Today I am in the Worthing, UK, home of Invensys Eurotherm and had an opportunity to talk with some of the Senior Engineers and think about the life of an plant operator and the use of these devices. As a result I decided to focus this post on three aspects:-
- Hands-Free Indication
- Primary Panel Graphics
- State of Play Indication
All three aspects need to be taken into consideration in the implementation of packaged control solutions.
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| An OK laptop accessory |
One thing that sticks out, is the use of the 'Light Tower' for critical indication of the quality of the process.
Light Tower signalling of course is all around us,... think Traffic signals and baggage belts... signalling basic information unambiguously and immediately to people.
With the light tower, an operator can rapidly check the overall state of his Unit or Equipment controller instantly and totally hands free. All operators have to multi-task, particularly those doing rounds or attending furnaces or other small control units, fementers or other components. Their multi-tasking typically is going to have to require the use of hands to hold things, carry things, feel things etc. - which means that any hands free indication, visible from many feet away is going to be mandatory.
Light Towers are a common signalling device, also known as an 'alarm beacon' and used for very definite 'call to action' signalling in many manufacturing and process settings.
- GREEN - OK - Good to Go !
- AMBER - WARNING - Take a gander ?
- RED - CRITICAL - Watch out Fred !
Although I may be interested in the layout of the plant, or the detailed information on each and every plant variable. I know that I cannot be watching that all day. I have other things to do.. multi-tasking and such. For the operator, there is much time spent doing housekeeping and operational tasks, particularly when operations are in AUTO mode. All I really want to know then - while I am doing other things - is what my 'light tower' tells me. about the particular parts of the plant I am responsible for. So 'GREEN is good, but if the AMBER light comes on, then I may need to drop what I am doing and go investigate further, possibly check a few things. When the RED light comes on. I have a problem. I will take a breath, get a seat, and then ignore the light and start working through the alarm lists and other detailed screens available to me.
PRIMARY PANEL GRAPHIC DISPLAY
One might contrast the 3D style control display, which might be seen on many control panels circa 2008 with control displays of the 1980/90s which were essentially 2D. 2D displays are still preferred by many operators, since from an information point of view, they are generally simpler and more focussed on the job at hand. The professional transfer of a display from 2D to 3D actually enhances the display to the point where it can easily be visualized by both trained and untrained personnel or visitors. This makes the 3D display much more suitable for training and reporting, but the 2D display more immediate and potentially faster for experienced operators.
An example of a 3D style control display [circa 2008]
Having taken a seat, or standing by the panel, my operator might check out a display, somewhat similar to the one shown above. Recent graphics chip technology allows the rapid display of 3D objects, which makes a good backdrop for the visualization of common plant elements, such as the Fermenter shown in the centre of the graphic. The 3D nature of the graphic allows cutaways to be created and visualized more readily. In the above example, the level of the fermenter can be seen against a cutaway and graduated glass display, which in reality would not exist. Shading, also another common element is used to help create a perception of solidity in the indicators, with frames much like traditional panel instrumentation.
At the bottom of the screen, are tabs which can be typically selected to view more detail about the particular plant or control element. Four blue arrowed navigation buttons can also be seen to allow TOUCH type scrolling of the display.
A piping diagram in white, de-emphasizes its importance from the dynamic coloured elements in the foreground.
Many modern displays consist of multiple fonts, widgets, and other cool components of the modern windows environments. The judicious use of these components and their layout, with attention to size, color, and importance, enable a good intuitive fast reaction to the operational requirements.
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| An example of an older 2D style Panel Display [circa 1998] |
STATE OF PLAY INDICATION
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| Sequential Function Chart |
In process control schemes, the state of play is indicated by modes and actual plant variables and trend displays. In batch, recipe and sequence controls, commonly found in unit control systems the state of a particular production run, sequence, batch becomes a dominating factor. An element that is commonly used is the display of the mode or state of the unit and it's next sequence step. Common modes or states of a vast majority of unit controls are:-
- INIT
- OFF
- RUN
- HOLD
Hands free indication on a display or a set of illuminated pushbuttons, is required and a common layout of this display is the sequential function chart. This chart, simple in design goes top down with the next available state indicated by lines. The current state is often marked by a change of color or an asterisk, shadow or highlight of some form.
In this post I have only scratched the surface of my control panel, and elevated my laptop to just ok with the addition of a light tower. In summary the evolution of the control display takes into account traditional illumination and control elements, which in some cases are translated to illuminated buttons on a panel display. The light tower has survived, possibly due to its ability to provide significant lighting and signalling at some distance from the panel. Sequential Function Chart elements provide at-a-glance indication of the state of a particular production run or batch. The use of 3D graphics has become widespread, enabling the audience and comprehension of the display to be extended.
Of course, if you wish to contribute any observations in this regard, or a story from your own experience, please feel free to make a comment.
CJS : Worthing UK, Jan 2012.
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