Standards and Calibration

Quick reference

• 00:04 Hello, I'm Ray Sheen.
• 00:05 Now key elements of the management and maintenance of any measurement system is
• 00:10 the use of standards and the calibration of those.
• 00:13 Let's explore both of those and see how a measurement system error can be managed.
• 00:18 I'll start with an explanation of a measurement standard.
• 00:23 In fact, let me back up for a moment and introduce the term metrology.
• 00:27 Metrology is the study of measurement systems.
• 00:30 Many organizations have a metrology department.
• 00:33 It may be just a one man show but that department is responsible for
• 00:36 the management of the measurement systems in the organization.
• 00:40 Now, I don't mean the operational management of those measurement systems,
• 00:44 but rather for managing the process of calibration and maintaining,
• 00:48 certifying, and sometimes even designing the measurement systems.
• 00:52 This organization will also normally guide the conduct of Gage R&R studies, but
• 00:56 more about that in other lessons.
• 00:59 The metrology department will determine the standards that will be used to
• 01:02 calibrate all measurements system.
• 01:04 A measure standard is an object system where experiment that
• 01:08 bears a defined relationship to the unit of measurement of the physical entity.
• 01:12 The standard defines a unit of measure, but just to be clear
• 01:16 this is a different definition of standard than what is used to set policies and
• 01:21 procedures, such as an ISO standard or IEC standard.
• 01:24 This is an actual physical item that is measurable.
• 01:28 These measurement standards are used as references for
• 01:30 determining the efficacy of a measurement system.
• 01:33 The precise value of a standard is known.
• 01:35 The measurement system measures the standard and
• 01:38 will ideally register that value.
• 01:40 If not, there is a problem with the measurement system that must be corrected.
• 01:45 The use of a measurement standard builds confidence in the measurement system.
• 01:49 The operators and
• 01:50 managers trust that the values registered in the measurement system are correct.
• 01:54 It also enables an organization to use different technologies for
• 01:57 measuring the same parameters and have confident that these
• 02:00 measurement values can be combined or compared for analytical purposes.
• 02:05 And with the use of this standards, a common language for
• 02:08 describing characteristics and performance can be used universally.
• 02:12 An aeroplane's air speed value is understood the same way
• 02:15 no matter what country the aeroplane is flying over.
• 02:18 Standards are often used to perform calibration.
• 02:22 Let's look at this process.
• 02:24 The purpose of a calibration is to ensure the measurement system
• 02:27 is registering accurate values,
• 02:29 that means that it is used to remove bias in the measurement system.
• 02:33 Calibration relies upon a standard.
• 02:35 The standard item is a known value.
• 02:37 The measurement system measures the standard item.
• 02:40 If the value registered by the measurement system does not match the known value,
• 02:43 the system is adjusted until it does match.
• 02:46 If a measurement system has relatively high precision errors, the calibration
• 02:50 checks should be accomplished several times to create a distribution, and
• 02:54 the adjustment is then made to shift the average or mean of that distribution.
• 02:59 Let's focus on the standard for a minute.
• 03:01 An obvious question is how do we know the true value of the standard.
• 03:04 What if the measurement system used to give the value of the standard
• 03:07 had errors in it?
• 03:08 That is why a metrology department will always use standards that are traceable to
• 03:13 national or international standards.
• 03:15 Many countries have national standards labs, which will calibrate measurement
• 03:19 equipment for organizations or provide a very precise and accurate measurement
• 03:24 of a standard that the company will use to perform their own calibrations.
• 03:28 If not,
• 03:29 the company will send the equipment off to these labs to be calibrated by them.
• 03:33 Then of course these natural labs will trace their standards back to
• 03:36 international standards of measure.
• 03:39 Measurement systems used in most companies especially those that have certified audited
• 03:43 quality systems will have a calibration system in place for
• 03:47 all measurement systems in use.
• 03:49 Most items have a duration period for that calibration.
• 03:52 At the end of that period,
• 03:54 the item is recalibrated in order to remove any stability concerns.
• 03:58 Measurement systems should not be used if the calibration time and
• 04:02 period has expired.
• 04:03 The organization's metrology department will usually have a list of all
• 04:08 calibrated measurement systems and track when calibration time periods expire.
• 04:13 They're responsible for
• 04:14 scheduling a recalibration of the system when appropriate.
• 04:17 So let's sum up the last few lessons concerning the measurement system errors
• 04:21 and what we can do about them.
• 04:23 First, the good news is that measurement system errors can be identified and
• 04:27 either controlled or even eliminated.
• 04:30 But that doesn't occur by accident, it requires actions by the metrology
• 04:33 department, the process management, and the operator.
• 04:37 Accuracy or bias errors can be eliminated and controlled by regular calibrations
• 04:42 with known traceable standards that are appropriate for the type of measurement.
• 04:46 Precision errors that are due to common cause variation in the use of
• 04:50 the measurement equipment can be identified and
• 04:52 quantified through the use of a Gage Repeatability and Reproducibility Study.
• 04:57 If this common cause errors cannot be controlled,
• 04:59 a different measurement system should be used.
• 05:01 Our next lessons will discuss how to do a Gage R&R study.
• 05:06 Stability or
• 05:07 drift errors can be identified by the regular use of Golden Standards.
• 05:11 These problems can be controlled by addressing the underlying cause of
• 05:14 the drift.
• 05:15 It might be the use of the measurement system procedures or
• 05:18 the monitoring management and maintenance of the measurement system itself.
• 05:22 Ultimately, if the stability cannot be controlled,
• 05:25 a new different system should be used.
• 05:27 Linearity or bias shift problems are based upon the ideal range of the measurement
• 05:32 system being used.
• 05:33 If there is a problem, the only option is to select a different measurement system.
• 05:38 And finally, discrimination is a resolution designed into the system.
• 05:41 Again, if it's a problem, you must pick a different system.
• 05:45 Standards and calibration are two of the important tools that we use to manage and
• 05:51 maintain our measurement system.

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