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- This topic has 3 replies, 2 voices, and was last updated 4 years, 11 months ago by PLCGuru.
- July 2, 2018 at 10:33 am #2895George BarnetteParticipantKarma: 171Rank: Jedi
Hi, folks. 1st post. You have an interesting forum. Anyway, I am writing a program for an air handler unit, RS5k V.20.04. The unit controls temp for a test cell that has extreme temp swings for testing new prototype vehicles. The temp will go from -40 to 140 F. The sequencing is -40 to plus 30–10 degrees per hour. From 30 to 140–20 degrees per hour. Doesn’t matter if in cool or heat (Increasing or decreasing.) So…worst case, the operator punches in a setpoint of 0 when the temp is at 125. My logic so far is set up to calculate the difference in setpoint to temp and enable a preset value into a timer, which will let a PID become enabled and I’m going to try to tune the PID to make setpoint based on the time needed. I have 2 calculation logic rungs one for the lower rate per minute and one for the higher one. I can post some of what I’ve written if it’s needed. Anyway, I don’t really have a lot of confidence that this will be easy to tune and to keep stable. The temp has to decrease/increase slowly because the liquid that heats/cools the cell would cause thermal shock to all the associated equipment. Makes sense. I was trying to figure out how to use a Ramp/Soak Function block and a PIDE for both heat and cool, but I’m having difficulty configuring these.
Would any of you pros have a sample program, or maybe a reference to A-B sample program library, or a better suggestion? Any input would be appreciated. Going to load it in Thursday.July 2, 2018 at 6:51 pm #2896PLCGuruKeymaster
Hi George and welcome to PLCGurus.NET!
I’ve implemented the RMPS instruction in a similar type scenario. My scenario was to ramp and soak forge dies to a certain temperature in varying increments, or a predefined number of “segments”. Once the dies were within setpoint and the Ramp/Soak is complete (a bumpless transfer if you will) I let the PIDE maintain setpoint from there.
I used the output of the RMPS to feed into the CVOper parameter of the PIDE running in “open-loop” control mode. The RMPS would output a percentage of maximum for the electric heater coil (i.e. 50% = 12 mA) and all scaling is performed in the PIDE.
Once the Ramp/Soak segments are complete and my temperature is within a reasonable error that will allow my PIDE closed loop to recover, I simply switch the PIDE into closed-loop (auto) mode.
This worked well for me, however, what you’re describing sound a little more complicated with the heating/cooling function.
Hope this helps!July 3, 2018 at 6:48 am #2897George BarnetteParticipantKarma: 171Rank: Jedi
Fred, Hi, and thanks so much for your information and such a speedy reply.
I’ll have a look at that RMPS block again and see if I can get closer to configuring what you are talking about. You run a good forum here and I wish everyone a happy 4th!!July 3, 2018 at 4:57 pm #2905PLCGuruKeymaster
Same to you George. Keep us posted on your progress! 🙂
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