[rku140]

Hi All,

Any one can share to explain NDC in the MSA study?, or PM me the article on this.

Thanks in advance.

Rgds,
ab

[sparky]

I take it by NDC you mean the number of distinct categories?

Taken from the minitab help pages:-

Minitab calculates the number in this statement by dividing the standard deviation for Parts by the standard deviation for Gage, then multiplying by 1.41 and truncating this value. This number represents the number of non-overlapping confidence intervals that will span the range of product variation. You can also think of it as the number of groups within your process data that your measurement system can discern.

Imagine you measured 10 different parts, and Minitab reported that your measurement system could discern 4 distinct categories. This means that some of those 10 parts are not different enough to be discerned as being different by your measurement system. If you want to distinguish a higher number of distinct categories, you need a more precise gage.

The Automobile Industry Action Group (AIAG) [1] suggests that when the number of categories is less than 2, the measurement system is of no value for controlling the process, since one part cannot be distinguished from another. When the number of categories is 2, the data can be divided into two groups, say high and low. When the number of categories is 3, the data can be divided into 3 groups, say low, middle and high. A value of 5 or more denotes an acceptable measurement system.


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[rku140]

Hi,

Thank you for the excerpt from Minitab. What is the method to increase the NDC to more than 5?. Will there is situation where the GRR is less than 10% but the NDC is less than 5, what do we do in this case.

Your expertise is highly appreciate.

Rgds,
ab

[sparky]

If I understand you correctly...

One way of increasing the NDC would be to increase your measurement resolution.

Is it possible you could post your data up here so that we could look at it and offer advice?

[rku140]

Hi,

Noted that from Treqna Base Manual, pg 89, the resolution is defined as the smallest unit in which the gage can measure and ideally the gage should be able to resolve the tolerance into approximately ten levels.

Kindly help to explain what is meant by ''the gage should be able to resolve the tolerance into approximately ten levels''?. why 'ten levels'?

Rgds,
ab

[sparky]

Originally Posted by rku140

Hi,

Noted that from Treqna Base Manual, pg 89, the resolution is defined as the smallest unit in which the gage can measure and ideally the gage should be able to resolve the tolerance into approximately ten levels.

Kindly help to explain what is meant by ''the gage should be able to resolve the tolerance into approximately ten levels''?. why 'ten levels'?

Rgds,
ab

General rule of thumb. (My understanding, I didn't write the manual.)

If you want to reasonably accurately measure 1cm, you ought to have a resolution of 1mm. Generally you would go one order of magnitude better than what you are trying to measure.

You can of course go further than this, and it will all depend on the accuracy you require; but this is the least that you should go.

HTH