Rule | Violation and indicators on the process |
RULE #1: Whenever a single point falls outside the 3σ control limits, in a row in Zone A or beyond, a lack of control is indicated. | a) Temperature control chart Batch #3 and #15 are outside 3σ control limits. b) pH control chart Batch #1 and #8 are outside the 3σ control limits. This test provides an “early warning” of a process shift. Since the probability of this to happen is rather small, it is very likely not due to chance. |
RULE #2: Conducting 2 out 3 beyond 2σ | a) Temperature control chart Batch #2 and #3 are 2σ away from centerline. b) pH control chart Batch #1 and #2 are 2σ away consecutively below the centerline. c) pH control chart Batch #6 and #7 are consecutively 2σ away below centerline. |
RULE #3: 3 out of 5 connectively fall on same side of centerline and more than 1σ away from centerline | Temperature control chart Batches #4, #5, #6 and #7 are 1σaway from the centerline, consecutively. Like the previous test, this test may be considered to be an “early warning indicator” of a potential process shift. The false-positive error rate for this test is also about 2%. |
RULE #4: Whenever at least 8 points in a row in Zone B, A, or beyond, on either side of the center line (without points in Zone C) a lack of control is indicated. | Not violated |
RULE #5: 6 points in a row steadily increasing or decreasing | Not violated |
RULE #6: 9 points on one side of centerline | Not violated |
RULE #7: 14 points in a raw alternating up and down | Not violated |
RULE #8: 15 points in Zone C | Brix control chart, all points in Zone C. This test indicates a smaller variability than is expected (based on the current control limits). |