PID Regler

[Thomkorn]

Hallo Zusammen, 

ich bin neu in der community und stehe seit längerer Zeit vor folgendem Problem:

Ich bin dabei eine Anlage zusammenzubauen, in welcher ich unter anderem Heizplatten regeln möchte. Die Regelungstechnik ist mir von der Theorie her bekannt, Erfahrungen mit LabVIEW hatte ich hingegen noch keine. Die Heizplatten ( insg. 2 Stück) haben eine Leistung von etwa 500W. Nun habe ich zwei Möglichkeiten die Heizplatten zu Regeln:

Lösung. 1: PID Regler der Fa. Omega

http://www.omega.de/pptst/CN7800.html

Dieser hat eine RS485 Schnittstelle, mit welcher ich laut herstellerangaben (Datenblatt) über einen USB Adapter mit LabVIEW kommunizieren kann. Hier müsste ich THEORETISCH den Regler Ein- und Ausschalten

Lösung 2: Ich schließe die Heizplatten an zwei Relais  an und steuere diese über das Modul NI 9472:

http://ohm.ni.com/advisors/compactdaq/pages/common/helppopup.xhtml?conversationContext=1&url=http://...

Ein Chassis für die Karte hätte ich bereits, da ich auch weitere Komponenten der Anlage ansteuern möchte.

Nun stehe ich vor folgendem Problem: Da ich noch keine Erfahrungen mit Labview habe würde ich es eher bevorzugen den PID Regler als solchen zu kaufen, um diesen nur noch über Labview ein- und ausschalten zu müssen. Leider weiß ich nicht, ob die Anbindung an Labview problemlos möglich ist.

Aus Sicht der Integrierbarkeit wäre die Lösung2 sicherlich die optimalste. Leider kann ich als LabVIEW-Anfänger nicht einschätzen, welcher Aufwand mich da erwarten würde.

Preislich gesehen sind beide Lösungen miteinander vergleichbar.

Hatte jemand von euch schonmal Erfahrungen mit einem Ähnlichen Problem sammeln können? Welche option würdet ihr mir empfehlen? 

Ich würde mich über Tipps freuen!

Grüße!

[GerdW]

Hallo Thomkorn,

drei Tipps:

1. dies ist ein englischsprachiges Forum und du erreichst wesentlich mehr Leute, wenn du deine Fragen auf englisch formulierst!

2. Für deutschsprachige Konversationen gibt es das www.labviewforum.de

3. Wieso spielst du hier mit der Schriftgröße rum?

On your questions:

- Using a serial port (either RS232 or RS485) is quite easy. All you need is proper hardware (don't use the cheapest USB stick you can get) and a good programming manual of your device.

- Switching two relais is also quite easy. And LabVIEW comes with predefined PID control functions…

[Thomkorn]

Thanks for your advise GerdW!

For people that might be interested in what i was asking here an english translation of the post above:

I am building an installation that should have the function to control two heated plates (each 500W). Besides that I want to control some valves, measure a distance and two temperatures wherefore i was thinking to buy the folliwing equpiment: NI9201, NI9211 and NI9472.

The biggest problem for me is to find a solution for the controling of the heated plates.I gained some knowledge in the field of control theory, but unfortuntely i have no knowledge about LabVIEW. So far i see there are two ways for the controlling of my heated plates:

Solution 1: Buy a PID controller like the one shown in the following link: 

http://www.omega.com/Manuals/manualpdf/M4704.pdf

With regard to this manuel there is a possibility to connect the controler to LabVIEW via an RS485 communication. The controler manuel includes a whole list of adress and content of data register. Since i have not worked with labview Im not sure if it helps to adjust and to turn on/off my controler. 

Solution 2: Find/build a PID-Programm on labview and conecting the plates trought a NI 9472 at a relay. 

Does anyone of you have some expierence and could give me some advises? As a labview-beginner im sarching for an easy solution for controlling my valves and heating plates and measure the temperature and distance within one program.

Thanks in advance! 

[nathand]

I've set up several heating systems controlled by LabVIEW. Usually the easiest way to do this is with a pulse-width modulation (PWM) signal, connected to a solid-state relay (SSR). The 9472 can generate a PWM signal. What are you planning to use as a controller for the system?

Once you have the hardware working, the software side is straightforward using the PID functions that are included with LabVIEW.

[Thomkorn]

Thanks nathand,

i know what a PWM is, but I tought that a PID would be enough to controll my tempretaure. Do I understand the principle correctly, that my output gives only a 0V or 24V and in order to find a value between the both (because 24V would heat my plates at the maximum, what is defentily too much) I need a PWM? 

Excuse me nathad, but i do not know what you mean by "What are you planning to use as a controller for the system?". My description above was maybe a bit uncleare therefore I tryy to summerize it 🙂 

My Hardware will most probably have the following configuration: 

http://ohm.ni.com/advisors/compactdaq/pages/common/intro.xhtml?configid=CD4929462&no_login=true

All in all i want to

controll: 

4 electrical valves (each 24V) -> NI 9472

2 heated plates -> No clear solution yet. Eather extern PID controller like OMEGA CN7833 or PID controller withing labview 

measure:

A distance with a linear potentiometer -> NI9201 

4 temperature (2 will be needed for the control of the heated plates, 2 are additionaly) -> Eather NI 9211or NI9271

Everything should be integrated in Labview. Unfortunatly I have no experiance in programming and therefore I would like to find the easiest way to integrate my PID controler 🙂 

Thanks a lot! 

[nathand]

The system configuration answered my question about what controller you're using - you are using a compactDAQ controller.

Are you driving your heaters directly from the 24volt supply? If so, you don't need a separate SSR - that would only be needed if you're using a much higher voltage to power the heaters.

PID outputs a continuous signal, over some range (for example 0-100%). A relay has only two states, on and off (0% and 100%). So, if you're going to use a PID controller to with a relay output, you generally let the PID output be the duty cycle for a PWM signal, because the duty cycle can vary continuously.