(SR-52) Electronic Systems Dependability

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An excerpt from Predict System Dependability with a pocket calculator, Electroic Design, vol.24-no.19, SEP 1977, pgs. 100-104

" A programmable unit speeds computations of reliability and maintainability models.
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  A handheld programmable calculator can rapidly predict dependability of electronic systems. Carefully prepared, a calculator program, once loaded onto a program card, can provide calculations almost as precise as even a large-scale computer. Furthermore, the calculator is easier to use and less expensive than any computer, large or small.

Set up system models
  Three subsystem models {Series, Parallel and AnyR-of-N configuration} have been programmed for a scientific pocket calculator (see Table 1). To use the models, you need to know the mean time between failure (MTBF) and mean time to repair (MTTR) for each system component. You can either rely on figures vendors supply or, if you have access to trouble reports for the components, you can easily compute MTBF and MTTR parameters. For MTBF, multiply the operating time period in hours by the number of units sampled, then divide this product by the total number of failures. To obtain MTTR, average the "out-of-service" times.
  By applying the models, you can predict MTBF and MTTR for the total configuration, as well as for every underlying subsystem. Not only that, you can also determine availability, reliability and failure probability from MTBF and MTTR …
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Equations for three models
  The formulas for computing total system dependability can be solved on any scientific pocket calculator. But solving them on the SR-52, or another programmable type, not only enables you to complete the analysis much faster, but also reduces the risk of error. If you use an SR52, the following material will serve as a background, since you need only to follow the "User Instructions" detailed in this article. For other programmable calculators, you have to recode the equations. Those with manual calculators will have to grind through the formulas step-by-step …
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Table 2. SR52 coding form
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Table 3. SR52 user instructions
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  To code the SR52 calculator, see Table 2. With this coding procedure, you can obtain a program card that, when inserted into the calculator, prepares it to perform the computations described in Table 3. … "

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