How to specify a calibration accuracy?

G

Gordon Clarke

#11
CalRich said:
There are times when a gage (e.g. OD micrometer) has a resolution of, say, .0001 but is only accurate to .0002 - check the specs or the gage's last calibration.
I'd be willing to go on record by stating that a measurement device's resolution is NEVER the true accuracy of the device. If this was the case why would extensive (and expensive) calibration ever be necessary? :notme:
With a bit of luck, the resolution "accuracy" could be the repetitive accuracy of the device.

Just to illustrate: is there anyone out there that really believes the speedometer on their car really shows the true speed in mph?
 
Last edited by a moderator:
Elsmar Forum Sponsor
G

Gordon Clarke

#12
The table gave me a thought. I know more about (i.e. I use more often) digital calipers than micrometers but I'm assuming the same would apply to a micrometer as to a digital caliper which is:
Specified (DIN 862) caliper measurement accuracy from 0 - 100mm is 0.02mm (when the displayed value is in 0.01mm on the caliper), from 100 - 600mm is 0.03mm and 600 - 1,000mm is 0.04mm. However measurement repeatabilty is 0.01mm, up to 1,000mm. However, still +/- the permissable deviation from the actual dimension.
The real secret behind reliable, repeatable measurement with a digital caliper is a constant measurement pressure, regardless of the user. This wil require a PM if anyone wants information on this.
 

Hershal

Metrologist-Auditor
Staff member
Super Moderator
#13
Actually, for use by a manufacturer, the 4:1 accuracy ratio is a good rule of thumb and keeps you safe. A better approach is use on measurement uncertainty, but for manufacturers, the 4:1 rule is MUCH easier to explain.

As to the source of the 4:1 rule, it is officially documented (to my knowledge) for the first time in the U.S. MIL-STD-45662 and subsequently MIL-STD-45662A. It may have been documented prior to that but I am not sure.

ANSI/NCSL Z540-1-1994 also carries the 4:1 Test Accuracy Ratio (TAR) in section 10.2.b and it has survivied in ANSI/NCSL Z540.3-2006 as well, but now is a Test Uncertainty Ratio (TUR). It should be noted that the Z540 documents are AMERICAN National Standards, and so I do not know if other Governments specifically allow, endorse, or require the 4:1 rule.

Hope this helps.
 
Thread starter Similar threads Forum Replies Date
M ECG lead leakage currents - How to specify ECG leads during electrical safety testing IEC 60601 - Medical Electrical Equipment Safety Standards Series 5
D Drawing (print) does not specify restrained or free state Inspection, Prints (Drawings), Testing, Sampling and Related Topics 2
L How do you specify your receiving inspection parameters? Misc. Quality Assurance and Business Systems Related Topics 2
B How do you specify a one sided tolerance for an MSA in Minitab v 16 Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 6
somashekar How do you specify color tolerance ... Manufacturing and Related Processes 6
P How to specify criteria for TECN (Temporary Engineering Change Notice) Document Control Systems, Procedures, Forms and Templates 3
I Guidelines that specify the frequency of ETO Sterilizer Re-Validation ISO 13485:2016 - Medical Device Quality Management Systems 5
E How to specify Paint or Plastic Color - Pantone or Manufacturer Specification? Manufacturing and Related Processes 15
J Change Management System - Does ISO 9001 specify you need a process flow? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 11
S Cleaning Protocol Validation - Do we also have to specify the level of cleaning? ISO 13485:2016 - Medical Device Quality Management Systems 7
L Material Safety Data Sheet - MSDS should specify how to make the material innocuous Miscellaneous Environmental Standards and EMS Related Discussions 10
G AS9100 4.9 Process Control - Specify process documents and their revision levels AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 6
lanley liao Question regarding the calibration of monitoring and measure equipment. Oil and Gas Industry Standards and Regulations 0
N IATF Calibration Lean in Manufacturing and Service Industries 3
Q Do these certificates of calibration meet ISO 9001 requirements for traceability to NIST? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 10
T Plug Gage Calibration Calibration and Metrology Software and Hardware 1
M Load Cell Calibration using a totalizer on a flow meter General Measurement Device and Calibration Topics 0
E Calibration Records needed ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 1
D Limited Range Calibration - 5000 lb Industrial floor scale General Measurement Device and Calibration Topics 3
D Calibration of Small Scales General Measurement Device and Calibration Topics 26
C How to Establish the Calibration & Measurement Capability (CMC)? ISO 17025 related Discussions 1
I IQOQ or just initial calibration required? General Measurement Device and Calibration Topics 3
B Calibration in real life ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 3
J Calibration cycle for monitoring & measuring tools used in medical device manufacturing General Measurement Device and Calibration Topics 5
A Is calibration of test weight required General Measurement Device and Calibration Topics 4
S Calibration Frequency for Slip Gauge Kit used for CMM Calibration? General Measurement Device and Calibration Topics 0
S Calibration/Verification of customer fixtures IATF 16949 - Automotive Quality Systems Standard 6
Ron Rompen Calibration by manufacturer ISO 17025 related Discussions 4
Q Calibration verification records 7.1.5.2.1 IATF 16949 - Automotive Quality Systems Standard 2
B AS9100D 7.1.5.2 Calibration or Verification Method using outside cal lab AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 1
W Next Calibration Due Date Calibration Frequency (Interval) 5
S Where do l get calibration standards to run a calibration lab? Other ISO and International Standards and European Regulations 2
A OEM On-Site Calibration issues during Covid19 ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 12
D Calibration tolerance question using Pipettes Medical Device and FDA Regulations and Standards News 1
M Calibration Certificate Result issued by an accredited external laboratory General Measurement Device and Calibration Topics 9
G Calibration of "Master Parts" Used as Gauges Calibration Frequency (Interval) 5
R Calibration lab environmental monitoring General Measurement Device and Calibration Topics 4
G Calibration of Rotronic probe but not digital readout? General Measurement Device and Calibration Topics 3
F Standard Calibration Procedures: Recommended Practice ISO 17025 related Discussions 0
T Temperature Requirements For In House Calibration - AS9100 AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 16
B Gage calibration frequency, ISO and IATF - What are the requirements Calibration Frequency (Interval) 3
Crimpshrine13 Laboratory Scope - Calibration vs. Test Methods - IATF 16949 IATF 16949 - Automotive Quality Systems Standard 3
Crimpshrine13 Calibration of pH Meter Probe Calibration and Metrology Software and Hardware 3
F ESD workbench "calibration" Manufacturing and Related Processes 2
C Correct Calibration Method for Dial Depth Gage General Measurement Device and Calibration Topics 6
F Nist traceable calibration certificates General Measurement Device and Calibration Topics 1
G Tool tracebility and First calibration requirements for aerospace (AS9100) organisation AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 5
D Calibration of Digital thermometer with surface probe General Measurement Device and Calibration Topics 1
T Calibration or Verification -> Cm and Cmk, etc. Definitions, Acronyms, Abbreviations and Interpretations Listed Alphabetically 3
G Is repeatability required for equipment calibration? General Measurement Device and Calibration Topics 10

Similar threads

Top Bottom