Hooking up sensor to DAQ

[Monse]

ok, here's my thing:  I have a DAQ (USB 6225) and I'm using 27 single ended inputs on it right now... and it's working great.  I've got some acceleromters, powered by a 12Vdc power supply, I have the negative end up that power supply going into my common channel of the DAQ and then the 27 signals going into 27 inputs....

Here's my question:  I am going to be hooking up 3 more accelerometers, which I do no have access to, to this DAQ, the information given to me is that each acceleromter will have 2 wires, a signal and a common.... I just have to make room for them in my code and include some wires for them to hook up to and that's it... but, I don't know if I should:

1) Use differential measurement and input the signal and it's corresponding common into 3 different pairs of differential input channels

2) Use single ended (like I have for the other 27 accelerometers) and just connect these new commons to the rest of my common channels on the DAQ

The only thing that makes me iffy about (2) is that... my original 27 accelerometers share a common power supply, the new ones are going to be on a different power supply... is it ok to bunch the new commons with the old ones?  Or will that introduce some kind of ground loop or voltage offset?

Basically, since I'm not going to have access to the new accelerometers, can anyone suggest how I should set up the DAQ to handle the new inputs?

Much Thanks

M.

[Hillman]

Hi Monse,

Thanks for the post!

You would most definately have a potential for a ground loop issue.

Your suggestion of doing some differential is good, or you could possibly use an DAQ device also.

Kind Regards, 

[Monse]

Really?  I just called NI and they said that hooking up the commons together would not be a problem.... 

If I were to go differential, I would still need to tie my commons together right?  Because doesn't a differential signal still require a common reference point.... even if it the common reference is the and the negative differential input are both the same common from the signal...

[Hillman]

Hi,

I would recommend using the advice if you spoke to someone in person - I haven't looked into this enough. 

But my advice came from a collegue and some previous service requests.

Did you speak to someone in the UK Office?

Have you tried the setup recommend?

Kind Regards, 

[Monse]

No, I spoke with someone in the US office.  The thing with this is that I will not have a chance to try it in person, I just have to build up my software and leave some open positions for the new sensors to be hooked up in the future...

[Hillman]

Hi Monse,

Thanks for the reply.

I would suggest doing your measurements all as differential, as this is the best option for noise as well as the potential for ground loops. 

Kind Regards, and Good Luck with it all.