Python - 2 * SCB68 A on NI 63 23 - 16 channel differential

[KramGeo]

Hello to all of you,

I have a problem that I don't understand at all;

I have a NI 6323 card with two SCB-68A cards as data connections.

I want to work in differential.

When I work in CSR or NRSE mode, I can access 32 channels.

When I put my terminal in DIFFERENTIAL mode, I can only have 8 channels instead of 16.

With 32 channel

-----

def cfg_read_task(Saturation):
                  Saturation.ai_channels.add_ai_voltage_chan('/Dev1/ai0:31',min_val=0.5,max_val=1.5,
                  terminal_config = nidaqmx.constants.TerminalConfiguration(-1))
                  Saturation.timing.cfg_samp_clk_timing(rate=sampling_freq_in, sample_mode=constants.AcquisitionType.CONTINUOUS,
                  samps_per_chan=buffer_in_size_cfg)

-----

With 8 channel and differential terminal

-----

def cfg_read_task(Saturation):
                  Saturation.ai_channels.add_ai_voltage_chan('/Dev1/ai0:7',min_val=0.5,max_val=1.5,
                  terminal_config = nidaqmx.constants.TerminalConfiguration(10106))
                  Saturation.timing.cfg_samp_clk_timing(rate=sampling_freq_in, sample_mode=constants.AcquisitionType.CONTINUOUS,
                  samps_per_chan=buffer_in_size_cfg)

-----

This script is working :

With 16channel and differential terminal

This script is  not working :

-----

def cfg_read_task(Saturation):
                  Saturation.ai_channels.add_ai_voltage_chan('/Dev1/ai0:15',min_val=0.5,max_val=1.5,
                  terminal_config = nidaqmx.constants.TerminalConfiguration(10106))
                  Saturation.timing.cfg_samp_clk_timing(rate=sampling_freq_in, sample_mode=constants.AcquisitionType.CONTINUOUS,
                  samps_per_chan=buffer_in_size_cfg)

-----

I attach my MAX image who see my two scb68-A cart.

Does anyone have any idea what I'm missing?

thanks for reading,

[Kevin_Price · Accepted solution]

You're probably missing the way differential pairs are fixed in the hardware and the way the AI channels are split across the 2 connectors.

You *can* declare channels ai0:7 as differential, but that just defines the + inputs.  The device itself will then use (and expect you to physically wire) ai8:15 as the - inputs.

Similar stuff holds true for ai16:23 (+) and ai24:31 (-) on the other connector.

So your task config should designate 'Dev1/ai0:7, Dev1/ai16:23' to give you 16 total differential channels.

-Kevin P

[KramGeo]

Hoooo Yeah, i'm dumb sometimes;

Thanks Kevin P! As usual, you have the right answer !

Version who work :

def cfg_read_task(Saturation):
Saturation.ai_channels.add_ai_voltage_chan('/Dev1/ai0:7',min_val=0.5,max_val=1.5,
terminal_config = nidaqmx.constants.TerminalConfiguration(10106),
units=nidaqmx.constants.VoltageUnits(10348))
Saturation.ai_channels.add_ai_voltage_chan('/Dev1/ai16:23',min_val=0.5,max_val=1.5,
terminal_config = nidaqmx.constants.TerminalConfiguration(10106),
units=nidaqmx.constants.VoltageUnits(10348))