Gage R&R Related Terms - EV, %EV, AV, %AV, GRR, %GRR, PV, %PV, TV, and P/T Ratio

O

orion - 2004

#1
I just took up a little studies on GRR method and got confused with all the terms and their representations, such as EV, %EV, AV, %AV, GRR, %GRR, PV, %PV, TV, and P/T Ratio.
Let's say I have this values:

EV = 0.20188 %EV = 17.62%
AV = 0.22963 %AV= 20.04%
GRR = 0.30575 %GRR = 26.88%
PV = 1.10456 %PV = 96.38%
TV = 1.14610
NOTE: These values are taken from MSA 3rd Ed(Pg 114),based upon 6 Std. Dev., and the K1,K2,K3 values are inverse of the d2 table.

So, is there any meaning to each of the value, and what they represent?

Another question is, for calculating AV, we use a K2 constant, derived fomr the d2 Table with g = 1. My question is, why is g = 1? What is one range calculation?

Thanks a lot.
 
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R

Rob Nix

#3
OK, I'll do it.

AV = variation due to reproducibility; most often associated with inspector to inspector error. This is the ability for one inspector to reproduce the same result as another inspector.

EV = variation due to repeatability; that is, the ability of the gage itself to repeat the same measurements.

PV = variation due to the parts checked. This is pretty much a useless measure. It simply tells you how much of the total variation is due to part to part differences in measurement.

TV = a time absorbing device in your living room. KIDDING. This is the total variation from all factors.

The decimal number (i.e. AV, EV, PV,...) is just a ratio, focus on the percentages. The percent (i.e. AV%, EV%,...) is how much of the total variation is due to repeatability, reproducibility, or part variation. NOTE: The percent may be of the total variation OR of the feature tolerance zone, depending on what you are comparing it to.

GRR = the combined effect of EV (repeatability) and AV (reproducibility), hence Gage R & R. (this is derived using root mean square (RMS)).

I don't know where you got "g" from (I'm writing this from the top of my head right now), but I'm guessing that since K2 is probably "2" parts, then g = 1 means 1 degree of freedom.

In your example, 17% EV and 20% AV is not too bad, but could be better.

I hope this helps.
 

Govind

Super Moderator
Leader
Super Moderator
#4
Gauge R & R Question

Rob Nix said:
OK, I'll do it.

AV = variation due to reproducibility; most often associated with inspector to inspector error. This is the ability for one inspector to reproduce the same result as another inspector.

EV = variation due to repeatability; that is, the ability of the gage itself to repeat the same measurements.

PV = variation due to the parts checked. This is pretty much a useless measure. It simply tells you how much of the total variation is due to part to part differences in measurement.

TV = a time absorbing device in your living room. KIDDING. This is the total variation from all factors.

The decimal number (i.e. AV, EV, PV,...) is just a ratio, focus on the percentages. The percent (i.e. AV%, EV%,...) is how much of the total variation is due to repeatability, reproducibility, or part variation. NOTE: The percent may be of the total variation OR of the feature tolerance zone, depending on what you are comparing it to.

GRR = the combined effect of EV (repeatability) and AV (reproducibility), hence Gage R & R. (this is derived using root mean square (RMS)).

I don't know where you got "g" from (I'm writing this from the top of my head right now), but I'm guessing that since K2 is probably "2" parts, then g = 1 means 1 degree of freedom.

In your example, 17% EV and 20% AV is not too bad, but could be better.

I hope this helps.
Unfortunately, I have the second edition only. Page 29 explains g=
number of parts X number of appraisers.

If we are using 5 parts and 2 appraisers 3 trails:
While calculating the repeatability, we use "all 10 ranges" to calculate the Rdouble bar.
Inorder to get repeatability we use this value multipled by 5.15 (for 99% CI) and divide by d2.
Since the d2 is taken from the table that matches g=10 and trails m=3, the d2 value is 1.72. (Page 29)

While calculating the reproducibility we are taking only "one range value" of the Appriasers average See page 28 & 30 for the calculation of appraiser std.dev.

Does this convince enough?

Govind.
 
O

orion - 2004

#5
Thanks for all the reply.
I have more questions, though.

1) Does anyone know what a P/T Ratio is? And the formula to calculate it?

2) Can a %PV, %EV and %AV exceed 100% ?

3) I notice that if %EV (for example) is calculated using Total Variation, it is called %Total Variation Analysis, and is using Tolerance Spec, it is called %Tolerance Analysis. What is the meaning of both Analysis, and their difference? Are these Analysis that differentiate between Product Control and Process Control?

Thanks again.
 

Govind

Super Moderator
Leader
Super Moderator
#6
orion said:
Thanks for all the reply.
I have more questions, though.

1) Does anyone know what a P/T Ratio is? And the formula to calculate it?

2) Can a %PV, %EV and %AV exceed 100% ?

3) I notice that if %EV (for example) is calculated using Total Variation, it is called %Total Variation Analysis, and is using Tolerance Spec, it is called %Tolerance Analysis. What is the meaning of both Analysis, and their difference? Are these Analysis that differentiate between Product Control and Process Control?

Thanks again.
Orion,
While some of us are getting back to with the answers for the questions, here is a resource you may want to explore.

This is a training material (web based & CD version) available from an organization in the USA.

http://www.reseng.com/courses_avail/

We buy credits from this organization for our company and train Engineers.
I myself went through the webbased self paced course (7~8 hours).

I find this material very useful. I always refresh my understanding reviewing this material.

Regards,
Govind.
 
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