Showing papers on "Process variable published in 1976"

Gain-adaptive process control

Abstract: In a process control system, a control signal to the process is provided to a process model having a predictive element and a delay element adapted to reproduce as closely as possible the action of the measured process variable to the control signal. The variable input signal to the process controller, upon which generation of the process control signal is based, is generated by multiplying the signal from the predictive portion of the process model by a correction factor generated in response to the ratio of the actual process measurement signal to the delayed model output signal.

Differential pressure transmitter

Abstract: A differential-pressure transmitter adapted to produce a signal proportional to a process variable such as flow rate in a line conducting fluid or the level of liquid in a tank, the process fluid being at a temperature markedly at variance with ambient temperature. The transmitter is constituted by high and low pressure sensors which are coupled to the force beam of a force balance transducer so that the beam is responsive to the difference between sensed high and low pressures derived from the process variable, the transducer being exposed to ambient temperature. Each sensor is constituted by a housing having a well therein covered by a sensing diaphragm and an insert seated in the well, the face of the insert being spaced from the diaphragm to define a fill chamber containing hydraulic fluid, the sensor diaphragm being exposed to the process liquid, whereby heat transfer takes place between the liquid and the hydraulic fluid. The insert is formed of a metal having a low coefficient of expansion relative to the material of the housing whereby variations in temperature produce changes in the dimensions of the housing relative to that of the insert and give rise to changes in the volume of the fill chamber to an extent compensating for the concurrent changes in the volume of hydraulic fluid as a result of said heat transfer, thereby rendering the sensor insensitive to temperature changes.

Override process control system

Abstract: An override process control system for regulating a process with a single final control element, such as a valve, from two or more process variables that are interdependent and must not exceed acceptable minimum and maximum limits. The system includes a like number of electronic controllers each acting to compare a respective process variable with a set point to produce an output signal reflecting the deviation of the process variable from the set point. The primary controller responsive to the process variable directly influenced by the setting of the final control element has its output signal applied thereto to regulate this element, whereas the other controllers which are responsive to secondary process variables operate on a standby basis. Coupled by individual lines to the several controllers is an override selector station which monitors the operation of the controllers, and in the event an unsafe signal is received from one of the standby controllers, forces the primary controller to respond to the unsafe signal until such time as the signal is again safe.