Computers and microprocessors in process control

Historical operating data is retained in the computer memory. Averages and trends can be displayed, for plant investigation and trouble shooting. 

Software to continuously update and optimise plant performance can be incorporated in the computer control systems. 

Programmable logic controllers are used for the control and interlocking of processes where a sequence of operating steps has to be carried out such as, in batch processes, and in the start-up and shut down of continuous processes. 

A detailed discussion of the application of digital computers and microprocessors in process control is beyond the scope of this volume. The use of computers and microprocessor based distributed control systems for the control of chemical process is covered by Kalani (1988). 

(1969) Chem. Eng., NY 16 (June 2nd) 136. Process instrument elements. 

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The use of computers and microprocessors (also known as programmable electronic systems [PES]) in process control continues to grow. They have brought about many improvements but have also been responsible for some failures. If we can learn from these failures, we may be able to prevent them from happening again. A number of them are therefore described below. Although PES is the most precise descnption of the equipment used, I refer to it as a computer, as this is the term usually used by the nonexpert. 

What are the basic and most important advantages offered by digital computers in process control Discuss the size, capabilities, and prices of the most recent digital microprocessors available in the market. Do you realize the inexpensive potential that they offer for process control ... 

Quite a few different set-ups have been demonstrated, in which an irradiation apparatus was combined with different methods of spectroscopy. In all these combinations, process control either by microprocessors or by personal computers, was achieved. Modem instmments contain a microprocessor for process control of the spectrometer and data transfer to a dedicated personal computer. Quite a few years ago data stations were integrated in the spectrometers. However, their flexibility is poor and their software is restricted to the instmmentation making adaptations to user specified problems very difficult. 

The simplest algorithm for a PID controller is the sum of Equations 8.1, 8.2, and 8.3 as shown in Equation 8.4. This is common in computer-based control systems, and all three control actions are considered to be operating in parallel. However, many industrial analog controllers and microprocessor DCS (distributed control system) controllers use a capacitance lag (filter) of about 0.05 to 0.10 in series with the process variable signal to reduce the effect of derivative action from setpoint changes and from short time constant noise described earlier. When the derivative time constant,... 

A.3 Microprocessors and Digital Hardware in Process Control A.3.1 Single-Loop Controllers A.3.2 Programmable Logic Controllers A.3.3 Personal Computer Controllers A.3.4 Distributed Control System... 

The calender was developed over a century ago to produce natural rubber products. With the developments of TPs, these multimillion dollar extremely heavy calender lines started using TPs and more recently process principally much more TP materials. The calender consists essentially of a system of large diameter heated precision rolls whose function is to convert high viscosity plastic melt into film, sheet, or coating substrates. The equipment can be arranged in a number of ways with different combinations available to provide different specific advantages to meet different product requirements. Automatic web-thickness profile process control is used via computer, microprocessor control. 

The character and the degree of automation in chemical control may have been covered in the above treatment of semi-automatic or completely automatic, and of discontinuous or continuous analysis, but something more should be said about the means by which automation proper has been performed in recent times. Whereas in the past automated analysis involved the use of merely, mechanical robots, to-day s automation is preferably based on computerization in a way which can best be explained with a few specific examples. Adjustment knobs have been increasingly replaced with push-buttons that activate an enclosed fully dedicated microcomputer or microprocessor in line with the measuring instrument the term microcomputer is applicable if, apart from the microprocessor as the central processing unit (CPU), it contains additional, albeit limited, memory (e.g., 4K), control logics and input and output lines, by means of which it can act as satellite of a larger computer system (e.g., in laboratory computerization) if not enclosed, the microcomputer is called on-line. 

FIA star 5010 Modular, semi- or fully automatic operation. May be operated with process controller microprocessor. Can be set up in various combinations with 5017 sampler and superflow software which is designed to run on IBM PC/XT computer 60-180 samples h Dialysis for in-line sample preparation and in-line solvent extraction.Thermostat to speed up reactions. Spectrophotometer (400-700nm) or photometer can be connected to any flow through detector, e.g. UV/visible, inductively coupled plasma, atomic absorption spectrometer and ion-selective electrodes... 

HPLC systems operate on a master-slave arrangement in setting up for automation. One module sets the timing and initiates the process, and the remaining modules accept a signal and follow the leader. In a gradient HPLC system, the master module can be a microprocessor-based controller, a computer software-based controller, an autosampler, or an integrator. 

Central Processing Unit (CPU) The computing and control part of the computer. The CPU in a mainframe computer may be contained on many printed circuit boards, the CPU in a mini computer may be contained on several boards, and the CPU in a PC is contained in a single extremely powerful microprocessor. 

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