Showing papers on "Process variable published in 1987"

Self-tuning process controller

Abstract: An industrial process control system in which an electronic controller acts in a controlled process subject to process "dead time" to maintain a process variable at a desired value. Applied as inputs to the controller are signals representing the process variable and a set point, the controller yielding an output signal that reflects the deviation of the process variable from the set point and acts to adjust a final control element in the system to cause the process variable to conform to the set point. To effect self-tuning of the controller, a microprocessor is provided which is responsive to the process variable signal and the output signal from the controller and functions while the controller is operating to identify in a discrete-time process model parameter-identifier the process dead time and the process parameters, and to compute tuned controller parameters, and to transfer the calculated controller parameters to the controller so that the controller can be tuned to prevailing process conditions.

Front panel for a process controller

Abstract: A front display panel for an industrial process control instrument which acts to maintain a process variable, such as flow rate, at a desired value. The instrument compares a signal representing the variable with an adjustable set point to produce an output signal that reflects the deviation of the variable from the set point, the output signal being applied to a final control element such as a valve which governs the process variable. The front panel of the instrument includes a bar graph indicator for the process variable, a bar graph indicator for the set point and a bar graph indicator for the output signal, all three indicators being of the gas discharge type and being integrated into a single panel defining a sealed envelope filled with an ionizable gas and provided with electrodes. Also integrated into the panel are touch-sensitive switches and other control and indicating elements.

Method and arrangement for process control in spot welding

Abstract: A method and an arrangement for process control in spot welding are described in which the mechanical and/or electrical process variables predetermined for the welding process are monitored during the welding and each change in the process variable within the welding operation can be readjusted via several manipulated variables. The welding process is subdivided into several areas for the control, an evaluation scheme being allocated to each of these areas. The curve behaviour for various materials and dimensions is determined on actual components and stored. Calibration of the welding machine is dispensed with.

Method and a process control system using the method for minimizing hunting

Abstract: A method for process control to minimize hunting using a controller wherein a PID arithmetic operation is performed with respect to a deviation of a setting parameter and a processed variable fed back from a process, and a resultant manipulation variable is applied to the process including the steps of monitoring the waveforms of the setting parameter and the processed variable from the process to obtain an oscillation period of the deviation, identifying process characteristics of the process, obtaining a phase angle of a frequency response of an open-loop transfer function of a system from the oscillation period and the process characteristics, and detecting a hunting of the process by the magnitude of the phase angle. A process control system includes a self-tuning controller having a control means for performing a PID arithmetic operation with respect to a deviation between a setting parameter and a processed variable fed back from a process, process identification means for identifying process characteristics and determining optimal PID parameters, monitoring means for monitoring the waveforms of the setting parameter and the processed variable from the process to obtain an oscillation period of the deviation, means for obtaining a phase angle of a frequency response of an open-loop transfer function of the process obtained from the oscillation period and process characteristics, means for detecting a hunting of the process by the magnitude of the phase angle, and means for performing a tuning operation of the controller in accordance with the detecting result by the means for detecting.

Temperature control arrangement for an extruding process

Abstract: An arrangement for controlling the process temperature in an industrial process involving an extruding operation includes a summing element which sums the difference between the process temperature and a setpoint temperature with the rate of change of the process temperature and conveys this sum to a proportional and integral controller so that the output thereof acts in an inverse manner with the process temperature. This output of the controller is summed with the change of temperature rate which has been fed forward, to generate a demand signal. The demand signal is shaped and compared to a ramp waveform to generate a variable frequencey pulse for controlling a heating and/or cooling device associated with the extruding device. A change of speed rate can also be summed to form the demand signal.

Interactive process simulation program for analysis and synthesis

Abstract: Interactive process simulation program called MICRO-APT has been extended with an algorithm, predicting process parameters in order to get a specified structure. This algorithm can be considered as a process parameter synthesis procedure as opposed to the usual analysis with a given set of parameters. Description of the algorithm and examples are given in the paper.

Two-line type communication system

Abstract: PURPOSE:To facilitate the maintenance of a process variable transmitter corresponding to a conventional analog control system and utilizing a digital communication state by enabling an analog data transmission state, a digital data transmission state and both the transmission states to be changed. CONSTITUTION:The process variable transmitter has constant current characteristics and is operated by a current of 4mA obtained through a transmission line. Then an analog data transmission function and a digital data transmission/reception function are provided. In the analog data transmission state, the process variable transmitter controls an output current IT in the range of 4-20mA corresponding to the process variable to send analog data. In transmitting digital data, the process variable transmitter 1 and a communication equipment 3 control output currents IT, IC.

Method and device for controlling a process variable

Abstract: In the case of a method for controlling a process variable, in the case of which a manipulated variable which influences the control variable is produced with the aid of a control device as a function of a reference variable and the process variable to be controlled, the manipulated variable does not vary within a range of the control variable which can be predetermined and is defined by a lower and an upper range limit. This is achieved in that the reference variable is equated with the control variable within the range which can be predetermined and, outside the range, the range limit which has been exceeded is maintained as the reference variable. This control system can be implemented in a simple manner with the aid of two solenoid valves, the first solenoid valve coupling the control variable to the reference variable within the range which can be predetermined while, outside the range, the second solenoid valve isolates the variable produced by the controller from the manipulated variable which actually influences the control variable. The two solenoid valves are driven by two switching devices which characterise the upper and the lower limit of the range which can be predetermined.