Hello everyone.
I am actually trying to record seismic accelerations in a laboratory using a SCXI-1530 and PCB 626A04 accelerometers. I am interested in the 0.1 Hz to 100 Hz range. From other measurements carried out under similar circumstances and with the same accelerometers but a different acquisition system (not NI) I expect to find accelerations up to max 10-4 g and an rms noise of 20 microg/sqrt(Hz).
When I measure the accelerations with the SCXI-1530 the accelerations I obtain are much higher: peaks at several 10-4 gs and rms noise of 80 microg. I have also made a mesaurement with the SCXI current supply off, in order to measure the underlying noise of the card. I then obtain peaks of at most 10-4 g and an rms noise of about 15 microg. In other words: with the accelerometer OFF I record acceleration levels in the order of magnitude of what I want to measure....
My problem is that the stated rms noise of the SCXI-1530 is 25 microV. The sensitivity of my accelerometers is 10 V/g so I expected to have an rms noise not above 2.5 microg....The performances of the card are not clear to me.
My question is: am I limited by the performance of the card itself or am I doing something wrong ?
Here are the details of the setup :
- A PCB 626A04 accelerometer (10V/g sensitivity) is connected to a SCXI-1530. This card is connected to a Multifunction NI DAQ with a PXI-6220 card.
- The settings of the SCXI-1530 are the following:
- sensitivity 10 V/g
- input range 1 mg to -1mg
- differential meas.
- low pass filter set at 2.5 KHz
- current source set on at 4 mA
Everything is connecetd to a UPS and all equipment is grounded to a clean earth.
I hope someone can help. Thank you.
