allscott
Member
- Join Date
- Jul 2004
- Posts
- 1,332
I am trying to tune a run out old water heating system for the screw of an extruder. I have come to the conclusion that the water flow has simply made extremely difficult if not next to impossible if you are not Peter Natcheway.
Here is the history.
The extruder is 25 years old. The original heating/cooling loop was controlled by a Eurother EM2 and it worked fine. The system consists of a water loop with an electric heater, this water runs through a heat exchanger that has a solenoid valve that is controlled for cooling. All heating/cooling is on/off control.
The EM2 was replaced with a clx utilizing a pide loop and a srtp instruction for the heating and cooling. The Engineer that started to design this system quit before he was done so it was never completed properly, however it worked.
So now I am thrust in to a system that wasn't completed and doesn't currently work with a limited knowledge of heating and cooling systems. My knowledge is limited simmply because every other one I have ever worked with has been simple to make work.
My issue is that whatever I do with the gains and how conservative I make them whenever the extruder starts to actually pump plastic the temperature starts to swing and it starts ringing and eventually gets out of control. This particular loop doesn't seem to ever require cooling so I have shut it right off with limited success.
I know that if a process is oscillating I should lower the P gain and that works to get the extruder up to temperature slowly but when it starts to run everything just starts oscillating.
Not understanding how the PIDE works totally and not understanding what it was doing when I tried to tune it manually (ziegler nichols) I decided to install a dedicated temperature controller (Eurotherm 2408). After an unsuccessful autotune I tried to tune it manually the best I know how with no success.
I'm convinced the problem is with the flow of water through the system. There just seems to be way much time between when the heater comes on and I see a reaction and when that happens things just swing, ring and get worse.
I know the first piece of advice I will get is to post some graphs but just with the setup I have that is hard to do. I am displaying graphs on a red lion but with the SRTP instruction they don't make a bunch of sense. I will post whatever I can if it helps.
Here is the history.
The extruder is 25 years old. The original heating/cooling loop was controlled by a Eurother EM2 and it worked fine. The system consists of a water loop with an electric heater, this water runs through a heat exchanger that has a solenoid valve that is controlled for cooling. All heating/cooling is on/off control.
The EM2 was replaced with a clx utilizing a pide loop and a srtp instruction for the heating and cooling. The Engineer that started to design this system quit before he was done so it was never completed properly, however it worked.
So now I am thrust in to a system that wasn't completed and doesn't currently work with a limited knowledge of heating and cooling systems. My knowledge is limited simmply because every other one I have ever worked with has been simple to make work.
My issue is that whatever I do with the gains and how conservative I make them whenever the extruder starts to actually pump plastic the temperature starts to swing and it starts ringing and eventually gets out of control. This particular loop doesn't seem to ever require cooling so I have shut it right off with limited success.
I know that if a process is oscillating I should lower the P gain and that works to get the extruder up to temperature slowly but when it starts to run everything just starts oscillating.
Not understanding how the PIDE works totally and not understanding what it was doing when I tried to tune it manually (ziegler nichols) I decided to install a dedicated temperature controller (Eurotherm 2408). After an unsuccessful autotune I tried to tune it manually the best I know how with no success.
I'm convinced the problem is with the flow of water through the system. There just seems to be way much time between when the heater comes on and I see a reaction and when that happens things just swing, ring and get worse.
I know the first piece of advice I will get is to post some graphs but just with the setup I have that is hard to do. I am displaying graphs on a red lion but with the SRTP instruction they don't make a bunch of sense. I will post whatever I can if it helps.
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