NOISE REDUCTION FROM BNC Connector 2120

[Stame]

I connected the analog output of the BNC-2120 to channel 1 of Tektronix TPS2024 ( Digital Oscilloscope) using BNC cable. While unconnected the scope doesn't show any noise. I tested it with other function generetor (grounded) and the noise is not there. But when the BNC-2120(powered when connected to the DAQ card inside the laptop), the noise level of about 10 mv is displayed in the scope. I used 1X voltage probe for this scope(which I believe is the appropriate).

Is there a way to reconfigure my VI, so that I can use ramp up- hold and ramp down in one output of BNC-2120 and and full 16 bits sinusoidal in other output of DAQ Acquisition and combine them to get the signal pattern that I am looking for? If so, any kind of help will be highly appreciated. I tired to do so but the DAQ Acquisition kept on giving me error( number of samples in channels are not the same ...)

[mikeporter]

Just out of curiosity, does the noise level change if the laptop is not plugged into the wall (i.e. running on battery)?

MIke...

[Stame]

The laptop is running on direct power supply and the cord is grounded too. The noise happens only when the DAQ card (powered by laptop) is connected to the BNC-2120 .

[mikeporter]

Ok, I was just thinking about an application I had once where we were working in a building that was originally built in the early 1940s.

I had this strange noise in the system that I couldn't track down. I thought I was protected from powerline noise because I was getting power through a UPS that filtered out line noise - or at lease was supposed to. I found the problem one day when one of the other guys was working behind the equipment rack and inadvertently pulled to power cord for the UPS from the wall. As soon as the plug came out, the UPS switched over to battery - and my noise evaporated.

Turned out later when the space was remodeled that while all the power runs to and from the room were wired correctly and the neutrals were tied to each other, they were only connected to earth ground through the shell of the power distribution box enclosure. Unfortunately back in the 1940s when the box was originally installed, the attitude was (to paraphrase an old movie), "Grounds? We don't need to stinking grounds!"

Aside from the noise, we were lucky that no one had gotten killed in the past 50 years!

Mike...

[johnsold]

What happens if you connect a 10000 ohm resistor across the AO terminals?

What happens if you connect the scope to a ground point on the BNC-2120?

Lynn