GB934414A - Improvements relating to electrical monitoring systems - Google Patents

Abstract

934,414. Protective arrangements. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Aug. 9, 1961 [Sept. 2, 1960], No. 30370/60. Class 38 (5). [Also in Groups XXXVIII and XL (c)] A monitoring system comprises means for producing an electrical signal corresponding in magnitude to the state of the apparatus being monitored and for actuating an alarm when this magnitude falls below a first predetermined value or increases above a second predetermined value. The invention is described in connection with a transmitter-receiver warning device which may be of the kind disclosed in Specification 876,998 to indicate the proximity of two relatively moving bodies (e.g. two cranes or a crane and a fixed wall) comprising a transmitter T (Fig. 1) and associated transducer S and a receiver R and its associated transducer M. To produce the signal corresponding in magnitude to the operational state of the apparatus low impedance devices R 1 , R 2 are inserted in series with the transmitter and receiver channels respectively and connected by a circuit including a high impedance R 3 , the arrangement being such that faults in either the transmitter or receiver circuits then result in the production of a signal output from the receiver which is either very much lower or very much greater than the signal output obtained when the apparatus is working normally. The receiver output signal then operates two relays C 1 , C 2 , one operating when the receiver output falls below and the other when it increases above the respective predetermined values, the relays operating respective groups of contacts M 1 , M 3 , M 2 , M 4 and W 1 , W 3 , W 2 , W 4 (shown in their unoperated conditions in Fig. 2). During normal operation of the apparatus contacts M 1 , M 2 close and M 3 , M 4 open, the contacts W remaining in the positions shown. When a fault occurs which results in a low signal output from the receiver the M contacts revert to the positions shown, the opening of the circuit of relay AL1 results in the operation of a first alarm and the closing of the circuit of relay AL2 results in the simultaneous operation of a second alarm. When a fault occurs which results in a high signal output from the receiver the contacts W operate and produce a similar operation of the alarm relays AL1, AL2.