Spurious frequency introduced

[pilo]

Hi,

Hi I am measuring 3 analog inputs all in differential mode.I used the 6035E card and CB-68LP connector board.

The first is a voltage connected to ACHO amd ACH8 and ACH8 is in turn connected to AIGND.

The second is a temperature reading but measurements are in voltage. ACH1 coonected to ACH9 and ACH9 to AIGND.

I do frequency analysis of the two analog inputs and get the correct results.Everything works fine so far.

Problems arise when I connect the third analog input.The third analog input is a vibration reading which is captured by an accelerometer connected to a Nexus 2693 charge preamplifier. Now the charge amplifier has a BNC output , so I have used a shielded standard cable which splits the signal into 2 signals to co
nnect the vibration signal to the CB68-LP board. Now the vibration signal is connected to ACH2 and and ground signal to ACH10 and ACH10 to AGND respectively.

When I do a frequency analysis of my signals, I notice that connecting the third signal has introduced a spurious peaks at arounud 1 kHz to both my previous two analog inputs.

Does anybody know what could be causing the problem

[JamesC]

Hi Pilo,

Are you using a PXI-6035E or a PCI-6035E?
One source could be the cb-68LP, this connector block is not shielded and might be picking up some noise.
Could you try the accelerometer on a different channel, say 6 and 15. Then if that doesn't work try the accelerometer signal as a NRSE signal and connect to CH3 and GND.

Just a suggestion, but I need to know what form factor your DAQ card is, and the voltage of the frequency signal.

Regards
JamesC
Applications Engineer
NI UK