Computer control modifications

Systematic consideration of human error is neglected because of the belief that computerization of processes will make the human unnecessary. Experience shows numerous accidents in computer controlled plants. Human involvement in critical areas of maintenance and plant modification, continues even in the most automated processes. 

Have proper revisions been made to die process control logic, instrumentation set points and alarm points, especially for computer control systems to properly respond to the modification ... 

The automatic apparatus consists of a viscosimeter and phototran-sistorized sensing devices mounted in a precision thermostat ( 0.005°C) connected to a cooled prethermostat ( 0.1°C). The base apparatus is commercially available (Schott Viscotimer, Jenaer Glaswerk, Schott Gen., Mainz), but the viscosimeter control functions and the time measurements are performed by using an electronic computer-controlled interface. This modification enables one to follow slow reactions and to reduce standard errors on the outflow times to 2 msec. The final results are evaluated numerically by an on-line computer-plotter system. 

Several systems for automation of spectrometers have been discussed. A computer-controlled Echelle monochromator allowed wavelength increments of 0.01 nm. A wavelength-scan and lamp-intensity control scheme for the popular Bausch and Lomb high-intensity monochromator has been described. The accurate synchronization of monochromator wavelength-scan and chart-recorder speed, and the possibility of rapid scanning allowing spectra to be displayed in real time on an oscilloscope, has also been discussed. Details have been provided for the modification of a commercially available mirror mount (Oriel model 1450) for use as a stepper-motor controlled grating mount. 

The system was computer controlled, and, owing to the complication of the process, would be difficult to operate otherwise. The procedure consisted of 5 steps (7 steps in a later modification [23]), which is much longer and more complicated than those for flame AAS, but system components are almost exactly the same as for flame AA, except using a 4 5 channel multi-functional valve. 

Transient modification of a local area on an adsorbate-covered surface may be achieved by focusing a laser beam onto a small spot of about 80 gm on the surface, and by adjusting this spot by computer-controlled galvanometer mirrors within 5 pm and on a timescale of 1 ms. In this way, the local temperature can t5 ically be increased by about 3K [36]. In the example shown in Fig. 8.15,... 

However, when critical size is attained, by definition 45 no rise in neutron density can be expected. It is therefore necessary to increase the size of the structure beyond the critical size but not to the extent that the period for doubling of the neutron density is too short, as will be explained later. Reactors having a reproduction ratio (r) for an operating structure with all control absorbers removed and at the temperature of operation up to about 1.005 are very easy to control. Reproduction ratio should not be permitted to rise above about 1.01 since the reaction will become difficult to control. The size at which this reproduction ratio can be obtained may be computed from modifications of the above formulae for critical size. For example, for spherical active structures the formula... 

Principles of safe design and operation. Precautions during plant modification. Special considerations with computer-controlled processes. Training of operators. 

Fused deposition modeling (FDM) is a technique that builds plastic objects by extmsion of a polymer-wax filament through a nozzle (Fig. 6.52). A modification of the technique, referred to as fused deposition of ceramics (FDC), has been developed to create ceramic components from particle-filled polymer filaments (73). Ceramic-polymer mixtures used in FDC are similar to those described earlier for injection molding of ceramics. The mixture is first extmded to form filaments with a diameter of 2 mm, after which the spooled filaments are fed into a computer-controlled extrusion head. Extrusion of the plastic mixture through a nozzle is used to form the object layer by layer. Subsequent processing steps follow those described for injection molded bodies. 

The problem with GC as an analysis tool for the evolved component is that it takes much more time to separate the evolved components than to analyse their mass in the MS. If the sample is heated by a linear thermal programme (as is the case in thermal analysis), then many interesting kinetic phenomena may occur during separation of components in the GC. This makes on-line GC analysis of the evolved components difficult. The evolved components could be trapped at moments of interest [116], thus overcoming the sampling rate problem. However, this is not the best solution. With the introduction of computer control and some modification of the conventional GC apparatus, the speed of GC analysis makes on-line evolved gas analysis possible. 

The situation proves to be completely different when it comes to computer installations. Experts are by no means agreed on which faults are to be considered likely and how faults can be avoided or remedied. The software - a completely new element in computer-controlled equipment -also raised new problems in the safety issue whereby only the checkability of the system and the ease of modification are to be mentioned here. 

Initially further development of the computer-controlled flow techniques was hindered owing to unavailability of suitable commercial software and general lack of experience in coupling personal computers to instruments. However, most of the advantages of current flow techniques are in part consequences of the incorporation of computers. The earliest automatic methods used devices suited to particular applications, which restricted their scope to very specific uses such as the control of manufacturing processes or to situations where the number of samples to be analyzed was large enough to justify the initial effort and investment required. Nowadays, computerized flow techniques allow the implementation of the same analytical method (hardware), with little or no alteration, on different types of samples simply by software modification. 

Chapter 2 stressed the need to consider the results of plant modifications before they are made and to prevent unauthorized ones. This applies to computers as well as traditional plant. No change should be made to hardware or software unless authorized by a professionally competent person who has carried out a systematic survey of possible consequences. It is easier to change a software control system than a traditional one and therefore harder to control the changes, but it is just as important to do so. Section 20.5 describes an unauthorized change to hardware that could have had serious results. 

Connecting a control computer to another system is a modification and should only be carried out after systematic study of possible consequences (see Section 20.4.3). If made, data flow should be possible only in the outward direction (see text through the end of this section). All systems should be secure. Houses need doors. The doors on control systems are less tangible than those on houses but just as important. 

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