temperature control in labview

[agentchick]

I am trying to use Keithley 2400 as output device to control the heater and NI-USB 4065 to read the resistance of RTD. The basic function has already done. When the RTD is above set point, the heater turns off; RTD is below set point, the heater turns on.

But the question is, how can I use the data I get from NI-USB to control the output of keithley. I mean if the set point was 100℃, when temperature was about to close to 100℃, I need the output current would be smaller and smaller. I just want the temperature of heater to be more precisely.

I posted the output package of keithley 24XX as follow, hope to know where I need to modify.

[Tim_McClung · Accepted solution]

Sounds like you are trying to do a feedback loop, correct?  You want to tell the keithley to decrease it's power output as you get closer to the setpoint with the goal of reducing over and undershoot.  

If I'm correct in this assumption I'd recommend looking at the soft PID VI in LabVIEW that will calculate a lot of this for you.  It looks like the command script you are sending has an output, which I'm hoping is more than on/off and has a variable setting.  If this is the case you can use the soft PID controller to input the power level and let the keithley handle the output itself.  This works well for slow applications like temperature control (I have a test executive that uses this design working right now.)

Let me know if this helps.

Cheers,

Tim