_INTERVAL_ADJUSTMENT_METHODS|"A Quantitative Comparison of Calibration Interval Adjustment Methods"]]).
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 [[http://www.isgmax.com/|Integrated Sciences Group (ISG)]] offers a free "Method S2" interval calculator (for MS Windows only) augmented by the "Method A3 Interval Tester" (adjusting for "sparse" data) called [[http://www.isgmax.com/calint_freeware.htm|IntervalMAX]]. [[http://www.isgmax.com/|Integrated Sciences Group (ISG)]] offers a free "Method S2" interval calculator (for MS Windows only) augmented by the "Method A3 Interval Tester" (adjusting for "sparse" data) called [[http://www.isgmax.com/calint_freeware.htm|IntervalMAX]].
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-Perhaps the simplest and most widely used methodology for optimizing calibration intervals is the "Automatic adjustment" or “Staircase” method (described in [[https://ilac.org/?ddownload=818|ILAC G24:2007, sec. 3, "Methods of reviewing calibration intervals"]]).+Perhaps the simplest and most widely used methodology for optimizing calibration intervals is the "Automatic adjustment" or “Staircase” method (described in [[https://ilac.org/publications-and-resources/ilac-guidance-series/|ILAC G24:2022, sec. 6.2 "Method 1: Automatic adjustment or “staircase” (calendar-time)"]]).
  
 ==== Using the “Staircase” method ==== ==== Using the “Staircase” method ====
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 Each time an instrument is calibrated on a routine basis, the subsequent interval is extended IF it is found to be within a certain percentage (e.g., 80%) of the maximum permissible error that is required for measurement, or reduced if it is found to be outside this maximum permissible error. \\ Each time an instrument is calibrated on a routine basis, the subsequent interval is extended IF it is found to be within a certain percentage (e.g., 80%) of the maximum permissible error that is required for measurement, or reduced if it is found to be outside this maximum permissible error. \\
  
-Of course this method assumes that the company is being provided with “as found” data for each calibration performed. \\+Of course, this method assumes that the company is being provided with “as found” data for each calibration performed. \\
  
-[[https://openclipart.org/detail/544/balance-scale|{{ :articles:gerald-g-balance-scale.png?direct&160|}}]] +A critical component when using this methodology is determining the percentage of the maximum permissible error. The higher the percentage, the greater the risk of an instrument being found Out-of-Tolerance (OOT); potentially resulting in nonconforming product escapes. The lower the percentage, the greater the cost associated with lowering the risk of an OOT condition; and reducing the potential for nonconforming product escapes. This percentage will often vary based on the type of instrumentation to which it is applied. \\
-A critical component when using this methodology is determining the percentage of the maximum permissible error. The higher the percentage, the greater the risk of an instrument being found Out-of-Tolerance (OOT); potentially resulting in nonconforming product escapes. The lower the percentage, the greater the cost associated with lowering the risk of an OOT condition; and reducing the potential for nonconforming product escapes. This percentage will often vary based upon the type of instrumentation to which it is applied. \\+
  
-Most often companies establish a "range" (or "window") for the optimization. For example, IF an instrument is found exceeding 75% of its maximum permissible error, then the calibration interval is shortened. However, IF an instrument is consistently found below 50% of its maximum permissible error, then the calibration interval is lengthened. And IF the instrument is found between 50% and 75% of it's maximum permissible error, then the interval is considered acceptable.+Most often companies establish a "range" (or "window") for the optimization. For example, IF an instrument is found to exceed 75% of its maximum permissible error, then the calibration interval is shortened. However, IF an instrument is consistently found below 50% of its maximum permissible error, then the calibration interval is lengthened. And IF the instrument is found between 50% and 75% of its maximum permissible error, then the interval is considered acceptable.
 ===== Initial Calibration Intervals ===== ===== Initial Calibration Intervals =====
  
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 ===== Usage-Based Intervals ===== ===== Usage-Based Intervals =====
  
-A topic rarely seen addressed is the establishment of calibration intervals based upon usage rather than time. This generally applies to dimensional gages +A topic rarely seen addressed is the establishment of calibration intervals based on usage rather than time. This generally applies to dimensional gages 
  
-<note>ASME B1.7-2006, "Definitions", defines a "gage" as: "//a device for inspecting / evaluating a limit or size of a specified product dimension.//". \\ +<WRAP center round info 80%> 
 +ASME B1.7-2006, "Definitions", defines a "gage" as: "//a device for inspecting/evaluating a limit or size of a specified product dimension.//". \\ 
  \\  \\
 More specifically, "Gages" are instruments WITHOUT indicators (e.g., Gage Blocks, Pin Gages, Ring Gages, Thickness Gages, Thread (Plug) Gages, Thread Pitch Gages, Threaded Ring Gages), used as a standard for comparative determinations (e.g., inspections). Gages are typically used for "Go/NoGo" or "Pass/Fail" measurements. \\ More specifically, "Gages" are instruments WITHOUT indicators (e.g., Gage Blocks, Pin Gages, Ring Gages, Thickness Gages, Thread (Plug) Gages, Thread Pitch Gages, Threaded Ring Gages), used as a standard for comparative determinations (e.g., inspections). Gages are typically used for "Go/NoGo" or "Pass/Fail" measurements. \\
  \\  \\
-In contrast, "Gauges" are instruments WITH indicators (e.g., Analog OR Digital Multimeters, Dial Indicators, Force Gauges, Pressure Gauges) used to obtain measurements. This includes Digital, Dial, OR Vernier devices, such as Calipers or Micrometers.</note>+In contrast, "Gauges" are instruments WITH indicators (e.g., Analog OR Digital Multimeters, Dial Indicators, Force Gauges, Pressure Gauges) used to obtain measurements. This includes Digital, Dial, OR Vernier devices, such as Calipers or Micrometers. 
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 The ONLY way that a "gage" can change is through either "wear" (e.g., from "grit") or "damage".  The ONLY way that a "gage" can change is through either "wear" (e.g., from "grit") or "damage". 
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 A simple way to utilize “usage-based” calibration intervals for gages is to purchase plain (Go / No Go) plug gages that have a black-oxide treatment to show wear patterns - indicating when the gage needs to be calibrated or replaced. As an added benefit, the black oxide treatment provides a mild layer of corrosion and abrasion resistance (reducing wear).  A simple way to utilize “usage-based” calibration intervals for gages is to purchase plain (Go / No Go) plug gages that have a black-oxide treatment to show wear patterns - indicating when the gage needs to be calibrated or replaced. As an added benefit, the black oxide treatment provides a mild layer of corrosion and abrasion resistance (reducing wear). 
-<note warning>Be advised that using an ultrasonic cleaner with solvent COULD remove all of the black oxide. So you should check with the manufacturer to get clarification of using this cleaning technique; vs. simply wiping them down to remove any grit. Alternatively, black oxide-treated gages can be oiled to add an extra layer of protection.</note> 
- 
- 
  
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 +Be advised that using an ultrasonic cleaner with solvent COULD remove all of the black oxide. So you should check with the manufacturer to get clarification of using this cleaning technique; vs. simply wiping them down to remove any grit. Alternatively, black oxide-treated gages can be oiled to add an extra layer of protection.
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