DAQCARD 6024e problems with laptop battery power mode

[aeroterp]

I have a DAQCARD 6024E on a Gateway M350XL laptop running Windows XP Pro. I've connected a 5B16 channel backplane with 10 strain gage inputs and 4 frequency inputs to a NI SC-2050 which connects to the 6024E through 10 ft of SCSI3 cable and a SCH6868EP.

I seem to have a problem that is the opposite of everyone else. When I plug my laptop into the building's grounded power supply (which is a 3-pin grounded connector), I am able to read perfectly clean signals on my analog inputs. However, when I run on laptop battery or if I use a DC-AC inverter to power my laptop (neither of which are grounded), I see a lot of high frequency noise on my analog inputs. I'm of the impression that its definitely a grounding issue.

I read on a different thread that the laptop's SpeedStep technology could be responsible for it and I tried to disable it by switching to the Always On mode and also tried using Speedswitch XP, which forces the processor to run at maximum performance. It didn't do anything to change the problem. So, I'm convinced that it is a grounding issue.

Can you suggest any workarounds?

[sergesl]

Hi,

Following is a great tutorial on ground issues and how to resolve them. http://zone.ni.com/devzone/conceptd.nsf/webmain/177A8B29FEDC0F5886256FA90083C0F8

[WM_John_Weeks]

There's a great book about grounding and shielding:

"Grounding and Shielding Techniques in Instrumentation" by Ralph Morrison.

http://www.amazon.com/exec/obidos/ASIN/0471245186/qid=1116000890/sr=2-1/ref=pd_bbs_b_2_1/102-4413716-9718501

It goes into all the problems in great detail, clearly written. Of course, the comment in the lab when I bought it 20 years ago was, "and you know, he actually *reads* this stuff". But it's a topic that anyone who uses electronic instrumentation *has* to be aware of.