GB1397966A - Pneumatic controllers - Google Patents

Abstract

1397966 Fluid-pressure servomotor systems COMPTEURS SCHLUMBERGER 12 July 1972 [12 July 1971] 32494/72 Heading G3P In a pneumatic controller providing an output S proportional to the magnitude and time integral of an input M' a force balance E has a chamber b to receive the input and further chambers a, c and d to receive set value, and positive and negative feedback signals, respectively. The chambers a', c are separated by a hinged closure from the chambers b', d and a nozzle B' connected through a restrictor C3 to a supply PA operates a relay D to provide the output S at a pressure of 2 bars less than the output from the nozzle. Positive feedback pressure is obtained from a pressure divider comprising a variable resistor Rl and a fixed resistor C4 having an input Pi' regulated by a 1 : 1 relay R including a nozzle B" and a flexible diaphragm m responsive to a pressure Pi which is equal to Pi' and determined by the values of a capacitor K and a variable resistor Ri. If derivative action is required, the signal M is obtained from a further force balance having a chamber b, Fig.1, to receive the input M, a chamber d and a nozzle B to regulate the output M' and two further chambers a, c to which the output is applied through a delay network comprising a variable resistor Rd and a capacitor Cd. Figs.3, 6, 8 and 11 show a PID controller including moulded parts 1, 6, 7 and 8, bored pins 14 for the input, output and supply connections, knobs 10, 11, 24 with tapered grooves 85 to constitute the variable resistors Rl, Ri and Rd for adjustment of the proportional, integral and derivative action and a switch 9 which may be rotated through 90 degrees to reverse the signal and set-value inputs to the controller. The force balance of Fig. 1 is contained in the part 1 which communicates through holes 4 sealed by gaskets 5 with the part 7 containing the force balance E and the relay R, the relay D being contained in the part 8. Four sealed chambers 66, 67, 68, 69 and a hinged closure 63 cooperating with a nozzle 70 form the force balance E. The closure consists of upper and lower members separated by a flexible diaphragm 58 and integrally connected with plates 59, 60 by portions which allow the closure to pivot, the portions in the plate 60, which is thicker than the plate 59, being thinned. Knife edges 61 and 62 bear on the portions through rubber seals 56 and 57 which are compressed to an extent limited by bosses 16 when the parts 6 and 7 are clamped together by bolts 15. The force balance in the part 1 is of similar construction. The relay R includes a flexible diaphragm 71 co-operating with a nozzle 72 while the relay D has a hinged member 34, Fig.6, to connect the relay outlet to a supply chamber 41 or to an exhaust passage 45, Fig.8, by operating valves 43 and 40.