Create Synced Continuous Pulse Train

[BPyke]

Hi All,

I'm trying to create a continuous pulse train that is in-sync with an external trigger.  I am using a NI 9402 module in a NI cDAQ-9172 chassis.  When I use PFI0 for the external trigger and ctr1 (both on the 9402 module), I get this error "Sample Timing Type specified is not supported for counter output tasks on this device. Change the Sample Timing Type to Implicit."  If I change the timing type to Implicit, then the pulse train is not sync with the external trigger.  Is this possible?

Thanks for the help.

Ben

[niNickC]

Hello Ben,

My name is Nick and I am an Applications Engineer for National Instruments.

Are you trying to start the pulse train generation using an external trigger?

This is done using the DAQmx Trigger VI. You can specify that the DAQmx task starts on a digital edge and the source of that edge (in your case PFI0)

The triggering section in getting started with DAQmx tutorial on ni.com goes into more detail about how to do this:

http://zone.ni.com/devzone/cda/tut/p/id/4329

Please let me know how you get on and if you have any more questions.

Nick

[BPyke]

Hi Nick,

Thanks for the information, unfortunately I still can't generate the pulse train.  I found a NI Example that looked promising (Gen Dig Pulse Train-Buff-Ext Clk-Cont.vi) but I get the following error.

Error -201296 occurred at DAQmx Write (Counter 1D Frequency 1Chan NSamp).vi:1
Possible reason(s):

Sample Timing Type specified is not supported for counter output tasks on this device. Change the Sample Timing Type to Implicit.

Property: SampTimingType
Corresponding Value: Sample Clock

Task Name: _unnamedTask<58>

I'm starting to think that NI 9402 module doesn't support an external trigger.  I can use it to externally trigger other modules, like an analog output (NI 9264) but not another channel on it.

Any other ideas?  Thanks

[niNickC]

Hi Ben,

Just to confirm for your application you are trying to output a pulse train whose pulse specifications (duty cycle and frequency) updates in sync with an external clock source? (Just like in the example?)

[niNickC]

Hi Ben,

After some reasearch I believe I have the solution to your problem. You are correct in that the problem is caused by hardware which does not support this operation. However, the incompatibility issue is with the chassis and not the plug in module.

Sample clock mode for pulse train generation requires the use of a buffer and this is not supported by the 9172. Newer chassis such as the 9174 or 9178 will work.

I am sorry I could not solve your problem with your current setup.

Please get in touch letting me know you got this message and if you have any further questions don't hesitate to ask.

[BPyke]

Hi Nick,

That is good news, I just ordered a 9174 chassis.  I should receive it this afternoon so I will test it right away.  Thanks for the help.

Ben