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Pre-Control - Statistical Software

$299.95+ S&H

Pre-Control Main Screen

Shown here is a new part file created for part #CR-9384 (shown in the blue title bar)

A part file contains characteristics that will be controlled using Pre-Control.  This part file has four characteristics

Just enter characteristics and their specifications

Then, check which ones to use to create Pre-Control charts and click a button to create the charts

Create as many parts files as you need and reopen them at a later time as needed




Pre-Control Chart

A pre-control chart contains instructions at the top, the actual pre-control chart, and a table at the bottom for keeping extremely simple records that prove the process has been controlled

This is one of many possible formats that can be printed







How to use a Pre-Control Chart

The specifications and pre-control limits are displayed on the chart.  Just print this sheet and provide it to the operator.

Operators use the following extremely simple rules when running a machine or process (these rules are summarized at the top of the page for the operator):

-First qualify the process by obtaining six consecutive readings (or pieces) in the green zone.  Restart the count if one falls out of the green zone.

-Once the process is qualified, take a sample of 2 readings (or parts) every hour (sampling frequency will be different for your process)

-If both readings fall in the green zone, or if one falls in the green zone and one falls in a yellow zone, then continue running

-If both readings fall in the same yellow zone, then adjust the process

-If one reading falls in the red zone, or the readings fall in opposite yellow zones, then stop the process, correct the problem, and re-qualify the process again with another 6 consecutive green readings

-That's it!  That's as complicated as it gets.

(The sampling frequency that you actually will use depends on how often a pair of yellow readings occurs.  The rule is:  Sample 6 times between adjustments.  So begin with a rather frequent sampling interval, and if you discover it normally takes three hours after one adjustment before another is required, then a sample of two readings should be taken every 30 minutes.  If you can normally run 6000 pieces between adjustments, then set the new sampling frequency such that a sample of two readings is taken every 1000 pieces.)


Date/Time Employee  Signal  Reaction to Out-of-Control Signal
11/6/2000 7:00 am JC 6G                   
11/6/2000 8:00 am JC GG               
11/6/2000 9:00 am JC GG                  
11/6/2000 10:00 am JC GG                   
11/6/2000 11:00 am JC GY Adjusted Process
11/6/2000 12:00 am JC GG                  
11/6/2000 1:00 pm JC GG                    
11/6/2000 2:00 pm JC Opp YY Tightened Loose Fixture
11/6/2000 2:10 pm  JC 6G               
11/6/2000 3:00 pm JC GG                
11/6/2000 4:00 pm  MK GG               
11/6/2000 5:00 pm MK GG              
11/6/2000 6:00 pm MK  GG                
11/6/2000 7:00 pm MK GG                
11/6/2000 8:00 pm MK GR Changed tool, sorted parts, 40 pieces scrapped
11/6/2000 8:15 pm MK 6G               
11/6/2000 9:00 pm MK GG                
11/6/2000 10:00 pm MK  GG                  
Example: How records can be kept to satisfy ISO-9000 requirements

In order to satisfy IS0-9000 requirements, some kind of a record must be kept to prove that process control has been maintained.  This is one way to do it.  (the Pre-Control software allows many other formats)

The operator simply completes the table under the pre-control chart, one row at a time, as samples are taken (the operator usually hand writes the contents of this table - it does not have to be typed)

Once the operator qualifies the process, they write "6G" under the signal column (meaning 6 consecutive green readings)

When a sample of two green readings is taken, the operator writes "GG" or "2G" under the signal column

If a sample contains a green and a yellow reading, the operator writes "GY", and indicates that an adjustment has been made in the "Reaction to Out-of-Control Signal" column.

If a sample contains opposite yellow readings or one red reading, the operator writes "Opp YY" or "GR" (or "YR") under the signal column and indicates in the "Reaction to Out-of-Control Signal" column not only what was done to fix the process, but what was done to assess potential nonconforming product that may have been made since the last acceptable sample.

If a sample contains two yellow readings in the same zone, the operator would write "Same YY"

When out of room on one sheet, the operator starts a new sheet.  Keep the completed sheets as quality records.  (These sheets take the place of a completed average and range charts and other similar control charts)

Now isn't this much easier than traditional control charting methods?   Its simplicity makes it possible to teach even temporary employees how to use pre-control (and how to keep records) in just a few minutes.  


Optionally Enter Data in Pre-Control Software for Automatic Analysis

Although the Pre-Control software does not require that data be entered, you may choose to do so and take advantage of the automatic data analysis features.

Either copy data that was previously written on printed pre-control sheets, or enter data directly into the part file as measurements are taken (if a PC is available where the measurements are taken)

As data is entered, an 'X' is placed on the pre-control chart to give a visual indication of the measurement location

Let the Pre-Control software create histograms, capability analysis, and even traditional control charts (average and range or individuals and moving range)


Histogram and Capability Analysis

Histograms and Capability Analysis are shown together on the same page

The capability analysis (on the lower half of the page) reports Cp, Cpu, Cpl, Cpk, and estimated fraction defective

Print histograms for data within a specified date range and/or for a specific order#, work order#, job#, etc.



Traditional Control Charts

Print traditional control charts (average and range charts or individuals and moving range charts) 

These are not used for real-time control - pre-control charts take care of that.  However, traditional control charts may still be necessary to prove the process is stable (a requirement for calculating Cpk), or for helping to diagnose a process problem.   

The traditional control chart (if used) with pre-control would typically be printed and interpreted after the process has completed (usually by someone knowledgeable with interpreting traditional control charts).  Thus, the average operator does not have to be trained in traditional control charts, only on the simple pre-control method.


Send e-mail with questions



Copyright ?2009 TQS Associates, Inc., all rights reserved.

Last modified: 02/23/09