aging kilns get older and the original instrumentation system can't be
repaired, many plants are making the next logical move and upgrading their control
technology. The costs for most of these systems are very similar, but the
difference in usability can be extreme. If you are contemplating a conversion to a computer interface system with
PLC control, it's important to keep a number of factors in mind.
biggest concern when looking at any instrumentation panel is the ability to see-at
a glance-if all control loops are within reasonable deviation values. I never
want to have to scroll through endless screens in order to find key
information. If you have a human machine interface(HMI) system that requires
repetitively scrolling through screens to find the data you need, you know how
frustrating that can be. And yet, the norm in screen design seems to be to
spend time developing "wow" graphics instead of putting time into
must think about what is most important and insure that the main screen shows
this data at first glance. The use of color to indicate deviation
and simple (but clear) graphics mean that this will be the screen that will be
used 90% of the time.
operating a tunnel kiln, the factors that affect the control of the kiln
include various internal pressures; set-point temperature; process variables
and output of each loop; burner operation/burner failure; pushing speed; and,
in some cases, O2
levels. The best screen design will
include all of these variables clearly, along with a kiln curve that shows all
of the thermocouple temperatures in correct graphical scale. All that should be
necessary to drill down into any of these data points is to click on that piece
of data to see what's behind it.
example, if you are concerned about the performance of a control loop, clicking
on the loop icon should immediately open a window to all tuning
output limits and graphical loop performance, including standard deviation from
set-point and output. You should end up with fewer menu buttons but easier
access to data. Being able to simply click on the data icon means you spend
less time finding the data and have more time to correct any
parameters are similar for periodic kilns. It's nice to see a curve with a
cursor to tell you the state of the program, along with modes of
and maximum deviations. The ability to zoom an area is often very helpful.
Individual zone performance screens, and an overall view of the
burner positions, deviation from set-point, and output, give a good top-down
view of the system. Remember, unlike the analog systems of old, where the
entire system (plus strip chart) was right in front of you, you only have a
15-in. monitor to view all of the data.
logging data, store everything! Any PV that has an input to the PLC should be
recorded, preferably in Excel format, and files should be auto-labeled by date.
Graphical storage is also possible and desirable. All of this should be fully
always make sure that the HMI system is accessible over the Internet, which
enables kiln operators to view the system operation from both inside and
outside the plant. Internet access makes middle-of-the night solutions easier,
and remote access reduces the time of correction-especially without the
midnight drive to the plant to see what's going on. In addition, specialists
can view the system and assist remotely to solve problems.
Find the Best Fit
are working with a developer, sketch out the kind of screens that you think are
necessary. Don't accept the canned, one-size-fits-all design, because you will
be the one operating the system for years to come. As we all know, sometimes
it's tough to find problems in kiln control, and time is always limited. A good
HMI system reduces the amount of time required to find the problem, and that
strikes me as what HMI should be all about.
views or opinions expressed in this column are those of the author and do not
represent those of Ceramic Industry, its staff, Editorial
Advisory Board or BNP Media.