Patent GB-1476509-A (GB)
Title: System for the multiplexed transmission of signals from seismic receivers
IPC: G01V1/22
Filed: 1974-07-08
Abstract: 1476509 Selective signalling SOC D'ETUDES RECHERCHES ET CONSTRUCTIONS ELECTRONIQUES 8 July 1974 [10 July 1973] 30207/74 Heading G4H [Also in Division H4] In a system for the multiplexed transmission of signals from seismic receivers C1-CN and in which a transmission path extends from a generator UC10 of coded pulse trains at the upstream end of the path to a register station UC18 at the downstream end, each receiver is coupled to the path by a multiplexing circuit BD1-BDN. The generator periodically supplies generator pulse trains having two parts, each constituting an alternate polarity violation, i.e. pulses of the same polarity following one another without a pulse of opposite sense between them, the parts being of opposite sense. Each receiver BD26 (Fig. 3) supplies its received information as digital signals and each multiplexing circuit includes at least one shift register BD27 which is filled with the digital signals and is coupled to the transmission path downstream to apply thereto digital signals as alternate polarity pulses (successive pulses being of opposite sense). In response to the first part of the generator train, a clock pulse source 238 applies (via appropriately set switch 234, 235) a predetermined number of pulses to read out the shift register on to the line at the proper time as determined by the arrival of the generator pulse train. The generator UC10 periodically applies to the line 7 bit words in alternating polarity form, the first three bits of which are for synchronizing and the remaining four are an instruction. There are two instructions. One causes data to be extracted from an output register containing digital information from the receiver at a particular station, and also initiates the deviation of a digital word representing the receiver output. The second causes the contents of a "repetition register", in series in the line, to be transferred to the next station. Fig. 3 illustrates the form of the transmission circuit at each station. The synchronizing part of the 7 bit words received at the input E are decoded at 237 and used to initiate the production of 27 clock pulses by the clock 238 and also to allow operation of the instruction decoder 239 which responds to the next four bits. The 7 bit input signal is also applied via a 3 bit delay to a regenerator 232 and thereafter, under the control of the first seven clock pulses, passes via the bipolarity regenerator 236, to the output S of the transmission circuit. At the end of this time, decoder 239 causes switches 234a, 234b to change to position 2 so that the clock may be applied to register 233 and the regenerator 236 may receive its input from the register 233 or BD27. If the first instruction is received, the switches 235a, 235b are set to position 1 and the digitizer register BD27, which contains a numerical indication of a receiver measurement, is read out into the bipolarity regenerator and thence to the circuit output immediately following the regenerated synchro and instruction signal. The measurement word is 18 bits long, and parity and symmetry bits are added in the regenerator 236, so that the total length of the word transferred to the output is 27 bits. This is entered in the repetition register 233 of the next station. If the second instruction is received, the contents of repetition register 233 are merely transferred to the next station. A complete read out sequence of synchro-instruction words from generator UC10 therefore starts with the first instruction, which as it proceeds down the line causes each station receiver to be read into the register of the following receiver, and is followed by a number of second instructions, related to the number of stations, which causes the contents of the repetition registers to be transferred round the loop and recorded in the registration device UC18. An alternative embodiment is disclosed which obviates the need for the bipolarity regenerator by using separate registers for the positive and negative input lines at the input E (Fig. 6, not shown), and output from the measurement digitizer being transferred via a polarity selector to separate positive and negative registers.