Noise on Data Aquisition Card

[NoraLa]

I am using a NI PCI-6024E Data Aquisition Card to read an analog voltage signal from a pressure sensor (0-100 mV). When I add a second channel to the DAQ-Assistant in Labview (independent if there is anything connected to that channel or not), I get a periodic noise every 2 seconds.

[PBear]

Hi NoraLa,
It sounds like you are experience ghosting, a situation that occurs when the charge left on the MUX and ADC does not have enough time to dissipate when scanning. I assume that you are getting this periodic noise on your original channel and not on the new channel. Try looking at this article for more information.
 
How Do I Eliminate Ghosting From My Measurements?<a href="http://digital.ni.com/public.nsf/allkb/73CB0FB296814E2286256FFD00028DDF" target="_blank">http://digital.ni.com/public.nsf/allkb/73CB0FB296814E2286256FFD00028DDF</a>

[NoraLa]

I am using unamplified pressure sensores (0-100mV), with an Output Resistance of 2.5 kOhm. So ghosting might be the reason for my noisy signal. Could the problem also be solved by using amplified pressure sensors or are there any DAQ boards that support multiple, unamplified analog inputs?

[PBear]

Hi NoraLa,
The Multifunction DAQ devices contain onboard programmable Gain Instrumentation Amplifiers to amplify or attenuate signals before interfacing with the ADC in order to maximize the resolution capabilities of your board. If you set the minimum and maximum of your range to correspond to your sensor, DAQmx will set the PGIA to the appropriate gain setting. For your board, this will be the -500mV to 500mV range. Since your board also has a -50mV to 50mV range and your sensor varies between 0-100mV, depending on the connection type (differential vs. RSE, how many wires you have coming from your pressure transducer) you may be able to use this higher gain setting