Long Term Stability of Heater using PID Controller VI

[thermomanager]

Dear LabView Community,

first, I would like to say hello because I'm new to the community!

I'm desparately trying to create a temperture controller using the basic PID Controller vi that is able to keep the temperature stable over several days.

I used the controller tutorial as template (https://zone.ni.com/reference/de-XX/help/371361R-0113/lvpidmain/fault_protection/) and really tried a lot of options of the parameters but it doesn't work.

At first, everything works very fine but after approx. 1 hour the output value of the PID-vi drops to zero, accordingly the temperature drops and it takes a few seconds for the process to get stable again (please see attached screenshot). Afterwards this occurs every few minutes.

I can't see that the system ressources get insufficient with increasing time or something like this. I monitored RAM and CPU and can see no correlation. Also, there is no difference if I activate data logging or not. If you need any more information, I will try to provide them. Thank you very much!

My System is

• Windows 10 64 Bit
• Labview 17 32 Bit
• CPU: Intel i7 3 GHz
• 16 GB RAM

[GerdW · Accepted solution]

Hi Thermomanager,

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@thermomanager wrote:

I'm desparately trying to create a temperture controller using the basic PID Controller vi that is able to keep the temperature stable over several days.

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When you want to run a program on 24/7 then you need to create that program to be able to run 24/7!

This means:

• Obey "THINK DATAFLOW!"
• Don't use local variables to implement data communication.
• Implement your program using basic programming schemes like state machines and/or producer/consumer.
• Don't use ExpressVIs or DDT wires! Why do you need to convert a waveform into a DDT wires just to get a single sample from your waveform?
• Use reasonable datatypes at all! No need for SGL for such simple calculations on a default Windows computer…

When you learn from the example VIs coming with LabVIEW you will create your VI similar to this:

Btw. don't use BMP for images when you can use PNG (or JPG)! Using PNG the filesize is just 3% of the BMP filesize…

[thermomanager]

Hi GerdW,

thank you very much for your very quick and constructive reply. My knowledge is obviously too small and I was already too stuck to realize that the express-vi signal splitter is the problem. Actually, my first approach was all together in one while loop, but because it didn't work out I read about 10 times faster controlling than reading and parallel processing a.s.o. and then dangerous half-knowledge made everything worse. So thank you for the reminder to think about the basics first.

Also sorry for the .BMP faux pas, I'll pay more attention next time.