PID control

[chattarbir]

Dear members

I am using PID advanced control for my experimental set up.

In my set up there are two places where i use PID control. One for my Mass flow controler and one for my pump

The pid control is working good for my MFC. i was able to fine tuning parameters for this PId

But surprisingly when is use the PID for my pump it is not giving good control. the tuning parameters lot of them that i tried are just going either to max output or to min output range. It seems to me that PID is not caring about the set point or process variable. If i remove the output range then pid gives negative output which is not required

What i fail to understand is that same Pid working good for one part and not for other.   

Has any body gone through this problem

Best Regards

chattarbir singh

[Ben]

Post images of your code where you use thePID functions.

You either have to use the array falvor or sepearte instances of the PID since they maintain the history internally to the instance on the diagram.

Again let us look at some picture (or code).

Ben

[oasisjo]

On 10 jul, 15:40, chattarbir <x...@no.email> wrote:
> Dear members
> &nbsp;
> I am using PID advanced control for my experimental set up.
> In my set up there are two places where i use PID control. One for my Mass flow controler and one for my pump
> &nbsp;
> The pid control is working good for my&nbsp;MFC. i was able to fine tuning parameters for this&nbsp;PId
> &nbsp;
> But surprisingly&nbsp;when is use the PID for my pump it is not giving good control. the tuning parameters lot of them that i tried are just going either to max output or to min output range. It seems to&nbsp;me that PID is not caring about the set point or process variable. If i remove the output range then pid gives negative output which is not required
> &nbsp;
> What i fail to understand is that same Pid working good for one part and not for other.&nbsp;&nbsp;&nbsp;
> Has any body gone through this problem
> &nbsp;
> Best Regards
> chattarbir singh

would be nice if you ad the vi so we can have a look at it

[chattarbir]

Dear Sirs

thank you for replying

I have attached the file to this post .

Regards

chattarbir Singh

[Ben]

You have wired your PID output to your set-point.

It is no wonder the PID putput is all over the place.

Ben

[chattarbir]

I have done the same thing with the Mass flow controler set point

It is working excellent,

But i could not follow what do u mean when u said that. my set point of flow rate has to be adjusted according to my pressure that is how it should be.

Can you be more explicit about what u mean

Regards

chattarbir singh

[Ben]

Sorry!

my bad. That was manual input it was wired to.

Ben

[chattarbir]

Mr Ben

If you could write bit more explicitly it will be helpful

Regards

chattarbir

[Ben]

Please detail the difference between the situation where the PID works for you and where it does not.

Also post the code that works and the code that does not.

Please clearly define how the PID is failing you and feel free to include graphs plotting the poor performance.

The more information you provide, the better our help will be.

Take care,

Ben

[Dr._Imad]

your pid is wired correctly, and I can simulate it to generate the output voltage correctly.

since you are saying the output saturates to the maximum or minimum, it is either, that

1) the system does not respond fast enough,  and /or

2) the tuning parameters are too large

Start with small values of prop gain (Kp) and and integral gain (KI) and set the derivitive gain to zero. 

For small values of Kp and KI, you should see the voltage slowly increasing to the max.  If it reaches the max, then decrease again Kp and KI.  Do that till you see the output voltage rising slowly, and monitor the variable readout, it should  increase slowly too.  If this is working, then  you can retune to increase the speed for proper control

<<One for my Mass flow controler and one for my pump>>

I assume by the pump you mean some analog voltage is required, and not simply an ON / OFF operation

I also assume you can manually control it by on  manual  mode (Pump auto? (T)  --> F)