TABLE OF CONTENTS Programmable Electronic Controllers have been arranged in several configurations in order to achieve various reliability and safety goals. These various arrangements of control system components are referred to as "system architectures." The common system architectures for programmable electronic controllers (PEC) are presented in this appendix along with corresponding fault trees and Markov models.
For comparison purposes a single board PEC with 8 inputs and 4 outputs will be used in a series of examples. Assume that the failure rates are determined by a FMEDA of each circuit. The results of the input circuit analysis indicate the following failure rate categories:
(All failure rates are in units of FITS, failures / 10 9 hours.)
The results of the output circuit FMEDA are:
The results of the common circuitry FMEDA are:
It is also assumed that the single board PEC is a series system (the failure of any component is considered a failure of the unit) with constant failure rates. The failure rates may therefore be added to obtain failure rates for the PEC.
A number of assumptions have been made in these models. It is assumed that:
Only a single failure can occur on the single board PEC. (One component failure will cause the entire single board PEC to fail.)
Constant failure rates and repair rates are assumed.
The models will be based on a de-energize-to-trip system with two failure modes - safe and dangerous.
Diagnostic test time...
