(SR-52) Practical Reliability & Serviceability Calculations for Complex Systems

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An excerpt from Computer System Reliability, Wiley, © 1980, pgs. 211-13 & 297-304

                      Chapter 12
  Practical Reliability and Serviceability
    Calculations for Complex Systems

                         UNITS IN PARALLEL AND IN SERIES
Units in Parallel
When considering reliability and serviceability of systems with standby systems, the following formula are often quoted:
       m = mean time between incidents of a single unit
        d = mean down time per incident
        s = serviceability of a single unit = …
        u = unserviceability of a single unit = …
        M = mtbi dual system = …
        D = mdti dual system = …
        S = serviceability of dual system = …
Similarly, U = unserviceability of dual system = u²
Also for a triplicated system: …
…
  The basic problem with these sort of calculations is that they do not cover the basic case where, say, 2 out of 3 units are required. To cover the calculations, the binomial distribution is more appropriate: …
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  Appendix 2 gives details of a program for calculating serviceability in units in parallel, for use on a programmable calculator. …
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                             Appendix 2
       Serviceability Calculations for Complex
    Systems Using a Programmable Calculator

Chapter 12 showed a method of calculating serviceability of subsystems and systems, including those where standby units are available. The program described provides an easy method of carrying out the calculations and can embrace the weighting factor serviceability scheme. The program listing given is for a Texas SR52 calculator but a flow chart is also included so that the program can be converted to run on other programmable calculators.
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BASIC THEORY
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WEIGHTING FACTOROPERATION
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TIMING
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UNITS IN SERIES
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FLOWCHART
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LISTING
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REGISTERS
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BEST!
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