LabPC analog input estrange behaviour

Hi,
I have a LabPC board and I have found ?an estrange? behaviour when I connect an analog input signal to one channel (e.g.: to channel 0) and I leave the rest of channels open. I know this is not the way to do it, but I would like to know what?s happening !
HARDWARE CONFIGURATION: RSE Mode, Bipolar Input, Gain=1
PROBLEM DESCRIPTION
EXPERIMENT 1: I connect an analog input signal (3 Vpp 1 Hz sinusoidal) to channel 0 leaving channels 1 through 7 disconnected (open). I open MAX, CVI or LabVIEW and acquire the signal on channels 1 through 7 and I measure in these channels a signal, which is the signal in channel 0 modulated with a 60 Hz sinusoidal (line signal). Of course, if I ground the corresponding channel the measured s
ignal disappears.
EXPERIMENT 2: I connect an analog input signal (3 Vpp 1 Hz sinusoidal) to channel 0 and another signal (1 Vpp 4 Hz square wave) to channel 1, leaving channels 2 through 7 disconnected (open). I open MAX, CVI or LabVIEW and acquire the signal on channels 2 through 7 and I measure in these channels a signal, which is the signal in channel 0 modulated with the signal in channel 1 and a 60 Hz sinusoidal (line signal). Of course and once again, if I ground the corresponding channel the measured signal disappears.
QUESTION: I suppose this must be some kind of crosstalk, but with this frequencies ? I have studied the analog input stage of the LabPC but I haven?t found any explanation. So what?s happening ?
Thanks a lot

Thanks for your answer, but I can not agree with it. I would if I would be scanning through the different channels, but this is not the case. May be the problem is that I didn?t express myself properly. I hope the attached figure clarifies the situation.
I have connected 2 signals in channels ACH0 and ACH 1, but I acquire only from channel ACH 2, which I left opened. In particularly I have acquired 100 points at 100 samples/s using LabWindows CVI?s DAQ_Op function from the Data Acquisition Library.
In this case, the only signal path I can think of is due to the multiplexer?s off channel impedance. If we assume that an unselected channel presents an impedance, in this case channels ACH0 and ACH1 are unselected, this impedance would generate a crossta
lk effect with adjacent channels due to their source impedance. What surprises me about this, is that we are talking about low frequency signals (1Hz and 3 Hz) and huge crosstalk levels (see measured signal in the attached figure).
Thanks again
Attachments:
Dibujo.jpg ‏65 KB

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