NI 5112 to 5114 DC Offset of 50-60 mV

[aparab]

thanks Nathan,

I have tabulated a few  observations  and queries

1.     so if I look at the DC  Accuracy , the 2% margin for Vertical Offset 2.5V Ofset  2% -> 50mV) is the spoilsport .  The signal I really need to measure accurately is 700mV  & here I am getting ±66mv Tolerance, i.e. 10%     that's a difficult situation for us. 

2.  Can a  voltage probe help somehow

3. is there any alternative  PCI card  available which is a work around for this issue

regards

Akshay

[Henrik_Volkers]

If you need to measure the 700 mV , 20 kHz AC signal , why not switch to AC mode?   

How does the signal look like? 

And what are the key values you need?

A picture or a vi with saved data ( just a vi with a graph showing the data and saved with 'make current values default' ) would help.

If you need the sine amplitude (and phase) have you tried the tone detection vi?  

Ah,...  are you able (or is it possible) to change/edit the software?

[aparab]

Danke Henrik,

We need  to measure the  700mV ac Signal which sits on a DC  Offser(2,5V)  &  we have to measure them at the same time.

Basically we have 2 different channels  Ch1 & Ch2 to measure,  both with  700mV + DC Offset, they carry the encoder information.  The offsets for the 2 channels can vary & hence we need the DC Offset information & amplitudes of the 2 channels.

grüß

akshay

[Nathan-P]

Akshay,

This is a perfect solution, by putting the digitizer into AC coupling mode, then any DC offsets will be removed before it reaches the ADC.  If the offset contains no vital information, this will allow you to measure the AC signal ( 700mV signal) at 0V, which will allow for the accuracy you need since you don't need to specify a vertical offset.

Regards,

Nathan

[aparab]

thanks

but we need the DC offset information at that instant of time..

[JDAILING]

the offset from the 2.5V is common mode. the 700mv change is not an offset, its a distortion.