Temperature Controlling using PID(labview) via manipulating voltage on Power Supply

[abhi474]

Hello,

I am working on an experiment on rotating fluid which is heated(via heater of 109 ohms) from bottom. The temperature of bottom plate(heated one) has to be maintained constant(set value),even if fluid is taking away heat. I am thinking of using PID algorithm provided by labview(2017). The PID will have process variables as readings of RTDs installed on heating plate and will give sensed temperature values. Now PID will compare it with Set value(SV)  and give output and accordingly it should Increase/Decrease voltage(in real time) on power supply(NI VISA) to get PV temperature equal to SV.

I wanted to know what kind of output PID will give, like is it required value of voltage that has to be increased for power supply? Or will I have to do something with PID .

output to convert it in required voltage?

Also when I get my required voltage, how do I write it to my power supply. Power supply(NI VISA) accepts string commands for voltage inputs and all.

I have attached schematic of my experiment. 

Any Help would be highly appreciated.

[cbutcher]

This setup sounds perfectly reasonable and can be split into a few separate tasks/problems. Which are you having problems with?

1. Change the voltage at the power supply based on a numeric control (e.g. have a VI/subVI which has a numeric input and produces a change in the power supply)
2. Read the RTD sensors and provide a numeric output (average of 3 in your case, perhaps) of temperature
3. Carry out PID (and tune the coefficients as needed) to translate changes in (2.) to changes in (1.).

If you can manage both steps 1 and 2, then you're most of the way there. Both of these tasks can be created as subVIs that can then run inside a PID loop, and update the system accordingly.

[abhi474]

Hello,

Thanks for your reply.

I am having problem in point no 3 only i.e how to translate changes in Reading of RTD(point 2) to changes in input to power supply(point 1).

Like I cannot connect output of PID directly to power supply, we need to figure out a way how to scale output of PID so that it results required change in voltage in power supply to bring temperature constant (can this be achieved by only varying gains of PID ??)

Please help!!

[GerdW]

Hi abhi,

how to translate changes in Reading of RTD(point 2) to changes in input to power supply(point 1).

This is done using the PID controller…

Like I cannot connect output of PID directly to power supply

Why can't you? What's the reason you cannot?

we need to figure out a way how to scale output of PID so that it results required change in voltage in power supply to bring temperature constant (can this be achieved by only varying gains of PID ??)

Yes.