I

*Tried to insert as a link to picture of chart but post count prevented this*

What we see is a cyclic pattern as the flow rate drifts away from its set point and in then corrected by the machines logic processor. Because this drift is gradual we end up with very low short term variation. So we have a low sbar which then plays havoc with the control limits on the xbar chart

We could attempt to decrease the threshold of drift the machine reacts to but the variation is already low enough where we wouldn't be concerned.

However we still need a way for operators to identify special cause variation.

I'm sure this can't be a unique problem so I am looking for any experience, advice, solutions.

Thanks