Triggering and data streaming for two different PXI devices

[Swapnil@CEA]

Hello,

Here are the details of the system I use:

Chassis: NI PXIe - 1071

Controller: NI PXIe-8820 Embedded controller

First Device: NI PXI  - 5922 Oscilloscope ===>Dev1/ai0:1

Second Device: NI PXI  - 4462 ====>Dev2/ai0:3

I also have the SMB 110 cable with me.

For data acquisition, I use Python 'nidaqmx' package.

My aim is to read the data from these two devices at the same time.

I have two questions:

1. Is it possible to use SMB cable for the above mentioned two devices for external triggering. If not, are there any other alternatives I am left with?

2. Is data streaming possible for this devices for the system specifications I mentioned above..?

The code is as follows:

with nidaqmx.Task() as task:

        task.ai_channels.add_ai_voltage_chan('Dev1/ai0') 
        task.timing.cfg_samp_clk_timing(Samples_Per_Sec=10000, source="",                                             active_edge=Edge.RISING,sample_mode=AcquisitionType.FINITE,              

                samps_per_chan=10000)
        data=task.read(samps_per_chan=10000)

Typically, I do know that the two devices of the same type triggered automatically. But I suppose its not true for two devices of different type. 

For ex: If I try to change my above code using both devices

with nidaqmx.Task() as task:

        task.ai_channels.add_ai_voltage_chan('Dev1/ai0,Dev2/ai0)
        task.timing.cfg_samp_clk_timing(Samples_Per_Sec=10000, source="",                                             active_edge=Edge.RISING,sample_mode=AcquisitionType.FINITE,              

                samps_per_chan=10000)
        data=task.read(samps_per_chan=10000)

I get an error saying "One or more devices do not support multidevice tasks".

Thanks,

Swapnil

[PezDeSpencer]

Hello Swapnil,

I want to try to answer your question with triggering, but first want to address something that seems odd. 

Are you controlling the Oscilloscope (5922) with the DAQmx driver? 

This seems incorrect to me, because this instrument is part of the modular instrument line and python support for this line can be found in the following two links.

LINKS:

https://www.ni.com/en/support/documentation/supplemental/16/python-resources-for-ni-hardware-and-sof...

http://nimi-python.readthedocs.io/en/master/

If you are trying to combine these two instruments into a single task I do not expect that to work and you should need to open two tasks. 

For triggering externally. The 5922 has a BNC trig line that you can use for external triggering. I would expect this external trigger to be coming from another instrument, likely a digital pulse. 

The 4462 has a PFI line that is a SMB connector that you could use as an external trigger source. Again you would likely route some digital pulse to trigger this off the PFI line. 

Are you trying to synchronize these two instruments acquisition? To let you know there is some filter delay with the 4462 as it is a sound and vibration card. The specification linked below tell you more about the filter delay. 

LINK:

https://www.ni.com/docs/en-US/bundle/ni-4461-4462-specs/resource/373770k.pdf

You can also think about doing triggering within the PXI chassis itself or using software triggers. I have attached some documentation about the PXI backplane and triggering. 

LINK:

https://www.ni.com/en/support/documentation/supplemental/18/using-pxi-timing-and-triggering-function...

https://www.ni.com/en/support/documentation/supplemental/10/synchronization-explained.html

Hopefully this is helpful. 

Best,

Spencer | NI AE

[Swapnil@CEA]

Hello Spencer,

Thanks for your answer.

Yes, I am controlling Oscilloscope NI 5922 using DAQmx driver i.e using python 'nidaqmx' package. Infact, I did not knew about the python 'nimi' package which is more specific to NI Oscilloscope. But, neverthless I can acquire data using 'nidaqmx' for NI 5922.

Also, I am trying to synchronize these two instruments acquisition. I will try to use the 'nimi' package and the triggering procedure you suggested. Thanks for sharing the links; its really helpful.

Regards,

Swapnil