pid temperature control daq 6009

[Rebel320]

Hi folks,

I am new to labview and i need to build a vi to perform PID temperature control of a heater. The heater is switched on using a solid state relay. I am using type K themocouple with 4-20mA transmitters. I have attached 2 word documents showing the hardware. Any help would be really appreciated.

[AnalogKid2DigitalMan]

IT Sligo class assignment? Can you post what code you have created thus far?

-AK2DM

[aeastet]

Use pulse width modulation to control your hearter and never turn the heater completely off. That was the two biggest things that I found that gave me the best responce and control.

[Rebel320]

I dont have any code written for it yet! Any ideas?

[DavidMaidman]

Do you have the PID toolkit? This has ready made PID VIs that are easy to use. If you are driving a SSR then you will need to use a PWM output - this can be easily done by taking the PID output (0-100%) using this to specifiy the duty cycle (pulse width) on your pulse output

[Rebel320]

Hi, Unfortunately i dont have the pid toolkit. I was thinking of using the Square Wave point by function for the pulse width modulation to control the SSR. Maybe it would be easier to get the toolkit? It is a bit expensive though!

[hecmar.arreola]

There are free PID VIs out there.  The toolkit is nice because it comes with an autotune wizard and has a lot of options (like I've been able to impliment ramp rates and such by using it).

Too bad the 6009 doesn't have on-board PWM through a counter.  What kind of pulse-width frequency do you want?  Don't expect anything crazy like khz with the 6009 hardware. 

Three solutions come to mind:

1. You can output a squarewave from the Analog Output to drive the SSR.

2. You can software time a Digital Output pin.

3. You can make a voltage-to-PWM converter board out of 4 op-amps and supply a voltage signal from your AO.  I have done this before when I needed really fast PWM (>khz).  Probably not needed for most temperature applications (just need hz as I doubt your feedback loop is any faster... but I've used some very tiny thermocouples that were indeed very fast).

[Rebel320]

Hi,  Thanks for the suggestions, I am not sure of how much PWM i need. I just need to be able to control a heating element coil(from a hair dryer!!!) and the temperature range will be from approximately 20-75 degrees celcius. If anyone has a vi for this application could you post it up for me to have a look at?  Thanks Guys