Acceleromter strange results ( Using NCXI 1531)

[tahoang]

Hi everyone,

 I am new to LabVIEW so please ignore any stupid mistakes 🙂

 So I am using NCXI ang Meggitt 780b and pcb 302A acceleromters to measure vibration of a small structure.

I set up both accelerometers according to their spec sheet and they produce the same output when I apply the same vibration. However, when I let the accelerometer fall freely ( not touching the ground), the output is about 20-30. I am not sure which unit is used but I assume it is 'g' because I set them up using range of g and sensitivity of mV/g. This happens to both accelerometers.

 Does anyone here has the same issue or understand why this happens?

 I would really appreciate any answer!

 Thanks.

[tahoang]

and btw, I checked using run option in the set up section

[Eric-E]

Hello,

Although I'm a bit unclear on how exactly you are acquiring the signals (in LabVIEW, but how so?), I would expect there is something configured incorrectly. The raw signal will be in voltage (mV) going into your DAQ card, but we commonly use acceleration tasks which may be configured in MAX (Measurement and Automation Explorer) to get a more meaningful value from this raw data. In this case, you should start by creating a task in MAX first. You can see the graph output in MAX to make sure everything is working correctly before transitioning to LabVIEW.

When a MAX acceleration task is used, the output we would read on the graph in MAX will be in G. It uses the scaled units that we select in the configuration tab: 

This outlines how to create a task with multiple channels if your sensors require different settings:

 http://digital.ni.com/public.nsf/allkb/F28C6BD62B0ED68F86257A6B00733E0E

[Henrik_Volkers]

Maybe because ICP (or IEPE)  sensors usually have about 10V DC offset ?