SPC Charts

the spc (statistical process control) charts processor analyzes a window of process data and calculates statistical measures that assess a process's performance and capability against its specification limits, using control charts and predefined rules why use spc charts use this processor to monitor whether a process stays within its specification limits and to catch early warning patterns using nelson rules, rather than only watching a raw value against fixed thresholds how it works the processor calculates a current mean and standard deviation ( stddev ) from the input data within the window, then derives control limits and capability indices from them upper specification limit (usl) and lower specification limit (lsl) are calculated from the current mean and standard deviation process capability ( cp ) is the ratio of the difference between usl and lsl to six times the standard deviation (6σ) cpu (upper capability index) and cpl (lower capability index) measure how centered the process is within the specification limits cpu = (usl average) / 3σ , and cpl = (average lsl) / 3σ process performance ( cpk ) is the smaller of cpu and cpl if valid data is present, the processor also calculates cpm and cpkm , which incorporate target mean if your input tag doesn't publish at a steady rate, use time interval to publish a value on a fixed schedule instead of waiting for the next incoming event enter 0 to disable the timer if your input already publishes at the expected rate nelson rule violations the processor flags a true value for each nelson rule your data violates one point is more than three standard deviations from the mean nine or more points in a row fall on the same side of the mean six or more points in a row continually increase or decrease 14 or more points in a row alternate direction, increasing then decreasing two out of three, or three out of three, points in a row fall more than two standard deviations from the mean in the same direction four out of five, or five out of five, points in a row fall more than one standard deviation from the mean in the same direction 15 points in a row all fall within one standard deviation of the mean, on either side eight points in a row occur, with none within one standard deviation of the mean, and the points fall in both directions from the mean parameters parameter details window size the number of data points considered for calculations affects the current mean, standard deviation, and specification limits defaults to 50 target mean the desired average value for the process, used as a reference point for evaluating performance required, along with valid data, to calculate cpm and cpkm defaults to 100 pass through value determines whether the processor's output is the calculated control chart fields or the original unchanged input value time interval sets a timer that publishes output on a fixed schedule if the input tag isn't polling regularly enter 0 to disable the timer related topics use the spc charts function docid\ h7fkyhww8xueztpnodsa6