回應： Cannot combine AI channels into a four-channel from two myDAQs

[LKKSPP]

Hello,

I used MAX explorer to add two analog input(AI) channels of myDAQ into a task. It works fine for this.

For now I need a four-channel's analog input application, so I get two myDAQs for that. I add both of two AI channels of the two myDAQs into a task but always get the message:

An exception occurred within the external code call by a Call ... VI "BlockState.vi:2" was stopped at node "" at a call to "DAQmxAssistant_DAQmx Control Task.vi:1"

Showed as below:

The pic below shows two myDAQ are used simultaneously for a four-channel AI application.

Could you please help or give some hint? The situation is quite easy to reproduced. Just get two myDAQs and add both of its two AI channels of each myDAQ to combine four channels into MAX explorer's task.

Thank you!

LKKSPP

[Billingsley]

Plz tell more informations such as

OS? WinXP or Win7

NI-DAQmx driver version?

NI-ELVISmx driver version?

Do you try another PC?  Can you duplicate the same problem?

 ( Sometimes virus will cause this problem. )

[LKKSPP]

Hello,

Sure. Configuration as below:

OS: WinXP

NI-DAQmx driver: DAQmx9.2.3 (NIDAQ923f1.exe)

NI-ELVISmx driver: installed from NImyDAQ423 DVD

Yes, can duplicate the same problem on two other PCs (Ghost restored).

Thanks!

[cpan]

Usually, such an incorrect behavior is the result of a memory corruption. Update the driver version could help.

I tried it on my two 6259 DAQ cards creating four AI channels with DAQmx 9.4 and got nothing wrong. Would you upgrade your DAQmx to 9.4 and try again?  You could donwload it from the link below:

http://joule.ni.com/nidu/cds/view/p/id/2604/lang/zht

[LKKSPP]

Hello cpan,

Thanks the new version of DAQmx driver. It responses more reasonable as the picture shown below.
It probably means that a task can only contain the channels of one myDAQ;  channels in different myDAQs are not allowed to combine into one task!  

I guess this is a limitation for student version of myDAQ, though i hope NI can get rid of this restriction.

For myDAQ, could you confirm the limit as I described above?

Thanks for the help anyway.

[Seth_B. · Accepted solution]

This restriction is common to many DAQ devices.  Some devices do support having channels from multiple devices in the same tasks, but these are still pretty rare (DSA and X Series devices in the same PXI chassis and modules in the same CompactDAQ chassis come to mind.)

The main reason for this is that all the devices in one task share the same timing source.  Unless you are using a CompactDAQ or PXI chassis or using an RTSI cable between PCI devices, there isn't a way for multiple devices to share the same timing source.  As a result, each device must be in it's own task.  This is the case for all non-CompactDAQ USB devices, not just myDAQ.

I hope this clarifies what you are seeing.

[LKKSPP]

Hello NI guys,

You guys really show a very good quality of service for your products that's why I enjoy NI so much!

Thanks for the quick replies to answer all my questions.  

(can i mark this problem as solved?)

Thanks again!

Jim Lou (LKKNLP)