Bad signal problem using single ended inputs with LabView

[Deke1955]

I have 6 volts 50Hz peak to peak on single ended signal inputs that should read between 150mV to 250mV any ideas about what is happening?

[Wayne.C]

Can you describe your setup a bit more?  I suspect you have not properly referenced the signal you are reading to the common of the input.

[Deke1955]

Centrebolt - thanks for your interest. Unfortunately, a colleague is trying to set this up and he is over 100 miles away. He is taking fotos of the setup and sending them to me next week but, sounds like he is taking the single ended signals to their respective channels and grounding all the 0 volt lines from all single ended channels to the board ground. This does sound correct to me and can only think he maybe has a connection problem.
Originally he thought he had some mains inteference and countered this by connecting a bias resistor from the 0 volt side of the signal to ground. Now this sounds a bot odd because he shouldn't have to connect bias resistors between 0 volts of single ended signals to ground, they should just go straight to ground.
So this takes us back to the possibility of mains interference still being their. He apparently tried grounding the metal cabinet to the system ground as well to make the cabinet act like a Faraday cage but, this did nothing.

I am going to travel later next week to have a look at the setup but, I am looking for any ideas before I go.

Thanks again for any help in advance.

Deke.

[Wayne.C]

Deke,

One way to troubleshoot the interference is to start by using one channel to read the common signal by connecting a single ended input to the same exact point on the board as the 0V lines.  It should read exactly 0V with no noise interference.  If you see noise, you know that a signal is being induced into your instrumentation.

Also, if the commons of the single ended inputs are physically connected inside your DAC device, only make one connection between the DAC common and the common on the board you are measuring.

[Deke1955]

Thansk Centerbolt will keep fingers crossed it is something simple.
I intend taking another datalogger with me from a different manufacturer that I am familiar with using as a comparison just to make sure the signals coming to the NI stuff are actually okay.

Thanks again for your help.

[Seamus_C]

Hi Deke1955,

What DAQ device are you using.  How is this device connected to your computer.  when you go onsite try to get screen shots of any problems you see and post them on this fourm.

Seamus

NIUK