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P-Pn CONTROL CHART
P- and Pn-charts are used to obtain data about
defective parts at various manufacturing plants.
The P-chart is used when the number n of
pieces to be checked is variable. The Pn-chart is
used when the number n of pieces to be checked
is constant. The former is a control chart repre-
senting the percentage of defects, while the
latter is a control chart representing the number
of defects.
This program writes data to and reads data from
CETL, and processes the data for output to a
plotter-printer in the form of control charts.
When the program is started, it asks whether or not the appropriate data is already
stored in CETL. If the data is not yet stored in CETL, you should switch the MODE
switch to CETL and input the dat ... Since CETL is described in detail in the CETL
Reference Manual, data input to CETL is only briefly discussed here.
First, input the file name, the number of records, and the number of items using the
N command. Input 6 as the number of items, and the number of data items+ l as the
number of records. Next, input data for each item as shown in List 1.
Use special care in inputting data under 'Expression.' The number O immediately after
FL (see List 1) represents a file number. When a different file is specified, change Oto
the associated file number.
As a prompt for data input, the screen displays "1-1
?". The first figure represents
the record number and the second figure represents the item number. Since the data to
be input comprises only the number of pieces to be inspected (item 2) and the number
of defective pieces (item 3), you should only input the relevant data. For the prompts
for irrelevant data, simply press the ,..J.key. (See List l .)
In the final record, input the previously calculated total number of inspected pieces
p::n) and the total number of defective pieces (2::Pn). This is the reason why the actual
number of records + 1 should be input as the number of records. The number of
groups should be 20 to 40.
To check that the data has been input correctly, use the T command to output the
contents of data cells to the display unit or printer. If an error is found, use the
J
command for correction.
Groups arc classified according to the lot number, etc. It is recommended that the
grouping be done such that the number of pieces inspected is 50 to 100 per group and
the number of defective pieces (Pn) per group is 3 to 4 on the average.
It should again be noted that the number of records
10
be input is the .ictu;!I number of
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