I guess it just that kind of a day......

My fearless leader just dropped a knot into my programing for the day..I have to put 3 heater loops (feeding 3 groups of 2 banks) into a AD DL260 ...


Tank #1 Bank A 18 kw Run to Set point
Control Loop #1
Tank #1 Bank B 18 kw Run to Set point < 10 deg


Tank #2 Bank A 18 kw Run to Set point
Control Loop #2
Tank #2 Bank B 18 kw Run to Set point < 10 deg


Tank #3 Bank A 18 kw Run to Set point
Control Loop #3
Tank #3 Bank B 18 kw Run to Set point < 10 deg

The temps are coming in from a AD F2-04THM 4 channel card...

My question is: Can I just set up a compare for each bank and feed that with a setpoint value that I set from the CMORE panel, or do I need to set up 3 (or 6) PID loops to run them?

The tanks are SS, the liquid is water, the cyclic heat demand will be fairly even...once the tanks are up to setpoint, one heater per tank should be able to maintain the load.

Thanks group...My head is just not up to speed today.

David:site::site:

Since it's temperature control, and I assume you have a lot of thermal mass, I would use simple deadband control.
Determine what the dead band will be, +/- 1.0 or 0.5 whatever, it could be an HMI entry.

Then using the setpoint from the HMI and the deadband, create two new values:
SP_low := (setpoint - deadband)
SP_hi := (setpoint + deadband).


Then simple compare logic with a seal in.

If Tnk_Temp < SP_low turn on the heat use the heat output to seal in it's self, and have If Tnk_Temp > SP_hi break the seal.

Hope I helped, may have confused.

Dave
what is your temperature tolerance on the heated water?

Since you are doing staged heat the least expensive maybe would be individual thermostats and relays near the tanks.

Of course if they really want PLC control and you have capacity sitting there doing nothing it would not cost that much more to run 3 more conduits for instrumentation on top of the 3 36 Kw feeds for the heaters.

Dan Bentler

Thanks Ken... I have put in the compare statements, we'll see how it works tonight at home.

Dan, the specs call out TC temps on the CMORE panel, so I already have the input card et al...TPTB just wanted to delete the 3 Watlow temp controllers from the front panel..3 less holes for water to get into. We want the water +/- 5-7 deg f, setpoints at about 185, about 250 gal/tank.

I thought that I had a copy of a program I did years ago that invoved TC/Heaters, but its on one of my 'spare' hard drives at home...and ya'll bring in fresh ideas for us all to ponder on.

Thanks to both of you...

David:beerchug::site:

With such a wide tolerance I would use +/- 1 degree as the deadband.
When temp is < 184 turn on heat when, temp is >186 turn off.

For the second heat I would use -10 and - 2.
If temp < 175 turn on 2nd heater, when temp is 183 turn off.

The Watlow controllers were PID, I assume they switched the heaters through solid state relays, time proportional.
If you need fine control you may have to use a PID function or you could use some form of integral action. e.g if the temp is above setpoint scale back the On time by the error and some factor.

Thanks everyone!

Roy...Solid state, what are they? We still use klank/bang contactors...I'm pushing to go to them, but change comes slowly in this org. Heck, I just got them to use finger safe term.blocks...no more having to crimp on spades....

David

David_Emmerich said:

Thanks everyone!

Roy...Solid state, what are they? We still use klank/bang contactors...I'm pushing to go to them, but change comes slowly in this org. Heck, I just got them to use finger safe term.blocks...no more having to crimp on spades....David

Click to expand...

Think I will reduce or even eliminate my hatred of finger safe. Crimping lugs is even worse maybe.
Now if someone would make flexible solid conductor!!!

Dave is this part of the digestor project?
How is that coming along?
You have gas yet?

Dan Bentler

No this isn't for the digester...the USDA/AWRU here in BG has been pulling samples every day and we are starting to get a good set of baseline data on the system. Gas production is good but not up to the levels that I want yet...a new gas storage ( really a silage) bag should be here on Sat. and will help that out greatly. We just flushed out the system this past weekend and have restarted it yesterday so that the USDA folks can monitor the full groth cycle in the tanks...and WKU wants a full size system asap...now if there were only 48 hrs every day I might have time for all I'm trying to do...

BTW: I have started to use DN-T6 blocks...60 amp rated, you can fit the wire in easily, and you don't need a tiny screwdriver.

David:beerchug:

:site:Thanks Guys...it works great...:site:

David:site:

Glad to help, glad it worked.

Have a nice weekend.


ken