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PID Control Working---but can't get up to set point
Posted Jun 20, 2012, 11:13 a.m. EDT Fluid & Heat, Chemical Reaction Engineering Version 4.2a 1 Reply
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Hey guys,
Here I have a pipe in which air is entering it, contacting a heat source, and leaving it.
I have a control algorithm programmed in COMSOL which is working...but it's saying that my achieved steady state in the process response is something that isn't my set point.
I.e., my set point is 343 C (air temp) but when I look at the temp profile it will control it, without oscillations, to like 320. I've played around with parameters for hours...but some just crash the program or others dont get to my set point. I found that if i multiply the algorithm by like 5e+05, and have my parameters as P = 1, I = 0, D=0, it doesnt crash but doesn't get to the right set point.
Any ideas? Do you think it's just a matter of setting my parameters correctly? I can't get up to the set point at all.
Thank you!
Here I have a pipe in which air is entering it, contacting a heat source, and leaving it.
I have a control algorithm programmed in COMSOL which is working...but it's saying that my achieved steady state in the process response is something that isn't my set point.
I.e., my set point is 343 C (air temp) but when I look at the temp profile it will control it, without oscillations, to like 320. I've played around with parameters for hours...but some just crash the program or others dont get to my set point. I found that if i multiply the algorithm by like 5e+05, and have my parameters as P = 1, I = 0, D=0, it doesnt crash but doesn't get to the right set point.
Any ideas? Do you think it's just a matter of setting my parameters correctly? I can't get up to the set point at all.
Thank you!
1 Reply Last Post Jun 20, 2012, 4:03 p.m. EDT
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Posted:
1 decade ago
Hi
a few questions:
- you talk about a set "point" but are you in 2D, 3D or 1D ? and how do you define the temperature of a point if you are in 2D ?
If you want to set the temperature of a BOUNADRY to a given value, and is not interested in the details of the PID controller, just to ensure the correct local temperature driven by your heat sorce => you can do that with a weak equation, adapting your heat source Q such that your aveop1(T)-T0 = 0 where aveop1() is an operator defined on the boundary. You can then define your gain in W/K by doing a sensitivity anaalysis of your T0
With T take care to use the right units as differential K and °C are the same, but not at all in absolute and COMSOL works by default in absolute Kelvin
--
Good luck
Ivar
a few questions:
- you talk about a set "point" but are you in 2D, 3D or 1D ? and how do you define the temperature of a point if you are in 2D ?
If you want to set the temperature of a BOUNADRY to a given value, and is not interested in the details of the PID controller, just to ensure the correct local temperature driven by your heat sorce => you can do that with a weak equation, adapting your heat source Q such that your aveop1(T)-T0 = 0 where aveop1() is an operator defined on the boundary. You can then define your gain in W/K by doing a sensitivity anaalysis of your T0
With T take care to use the right units as differential K and °C are the same, but not at all in absolute and COMSOL works by default in absolute Kelvin
--
Good luck
Ivar