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Products Software SPCView Program Features Process Control Chart Screen


SPCView Statistical Process Control Analysis Software from Integrated Sciences Group  SPCView 1.7 - Process Control Chart Screen

SPCView Statistical Process Control Software - Process Control Chart Screen


Develop and Evaluate Control Charts 
The plot on the Process Control Chart screen shows each control point in the process control history with optional one-sigma upper and lower uncertainty limits.  Each control point is either a deviation from the nominal value shown on the Process Control Data Screen, a deviation from the declared value of a check standard, a deviation from the mean of sampled process data, or a deviation between the current measured value and the measured value of the previous control point.
The control chart also shows the upper control limit (UCL) and lower control limit (LCL) defined on the Process Control Data screen and a linear fit to the plotted data. The linear fit, representing the drift over time of the process of interest, is bounded by upper and lower standard uncertainty curves. This drift over time provides a tool for forecasting process trends.


The control data history table is displayed below the control chart.  Records can be added to the table, modified or deleted in the same manner as on the Process Control Data screen.  Upon exiting the Process Control Chart screen, you will be asked whether or not you want to implement these changes in the process control data history.


Projecting Trends
One of the central objectives of process control is the detection of drift or other mechanisms by which process (or subject parameter) bias changes with time.  In SPCView, such drift is shown on the process control chart as a linear fit of process (or subject parameter) bias vs. time. The fit is obtained by a weighted or unweighted linear regression analysis of the control data points.  The upper and lower curves bracketing the linear fit are one standard deviation, a standard deviation representing the uncertainty in the curve fitting process.
If a positive or negative drift mechanism is present, the rate of drift is estimated as the slope of the linear fit. The "intercept" of the linear fit comprises an estimated initial value for the process history.  Depending on the drift rate, the time at which the linear fit will intersect either the UCL or the LCL will be displayed in the Curve Fit Information section of the screen. The times at which the upper and lower uncertainty curves will intersect the control limits are also displayed.

Process Evaluation
Evaluating whether a process is in or out of control is essentially a matter of deciding on whether observed control points are in or out of control. The occurrence of an out of control point is called an out of control event. Clicking Evaluate on the Menu bar activates the Process Evaluation Worksheet, which can be used to view the confidence for rejecting a process as being out-of-control at a selected point.  This worksheet also provides visibility of the risk of falsely rejecting an in-control process.


Interval Analysis

The interval of time suitable for taking the next process control point (e.g., for process monitoring or  parameter calibration) is determined through the use of the SPC Interval Worksheet, which is activated by clicking Compute Interval on the Menu bar.


Analysis Reports
Hardcopy reports of SPC analysis results and of the control chart can be generated through the use of the SPC Report Options Screen accessed by clicking Report on the Menu bar and selecting the Print option.



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Page Updated February 12, 2015