Analog input on Python NiDaq

[hanhao1991]

I am trying to controlling a NIDAQ 6001 via NI-DAQMx Python API. When trying to collect voltage from AI channel, I encountered wired result.

I let AO0 to output 1 V, and then tell AI0 and AI4 to collect result. 

• Not wire anything, both channel give random readings
• Wire AO0 to AI0, AI0 gives random reading within 1-1.2 V, AI4 gives random reading 0.2-0.5 V
• Wire AO0 to AI4, AI0 gives random within (-1.1)-(-0.6) V, AI4 gives 1.00014 V as expected
• Wire AO0 to AI0 and AI4, AI0 gives 2.2e-5 V (almost 0), AI4 gives 1.00014 V.

I wonder how I could get AI0 to get correct readings?

Following is the code:

import nidaqmx
import time


Task_AO_Chan0 = nidaqmx.Task()
Task_AO_Chan0.ao_channels.add_ao_voltage_chan('Dev1/ao0')

Task_AI_Chan0 = nidaqmx.Task()
Task_AI_Chan4 = nidaqmx.Task()
Task_AI_Chan0.ai_channels.add_ai_voltage_chan('Dev1/ai0')
Task_AI_Chan4.ai_channels.add_ai_voltage_chan('Dev1/ai4')

Task_AO_Chan0.write(1)

for i in range (0,10):
    time.sleep(0.5)
    out0 = Task_AI_Chan0.read()
    out4 = Task_AI_Chan4.read()
    print(out0,'\t',out4)


Task_AO_Chan0.stop()
Task_AO_Chan0.close()

Task_AI_Chan0.stop()
Task_AI_Chan0.close()
Task_AI_Chan4.stop()
Task_AI_Chan4.close()

[santo_13]

AI0 and AI4 are a differential pair as AI0+ and AI0-, in your code, I don't observe you configuring these two channels as single-ended.

Also, have you connected AI GND and AO GND together?

Can you share your exact wiring to be sure how you connected? some pictures or a simple wiring drawing (exactly how things are connected)

[hanhao1991]

Thank you for the prompt reply!

Yes connecting the GND of AO and AI0/4 helps, but AI0 still have larger errors than AI4. 

In the following figure, if I set AO0=0.2V, then

            the black+red connection gives AI0 = 0.22-0.27 V

            the black+green gives AI4 = 0.20004 V

It may due to the AI0 and 4 should be set to single-ended. Sorry I did not know that and wonder how the code should be written.