Wiring USB 6218 to a given temperature transmitter

[masch++]

Hi all,

we own a USB 6218 and want to measure temperatures using a "Enda MU-PT100-U010-50/100" temperature transmitter. A data sheet is attached to this post.

There are three terminals at the bottom of the transmitter:

-"4": 0...10 V

-"5": GND

-"6": +10...35 V dc

From my understanding, the transmitter needs an input voltage of e.g. 24 V dc between terminal "5" and "6". We allready have a fitting voltage source. 

The transmitter seems to encode the temperature to a 0...10 V voltage between  "4" and "5".

Now my question is:

Can I connect terminal "5" (which is connected to a 24 dc voltage source as I explanied) to an "AI GND" (and "4" to an AI) on the USB 6218 without damaging it?

This question might sound weird, but I just wanted to make sure I don't destroy our expensive equipment 😉

Thank you very much and kind regards

Christian

[Martin.Peters]

Hi Christian,

thanks for your question. It's always good to be cautious. 🙂

From the document you provided it is safe to say you may connect the device to your USB-6218. Please be aware though that the AI GND connector is used for referenced single ended (RSE) measurements. Since your temperature transmitter is a grounded signal source and does not include a galvanic isolation between supply voltage and signal output, it is recommended to perform a differential measurement (DIFF) or a non-referenced single ended measurement (NRSE). Please refer to your user guide on how to wire signal sources starting page 4-36:

NI USB-621x User Manual - 371931f.pdf
http://www.ni.com/pdf/manuals/371931f.pdf

For additional insight on setting up measurement systems, find more information here:

Field Wiring and Noise Considerations for Analog Signals - National Instruments
http://www.ni.com/white-paper/3344/en/

If you have any further questions let me know.

Cheers

Martin

[masch++]

Hi Martin,

thanks a lot for your reply.

Some months later I struggle once again with this project.

Additional to the mentioned temperature transmitter (which gives 0..10 V) I want to connect two further sensors to my USB 6218. Those give 4..20 mA signals.

I connected the sensors (with 500 Ohm resistors) to AI2 / AI10 and AI3 / AI11 as I plan to measure the signals differential.

As long as I measure only those two signals, this works fine. As soon as I connect the temperature transmitter to the DAQ the signal becomes very noisy (in fact, it is sufficent to connect only one cable of the temperature transmitter to any AI to ruin the measurement).

I allready tried to connect all '-' - cables to the AI GND. This did not help. Could this have something to do with missing BIAS-resistors? If yes, should I aim for 10 kOhm resistors? And how should I exactly connect them to AI GND?

If not, what else could be the reason for my problems?

kind regards

Christian