NI 9265 to control 4-20 mA Mass flow controlller

[bieniekm]

Hello all,

Right now I am trying to create a control interface for a test stand using LabVIEW, the PID add-on, a cDAQ-9178, and a 9265 current output module. 

I have a main VI that has a loop with a few case and sequence structures based on what mode the interface is. My question is, if I use DAQ Assistant to tell the NI9265 to output a current of say 10 mA, will it continue to do so until I reupdate the channel? My issue is that I want to use PID to control my flow controllers, but I need it all wrapped up in loops and statements so I will only be updating the desired current output every second or so, but I want said current output to be continuous. I don't want to send a "pulse" of 10 mA current, I want it to continue to send 10 mA until I give it a new value to emit.

Sincerely,

Mitchell 

[GerdW]

Hi bieniekm,

tell the NI9265 to output a current of say 10 mA, will it continue to do so until I reupdate the channel?

Yes.

loop with a few case and sequence structures … I want to use PID to control my flow controllers, but I need it all wrapped up in loops and statements

Sounds like really bad software design…

[Dennis_Knutson]

When you use a DAQmx Write, the output will remain until you use another DAQmx Write. This is something you can readily test. Are you seeing a different behavior? I would not use the assistant and I would not clear or stop the task until the VI is terminated.

[bieniekm]

GerdW,

I'm fairly new to LabVIEW, so I'm not sure what good software design would be. But breaking down my code, I've got a while loop that keeps my program continously running, with a case structure inside that differs between an "off" and "on" state, with each of those states having a sequence structure. Would this be bad form? Are you open to critiquing code?

Sincerely,

Mitchell

[Dennis_Knutson]

A sequence structure is never a good design pattern. You should look at using a state machine.

[Hooovahh]

A few links

http://www.ni.com/white-paper/7595/en/ 

https://www.ni.com/en/support/documentation/supplemental/16/simple-state-machine-template-documentat...

If you have questions feel free to ask.  Of course making a new thread might be best if the topic changes from a 4-20mA output device to software design.