Hi,
I've noticed in my measurements that there are two particular frequencies that always appear, regardless of what I'm measuring. I use a DAQ board (PCI 6010) to perform voltage measurements, and Signal Express to control and analyze the data. I use a differential measurement (between ai0 and ai8, I believe) to measure the voltage output of a piezoelectric (to prevent charging). I always see a noise signal - artifacts? - at about 4 kHz and at about 9 kHz. I've found that the input range that I select is extremely important, for instance, if my signal is 20mV p2p and I've chosen an input voltage range of +/- 5 V, there is considerable noise, with these two frequencies very prominent; if I narrow the input range to perhaps +/- 30mV, the noise is much reduced, but the two frequencies are still there. These signals have appeared in data that I've taken over many months, on various systems, and at different times of data, etc. - but they do not appear if, using the same piezoelectric, I look at the data with an oscilloscope.
I certainly could simply filter these frequencies out - I use the bandstop filter function to remove the 60 Hz noise, but in my research I'm interested in the frequencies that are excited in a system that are in this frequency range, and I worry that by trying to filter these two out I may also remove some important data along with it.
Is this a common problem?
Thanks! Myra
Sorry if this is the wrong discussion board to use - I wasn't sure where to post 🙂
