pc study

Ganesh,
 
1)      No, one purpose of a control chart is to detect if a process is in control.  You don’t have to wait for a “stable” process to begin charting or even to calculate control limits.
2)      Sampling frequency basically depends on how fast the process changes.  There are mathematical methods, but it all comes down to sampling often enough to catch process changes while also sampling in an economic manner.  You don’t want to burden the operators or increase cost by sampling too frequently.
3)      Make sure that you have a rational sample group with an adequate sample quantity.  The quantity may be anywhere from 1 sample up, but it should be rational to the process and give you the sensitivity that you need to detect shifts in the process.
 
I hope that this helps a little.
 
Rick