|
Process
Control Data Screen Features
The
overall functions and features of SPCView are accessed from the
Process Control Data screen, which includes
a menu bar and activation buttons for quick access to drill-down analysis screens and
worksheets, a section containing key information about
the subject parameter being analyzed, and a table containing process
history data.
Menu
Bar
The
Menu bar provides access to a wide variety of program functions and
options including saving and opening analysis files, printing options,
editing options, data importing and exporting options, and an option for
setting the default date format.
Parameter
Identification Data
The
upper portion of the screen includes parameter identification data, nominal value, estimated parameter value, estimated uncertainty, subject parameter bias, measuring parameter bias, in-tolerance probabilities, sample size, and control limit information.
Data can be entered directly or imported from an UncertaintyAnalyzer
file.
Control
Limit Options
This
option allows you to display either the upper and lower control limits
or the upper and lower control offsets. The upper control offset
is the difference between the upper control limit and the
process nominal or mean value. The lower control offset
is the difference between the process nominal or mean value
and the lower control limit. The
lower control offset is expressed as a negative number.
Control
limits (or offsets) can be entered as two-sided asymmetric, two-sided symmetric,
single-sided upper, or single-sided lower values. Control
limits can be entered directly in the Upper Control Limit (or Offset) and Lower Control Limit
(or Offset) boxes and the associated confidence levels will be computed automatically.
When
the option is exercised, the result is shown in the Upper and Lower
Control Limit/Offset boxes of the Control Data part of the screen.
Alternatively, the nominal value for a parameter or process, along with
the estimated uncertainty from an UncertaintyAnalyzer session, can
be used to set control limits for a specified level of confidence.
This second option is done using the Set Control Data button.
Process Control Options
There
are four process control options to choose from.
-
Measurement
Process
-
Parameter
Value vs. Date
-
Parameter
Interval Analysis
-
Sampled
Process
The
Measurement Process option concerns the control of the measurement process itself. A measurement process is viewed as consisting of a measuring device or devices, a measuring environment, a measurement procedure and includes human and other perception elements.
The option for displaying Control Limits (relative to the Nominal Value)
is disabled and only Control Offsets are enabled.
This is because the Control "Limits" plotted on the
Control Chart are bounding limits for deviations between measured check
standard values and a priori assumed values -- not deviations from nominal. This
is necessary because the check standard assumed value may change from
control point to control point.
The Parameter Value vs. Date option focuses on parameter as the subject of control rather than the
process that measures it. The parameter being measured is assumed to
drift or change in value over time. This
option involves keeping a running history of the value of a parameter (or the parameter's deviation from nominal) over time.
The
Parameter Interval Analysis option also assumes that the value of a measured parameter
changes from measurement date to measurement date. For
many parameters, the longer the interval between measurements, the greater the change (on
average). The usual parameter data are entered in the process control history
table along with "as-found" and "as-left" values for each control point.
The Sampled Process option applies statistical process
control to the output of a manufacturing or other output process and not
the measuring system. The process is controlled by (1) measuring the value of a parameter characterizing the process output, (2) entering the measured value,
together with measurement uncertainties, in a process control timeline and (3) evaluating the process statistically.
Process
Control Histories
In controlling a measurement process, monitoring
the drift in a parameter value, or monitoring the output of a process,
measurements are made at various times to obtain a "process control
history." The history for a selected process is stored in the
Control History Data table located on the bottom portion of the
screen. Each row of the table contains a process control record
comprised of the measured value of the parameter or process of interest,
the uncertainty in the measurement, the date of measurement, process
sample size, and other relevant information.
Measurement data and uncertainty analysis results
obtained from UncertaintyAnalyzer can be imported
directly into the Control Data History table by clicking the Update Record
button. A record update can be undone by clicking the Undo Update
button. Data can also be imported from an external application via
the Run External Application screen, copied and pasted from the Windows
clipboard or manually entered in the table. Records can be deleted
by clicking on any cell in the desired row and selecting the Delete
Row option from the Edit menu.
Once enough
process control history is assembled for
plotting (greater than or equal to three points), a control chart can be
generated by clicking the View Chart button, which activates the Process Control Chart
Screen.
|
SPCView 1.7 - Process Control
Data Screen
