GB1389470A - Set point controller - Google Patents

Abstract

1389470 Set-point control MOBIL OIL CORP 20 Oct 1972 [12 Jan 1972] 48435/72 Heading G4H [Also in Division H2] Apparatus for use in a process control system comprises a stepping motor having a permanent magnetic rotor, a permanent mgnetic stator and a plurality of motor windings, and a potentiometer having a direct coupling between a motor driven shaft and a rotatable shaft of the potentiometer. Data measured by transducers associated with the processing system supply information relating, e.g. to temperature, pressure or flow rate to a computing device which provides a digital pulse train of equiweighted pulses the number of which relates to a dsired change in, e.g. the setting of a valve in the system. These pulses are applied to logic circuitry whereby they are routed sequentially to the windings of the stepping motor to cause its rotor to rotate by a number of increments corresponding to the number of pulses in the train to alter the setting of the potentiometer shaft and therefore its output voltage, which voltage is used an an analog control loop to move the valve to the desired setting. The computing device may alternatively supply a pulse the length of which is significant and clock pulses are supplied to the logic circuits whilst this pulse is present.