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Python Synchronization of multiple analog inputs CDAQ-9185

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Hi,

 

I have been using the Python nidaqmax package to simultaneously acquire analog inputs from two NI9239 (BNC) plugged into a cDAQ9185. 

My issue is that I am not managing to use the same clock for all the channels to synchronize my measurements. 

 

The code worked fine when using the internal clock of each of the NI9239 respectively ( i.e in the code replacing the underlined lines with  source = "/cDAQ9185-213AB07Mod1/ai/SampleClock" in task A, and  source = "/cDAQ9185-213AB07Mod2/ai/SampleClock" in task B). 

 

However, when using one of the cDAQ9185 clock as a common clock (as in the code below), the code returned errors. The different sources can be seen in the attached screenshot of the NIMAX software. I have also tried using "/cDAQ9185-213AB07/80MHzTimebase" without success.

 

Another attempt consisted in using the internal clock of one of the module as the common clock as it seems to be the case in: Résolu : Python multi-tasking using cfg_samp_clk_timing question - NI Community  ( i.e in the code replacing the underlined lines with  source = "/cDAQ9185-213AB07Mod1/ai/SampleClock" in task A, and  source = "/cDAQ9185-213AB07Mod1/ai/SampleClock" in task B). But this also returned errors.

 

Any help to achieve this synchronisation would be much appreciated. 

 

Here is my code below: 

-----------------------------------------------------------------------------------------------------------------------------------------------------

import nidaqmx
 
npnts = int( fs_acq * duration) # number of sample per acquisition
 with nidaqmx.Task() as a_task, nidaqmx.Task() as b_task:
 
# Create analog input DAQmx Task from  NI9239 A (module 1)
 a_task.ai_channels.add_ai_voltage_chan(
"cDAQ9185-213AB07Mod1/ai0:2"
, name_to_assign_to_channel="hotwireA"min_val=-10, max_val=10)
 
 # Create analog input DAQmx Task from  NI9239 B (module 2)
b_task.ai_channels.add_ai_voltage_chan(
"cDAQ9185-213AB07Mod2/ai0:2"
, name_to_assign_to_channel="hotwireB",min_val=-10, max_val=10)
 
# Configure timing for ai task module A
 a_task.timing.cfg_samp_clk_timing(rate=fs_acq, source = "/cDAQ9185-213AB07/ai/SampleClock", sample_mode = nidaqmx.constants.AcquisitionType.FINITE,samps_per_chan = npnts
 
 
 b_task.timing.cfg_samp_clk_timing(rate=fs_acq, source = "/cDAQ9185-213AB07/ai/SampleClock",  sample_mode = nidaqmx.constants.AcquisitionType.FINITE,samps_per_chan=npnts ) # you may not need samps_per_chan


a_task.start() # start performing the task
b_task.start()
 
 a_task.wait_until_done()
b_task.wait_until_done()
 
-----------------------------------------------------------------------------------------------------------------------------------------------------
 
Error: 
"name": "DaqError",
"message": "Requested sample clock source is invalid.\nProperty: DAQmx_SampClk_Src\nCorresponding Value: /cDAQ9185-213AB07Mod1/SampleClock\n\nDevice: cDAQ9185-213AB07\n\nTask Name: _unnamedTask<2>\n\nStatus Code: -200414",
-----------------------------------------------------------------------------------------------------------------------------------------------------
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Solution
Accepted by topic author MarilouJourdain

You can use channel expansion and add multiple channels into a single task. DAQmx driver will handle the timing routing for you.

 

import nidaqmx
npnts = int( fs_acq * duration) # number of sample per acquisition
 with nidaqmx.Task() as task
 
# Add channels from NI9239 A (module 1)
 task.ai_channels.add_ai_voltage_chan(
"cDAQ9185-213AB07Mod1/ai0:2"
, name_to_assign_to_channel="hotwireA", min_val=-10, max_val=10)
 
 # Add channels from NI9239 B (module 2)
task.ai_channels.add_ai_voltage_chan(
"cDAQ9185-213AB07Mod2/ai0:2"
, name_to_assign_to_channel="hotwireB",min_val=-10, max_val=10)
 
# Configure timing
task.timing.cfg_samp_clk_timing(rate=fs_acq, sample_mode = nidaqmx.constants.AcquisitionType.FINITE,samps_per_chan = npnts ) 
 
task.start() # start performing the task
task.wait_until_done()
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Thank you for your prompt reply. This worked perfectly, thank you !! 

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