Measure
crosstalk inside daq
Hi,
I am pretty new to labview and I wanted to measure 7 analog channels at once. The problem is that when I measure each channel seperately, I get different result than when I measure them all at once. I read about ghosting and created a unity-gain-buffer using an op-amp to lower the source impedance. However, it hasn't helped much.
I was wondering if I am doing something that I am not supposed to do.
Below is my labview program. I used clock 1 (digital pulse waveform) to generate a clock. According to this clock 1, an 8-bit digital waveform is generated. I am using the most significant bit of this 8-bit digital waveform as clock 2 which is used to sample the analog input waveform. The series of 8-bit digital waveform is the array of 10 numbers in the picture. I am feeding clock 1 which is generated from PFI 12 and PFI 15 is reading this clock and using it to generate the 8-bit signals. I am using USB 6251 to do this.
The weird thing is that when I use oscilloscope to check the data that I am measuring, I see a peaking in my data and this peaking occurs exactly when the clock 1 goes high. However, clock 1 is only connected to PFI 15 and is isolated from the circuit I am measuring. Now I am wondering if there's a crosstalk inside DAQ box.
My first question is whether I can use a clock to generate 8 bit signal and use one bit of this 8-bit signal as a clock to sample data. The second thing is how do I make sure that what I sample from DAQ box is really what's happening inside the circuit. It seems weird that when I sample 7 channels at once, it gives me different values than when I sample only a single channel. Again, I've used unity-gain-buffer to try to remove the ghosting effect. I am sampling at a period of 400 microsecond.
Thank you.
