how do I control analoge output offset

[Timmar]

Dear Labview Gurus

I have inherited some code that enables an analogue output signal to be generated with an offset.

I have tweaked it and it appears to work, much to my surprise.  I am unsure of exactly how it is doing it though.

I am wiring apfi 0 to a 5V reference, my initial expectations were to see a 5v offset.

What I want to know is why does it work. Does anyone know where I can find a user guide on this functionality.

I am using a PXI6289 and am trying to generate sub milivolt resolution signals with a 2.5v offset. (in this example, I am using larger voltages so I can measure it with a multimeter)

Here is my code

Thanks in advance

[KyleTTU]

Hi Timmar, 

Just so I can better understand your question, are you assking how the code as a whole functions or how the DAQmx Property Node for a DC Offset operates?  What I have found very helpful when trying to decipher new code is to use the Context Help by clicking the "?" button located by the search bar.  This will allow you to hover over each of the vi's and see a basic description of what they are doing.  To see further details on how they work, you can always click the detailed help link when hovering over the specific vi. 

One question I have is are you trying to write a waveform to your output?  I see you have four writes in a row, the first and last outputting zero, is there a reason for this?  I only ask because there are definitely more efficient ways of doing this and I'm curious as to what purpose this serves in the overall application.  

Regards, 

Kyle S

[Timmar]

Kyle,

Thanks for your response.

My code is proof of concept only, I was using a multimeter and the pause button to jump through the different voltage state. Don't fear, my normal code is not like that.

The onine help is OK, but I didn't know that that feature even existed.

Part 2 of the puzzle if finding an architecture diagram of how the analogue hardware does what it does.

Part 3 is the grey area between Daqmx and the hardware.

Brian P. informs me that the driver uses DAC to create the offset, Consuming the top 8 bits of accuracy.

I understand and accept this but it is funtionality that is difficult to prdict based on the absense of literature.

I hoped my posting could be educational to others and perhaps stir up a white paper that the search engine was unable to find

Kind regards,

Tim L

[KyleTTU]

Hi Tim,

One good reference I use are the white papers based on our different Series of boards.  In your case, you are using an M Series Device. Below I have linked a document that outlines the benefits and features of an M Series and may shed some light onto what you're looking for. 

World's Most Accurate Multifunction Data Acquisition Device

http://zone.ni.com/devzone/cda/tut/p/id/4869

Regards, 

Kyle S