Method and an apparatus for automatically tuning a process regulator
AssigneeHightech Network AB
InventorsKarl J. Astrom, Tore Hagglund
Life of this patent
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Abstract
Method for adjusting the setting of a digital process regulator on the basis of the result obtained from a simple relay feedback experiment. When an adjustment of the regulator setting is to be made, the relay feedback is connected in the control feedback circuit instead of the regulator in order to cause self-oscillation. The self-oscillation signal is utilized to calculate the new setting of the regulator.
Claims11
A method for tuning automatically a process regulator (2), in which a relay feedback (4) can be connected alternatively to the regulator (2) in the control feedback circuit of the process, and wherein, whenever retuning of the regulator is required, the relay feedback is connected in the circuit instead of the regulator in order to cause self-oscillation of the system process/relay feedback circuit, and in which said self-oscillation is used to calculate the setting of the regulator, said process comprising the steps of
- (a) indicating within one period of self-oscillation a time point (t.sub.max) at which a local signal peak value first occurs;
- (b) dividing the signal obtained within a half period into a selected number of n sampling intervals with intervals h.sub.i therebetween;
- (c) calculating the regulator control setting successively from various sampling intervals within the first half period of the oscillating period with a starting point from a model of the process beginning from the sampling interval occurring after said time point (t.sub.max);
- (d) comparing the result of the calculations with given compatibility conditions;
- and
- (e) terminating the successive calculations, and applying the calculated control setting to the regulator (2) immediately upon reaching a calculation which satisfies the aforesaid compatability conditions.
Apparatus for automatically tuning a process regulator with the aid of a relay feedback (4) which can be alternatively connected to the regulator (2) in the feedback circuit of the process (1), said apparatus comprising (a) a computer and control unit (5) which when coupled to relay feedback, is effective to (a) detects a self-oscillating period of the system, (b) divide said period into half-periods at a selected number n of the sampling points, (c) detect a time point t.sub.max within one of the oscillation half-periods at which a local signal peak value occurs for the first time and effect successively a calculation of a process model for each sampling moment during the first half-period after t.sub.max, and (d) to compare each calculation with stored compatability conditions, and immediately upon reaching a calculation which satisfies set compatability conditions inhibit calculation of the model for the next sampling period in line, and with control to the regulator (2) adjust the calculated model for control in the regulator.
Dependencies are inferred from the claim text.