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Cannot sync 9237 with other AI channels in cDAQ using ext sample clock

In my application, I have a cDAQ configuration with AI modules 9205, 9211 and 9237.  I want to create an AI task with these attributes: continuous samples, external sample clock, PFI0 (from 9205) clock source.  The task uses channels from all the modules.  When I tried to save the task, I got error -200414.  The task will only save w/o error if I do not include channels from 9237.  What does the error really mean?  Can I not sync the 9237 with other AI modules when using ext clock?

BTW, I don't have the actual HW.  I just created simulated devices in MAX so I can try things out.  This may or may not matter, but you never know.

S.
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Seaman,

The 9237 is a bridge module, so you can't actually use it in an analog input task.  The 9237 needs to be used for either a strain gauge or a custom voltage with excitation task.  Since the cDAQ chassis only allows one analog input task at a time, you won't be able to acquire from the 9237 at the same time as the 9205 or 9211.  As the manual explains, "The cDAQ-9172 has one AI timing engine, which means that only one analog input task may be running at a time on a chassis."  The 9237 must be in a separate task from the 9205 and 9211.

Sorry for any inconvenience.

 

Elijah Kerry
NI Director, Software Community
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Hi Seaman-

The source of this limitation is not that you are restricted to a single measurement type in a task, but rather that the timing architecture of the 9237 is different than the other modules you're using.  The 9237 is a sigma-delta module that requires the use of a sample clock that is internally-derived from an oversample clock timebase.  The other modules simply use a sample clock that is externally-provided or derived from an internal sample clock timebase.  These differences make it very difficult to synchronize the two modules using an external sample clock alone.

A better option for strain measurement synchronization with MIO modules via an external clock would be the NI 9219.  You should be able to add a simulated 9219 to your task and acquire from all channels with the PFI0 sample clock source on the NI 9205.

Hopefully this helps-

Tom W
National Instruments
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I wanted to clarify and correct my previous post.  Tom explained the source of the error you were experiencing regarding the sample clock.  It doesn't have to do with how the various channels in the task are created, but for the sake of anyone else reading this post I wanted to correct my previous statement.

As I explained, all analog inputs acquired on the same cDAQ chassis must be grouped into one task.  However, you can create channels in that task of various measurement types.  Simply re-use the polymorphic DAQmx Create Virtual Channel VI to specify the measurement type for different inputs.  I went ahead and threw together a simple example that uses the 9237, 9211 and 9205 to illustrate this.

Sorry for any confusion.

PS:  You'll need to specify the correct physical channels to run it.

Message Edited by Elijah K on 04-11-2007 11:47 AM

Elijah Kerry
NI Director, Software Community
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Thanks for the help.  I understand the problem much better now.  I'm afraid the NI 9219 won't work for me since I require a sampling rate over 2kHz.  Guess I need to look for other options.

S.
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Hello

I found this article in NI website and example LabVIEW VI describing how to sync AI DAQ in two cDAQ-9172 chassis.

http://zone.ni.com/devzone/cda/tut/p/id/5376. This example shows how to sync AI DAQ when you have a 9211 or 9215 cDAQ modules. (I found that it did in fact work with 9211 modules). However I wanted to try it with 9234 modules.

Here is my setup:

Chassis #1 - cDAQ 9172

   Module 1 - cDAQ 9234

   Module 5 - cDAQ 9401

Chassis #2 - cDAQ 9172

   Module 1 - cDAQ 9234

   Module 5 - cDAQ 9401

The two cDAQ 9401 modules are connected with a DB25-25 cable.

 

But when I tried this example I too get the error "Error -200414 occurred at DAQmx Start Task.vi:1"

   Possible reason(s):

   Requested sample clock source is invalid.

   Property: SampClk.Src
   Corresponding Value: /cDAQ9Mod5/PFI0

   Device: cDAQ9

   Task Name: _unnamedTask<AC>

 

So it sounds like the same error that the previous user got with his 9237 modules.

Can you please comment on this and let me know what the problem might be.

 

Thank you

Sundaram Raghuraman

 

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It is not currently possible to synchronize tasks across chassis that use AI modules with delta-sigma ADCs, such as the 9234 and 9237.  The DAQmx help has a full list of these modules in the C Series Device Groupings section.

 

The delta-sigma modules synchronize by sharing a sample clock timebase (and sync pulse), not a sample clock.  There is currently no way to share that signal between cDAQ chassis.

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Hi Tom,

 

How can I synchornize the module two 9237 and one 9205 with the 9178 chassis ?

Can't I use the external clock, and how?

Hope for your reply.

 

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Hi dfffs-

 

If I read correctly, you just want to synchronize multiple modules in the same chassis.  Do you want to use an external clock, or are you asking if you must use one?

 

If using an external clock is not a requirement, you can synchronize the modules using the internal clock by just including channels from the multiple modules in a single DAQmx task.  You can do this by calling the DAQmx Create Virtual Channel VI of your measurement type multiple times, or you can combine channels from multiple modules using comma-separated lists (like 'cDAQ1Mod1/ai0:7, cDAQ1Mod2/ai0:7').

 

If you have a more involved question than this, please post a new discussion forum thread.

 

Hopefully this helps-

Tom W
National Instruments
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Hi, Tom

 

Thank you very much. I think I know how to synchronize multiple moduels without external clock now.

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