DAQ Noise with Laptop

[jeffdillon]

I'm directly measuring the voltage from a 1.5V battery for example
using differential input with unshielded 1m cable from the terminator
board to card. Even using the Test Panels with my DAQCard 6024-E
PCMCIA card in my laptop I see lots of noise, +/- 1 volt or more. When
I remove the AC power and just run on the laptop batteries, the noise
is reduced, but still evident. In my vi's I get around it by
averaging, but is there any other way to reduce the noise?

Jeff

[Ben]

It sounds like you are trying this in a an extremely noisy environment!

1m of unshielded wire could induce that much noise only if your environment is real bad.

MOST laptops will float rleative to ground. Even when plugged in. Try running a ground wire to the AI GND input to see if that helps. The diferential input is good up to the CMR level of your device.

Ben

[Ben]

Additional thought on wires.

try twisting them to see if the noise level goes down. If so use use shielded twisted pair cable to shield from your noisy environment.

Ben

[BiG-C]

A battery is a floating signal source, it has an isolated ground-reference point. If you want to use differential (diff) analog input mode you must tie the ground reference of the battery to your DAQCard analog input ground to establish a local or onboard reference for the signal. E.g. if you have +ve and -ve battery terminals connected into ch0 and ch8 input respectively, place a wire from ch8 to aignd.

Alternatively, you could just use single-ended ground referenced (rse) mode, where you just connect +ve and -ve battery terminals into an analog channel input and analog input ground (aignd) respectively.

I have attached a jpg of summary of available analog input configuration for DAQCards, it was taken from an NI user manual for E series DAQCards.

Not su
re if you know how to change the input configuration, but it is done through MAX. When you go to Devices and Interfaces branch and right click your device and select Properties, then go to the AI tab and it is under Mode menu item.


Gluck!