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by Robert Wall, Plastics Division, Monsanto Chemical Co.
Present Status of the Graphic Panel The graphic panel is still around. Particular usefulness is in training new men and during initial startup
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F E W YEARS AGO, the
graphic
panel was one of the most talked about developments in instrumenta tion. Although it has received rela tively little publicity recently, it has not lost favor. T h e graphic panel has become an accepted instrumen tation technique, a n d it is applied where and as appropriate. It re ceived major attention because it was one of the most striking a n d
attractive of the initial develop ments in the recent marked expan sion of instrumentation into new components, new methods, and tech niques of control. T h e key to a study of the extent of use a n d utility of graphic panel applications, and of other types of panel arrangement, is consideration of the objectives a n d functions of panel arrangements. Process con
trol requires quantitative informa tion regarding m a n y process vari ables, and information indicating the significance of these measured q u a n tities in the control of the process. T h e objective of all methods of panel arrangement is to convey some information relative to the function of the measurements, a n d their relation to other measurements, a n d to facilitate the use of these q u a n tities in control of the process. VOL 49, NO. 12 ·
DECEMBER 1957
65 A
I/EC
INSTRUMENTATION
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A Workbook Feature
M i n i a t u r e instruments were the basic development permitting the use of all of the descriptive panel arrangements. T h e conventional sized instrument limited the freedom for descriptive arrangements, although systematic groupings of instruments were used as far as possible. T h e availability of miniature instruments m a d e possible the fully descriptive instrument arrangement known as the graphic panel. This development h a d been anticipated for some time, hence a rather marked immediate use of this technique resulted. T h e instruments of a graphic panel arrangement are placed on a process flow diagram d r a w n on the control board. T h e significance relative to the process of any value indicated by any instrument is thus easily a p p a r e n t to anyone with a simple understanding of the process. T h e utility of the technique has followed a balance of its advantages in presenting information descriptive of the process with the cost, disadvantages, and limitations of the method. T h e most realistic objective is to determine the panel arrangement that will make possible the m a x i m u m information from a n d utility of the instrumentation provided. T h e more information a n operator has available for control— presented in a n arrangement offering m a x i m u m accessibility a n d understanding—the easier and better the control will be. T h e graphic panel is definitely very attractive, a n d , other factors being equal, it has been selected often for this reason. An attractive work environment is conducive to better work performance, a n d the appearance factor thus has value.
Uses of the Panel
T h e graphic panel definitely expedites the training of new men, and is helpful during the chaotic days of initial startup when no one is really familiar with the plant or the peculiarities of the process. T h e training advantage is probably of rather minor significance during normal plant operation with low labor turnover. T h e r e is also some question as to the informational advantages of the graphic panel for experienced men. 66 A
Size of Control Board
For a large a n d complex process the graphic panel control board m a y be very long—requiring a very large and expensive control house. T h e r e is some disadvantage in accessibility of d a t a for a very large control board. A lot of moving about is required to keep u p with control information spread over a large board, so m u c h so that some have facetiously recommended that the operators be provided with roller skates. Multipoint recorders are not suited for this type of panel arrangement. T h e uses of multiple unit processes in parallel are not easily presented graphically. Any revision of the process will require a more or less drastic reworking of the control panel if it is to r e m a i n accurate. T h e r e is a trend toward more compact panel arrangements for large and complex control systems, where the size of the graphic panel would have an adverse effect on the accessibility of data, or the control house required would be inordinately large. Descriptive arrangements of instruments are also used in these. Often a process diagram is d r a w n above the panel, labeled with instrument n u m b e r s , and equipped with alarm lights, etc. T h e limit in the direction of compactness is probably the console control panel, where the instruments are compactly grouped about a central control desk, with the objective of m a x i m u m accessibility of control information. Such arrangements require considerable training of the operators, and the compactness complicates the maintenance problem. These compact systems seem to be the trend for the large complex systems requiring the rapid assimilation of considerable d a t a for control decisions. T h e graphic panels seem to be used more for small to moderate-sized plants, or for large systems of several relatively independent units.
where the application is appropriate. T h e extent of use of the graphic panel is not readily determined accurately. It is m u c h used on small package units, as water treating systems, etc.—i.e., subunits to the major process. These are usually operated on a n " o d d j o b " basis, and the self-explanatory features of the panel are very helpful. T h e graphic panel has extensive use in moderatesized process control systems—i.e., where the graphic panel does not of itself d e m a n d a n excessively large control house, or control of the process so complex as to require continuous observation of information spread over a very long panel. T h e very large and complex systems tend toward the compact arrangements, with the console control system becoming dominant. This arrangement transforms easily into d a t a reduction systems and is in the direction of advanced developments in process control techniques.
Selection of Panel Arrangement
T h e decision as to the type of panel arrangement to be used for an instrument installation should be based on careful study of control of the process, a n d that panel arrangement which will provide the most efficient accessibility a n d use of control information should be selected. Very definitely a decision should not be m a d e to use a certain panel arrangement arbitrarily. T h e assistance of the instrument companies can be extremely helpful in determining the best panel arrangement of instruments. This is good advertising for them, and generally leads to a more attractive and a more satisfactory control system for the user. An interesting example of a graphic panel (see photograph) recently appeared at the Texas City plant of Republic Oil. T h e r e is an excellent balance of control house size with paneLsize.
Limitations
T h e graphic panel thus has a n u m b e r of limitations. I t is a rigid method, with little freedom in its application. Within the limitations it is very useful, a n d the principle is often helpful to a composite system even if not used completely. I t definitely has a great deal of use
INDUSTRIAL AND ENGINEERING CHEMISTRY
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