Controlling condensing temperature by controlling opening valve

[alhabeeb]

I modified the code, and it works but I need to determine the gains because I just assumed them

[GerdW]

Hi alhabeeb,

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@alhabeeb wrote:

I modified the code, and it works

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It looks much better now.

You should add a small wait inside the loop and limit the output range of the PID.

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@alhabeeb wrote:

I need to determine the gains because I just assumed them

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Yes. See my comment on step responses above...

You could also try to determine PID gains from analyzing your system:

• heat capacity and massflow of the hot fluid
• heat exchange rate and (thermal) delays in the cooler
• input temperature and (max) massflow of tap water
• …

After all it's a "simple" physical system! 😉

[alhabeeb]

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@GerdW  a écrit :

Hi alhabeeb,

---

@alhabeeb wrote:

I modified the code, and it works

---

It looks much better now.

You should add a small wait inside the loop and limit the output range of the PID.

---

@alhabeeb wrote:

I need to determine the gains because I just assumed them

---

Yes. See my comment on step responses above...

You could also try to determine PID gains from analyzing your system:

• heat capacity and massflow of the hot fluid
• heat exchange rate and (thermal) delays in the cooler
• input temperature and (max) massflow of tap water
• …

After all it's a "simple" physical system! 😉

---

Should I use case structure to add limits to PID?

[GerdW]

Hi alhabeeb,

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@alhabeeb wrote:
Should I use case structure to add limits to PID?

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No, you should read the LabVIEW help for the PID function…

[alhabeeb]

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@GerdW  a écrit :

Hi alhabeeb,

---

@alhabeeb wrote:
Should I use case structure to add limits to PID?

---

No, you should read the LabVIEW help for the PID function…

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Ohh, Yes it is very straightforward.

Thanks

[alhabeeb]

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@GerdW  a écrit :

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To determine the PID gains you can do some step-response tests and apply the common rules on the step response measurements.

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Thanks for all your support. I'm new to use Labview, and I know a little about the control. Would you give me more details about how to determine the gains? 

Thanks

Baqer

[GerdW]

Hi alhabeeb,

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@alhabeeb wrote:
Would you give me more details about how to determine the gains? 

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Have you tried to search for manuals (using your favorite web search) on your own? "Searching for relevant information" is basic knowledge for engineers!

I found this article easily…

[alhabeeb]

I used this, and it worked with my system.

[GerdW]

Hi alhabeeb,

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@alhabeeb wrote:

I used this, and it worked with my system.

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So you implemented a plain P-controller!?

This is (in my experience) VERY unusual for a thermodynamic system, involving heat exchangers with massflow-dependent properties!

[alhabeeb]

Hi,

Right now my test bench is not completed, so I just attached a thermocouple on the tap water pipe to represents the (T_f_out) and run the VI. When  the T_f_out greter than the setpoint the valve opens and when it is lower the valve close. If the T_f_out high greter than the setpoint, the valve is full open.