topic Extracting control limits from column info in Discussions

Extracting control limits from column info

Abby_Collins14 — Fri, 09 Jun 2023 16:11:44 GMT

I am trying to extract control limits from column info, I have used the below code to extract spec limits, but if I do the same for control limits, it does not work because it treats everything as one element in the list.

p = c << get property( "Spec Limits" );
plst = Eval List( {Arg( p, 1 ), Arg( p, 2 ), Arg( p, 3 )} );

Any ideas? Thanks!

Re: Extracting control limits from column info

jthi — Thu, 08 Jun 2023 16:52:01 GMT

Which control limits are you trying to extract? Columns might have multiple and you have to pick correct one and then have some extra args. Below is one option

Names Default To Here(1);
dt = Open("$SAMPLE_DATA/Quality Control/Coating.jmp");
obj = dt << Control Chart(
	Sample Size(:Sample),
	KSigma(3),
	Chart Col(:Weight, XBar, R)
);
obj << in Column;
wait(0); // to make sure properties have time to be set
cl_colprop = Column(dt, "Weight") << Get Property("Control Limits");
show(cl_colprop);

xbar = Arg(cl_colprop, 1); // XBar in this case
r = Arg(cl_colprop, 2); // R in this case
avgxbar = Arg(xbar, 1); // Avg
lclxbar = Arg(xbar, 2); // 
uclxbar = Arg(xbar, 3);

avg = Arg(avgxbar);
lcl = Arg(lclxbar);
ucl = Arg(uclxbar);

show(xbar, r, avgxbar, lclxbar, uclxbar, avg, lcl, ucl);

Re: Extracting control limits from column info

Abby_Collins14 — Thu, 08 Jun 2023 17:51:42 GMT

Thanks! I'll give this a try. Each column has one set of control limits and I am trying to extract the upper and lower limits from all columns and save them in separate lists (ie one list of all of the lower limits and one list of all of the upper limits).

Thanks! :)

Re: Extracting control limits from column info

statman — Thu, 08 Jun 2023 21:21:10 GMT

Sorry, I'm confused by your request. There are multiple ways to calculate control limits. The fundamental Shewhart type control charts use rational subgrouping as a basis for calculating control limits. In the absence of a rational subgroup, you could use the moving range as a surrogate "subgroup" for estimating control limits. In any case, control limits are not an arbitrary calculation.