Abstract: Control of a multi-variable process involves multi-dimensional representation of the values (Qa-Qh) of the process variables according to individual coordinate axes (Xa-Xh), and response based on sets of values for the process-variables accumulated from multiple, earlier operations of the process. An acceptable range (UL-LL) for each process variable due to the current values of the other variables is defined from the accumulated values, and the existence of an alarm condition in which the current value (Qg) of a variable lies outside the range defined for it, is detected and displayed (UC) on the relevant axis (Xg). The change of the values (Qa,Qb) of one or more of the manipulatable variables (a-c) required to rectify the alarm condition is determined iteratively, and implemented by operator or automated response.

Abstract: Operation of a multi-variable drilling-rig is carried out within an envelope defined by convex hulls (TC,BC) that are derived from sets of historical values for the variables accumulated in a store (3) from previous operations. A display unit (5) shows the real-time values (Q01–Q10) of the variables on parallel axes (X01–X10) together with upper and lower limits (Up01–Up10, Lp01–Lp10) of the viable ranges for each variable to remain within the envelope, taking into account the current value of each other variable. The adjustment of the value of a variable (Q03) required to correct for a variable (Q08) found to be outside its viable range, is determined tentatively before implementation, by adjusting that value in the display to bring about re-calculation and display of the changes in viable ranges that would result from such adjustment.

Abstract: Control of a multi-variable process involves multi-dimensional representation of the values (Qa-Qh) of the process variables according to individual coordinate axes (Xa-Xh), and response based on sets of values for the process-variables accumulated from multiple, earlier operations of the process. An acceptable range (UL-LL) for each process variable due to the current values of the other variables is defined from the accumulated values, and the existence of an alarm condition in which the current value (Qg) of a variable lies outside the range defined for it, is detected and displayed (UC) on the relevant axis (Xg). The change of the values (Qa,Qb) of one or more of the manipulatable variables (a-c) required to rectify the alarm condition is determined iteratively, and implemented by operator or automated response.