Sine wave noise signal on analogue when nothing connected

[KWaris]

Hello Everyone,

I have been pondering over the problems of noise I had always seen on analogue signals but never got rid of it. Today I was just learning about scan engine and I found that If I add my analogue module under cRIO target for the scan mode, and deploy the variables and see the analogue values on the distrubed manager, these continuously changing analogues on the second decimal are not really random but if we see the graphical trends in the distributed manager, these continously changing analogue values for any channel actually make a perfect sine wave vertically shifted by -3.1V.

These readings I have found using NI 9205 module with no transducers/sensors connected on the modules terminals. I just have the cRIO on my desk with all the modules inserted into the slots. I am sure that the transducer signal is always superimposed with this sine wave signal. What is the reason for this sine wave signal when nothing is connected. Can I get rid of it ?

Thanks for reading

Kind Regards

[asbo]

Have you analyzed it at all? What frequencies are present in the noise?

[BrentonLang]

Do you have fluorescent lights in the room? They transmit the mains frequency rather well. Most countries have an alternating current frequency of 50Hz, but I think America is typically 60Hz.

Might be your issue ??

If the analog input reference is not grounded, the voltage range of the noise can be quite noticeable.

Edited June 28, 2012 by BrentonLang

[Tim_S]

Do you have fluorescent lights in the room? They transmit the mains frequency rather well. Most countries have an alternating current frequency of 50Hz, but I think America is typically 60Hz.

North America and northern South America are 60 Hz. In general, the rest of the world is 50 Hz.

Tim