These control chart settings apply to each station of the measure and override the control chart
settings for each station.
Subgroup size
Enter a value to use as the same subgroup
size for all samples of the data collections.
Control chart
Select a control chart based on measure type and subgroup size.
Note
The control chart type and subgroup size must be the same at each station
of the measure.
- Continuous control charts
- Continuous
control charts plot continuous measurement process data, such as
length or pressure, in a time-ordered sequence. The two main types
of continuous control charts are charts for data collected in
subgroups and charts for individual measurements.
- Use an I-MR Chart to monitor the mean and variation of your process when
you have continuous data that are individual observations
not in subgroups.
- Use an Xbar-R Chart to monitor the mean and variation of a process when you
have continuous data and subgroup sizes of 8 or less.
- Use an Xbar-S Chart to monitor the mean and variation of a process when you
have continuous data and subgroup sizes of 9 or more.
- Use an I-MR-R/S Chart to monitor the mean of your process and the variation
between and within subgroups when each subgroup is a
different part or batch.
- Use an EWMA Chart to detect small shifts in the process mean, without
influence by low and high values. The EWMA chart monitors
exponentially weighted moving averages, which remove the
influence of low and high values. The observations can be
individual measurements or subgroup means.
- Attribute control charts
- Attribute control charts plot defects or
defectives. Select your attribute control chart based on whether
your data represent a count of defectives and follow a binomial
distribution, or whether your data represent a count of defects and
follow a Poisson distribution.
- Use an NP chart to monitor the number of defective items where each
item can be classified into one of two categories, such as
pass or fail.
- Use a P chart to monitor the proportion of defective items where
each item can be classified into one of two categories, such
as pass or fail.
- Use a Laney P' chart (P' is pronounced as P prime) to monitor the
proportion of defective items that are produced by your
process and to adjust for overdispersion or underdispersion
in your data.
- Use a C chart to monitor the number of defects per unit, where
each item can have multiple defects. You should use a C
chart only when your subgroups are the same size.
- Use a U chart to monitor the number of defects per unit, where
each item can have multiple defects.
- Use a Laney U' chart (U' is pronounced as U prime) to monitor the defect
rate for your process and to adjust for overdispersion or
underdispersion in your data.
Control limit calculation method
Control limits are the horizontal lines
above and below the center line that are used to judge whether a process is out
of control. The upper and lower control limits are based on the random variation
in the process. By default, the control limits are displayed 3 standard
deviations above and below the center line.
Control limits are calculated from the process parameters. You can choose to use estimated
process parameters or enter the known historical values to use to calculate the
center line and control limits. For more information on control limit
calculations, go to
Control limit calculation details.
-
- Calculate using recent data
- You can specify how much data to use for the parameter estimates if you do not have
known historical values.
-
- Number of observations /
Number of subgroups
- For continuous measures, specify the number of
observations; the default is 100 observations. For
attribute measures, specify the number of
subgroups; the default is 25 subgroups.
Using
more data to estimate process parameters gives
more accurate control limits.
-
- Provide parameters
- Enter the historical values for the parameters that Real-Time SPC uses to calculate the
center line and control limits. If you do not have known
parameters, use the Calculate using recent observations or
Calculate using recent subgroups option.
-
- Do not use control
limits
- You can suppress the display of control limits for any
control chart. This setting affects the control charts for
all the stations. Data are still plotted, but only Test 2,
Test 3, and Test 4 are available.
