temparature control using pid

[Swapnil.mi]

i have thermocouple using which i want to control temparature at set point using pid.i am using NI9211 module. i have created the vi attached.also getting problem in xy graph display(no display is there).could anybody help please?should i used comparator.how?

[RavensFan]

I can help you with the XY graph problem.  Open up the Build XY graph Express VI and uncheck the box that says clear data each call.

I think there is a bug with this express VI that should be investigated.  I was surprised to see that setting checked off.  So I dropped a new Express XY graph VI and saw from the context that the setting wasn't set (actually the help didn't say whether it was or wasn't set)  I opened the express VI and saw the box was checked.  To me that seems like the wrong default behavior and is certainly wrong because when you hit OK without changing anything, suddenly the context help shows that it is set to clear each call.  If I go back again and clear the check box and hit OK, then the context help shows that the Express VI is set to NOT clear each call.

I vote bug.

1.  Dropping express VI does not show whether it is set to clear or not clear in the context help.  (Though testing in a VI after this step indicates that it is Set to Clear each call)>

2.  Opening the express VI shows that the setting is set to clear.  (I would say wrong default behavior).

3.  Closing the dialog box by hitting OK without changing anything causes the Set to Clear to be set and shows up that way in the dialog box.

As for your questions about "temperature control using PID", you didn't ask any questions so I don't know what you are looking for.  Try looking in the example finder for "PID" and you'll find numerous examples with PID control systems.

(PS.  Please, when composing your messages, capitalize the word "I" and the beginning of your sentences.  And also put two spaces after your periods.  The lack of capitalization and spacing between your sentences makes your message that much harder to read unnecessarily.)

[Swapnil.mi]

Hello, thanks for your help.  I had uncheck the box that says clear data each call but problem with xy graph still was there. 

So i have given my pid output first to simulate signal block then to xy graph now its giving some wave. 

And about temparature control using PID, I want to control relay using PID output . 

i have got input of thermocouple using NI-9211 module.  using DAQ it is given to PID but now How to control relay to on-off heater supply ?    

[Bill_5335]

Have you thought about using a solid state relay to control your heater?  http://watlowelectric.net/literature/prodtechinfo/files/controllers/ssre_c.pdf

Here's a link to Watlow with an example application.

What is the current and voltage requirements for your heater? 

At a previous employer, they controlled heaters by varying the pulse width of the signal.  Are you going to use something similar?

Good luck,

Bill