Process Window Index - Formula

Formula

The Process Window Index is calculated as the worst case (i.e. highest number) in the set of thermal profile data. For each profile statistic the percentage used of the respective process window is calculated, and the worst case (i.e. highest percentage) is the PWI.

For example, a thermal profile with three thermocouples, with four profile statistics logged for each thermocouple, would have a set of twelve statistics for that thermal profile. In this case, the PWI would be the highest value among the twelve percentages of the respective process windows.

The formula to calculate PWI is:

\text{PWI} = 100 \times \max_{i=1\dots N \atop j=1\dots M} \left\{\left| \frac{\text{measured value}_{} - \text{average limits}_{}} {\text{range}_{}/2} \right|\right\}

where:

i = 1 to N (number of thermocouples)
j = 1 to M (number of statistics per thermocouple)
measured value = the th statistic's measured value
average limits = the average of the high and low (specified) limits of the th statistic
range = the high limit minus the low limit of the th statistic

Read more about this topic:  Process Window Index

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