Problems with multiple acquisitons

[mayankb]

Hi all,

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.

Thanks,

Mayank

[Dennis_Knutson]

I found a couple different meanings for AFM so please be more precise. Provide a link to or attach the data sheet. Provide details on how you are configuring the termination (diff, rse, etc). Provide details on what channels you are using. Provide details on what programming language you are using or whether you are using the MAX test panel.

[mayankb]

Hi Dennis,

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.

Mayank

[Dennis_Knutson]

The sensor is not irrelevant since you need to know the output impedance, the required connection type, etc. Since you don't want to provide the details, I'll let you try to solve the issue with what you said.

[mayankb]

Hi Dennis,

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."