GB1347304A - Process and apparatus for the automatic control of a variable - Google Patents

Abstract

1347304 Automatic control systems SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ N V 23 Aug 1971 [25 Aug 1970] 39349/71 Heading G3R A variable control system with proportional and integral action includes a signal limiting arrangement in which the magnitude of the limit may be determined by the error signal or by measurement of a controlling parameter of the system. In the system shown in Fig.1, a ship's propeller 1 is driven by a steam turbine 2. The speed of rotation of the propeller shaft is detected by a meter 5 which feeds a signal n b to a circuit 6 for comparison with a demand signal n a . The resultant error signal is passed to'a comparator 7 which also receives a signal X from a differentiating feedback network 12. A high-gain amplifier 8 forms a signal Z which is passed to an integrator 11 by way of upper and lower limit circuits 9, 10. The integrated output I is fed back to the network 12, and is also used to control a steam valve 4 in the supply line 3 to the turbine 2. In a modification, Fig.3 (not shown), a function generator, (16) transforms the signal I into limits (+L, -L) for circuits 9, 10 such that the magnitude of L increases for small values of I. In a further arrangement, Fig.4 (not shown), the rate of flow in steam line 3 is measured, differentiated, and compared with a reference value to determine values for the limits (+L, -L) which will limit the maximum rate of change of steam supply to the turbine. The system may employ electric, pneumatic, or hydraulic signals in analogue or digital form. A digital computer may be included. In addition to ship propulsion, the system may be used to control the movement of a crane or a radar aerial.