Read Multiple 9181 Chassis Simultaneously

[rifenbug]

I am designing a new project and I need to know if I can get away with purchasing 2 9181 chassis instead of one 9188 chassis.  I will be using a 9213 for thermocouple readings and a 9208 for 4-20mA current readings.  The signals dont nee to be syncronized and will only have to read once a minute or so.  My question is whether or not I can read the signals from both chassis at the same time through MAX and easily imput into a LabVIEW program.  

 

I am currently using a single 9188 to accomplish the same tasks at a different location but am trying to cut costs on the next project.  The 9184 is not an option due to the software version I am running. 

[hooovahh]

If you go with two single slot chassis you will lose the synchronization between them.  If you are okay with that then you should be fine.  Reading two single point measurements between hardware is no problem.  

 

But I don't think you'll be able to put them in the same task because the tasks will try to synchronize the hardware.  If this is as seldom as you say then yeah just take two single point readings whenever you want.  They won't be "at the same time" because they will be software controlled meaning you probably have at most a few milliseconds between each reading.

[Tim_S]

That kind of question is tricky, if not impossible question to answer without knowing a lot more about your system and implementation.

 

Can you get data from two cRIO chassis to one PC? Yes. I'm not sure how to do so through the MAX/scan engine as my requirements didn't lead me that way. Offhand, the requirement for "a reading once a minute or so" would lead me towards shared variables instead; I don't recall if shared variables were available in LabVIEW 8.5, though.

[hooovahh]

Can you get data from two cRIO chassis to one PC? 

The hardware discussed is cDAQ hardware, not cRIO.

[rifenbug]

The slight delay between the readings won't be an issue, but I am a bit concerned about not having them in the same labview exe.  The way I currently work it with my one 9188 is to bring the channels in through MAX and then have a DAQmx global channel running each of the channels in the labview program.  The end use will have the channels from each module in the same program, likely shown in different tabs in the same exe.

 

I am not a programmer by any means but was the closest thing available the company had, so I am not very good with this and really only know enough to get by on the current task at hand, so I apologize for the lack of knowledge. 

[Tim_S]

The hardware discussed is cDAQ hardware, not cRIO.

DOH! I shouldn't be answering questions before the caffeine drip has kicked in.

[hooovahh]

The slight delay between the readings won't be an issue, but I am a bit concerned about not having them in the same labview exe.  

Uh...why would they not be in the same EXE?  Is that a requirement?  It does make my statement about a few milliseconds potentially not true.

[rifenbug]

Uh...why would they not be in the same EXE?  Is that a requirement?  It does make my statement about a few milliseconds potentially not true.

What do you mean by not being in the same task?  I think I understood that as not being able to run them at the same time in one exe.  I do indeed want them in the same exe.

[hooovahh]

They cannot be in the same DAQmx task.  You will have two separate tasks, one for each chassis.  Putting the tasks together means you are telling the DAQmx drivers to have these two signals share the same timing which can't be done without synchronization.  But I could be wrong if the task is setup to be single point, in that case the DAQ drivers may recognize it is a software timed read and it may allow it.