practical info source??

Hi, I'm looking for a recommendation of a book, website, etc. that has some practical process control advice....temperature loops in particular. I have
a temperature loop where we are heating a full vessel of water from room temp to 123C by recirculating through a heat exchanger. The heat source is steam but but there are two parallel control valves, a 2" coarse control valve and a 1" fine control valve. I'm struggling a bit on how and whether to apply PID control to both valves and looking for some practical advice to get started.
Thanks, WH
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WH wrote:

I have managed dual, parallel valves by putting the small one on the PID temperature controller, and using that controller's output as the process variable for a slower tuned PI controller, whose setpoint is a constant somewhere around 50%. This forces the large valve to restore the small one to the middle of its range after a load change, so the small one is in an optimal position to make smooth and quick (but modest) corrections from that starting point.
If you put the small valve in manual and close it, the large one (if left in automatic) smoothly closes. During startup, open the small valve to anything less than 50% and it is the total control. But be careful leaving it in manual above 50%. This forces the large valve to smoothly go to 100% at a speed proportional the the amount of output on the small one, above 50%.
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Thanks John. That's great info! I'll give it a go. -Warren

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Not Temperature specific but have a look at these:
http://www.controlloop.co.za / http://www.tcnj.edu/~rgraham/PID/popelish.html
[snip]

Groetnis, Jurie.
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I'm probably missing something here (as I often do). Is the vessel pressurized? Because if it ain't you're gonna have a hell of a time heating water to 123C.
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