Advanced Digital Control Research Articles

Advanced digital control for New Zealand glasshouses

This article describes environmental control of a glasshouse, using a microcomputer and digital control theory. Experiments were performed on a small glasshouse, in which temperature changes in response to variation in heating and cooling actuations and to changing solar radiation conditions, were monitored. The parameters of a dynamic model describing these temperature variations were identified using the measured data sequences. Simulations were performed to predict the variation of the glasshouse temperature in response to controlled actuation signals of fan speed or electrical heating, which could either be continuously varied, or which were constrained to take only on/off values. During the simulations, the model was subjected to the measured solar disturbances to determine the ability of the derived controller to eliminate temperature variations due to outside influences. In all cases, the digital control based on a predictive model produced a more closely controlled temperature in the glasshouse than the simple proportional controllers which had been used previously. It was concluded that the ease with which microcomputers may be used to assist in the design of controllers makes it possible to use an algorithm which produces a robust and readily applied controller.

Design of Advanced Digital Control Algorithms for Water Turbines

Microcomputers will be applied more intensively for the speed governing of water turbines. One advantage of these digital controllers is the possibility to design arbitrary control algorithms. For the determination of the optimal structure of the digital control algorithm and the calculation of the controller constants ("controller parameters") simple but accurate mathematical models for the dynamic behavior of the water turbine are necessary. Therefore more exact nonlinear and simple linear models are compared by simulation on a hybrid computer system. For a Francis turbine, a simple linear model was finally used for the design of an appropriate digital control algorithm. This complex digital algorithm was also simulated on the digital part of the hybrid computer system. For the determination of the controller parameters a synthesis method was programmed on the computer. Finally an outline of adjusting rules and the robustness of this algorithm is given.

Comparison of Digital Control Algorithms for Industrial Robots

Today most of the industrial robots applied in practice are controlled by means of conventional, linear control algorithms which are implemented in the control computer. The development of faster, weight weight robots yields to additional control problems. For this new generation of robots advanced digital control algorithms are necessary and have to be available in the nearest future.The model for the dynamic behavior is those of a nonlinear, timevarying, multivariable system. Such models are too complicated for the development of control algorithms. Further difficulties arise from the choice of optimal algorithms as well as parameters. A powerful tool for solving these problems is simulation.Therefore, a sufficient accurate model of an industrial robot with simple kinematic structure including the drives and gears was implemented at the analogue part of a hybrid computer system. Various digital control algorithms with the same structure but of different order have been simulated at the digital part. The resulting paths were plotted and offered the possibility to compare these.

37. How to select and specify process pumps: J K Jacobs,Hydrocarbon Process Petrol Refiner, 44 (6), 1965, 122–138

The piping and instrumentation diagram (PID or P&ID) shows the engineering details of the process equipment, instruments, valves, actuators, shared display devices, piping and fittings; and their arrangement. The ISA-5.1 symbols and nomenclature for P&I diagrams is explained and examples are given. The principles of operation of gate valves, globe valves, plug valves, ball valves, diaphragm valves, butterfly valves and relief valves are described. Calculation of pressure drop in pipelines and process equipment is reviewed for Newtonian, non-Newtonian and two-phase flows. The design and selection of compressors and pumps should be treated as part of the design of a hydraulic system that also comprises the equipment, piping and associated valves and fittings, and the pump and valve must be designed together to guarantee operability over the desired range of control. Mechanical design of piping under the ASME B31.3 code is introduced and a method is given for selecting the optimal pipe diameter. An overview of basic control schemes for typical unit operations is given, including level control, pressure control, flow control, ratio control, cascade control, reboiler control, condenser control, distillation column control and reactor control. The purpose and placement of alarms is discussed. A brief overview is given of current topics in advanced digital control and process automation