Patent GB-961949-A (GB)
Title: Method of and system for discriminating failures
IPC: G05B9/02
Filed: 1960-10-07
Abstract: 961,949. Radiation-sensitive flame monitors. SCULLY SIGNAL CO. Oct. 7,1960 [Dec. 3, 1959], No. 34515/60. Heading G1A. [Also in Division G4] A monitoring system, particularly a flamemonitoring system, discriminates between failure due to loss of the input, monitored, signal and that due to a fault within the system, and includes means to provide a periodic checking signal which exists only in the presence of the monitored signal, an indication being given when (a) the system is working normally (b) there is a fault in the system (c) the monitoring signal is lost. Fault (b) may switch in a standby monitoring system and fault (c) may operate an alarm and a control circuit. In Fig. 1, the feedback system 20, 21 between a signal sensor output 4 and a switching system 7 provides a periodic checking signal to the input of system 6 in the form of a modification of the principal, or monitored, signal input in accordance with Specification 793,511. System 8 provides a "normal operate" signal to indicator 9. If system 8 fails to receive the checking signal it applies a simulated sensor output signal to the input 5 via lead 22 and one of two indications will be given at 9 depending on whether this simulated signal is transmitted indicating that system 6 is in order but the monitored signal has ceased or when no signal is transmitted indicating that system 6 has failed. In a modification (Fig. 2, not shown) the checking signal is supplied to a modifier connected to the output of the monitored signal source. The source itself is checked in a further embodiment (fig. 3, not shown) by applying a simulated input signal, generated in a separate circuit, ahead of the modifier or the sensor. Flame monitoring apparatus is shown in Fig. 4 and comprises a flame probe sensor 3 or a photoelectric sensor 3a; system 6 consists of an amplifier T1, T2, an output system 7 includes a switching relay RY1 controlling switches I and III, the checking signal recovery part of system 8 includes relay RY2 and integrating capacitor C5, and the discriminator part of system 8 includes memory relays RY3, RY4, The indicating system 9 consists of three lamps, and may include alarm control apparatus &c. Normal operating condition and provision of the checking signal. The negative D. C. input from sensor 3 is applied to the grid of T, and so blocks it whereby T2 conducts to energize relay RY1. Capacitor C4 will then discharge into C5 on engagement of switch III with contact B, and relay RY2 energizes. On energization of RY1, switch I thereof will open to simulate the loss of input at 5 causing T1 to conduct, T2 to cut off, and relay RY1 to be de-energized, this cyclic action of relay RY1 being repeated under normal operating conditions and providing the checking signal. Relay RY2 remains energized as long as the checking signal is present and causes energization of RY4 and operates lamp LP1 to indicate normal operation. RY2, RY4 are maintained energized and relay RY1 pulses continuously. When any part of the monitoring system fails relay RY1 will stop pulsing and remain in either its energized or de-energized position, and due to the loss of the checking signal, relay RY2 will release, RY3 will be energized, switch IV" thereof closed and simulated input signal fed to input 5 via rectifier REG3 and loop 42. There will be no output from amplifiers T1, T2 and lamps LP1, LP2 will both be energized. When the input signal is lost, relays RY1 and RY2 de-energize and RY3 is energized as before to send a simulated input signal to the input 5 over line 42. This will be transmitted to the output to energize RY1 and RY2 which will remain energized together with RY3, RY4 to extinguish LP1, operate indicator LP3 and/or an alarm, via switch V of relay RY3 and contacts Ca and switch IV of relay RY2. Specifications 793,512, 807,033, 823,880, 823,881, 823,882 and 916,950 also are referred to.