Hi Neal,
Thanks for your reply. Well this is a discovery for me. It seems your sales engineer are not fully aware of this fact.
I wanted a card with analog output of 18 bit or higher resolution and equivelant accuracy. We did come across 628x. however since the outputs are only 16 bit resolution we rejected that. and the sales engineer stressed me on purchasing 4461 for the purpose. The NI sales engineer told me that the accuracy of this card is in few nano volts and that it can sense the change of voltage within few nanovolts accuratly. also it can generate signal with similar accuracy and resolution.
I also told them my requirement of being able to generate signal between 6 to 8 v with minimum 18 to 20 bit accuracy. That time the engineer replied that it can be done as it provides DC coupling and hence you can generate the signal in the said range with this card (I made him aware that i am not from electronic background and that by DC coupling does he mean that i can set the offset voltage internally? to which he replied yes).
For last two days i was trying to figure out the reasons of huge noise (+/- few mV) that i was sensing at the input and i was doing all possible checks with my other circuits. I never knew that this was due to the worse accuracy of the cards that i bought.
Now please put urself in my place and advice me what to do? I am finding myself helpless after burning about 9000 USD for those cards.
Alok.