Code to control a temp over time profile

[chrissheffuni]

Hi,

      I have been using LabVIEW for a couple of years to acquire data which I seem to be ok with. I have now been given a new problem. I need to Get LabVIEW to control a heating element which will heat water from ambient temp to 65 degrees celsius and then back down to ambient over a period of days in seconds, 864000 seconds to be exact. I have an excel spreadsheet with the temperature profile with 42 data points temp/time. the profile is not linear and I tried to get exel to give me a polynomial equation which doesnt fit at all. im planning on using an NI 9263 analogue output card and a 10v input module to measure the temp and feed back to the control loop. I think!!

Any help would be greatly appreciated on how to create the code to do this job.

Chris

[Larry.C]

Hi Chris,

Would it not be possible to control the temperature through PID control, where your excel sheet is used to define the reference temperature you are trying to maintain.

Regards,

[chrissheffuni]

Sounds like a good idea! although i have never used PID control or done any control applications to be honest. Will I find some example code in the LabVIEW help files?

Thanks

[johnsold]

Chris,

Why re-invent the wheel?  For ~$300 (US $) you can buy a PID controller from Omega with Ethernet, RS-232, or RS-485 communications.  Let the controller do the heavy lifting.  Set and Read temperatures from the LV program.

Omega's stuff works well.  The documentation tend to be poor, usually written by someone in east Asia who does not write well in English.

Lynn

[Larry.C]

Hi Chris,

My favourite example in LabVIEW for PID control is a vi which controls a tank's fluid level. You are able to set the reference level and set PID controls to alter how it gets to the reference. It is a very good starter example into PID control.

To find this example go to LabVIEW and then  Help >> Find Examples

In the following dialog box click on the search tab and type simulation tank. You should then find the following vi:

Simulation - Tank Level.vi

Another good resource can be found here, this is an article explaining how to use the PID toolkit in LabVIEW more generally.

I hope this info helps!

Kind Regards,