TABLE OF CONTENTS A static switch is defined as a switch that has either to close or open a circuit during a mission. A static relay, a common single-acting switch, a squib, and a stop valve are examples. Such switches have a multiplicity of modes of function and of failure, such as close normally, fail in the quiescent mode, fail on command, fail open on command, fail closed on command, fail open after closing normally, etc. All such modes need to be considered when determining the reliability of static switches. First, the reliability of a single switch will be determined.
A static switch is considered to have the following function modes: normal (not failed in any mode); failed closed or failed open on command; failed closed or failed open in the quiescent function mode; failed closed after failing open; failed open after failing closed; failed open after closing normally; failed closed after closing normally; failed open after opening normally; and failed closed after opening normally.
The function cycle of a single, normally open, switch is shown in Fig. 9.1. Such a switch's reliability is given by
| R s,sw/o( t) | = | probability the switch will not fail either open or closed by t s, when it is called upon to close and thus transmit a signal or provide the flow of a current, and the probability it will close normally on command, and |
