differential ai usb-6008

[breakthrough2008]

hello everyone, i'm new to labview. i have two questions about ni usb-6008. first, can anyone tell me how to configure 6008 for differential ai in the block diagram? second, the manual of 6008 says it has a 1.4v raed when its ai is short-circuited, so should this 1.4v be counted when i measure voltages in actual experiments?

[david.bolt]

Hi Breakthrough

Im trying to understand your configuration problem furthur... referring to page11 of the USB-6008 manual, on the block diagram connect the positive lead to the AI+ terminal and the negative lead to the AI- terminal to accomplish the differential operating mode, as an ideal differential system only responds to the potiential difference between these two terminals, and not a ground reference. I ve included a screenshot below to help. Is this what you were referring to? I am more than happy to help furthur with the configuring of the 6008. With reference to your second problem, can I ask why you are wanting to implement a short circuit so I can help furthur? Many thanks.

Regards

David

Applications Engineer

National Instruments

 Link to manual:

http://digital.ni.com/public.nsf/allkb/7D8EDCD0C3887EEA86257075004CE733?OpenDocument

[breakthrough2008]

thank david. maybe i did not make it clear. for the first question, i mean how to configure differential ai input in a vi block diagram. for the second question, i mean whether there is a constant shift in 6008 ai input measurement. the 6008 manual says its ai circuit is different from other a/d converter circuit. i remember somebody said even if its ai terminal was short-circuited, there was a constant 1.4v reading in ai measurement. so in real ai measurements, how should i interpret the ai measurement reading in my vi?

[Dennis_Knutson]

If you are using the DAQ Assistant, there is a selection for differential. If you are using the DAQmx Create Channel, there is an input called 'Input Terminal Configuration'. Right click and create a constant or control.

Turn on context help or click the Hlpe button on the DAQ Assitant.

And you trust this 'Somebody' ? Why?

[david.bolt]

Hi Breakthrough

Thanks for replying. I agree with Dennis Knutson's post, please try this and select differential mode in the drop down menu. I have included a screenshot of where this can be located below. The short circuit voltage of 1.4V is incorrect as this voltage varies with the input signal that is used. Please send me your code so I can help furthur as I dont understand why you are wanting a short circuit voltage.

Many thanks and hope to hear from you soon

Kind regards

David

Applications Engineer

National Instruments UK