thyristor oven control with PID in labview?

[000000001]

hello.I am trying to control one oven using NIDAQmx USB6221 board conected to a pair of PAC15 thyristors that provide the power to the ovens resistors. My problem is that my PID does not react as it should when (for example) the oven is at a midle temperature (lets say 200ºC) and i select a setpoint of (for example 350ºC) , the PID does not put on its output the apropriate power so that the thyristor could heat the oven. If i put gain scheduling i can solve this problem....to a certain value of temperature but the it hapens again for another value of temperature (lets say 350ºC to 650ºC ).

thanks

JOSE

[ajangot]

Hi,

it's seem to be the configuration of your PID. What are constants?

Can you send your VI or a diagram's screenshot ?

Regards,

[000000001]

Sorry the delay on my anwser but it has been impossible to post my reply...

Here is my blocks diagram...

I'm afraid i dont have any feedback on the PID...can this be my problem?

thank you

JOSE

[000000001]

Here is the blocks diagram.

thank you again

[ajangot]

Hi,

I tried to make a simple VI of your problem. I join this VI. I don't understand where is your problem, my VI seems to perfectly work. Can you explain or detail your configuration of PID?

Regards,

[ajangot]

With the VI, it's better 😛

[000000001]

My problem is that everything seems to work ok, but when (for example) the oven temperature is 200ºC and i put the setpoint to 300ºC the PID needs more

proportional gain (Kp) to put the oven to that temperature 😞

the same hapens for other temperature (for example 300ºC-->400ºC)

I've tried gain scheduling as you can see by my VI but it does not solve my problem to all the temperatures...

thanks once again

JOSE

[000000001]

I tried to open your VI but i canot because i have one older version of LABVIEW 😞

by the way the formulas you see on the output of my PID are for linearizing the Thyristors power...

thanks

JOSE

[ajangot]

I have few things about your VI.

• Try to avoid to cross wires, it's very difficult to read your diagram. 
• You don't need the vi "wait", your while loop is already timed, so you can delete it.

About your problem, I think that it's better to schedule PID with the process variable that the VP-SP.

I advise you to see example "gain scheduling simulator", you can found it to press help>>find exemples and search PID.

Regards,