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 Shewhart Control Charts
Control charts are constructed to decide whether a process is under statistical control and to monitor any departures from this state. This means that stability of some process properties over time is tested using certain statistical assumptions about the process (data it produces). Commonly considered properties are mean, variance (standard deviation), distribution shape or proportion of faulty items. The Shewhart control charts were invented in 1932. They are based on monitoring events, which are very unlikely when the controlled process is stable. Any incidence of such an event is taken as an alarm signal suggesting that stability of the process was broken and the process changed. Upon receiving such signal, possible causes of the change should be investigated and some correcting steps taken. One example of such an unlikely event is the situation when the control limits (UCL or LCL) are exceeded.

Special features:
X-Bar Charts for data with missing cells
Charts for asymetric data
X-Bar and S / R
X-Individual and R
NP, P, C, U - Charts

Shewhart Control Charts - Pdf manual

Examples

X-Bar Chart Output Protocol:
 Control chart x-individual Task name : Sheet1 No transformation Max. subgroup size : 1 No of rows : 52 Chart type : x-individual Variability : R Central line : 7.045072115 Central line : 0.461397059 Defined by : Process data Defined by : Process data LCL : 5.817952278 LCL : 0 UCL : 8.272191953 UCL : 1.507384191 Defined by : Process data Defined by : Process data Capability indices : Index : Value : Lower limit : Upper limit : Cp : 1 0.864540983 1.135006554 Cpk : 1 0.842446855 1.1.4601 Estimate (Heavlin) : 0.842446855 1.1.4601 Estimate (Kushler) : 0.862097414 1.137902586 Estimate (Franklin) : 0.872168099 ------ Cpm : 1 0.865205478 1.134346174 Cpmk : 1 Rules violation : No. : Mean : Range : Rule : 45 1.5.3125 1.453125 1 point outside control limits 46 7 1.1.6875 1 point outside control limits

Different types of control chart constructed by QC-Expert

Regular Control Chart X-bar / X-Individual and R:

X-Bar and S Chart for unequal group size

Chart X-individual and R for asymetrically distributed data using Transformation

NP Chart for attributes

P Chart for attributes

C Chart for attributes

U Chart for attributes