# How to compute Control Limits for Stability tests?

D

#### Dawn

Stability tests

I need to know how to calculate control limits for stability tests. Any experts?
Thanks ahead of time !!

#### Marc

##### Hunkered Down for the Duration with a Mask on...
Staff member
I'm posting a reply to 'light the bulb' - maybe attract a reply. I'm not a statistical person. If you get real needy, e-mail Howard Atkins - he's the moderator of one of the forums. He's pretty statistical.

Anyone have an answer for here?

D

#### Don Winton

Dawn,
I may be able to help, but need more info. Can you provide additional details of your requirement.

Best Regards,

D

#### Dawn

I am writing a procedure on claculating stability. When I read in the MSA book a calculation which I don't have with me right now, but I was confused as to how to claculate the control limits. We have started stability tests on a chart, and it is a regular Xbar chart. We need to calculate the control limits to get an accurate range of the readings. Does anyone know of SPC programs which will give you the actual stability of the master part?
Thanks for the help!

D

#### Don Winton

Dawn,

You have started stability tests using a “regular” Xbar chart. However, you did not mention a chart for dispersion (R, s, sigma, etc.)?? Assuming a dispersion charts exists, then the calculation of the limits is straightforward for a “regular” control chart. If a chart for dispersion does not exist, that is another matter.

Control limits do not give an accurate range of the readings. Rather, the purpose of control limits is to determine when a process is in or out of a state of statistical control. A process can be in control and still not be stable. Perhaps you are referring to process capability? It sounds, however, that what you are trying to do is not typical. Perhaps I am still missing something. Additional details may be required.

There are many SPC programs, but I prefer Statview with the QC module installed.

Best Regards,

#### Marc

##### Hunkered Down for the Duration with a Mask on...
Staff member
I used Statview in the somewhat distant past and liked the software.

D

#### Dawn

Thanks Don,
We have a customer who wants us to perform stability tests on every gage we use to machine their parts, including micrometers. We do not have an SPC program which calculates stability.I have discussed this with someone and was informed to use moving range charts and we should be ok with that. Haven't tried it yet. Thanks!!!

D

#### Don Winton

Dawn,

Be sure to discriminate the difference between “stability” and “statistical process control.” I would suggest that your customer does not know the difference, either. Rather than stability tests, would not repeatability and reliability (R&R) tests be more suitable? Maybe, Maybe not.

Best Regards,

Staff member
Enter MSA...

D

#### Don Winton

Agreed, Marc. MSA needs to be applied here. SQC has gone as far as it can.

Thread starter Similar threads Forum Replies Date
How to compute or estimate a micrometer or caliper flatness using optical flat General Measurement Device and Calibration Topics 2
R How do I extend Correction factor of Calibration cert to compute instrument accuracy Measurement Uncertainty (MU) 1
M Using Minitab to Compute & Compare the Mean and Standard Deviation Amount Using Minitab Software 7
How to Compute the Accuracy Class for a Weighing Scale? General Measurement Device and Calibration Topics 4
How to compute the Permissible Errors for Class 2 Weighing Scale General Measurement Device and Calibration Topics 2
Q Accuracy: Is there a specific formula to compute Measurement Device Accuracy? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
B Minitab v15 Precision to Tolerance does not compute? Using Minitab Software 1
Method to compute Cpk for Attribute Data? Capability, Accuracy and Stability - Processes, Machines, etc. 3
D How to Compute "Inventory Turn Over Time" - TS 16949 Clause 7.5.5.1 IATF 16949 - Automotive Quality Systems Standard 5
D Is it acceptable to use S bar to compute CPK? Capability, Accuracy and Stability - Processes, Machines, etc. 1
G The basics of how to compute Productivity in a company Manufacturing and Related Processes 7
D Stability, Linearity vs. Bias - Do we need to compute them all? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 6
A Precision/Tolerance Ratio for 1-sided Specification - How to Compute Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3
L What is the standard method used to compute Attrition rate Misc. Quality Assurance and Business Systems Related Topics 9
M Attribute MSA-CrossTab Study Example in MSA Manual:How to compute the Expected Count? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 1
T More GD&T - We can't compute Cpk using GD&T Capability, Accuracy and Stability - Processes, Machines, etc. 2
Software for design control ISO 13485:2016 - Medical Device Quality Management Systems 3
Quality Control/Assurance in the Metal Industry Quality Tools, Improvement and Analysis 10
Defining risk control measures IEC 62304 - Medical Device Software Life Cycle Processes 13
Warehouse temperature and humidity control EU Medical Device Regulations 7
IATF16949 Control Plan FMEA and Control Plans 1
Control Number for Class III and IV devices Canada Medical Device Regulations 0
Document Control Metrics Document Control Systems, Procedures, Forms and Templates 3
Document Control Software Document Control Systems, Procedures, Forms and Templates 2
Controlling Expandable Forms in Paper-Based Document Control System Document Control Systems, Procedures, Forms and Templates 10
ISO 13485 7.3.9 Change control in medical device software ISO 13485:2016 - Medical Device Quality Management Systems 6
UDI Questions on Control Units Other US Medical Device Regulations 6
Quality Control Datasheets Inspection, Prints (Drawings), Testing, Sampling and Related Topics 2
Control-self assessment Internal Auditing 5
Master Control QMS software Quality Tools, Improvement and Analysis 0
Prototype control plan FMEA and Control Plans 2
Records Control - Does each individual record need to be numbered? Records and Data - Quality, Legal and Other Evidence 2
Document Control Procedure Header Content Document Control Systems, Procedures, Forms and Templates 3
FMEA - Current control and occurrence rating FMEA and Control Plans 3
Which department should prepare the control plan? could you show me a standard regarding to this matter. FMEA and Control Plans 17
Control Plan & PFMEA Review Procedure? FMEA and Control Plans 1
What are the software audit and control steps Reliability Analysis - Predictions, Testing and Standards 2
Fabric roll inspection - What type of Control Chart to use? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 2
Monitoring and Control Instruments RoHS, REACH, ELV, IMDS and Restricted Substances 3
ISO14971:2019 - Verification of implementation and effectiveness of risk control ISO 14971 - Medical Device Risk Management 3
Risks arising from control measures vs. ineffective control measures ISO 14971 - Medical Device Risk Management 11
Need Change Control Yes/No Decision Tree Template ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 1
IQ, OQ, PQ protocol, and report templates for Distributed Control Systems in Pharmaceutical Manufacturing Systems. Qualification and Validation (including 21 CFR Part 11) 0
Risk control measures as per ISO 14971 ISO 14971 - Medical Device Risk Management 6
Linking Control Plans and PFMEA's FMEA and Control Plans 3
How to add exemption or statement to control of document procedure? ISO 13485:2016 - Medical Device Quality Management Systems 5
PFMEA and Control Plans on legacy product FMEA and Control Plans 5
IATF 16949 requirement - error-proofing in control plan IATF 16949 - Automotive Quality Systems Standard 3
8.5.1.1 Control of Equipment, Tools, and Software Programs - Questions about the extent of control of NC programs AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 5
Version/Revision Control of CAD files Document Control Systems, Procedures, Forms and Templates 2