The FabTime Cycle Time Characteristic Curve Generator is an Excel-based tool for exploring cycle time and utilization trade-offs for single tools with failures. You can enter parameters for process time, mean time between failures, downtime percentage, and system coefficients of variation for up to three scenarios. The calculator then displays characteristic curves for the scenarios, allowing you to get a quick visual impression of the impact of both downtime and variability attributes. The curves are based on a queueing approximation that we first were shown several years ago by Ottmar Gihr of IBM Germany. The formula for system variation used in the spreadsheet was modified slightly on 11/12/01 to follow Equation 8.6 in the text Factory Physics, Second Edition, by W. J. Hopp and M. L. Spearman (with thanks to Mark Spearman for the suggestion!). The spreadsheet was modified again on 05/03/02 to allow coefficients of variation greater than 1.
Please feel free to use this spreadsheet, and to pass it along to others — we only ask that you attribute the source, and maintain our copyright notice!
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