Ch-Earth Ground Isolation

[alysko]

   Dear Sir/Madam,

What is the difference between the "Channel Earth Isolation" (found mostly in newer USB DAQ products) and the other 2 types of isolation (ch-ch and bank)?

Thanks!

Regards

Albert

[samantham]

Hello Albert,

-  Channel Earth Isolation is the isolation between a board’s channel and the earth ground of the board.  Isolation is a rating of the maximum voltage differential that can occur between these two.  This type of isolation is also a part of bank and channel-to-channel isolation.

-  Bank Isolation is where groups of channels form three “banks” (analog I/O, digital input, and digital output) that have a separate ground plane from each other and earth ground. 

-  Channel-to-Channel Isolation is isolation in-between analog I/O channels and bank isolation for digital I/O channels. 

I found the screenshots in the product manuals located on the product page under the Resources tab.

Message Edited by samantham on 11-28-2007 03:23 PM

[alysko]

   Dear Samantha,

Thank you for the explanation.

Let me just re-confirm. The channel-earth isolation means that all the banks are not isolated from one another, but all of them (as a group) are isolated from the earth (PC earth). Is this correct?

Then there is another question - is the analogue ground isolated from the PC earth (say, I want to use differential inputs)?

Thank you.

Regards

Albert

[samantham]

Hello,

You are correct about the channel-earth isolation.  Yes, the AI GND / AO GND channels are isolated from the PC ground.  In the first Figure form the previous post, you can see from note 2 that Vc includes AI GND.  In addition, there is another resource for a USB isolation diagram.  The link is provided below and the diagram is Figure 11-1.

NI USB-621x User Manual