GB953027A - Improvements in or relating to control circuit arrangements - Google Patents

Abstract

953,027. Electric selective signalling systems. LICENTIA PATENT-VERWALTUNGSG.m.b.H. Feb. 12,1962,No. 5288/62. Heading G4H. In a control circuit, for example in which it is necessary that certain switching operations should be carried out only after certain other switching operations have been performed, logic circuits are used to determine whether or not an operation can be performed. The logic circuits comprise AND and OR gates as illustrated. Circuit 1 is similar to circuit 2, all AND gates being replaced by OR gates and vice versa. Each gate A1, A2, ... corresponds to a certain combination of conditions upon which the permissibility of operating switch unit 13 depends. The signals fed to circuits 1 and 2 are the inverse of each other, i.e. are X and X. In use if, for example, signals x 11 , x 12 , ... arrive at AND gate A1, gate 010 will give an output F1. If the system is operating correctly, signals #X 11 , #X 12 , ... arrive at OR gate 01, which gives no output. Gate A 10 gives no output F2 and output F2. The system is operating correctly if F1 = #F2. Signals F2 and F1 are therefore fed to logic circuit 15, which gives an output R if F1 = F2. Outputs R, F1 and F2 feed AND gate 11, and if a further actuating switch 10 is depressed a further signal K is fed to gate 11, whereupon it gives an output permitting actuation of unit 13. An alarm 9 is operated if there is no output R from circuit 15.