Patent GB-1399380-A (GB)
Title: Process control system
IPC: G05B13/04
Filed: 1972-07-04
Abstract: 1399380 Process control SOC GENERALE DE CONSTRUCTIONS ELECTRIQUES ET MECANIQUES (ALSTHOM) 4 July 1972 [5 July 1971] 31303/72 Heading G3R In a process control unit for progressive control in which a model 2, Fig. 2 having a transfer characteristic M(p) simulating the properties of the actual process 1, a control signal U, representing one or more parameters to be controlled, being fed to both the model, and via input unit 4 to the process, the resulting output signals from the model and the process (the latter being measured signals) being combined to produce a deviation signal e added after passage through unit 6 to the output of the unit 4 to provide process control signal, the response stability of the system is improved by providing a supplementary control signal # also added to the process control signal. When a plurality of parameters are controlled, each parameter is regarded as a vector component of a vector signal U, the above-mentioned signals being in such case also of a corresponding vector form. Derivation of supplementary control signal # Unit 10 receives the deviation signal e, each of whose components ej pass to a linear corrector 12 comprising, for each component, a cascade of operational amplifiers (30), Fig. 11 (not shown), whose outputs are recombined to form signal v, at output (33), fed to a non-linear unit 13, see also Fig. 5 (not shown), receiving also the deviation signal e process output signal #p and control signal U, and comprising, for each component of e, #p, U, multipliers (18, 20) Fig. 4 (not shown), and filters (19) there being, for each component of e, #p, v as many circuits (18-20) as there are components of v. Filters (19) have a transfer characteristic of any of the Figs. 7-10 (not shown). The outputs of units (22) (Fig. 4) for a given component of each of e, #p, U are combined to provide the corresponding component of the supplementary signal #, (Fig. 5), vector # having a faster response time than that of the process. Single parameter examples, with given transfer function of model 1, are disclosed in relation to Figs. 12, 13, 14, 20 (not shown). Modifications. To reduce the influence of system noise, the outputs #m, #p, Fig. 15 of the model, and process are fed to respective identical filters 34, 35 comprising amplifiers (41) Fig. 6. (not shown) producing a set of filter output signals # mf-p n# mf , #pf-p<SP>n</SP># p f, {p being'the Laplace variable}, which are combined to produce a corresponding set of deviation vectors fed to unit (37), see also Fig. 17 (not shown), providing the signal v received by unit 13 along with signals ef, and #pf. Alternatively, Fig. 18 (not shown), unit (13) may receive the complete set #pf-pn#pf, and a corresponding control set U f -p<SP>n</SP>U f  derived from filter (38). The system may be realised in digital form, Fig. 21 (not shown), the input U being a programmed signal. Instead of filters (34, 35), a single filter (45), Fig. 19 (not shown), may provide a set (#F-p<SP>n</SP>#F) of modified filter output deviation signals from the deviation signal (e). The process controlled may be one of distillation, or fractionation in a column, in which case temperature and flow-rate are controlled, or of alternator control, voltage and frequency being the process outputs, active, and reactive power being controlled, or of aircraft control.