Patent GB-1450176-A (GB)
Title: Arrangement for automatically initiating a state of higher security  in installations for example railway control installations  wherein substations are cyclically called by a central station
IPC: B61L7/08
Filed: 1973-09-20
Abstract: 1450176 Selctive signalling SIEMENS AG 20 Sept 1973 [20 Sept 1973] 44293/73 Heading G4H [Also in Division B7] An arrangement for automatically initiating a state of higher security in substations cyclically called by a central station in safety installations in the event of various disturbances in the remote transmission of encoded blocks of information, has in each substation a short-time signal generator set by a block code tester to initiate a trouble indication on expiry of the short time from the last setting, and a longtime signal generator set in response to errorfree blocks intended for the substation to initiate the state of higher security on expiry of the long time from the last setting. Fig. 1 shows one of a number of substations cyclically called from a central station. Blocks of A.C. signals are passed through a receiving amplifier E1 to a demodulator D1, the blocks being error-tested at P1. Each error-free block causes setting of a short-time monostable K1, which is also set if a level detector T1 detects signal level as being insufficient (so that the safe state, see below, is set up under control of the long-time monostable, see below, in the case of failure of transmission). If a given address is detected, at A1, in the block, a control action is performed at S1, and a long-time monostable Z1 is set. If at any time either monostable K1, Z1 is not in the set state, and AND gate G10 sets the controlled apparatus at S1 into a safe state. In a modification (Fig. 2, not shown) P1 is fed from D1 only if the level at T1 is sufficient, the safe state is controlled from Z1 alone, and an indicator is actuated if Z1 is in the set state while K1 is in the reset state. The level detector contains an RC integrator followed by a Schmitt trigger. In another modification (Fig. 3, not shown) the substation is addressed by the frequency band used, so A1 is omitted and the lower output shown of P1 controls Z1 directly and the right hand output of P1 controls Sl. G10 is replaced by an OR gate fed by the inverse output of K1, Z1 to set up the safe state if either of K1, Z1 is not in the set state, as before. Another level detector, fed in parallel with the input to E1, monitors the frequency band of this substation and at least one other to set a monostable if the level is sufficient. A signalling device is actuated if this monostable is ever in the reset state. The time-out period of this monostable is shorter than that of Z1. The substations may be on respective railway trains, and in the embodiments using an address comparator A1, the given address may be that of a track section occupied by the train. The safe state may be that of emergency braking. Alternatively, the substations could be stationary substations for point setting and signal control, and the safe state that with the STOP signal actuated. The central station may initiate the safe state deliberately by omitting an address, or the transmission frequency band, or the blocks while retaining a sufficient level. Thus the safe state may be initiated after the short or long time selectively.