I am using NI PCIe-6361 board to acquire sensor data from an AFM unit. I need to acquire all three X, Y and Z sensors data simultaneously.
When I try to acquire all three signals simultaneously, the AFM unit starts behaving weirdly (doesn't regulate the cantilever tip to the desired set point anymore to do proper scanning ) the input data is getting corrupted. However, when I acquire one channel at a time, the AFM controller works perfectly fine and all the three acquired inputs make sense.
I am not sure what's going wrong with multiple acquisitions.
AFM is Atomic Force Microscope. The AFM part is irrelevant here in the sense that it can be thought of a black-box with an inbuilt controllers and some I/O ports to send/receive image data.
I am using LabView to read 3 ADC channels simultaneously. I am using PCIe-6361 with BNC-2110. Actually, the sensor output of AFM (essentially a voltage signal) is being fed to the ADC ports of the PCIe board. The problem is that when I try to acquire multiple sensor output simultaneously, the sensor output (which was being maintained at some reference voltage) starts getting corrupted. If I remove two of the channels and read just one sensor, the output remains unaffected.
My first guess is that I probably need something like a voltage follower circuit that can take care of the excess current being drawn. I'll try it sometime tomorrow and see if that solves the problem.
All the connections are single-ended BNC. It appears to me that the impedance is 10k-ohm. The AFM (MFP-3D) manual explains it in one of the places:
"Many signals can be accessed from their corresponding BNC, located on the front panel of the controller. The signals on these BNCs range within +/-10V limits and have input impedances of 10kΩ."