digital trigger source

[Tui]

Hi,

Basic question I'm sure, but have not found an answer despite much searching.

I am developing an application that reads loadcell data(Analog input data) when a photocell is triggered(Digital input), using Labview 8.2 and cDaq 9172 with the Ni 9421 digital card in slot 4

Can I use a start Trigger that will activate the analog input data  when the collection when an input signal is high? 

I'm finding that the Trigger source does not list my DI card, why?

[Kallis]

From what I see you need Trigger option in the Analog Input module that you are using, if you want to use hardware triggering. Otherwise wait for a digital line to go high in your software and then start acquiring data from Analog input module.

BTW, which analog input module are you using to acquire loadcell data?

[Kallis]

From the datasheet for cDAQ AI modules, it seems that to do triggering you need to use a cRIO chassis. Since you are using cDAQ chassis, you may have to implement software triggering.

[KyleBryson]

Hi Tui,

cDAQ can accept digital triggers through an NI 9421, but the 9421 must be placed in slot 5 or 6.  Moving the module to one of these slots should make its channels appear as options for a start trigger.

Please post again if you have more questions or that does not solve your problem.

Regards,
Kyle

[Kallis]

Thanks to Kyle, I stand corrected.

[Tui]

Thank You for your replies,

Yes, I do get my source terminal if i use slot 5(I thought these were reserved for encoders), but I'm still not able to trigger data collection when my input goes high.

I'm obviously missing something here.  Have tried to get this to work using the examples available(Aq digtal signal using digital edge trigger), but no joy.

I have implemented this in a high speed timber sorting line using software triggers, eg monitoring the inputs.  But as I have several threads/loops running timing becomes an issue.  One thread will monitor the inputs, while another thread gets the data. 

What I am trying to achieve is a setup where the Digital Edge Trigger starts the data collection.  In addition I would like to filter the input signal to eliminate noise, eg the input signal should be  on for say 50mS before data collection starts.

Now, this is a bit on the side of my original question, but any advice would be appreachiated.

[Kallis]

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@Tui wrote:

 Have tried to get this to work using the examples available(Aq digtal signal using digital edge trigger), but no joy.

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Tui,

You are interested in acquiring analog signals. So you should be using the Analog input VIs.

Can you post the VI that you are using?

[Tui]

Have enclosed a Vi based on a modified example.  While this gives data when run against a simulated cDaq device, I do not get any data when run in the production environment

[Kenn_N]

Hey Tui,

Thanks for contacting National Instruments support.  I am curious what AI module you are using.  I do see that you are using the 9421, and I assume you are using the 9237 for load cells.  Based on that you should be able to use Measurement and Automation Explorer (MAX) to verify that connections are correct and test your triggering.  Once you have that verified you can then use the task you created to auto-generate LabVIEW code to get started with.  This should allow to start from a working example and then make changes until things break. 

To create the task in MAX, right click on Data Neighborhood and select Create New... Then setup a NI-DAQmx task and In the setup on the DAQmx task in MAX you can select the triggering tab to specify the trigger from module 5 and then run the task to see if it works.

There is a video to do all this online in our DevZone that you can view that will help through these steps.

Regards,

[Tui]

I was a bit quick when I said it did not work,  it does!( using 9237 for the loadcells)

Kenn, Why use Max, isn't it a bit simpler to use the Daq Assistant?  As I understand they both do the same?

Similar question, in my type of application there is little to be gained by using Daqmx in place of Daq Assistant?