Weird behaviour when reading a DAQmx Channel property node (bug?)

[MarkMoss]

When I attempt to use a DAQmx Channel property node to read the properties of a global virtual channel, I get the following error unless I first create a task *and* set the timing for that task to a mode supported by the hardware.  I've attached a screenshot of the VI showing two pieces of code that result in the error, and a third piece of code which works as expected.
 
The specific error I receive is:
 
Property Node DAQmx Channel (arg 1) in DAQmx Channel Read Weird Behaviour.vi <append>Property: SampTimingTypeYou Have Requested: On DemandYou Can Select: Sample Clock
Device: cDAQ2
Task Name: Module 7 AI0 Strain
 
I'm using the following:
Windows XP SP2 (32-bit)
LabView 8.5.1
DAQmx 8.7.0f1
cDAQ-9172 chassis (S/N 1346A04)
NI-9237 (S/N 134252A) in the cDAQ chassis' slot 7.
 
Is this behavior "by design", and is there a better work-around to allow me to get the global virtual channel properties without first having to create a task and setup the sample timing?
 
Thanks,
 
Mark Moss
Electrical Validation Engineer
GHSP


DAQmx Channel Read Property Node.png:
http://forums.ni.com/attachments/ni/250/42144/1/DAQmx Channel Read Property Node.png

[mickeyw]

Hi,
 
Is there a specific error&nbsp;code you are getting? It seems like a fairly common problem with channel property nodes after some initial research. This <a href="http://forums.ni.com/ni/board/message?board.id=170&amp;message.id=81492&amp;requireLogin=False" target="_blank">thread</a>&nbsp;answers a similar problem, I hope it is of some assistance to you. I will continue to look into the problem.
&nbsp;
Regards,

[MarkMoss]

The error code is -200077.
&nbsp;
From other threads, I gather that this error code&nbsp;means that the property or value isn't supported by the underlying hardware.&nbsp; The error source string lists the property and unsupported value as "SampTimingType" and "On Demand", respectively.
&nbsp;
The weird part is that I'm not trying to set "SampTimingType" to "On Demand".&nbsp; Instead I'm trying to read the "Analog Input:Strain:Strain Gage: Poisson Ratio" property.&nbsp; Reading the "Analog Input:Strain Gage: Poisson Ratio" property fails unless I explicitly create a task and set the task timing to "Continuous Samples" first.
&nbsp;
Also, this doesn't appear to be specific to the poisson ratio property.&nbsp; I get the same error for each of the other channel properties I tried to read.
&nbsp;
Mark Moss
Electrical Validation Engineer
GHSP

[mickeyw]

Have you tried uninstalling and re-installing the software (both Labview and MAX)? This solved the problem on another thread from a poster who was having the same problem. I am still looking into other ways of solving the problem.
&nbsp;
Let me know how you get on.
&nbsp;
Regards,

[stilly32]

This is expected behavior. When you query a task property DAQmx verifies the task to ensure the settings are correct - which in your case they're not because the 9237 does not support On-Demand timing (which is the default when no timing is specified). This isn't a problem with most devices becuase most devices support On-Demand... in your case I would just set the timing to some value, you can always change it. Is there a need to query these values before you setup the task or is it just something you noticed?Thanks, Andrew SMIO PSE

[MarkMoss]

stilly32 wrote:
This is expected behavior. When you query a task property DAQmx verifies the task to ensure the settings are correct - which in your case they're not because the 9237 does not support On-Demand timing (which is the default when no timing is specified). This isn't a problem with most devices because most devices support On-Demand... in your case I would just set the timing to some value, you can always change it.
Is there a need to query these values before you setup the task or is it just something you noticed?

Thanks,

Andrew S
MIO PSE


That makes sense.&nbsp; I didn't realize that LabView/DAQmx had to create a task internally to query global virtual channel properties.&nbsp;In my case, I can't add the global virtual channel to my task directly since I need the first channel in my task to be a physical channel.&nbsp; Instead, I call the DAQmx Create Virtual Channel VI with all of the setup parameters coplied from the global virtual channel.&nbsp;Mark Moss
Electrical Validation EngineerGHSP