Choppy signal ("stairs") from USB-6002

[blazej13]

I'm geting a sort of a choppy signal from USB6002. After unsucsessfully trying solving ground problems, I connected just a capacitor with a discharging resistor directrly to the input- the same thing- you can see the "stairs". I also used elementary data readout, without the buffer, still the same thing (the time unit is 100 ms, 200 s total in x axis) Anyone may help?

import nidaqmx
import time
with nidaqmx.Task() as task:
task.ai_channels.add_ai_voltage_chan("Dev1/ai0")
d=[]
for i in range(2000):
d.append((task.read()))
time.sleep(0.1)

import pylab as plt
f=plt.figure()
a=f.add_subplot(1,1,1)
a.plot(d)
plt.show()

[santo_13]

Some additional details would be helpful,

• Are you using USB6002 as AO or AI?
• Graph shows 5mV steps - what is the capture device and configuration
  • Instrument is not evident from the python code
• What instrument is generating the signal that is captured by the AI?
• Circuit diagram of the test setup?

[blazej13]

I'm using USB6002 as AI, both RSE or DIFF mode have the same behavior

The signal is generated by the pressure sensor, I replaced it however with the test circuit consisting of capacitor discharged through a resistor (see the circuit below)- I have the same steps.

The USB device is connected to the laptop working on battery- there are no other devices connected there. I dont see any options to configure USB 6002 through NI Daq software.

I used the input now in the DIFF mode- I have the same steps still...

The capacitor was charged by an external power supply, which was then disconected and taken away, as seen on the first plot. The steps ~5 mV are clearly seen on the second plot, which shows the same signal (zoomed view).

[blazej13]

Fig.1. Discharge of a 2200 uF capacitor

Fig. 2 Magnification of recorded signal, see the right scale [V]

 Fig 3. Test diagram

Fig 4. Test circuit