JMP-scripting: Control chart not created because avg UCL

Question

Hi Everyone,

I'm currently struggling with an issue.  We run a script to pull charts for our customers.  One of these charts is a control chart.  I place the limits manually.  Now I have a chart with an average, which exceeds the upper limit.  JMP refuses to create the chart

Error for Control Chart on data table Sorted tabulated results for 70705499: Control limits out of order: must be LCL<=Avg<=UCL

Is there anything I can do, so that JMP generates the chart anyway?

JSL:

Control Chart(
      Sample Label(Column(1)),
      Group Size(1),
      Chart Col(
            Column(i),
            "Individual Measurement"),
      Get Limits("C:\Temp\limitsForCC.jmp")
);

i is a counter which loops over all columns.

I cannot change the chart type, as the chart needs to look exactly the same as before (so no different chart types, no chart builders, ...)  I just need an option that will ignore the error and create the chart anyway.

Please keep in mind that I'm a developer, and not a statistision (meaning I know next to nothing about statistics, but I know about coding).

Thank you,

Kind regards,

Jan

Mark_Bailey · Accepted Answer

As the error message says, the process mean must be between the lower control limit (LCL) and the upper control limit (UCL). The limits are either calculated from the same data that is plotted or they are previously calculated with an historical sample of data collected when the process was known to be in control and applied to a new set of data. The Shewhart charts center the process mean between the LCL and UCL, which are usually 3*sigma (sigma is short-term measure of process variation as a standard deviation.)

Your problem description suggests that the limits are already determined, so the LimitsForCC.jmp data table must be missing the value for the center line.

Generally speaking, these limits and center are associated with the process, not the data. The data are use to confirm or reject the process values.