29.3.2 Statistical Process Control (SPC)
· We can do SPC checking using analog inputs, and built in statistics functions.
· Recall the basic equations for a control chart.
· The general flow would be,
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1. Read sampled inputs.
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2. Randomly select values and calculate the average and store in memory. Calculate the standard deviation of the stored values.
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3. Compare the inputs to the standard deviation. If it is larger than 3 deviations from the mean, halt the process.
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4. If it is larger than 2 then increase a counter A, or if it is larger than 1 increase a second counter B. If it is less than 1 reset the counters.
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5. If counter A is =3 or B is =5 then shut down.
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6. Goto 1.
