daq assistant displays distorted signal

[Lahan]

Hello, I am trying to use Daq assistant to display a simple sine wave, 100hz, coming from a function generator in continous mode.  What I actually got was a distorted sine wave.  I also tried creating another daq assistant that takes the originals read data and outputs it to a scope and it too is distorted.  Is this normal?

Taking data and displaying in "N" sample mode created an undistorted sine wave.

My setup for the read DAQ Assistant is in the attachment. 

Device is the DAQCard-6062E (PCMCIA).

[thh25]

Hello

I'm quite new to DAQs but I also had a distorted signal from a function generator so I added a resistor between the ground terminal (number 20 dependent on which channel you use) and the sheild.. This worked perfectly and dont have any problems. I guess this is dependent on the card and connector block. I have a PCI 6010 and the recommended unshielded connector block.

Hope this helps

thh

[Lahan]

Thanks for the reply.  What value did you use for your resistor and by "Shield" do you mean the connector block casing?

[Joe D.]

Hii Lahan,

The problem that both of you are having seems to be related to a ground loop. I highly recommend that you look at the Field Wiring and Noise Considerations for Analog Signals. As for the resistor values, generally values between 10 kΩ and 100 kΩ work the best but I do a little experimenting to see what values work the best for you. 

[Lahan]

Hello folks,

It is not grounding.  The problem appears while using XP professional SP3, labview 2010.  Tried it on another laptop with the same operating system and the problem was there too, labview 2009. 

So I had a go at a windows 7 laptop with labview 2010 and I got an undistorted wave.

Strange. 

[thh25]

I didn't see any difference with different OS and systems. As for the resistance, I just put a random one, try some out, maybe above 1kohm, I'm guessing.

I had the resistor placed between the ground wire coming from instrument to the shield port. The ground wire was placed in the negative terminal (differential used). Not sure if this arrangement makes sense but it worked like a charm.

[Lahan]

Tried the resistor ground method, tried to earth ground.  Same results.  Only way I can get rid of the distortion was to use win 7.  I don't know why that is to be honest.

[Joe D.]

Hi Lahan,

I still think that this might be a wiring issue can you post a wiring diagram? Also do you get the same behavior out of test panels in Measurement and Automation Explorer?

[JÞB]

RSE would be a clue

(Nice work Joe)

[Lahan]

Test panel in MAX would also show that distortion in continuous mode, in fact that was where I did my very first capture with NI software and an NI daq, nothing wrong with N sample mode.

Attaching the wirings I've tried