Patent GB-1402565-A (GB)
Title: Industrial control system utilizing high speed digital computer
IPC: G05B15/02
Filed: 1972-08-17
Abstract: 1402565 Automatic control systems FOXBORO CO 17 Aug 1972 [20 Aug 1971] 38430/72 Heading G3R An industrial process is controlled by a system in which a plurality of conditions are sensed by transducers which transmit pulses to a digital computer store, the computer having means to operate on the stored values and to store the result for subsequent transmission to actuators which influence the measured conditions, the transmission being in the form of pulses whose frequency is significant. In the embodiment, process variables such as temperature and pressure are measured at 16A - - - 16C by devices which produce pulses whose frequency is indicative of the measured value, possibly by the use of A/D converters 24. These are sequentially scanned and the frequencies converted into digital numbers which are stored at 64, there being one store 64A, 64B &c. for each channel. Periodically, e.g. once per second, the numbers are transferred to a computer store 100 upon which an unspecified programme operates to produce correcting values which are placed (in digital form) in a further store 102, from which the stored numbers are converted into pulses, the number of which in unit time corresponds to the respective digital number, and the pulses are sequentially supplied to control devices 18A, 18B, e.g. valves. Conversion of pulse frequency into digital numbers. The inputs are periodically (many times per second) and simultaneously connected to respective stages of a shift register 30, which is 'read' serially by logic circuits Fig. 2 (not shown) arranged to produce a train of '0' or '1' pulses the position of each pulse in the train being indicative of the variable to which it relates, and its state (0 or 1) depending upon whether that particular input has changed its state since the last sample was taken; if it has, the resulting '1' is fed to the appropriate stage of store 64 which thus, at the end of each base period of one second has as many '1's stored in it as there were pulses on the corresponding input line in the same time. Conversion of digital numbers into pulse frequency. The correcting values are stored in 102 in the form of 12 bit digital words, one such word in each store 102A, 102B &c. corresponding to a respective control device 18A, 18B &c. The columns and rows of the complete store 102 are transposed in a further store 112, which enables all the corresponding bits (i.e. all the most significant bits (MSB), all the next most significant bits (NMSB &c.) for each channel to be read simultaneously. If such a bit in a particular channel is a '1' this produces a pulse in the appropriate output line 22. The MSB's are read at twice the rate of the NMSB's, which in turn are read at twice the rate of the second NMSB's and so on, so that the number of pulses produced on each output line in a given period (one second) depends upon the significance of the '1's which occur in the digital word stored in 102. Thus the output pulses are not evenly spaced and 'pulse frequency' in this case refers to the actual number of pulses which are produced in unit time. Details are illustrated in Figs. 4 - - 7 (not shown).