How do I connect a 2-wire voltage source to the BNC 2110?

[Jim B]

I've connected the 2 wires (+,-) of my voltage source to the inner and outer wire of a BNC coaxial cable and can read the proper voltage with a multimeter at the BNC end of the cable but cannot read the proper voltage (off by a considerable amount) using single-point and continuous voltage measurement vi's when the BNC cable is connected to the BNC 2110 (BNC 2110 is connected to the PCI-6110E DAQ).

[JaredA]

Hey Jim,

Just to try and clarify some things, is there any particular reason that you are connection a voltage coming from 2 wires to a BNC cable, and then connecting the BNC cable to the BNC-2110? Wouldn't it be better off if you connected the 2 wire supply into a terminal block that is already configured for that type of connection?

Back to the issue at hand... the voltage is being passed correctly through the BNC cable as you can tell with a multimeter. But the values that you measure on your computer seem to be off.

It sounds like you are using LabVIEW to display the signals. It is recommended that when troubleshooting your system that you use the Measurement and Automation Explorer to display the signals coming in through your card. This helps to separ
ate any possible causes of error in the software or in the hardware. It might be the case that you have the wrong input terminal configuration set, which thereby is giving you the wrong values.

My initial recommendation is to go into MAX and run a Test Panel under DAQmx with that device. If you are unable to get the signal acquired correctly in that, then the problem is with your hardware and you are going to have to either reconsider your setup or try to reinstall the card/driver. If it is working, then the problem is with the LabVIEW program. When first starting off in LabVIEW, make sure that you use a shipping example that was tested before and known to work.

Go to http://www.ni.com/support/install/ to get started troubleshooting your DAQ system.

I hope this information gets you on your way.

Jared A
National Instruments

[Jim B]

Jared,
Thanks for your comments. The reason I'm not using a terminal block as you mentioned is that I have an acoustic device connected to the BNC-2110 and would like to connect a lasers output so that I can collect data from both insturments simultaneously. The acoustic device is BNC configured and is controlled through a pulse/receiver that interfaces with the BNC-2110.

I don't think there is an issue with the hardware or software since the acoustic system works fine on all four channels. I also get the proper signal with the acoustics using the test panel and a Labview program that aquires the acoustic data.

The BNC-2110 connectors bring in the voltages by using the center pin as one terminal and the outer casing that the BNC cable connects to as
the other terminal right?

It seems as though the BNC-2110 connector is not seperating the +- components of the incoming signal.

Any other suggestions?

Thanks,
Jim

[jeremy_rutman]

From my own similar problems I can say that whats happening is the bnc2110 for

some unfathomable reason connects the negative terminal (bnc shell) to ground

thru a 5k resistor when you are in 'FS' (floating source) mode.

I can't figure out a solution since if you dont use FS mode but rather ground referenced source 

(to disconnect the 5k resistor to ground) then the bnc2110 manual (p6) says : you should

connect the negative terminal (bnc shell) to ground yourself!

Pls let me know if you have found a soln to this.