摘要:
An electrical circuit arrangement including a plurality of bistate devices such as vibration detection devices (2 to 7) connected therein. (Figure 1) each occupying a particular position in the circuit, and each having a resistor (R 2 to R 7 ) associated therewith, such that a predertermined value of resistance normally prevails and the value is changed when any device changes state, comparison means (13 to 17) for comparing a parameter such as the current in the circuit with a reference parameter to indicate the identity of any device which has changed state and the position in the circuit of any changed-state device. In a second embodiment (Figure 2) the bistate devices (2 to 6; 30 to 34) and resistors (R i to R s ) are connected in a multi-terminal network (1, 1; 35. 36) and connected to monitoring means (39) such as a microprocessor, via a switching unit (40), the monitoring means (39) being operable in a plurality of different modes to monitor the devices (2 to 6; 30 to 34) across different combinations of pairs of terminals (1,1'; 35, 36) such as to identify the position of any changed-state device in the circuit and to identify any failed or faulty device and to allow the circuit to continue to operate despite any failed or faulty device.