One of the many advantages SPC offers is its ability to automatically calculate the control limits for a process. This particularly comes in handy if your process is new and you want the SPC program to generate control limits.
SPC offers two options to automatically recalculate control limits:
Auto recalculation: Is used
in place of Values or Points. Once the control limits are
automatically calculated, select either Values or Points for the
life of the process.
Force Auto Recalc: Is used
in addition to Values or Points. This option provides the
flexibility to reset control limits during runtime. As a result,
when you send an application to production, you can have SPC
recalculate the control limits so that they are accurate for the
process. Once the control limits are automatically calculated,
disable the Force Auto Recalc option.
Important: The Quality Control rules
you have always followed for control limits still apply to both SPC
automatic recalculation options, as follows:
When your process is new or
in optimum condition, calculate the limits using the Auto
Recalculation or Force Auto Recalculation option.
Once you determine that SPC
has automatically collected enough data to calculate the correct
control limits, disable the automatic calculation option.
The calculated control
limits are then used for the life of the process.
Remember that the control
limits produced by auto recalculation are valid only when your
process is "in control." If you calculate them while your process
is going "out of control," then the limits will be incorrect.
A global variable SPC_RESIZE_OUT_OF_BOUNDS causes graph re-scaling and re-centering.
SPC_RESIZE_OUT_OF_BOUNDS is enabled by default.
When the SPC_RESIZE_OUT_OF_BOUNDS is disabled charts are not re-scaled and re-centered.
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Step 3.4. Set limits for variable quality characteristics. |
