TIME WEIGHTED CHARTS
Use this tool to supervise production quality, in the case where you have a group of measurements or a single measurement for each point in time. The measurements need to be quantitative variables.
This tool is useful to recap the mean and the variability of the measured production quality.
Integrated in this tool, you will find Box-Cox transformations, calculation of process capability and the application of rules for special causes and Westgard rules (an alternative rule set to identify special causes) available to complete your analysis.
The time weighted charts tool offers you the following chart types:
- CUSUM or CUSUM individual
- UWMA or UWMA individual
- EWMA or EWMA individual
A CUSUM, UWMA or EWMA chart is useful to follow the mean of a production process. Mean shifts are easily visible in the diagrams.
UWMA and EWMA charts
These charts are not directly based on the raw data. They are based on the smoothed data.
In the case of UWMA charts, the data is smoothed using a uniform weighting in a moving window. Then the chart is analyzed like Shewhart charts.
In the case of EWMA charts, the data is smoothed using a exponentially weighting. Then the chart is analyzed like Shewhart charts.
CUSUM charts
These charts are not directly based on the raw data. They are based on the normalized data.
These charts help to detect mean shifts of a user defined granularity. The granularity is defined by the design parameter k. K is the half of the mean shift to be detected. Normally to detect 1 sigma shifts, k is set to 0.5.
Two kinds of CUSUM charts can be drawn: one and two sided charts.