Downward voltage spikes noisy NI - 9215

[tg94]

I am trying to collect data from a humidity sensor (Testo 6621 - https://www.testo.com/pt-BR/testo-6621/p/0555-6621) with NI 9215, but I am having a lot of downward voltage spikes noisy (as can be seen in Fig. 1). I tought it could be a problem with ground wire as I already read here before, but I tested, and it is ok.
A second tought was that the problem was with humidity sensor. However, it is sending the correct voltage but when it cames to NI-9215 he get the downward voltage spikes noisy.
Can someone help to solve this?

[wiebe@CARYA · Accepted solution]

No expert, but it might help if you ground the other inputs (if not already grounded)...

[FloresFe · Accepted solution]

Hey tg94,

For troubleshooting signal problems, this document is a great reference: 

Troubleshooting Offset, Incorrect, and Noisy Readings of NI Multifunction DAQ
https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z000000P9K1SAK&l=pt-BR

In that article, you can find the one below:

Field Wiring and Noise Considerations for Analog Signals
https://www.ni.com/en/shop/data-acquisition/measurement-fundamentals/field-wiring-and-noise-consider...

There, you'll find several considerations about dealing with noise signal and why they may happen. Please, go through the article the check what fits to your system and application. One I ask you to review carefully is the  Measuring Floating (Nonreferenced) Sources section. I believe that your noise might be coming from the fact that both your signal source and measurement system are floating.

Could you review that and give us a feedback you were able to minimize the noise?

Have a great week!