Suppose a chemical reactor is heated by steam. A temperature controller varies the amount of steam admitted to a “jacket” surrounding the reactor:
Ever since this process was placed into service, operators have complained about poor temperature control. Several technicians have tried to tune the PID controller, but no combination of tuning constants seems to solve the problem of random reactor temperature fluctuations.
Then one day you notice that the “random” fluctuations of temperature are not really random at all: they directly follow fluctuations in steam supply pressure over time.
Explain the nature of the control problem (why do variations in steam supply pressure affect the reactor temperature?), and propose a solution for it.
As the steam supply pressure rises and falls, a greater or lesser steam flow will result through the temperature valve (TV) for any given stem position.
The simplest and most direct solution to this problem is to stabilize the steam supply pressure: determine what is causing the pressure to fluctuate, and fix it!
Like so many real-life problems, there are usually multiple solutions. Try brainstorming more than one practical solution to this control problem! (assume possible cases).
Join the Discussion! Share your answers with us through below comments section.
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View Comments
If you weren't able to stabilize the steam pressure supply, perhaps you could instead create logic that reacts to a steam pressure transmitter that correspondingly adjusts the TV to adjust for it.
Thanks for posting these thought experiments by the way! I'm a new intern working in process control and just found this website. Really nice resource.
salut. je tient a vous remerci pour ses infos ,car tous ce que je reherche je le trouve sur ce site avec des resumer bien expliquer. merci encors une et bon continuation.
Translated from french:
Hi. I want to thank you for this info because all that I am looking for, I find on this site with summaries, explained well. thanks again and good luck
Add a flow meter and use cascade control requires capital
If you have header pressure try to add a feedforward signal to the TC
what cause temperature transmitter to reading very high
Check the temperature sensor/element healthiness.