DAQmx configure a module 9205 for differential readings

[lmd2]

when I try to select a channel (cDAQ1Mod3/ai0) from the physical channel (I/O) drop down there are 32 channels listed, I need to configure the module for 16 differential channels but can't find where this can be configured. Ultimately I need to read 3 modules simultaneously, a 9205 reading 16 pressure transducers (3.3V max), a 9211 reading J-type TCs, and another 9205 configured on the fly to read millivolt sensors (RPMs, torque, etc). because config is done on the fly, the tasks are not predefined in MAX (and everytime I try to read two tasks continuously in a while loop I get error -50103: The specified resource is reserved). I found an example for reading two tasks asynchronously (not what I need) but it doesn't work anyway.
any help will be greatly appreciated
thanx
lmd2

[xseadog]

hi lmd2,

have you used MAX to test functionality?

On the test panel -Analog input -one can select the three types of configuration Differential, NRSE & RSE

That should solve the problem.

xseadog

[lmd2]

thanx,
on the test panel, the input configuration is set at Differential; the channel name drop down still shows cDAQ1Mod1/ai0 - 31. If I select a channel > 15 I do not get an error, but read what appears to be open V (nothing is connected to the module at this time). Intuitively the control should not show > ch 15. How do I know if I am reading differential on ch 0 - 15 and how can I know an EXE will retain this test panel setting. Isn't there a way to set mode within the code?

[xseadog]

Hi again,

if you select a channel greater than n/2 ( n=max number of channels) then the option to select Differential is disabled.
Thus the software will not allow you to 'fool it'

xseadog

[lmd2]

alright, thanks for your help,
if I understand you correctly, as long as the user selects channels =< 15 (the EXE will not permit otherwise) a differential reading will be made. somehow that doesn't feel definitive enough but when we get the sensors hooked up I'll prove it out.
thanks for your time
lmd2

[Mark_E]

Hi Lawrence,

The differential channels are not assigned as 0-15 on the NI 9205. They’re actually paired in groups of 8, so the differential channels are 0-7 and 16-23. This is in the NI 9205 Operating Instructions and Specifications (February 2008) manual under the “Differential Measurements” section. You will notice that the pins are physically located side-by-side as a pair (seen in MAX device pinouts or the above manual).

xseadog is right when he said that if you choose a non-differential channel the option for differential disappears. This is true when using test panels or an Express VI. If you are doing this with the discrete DAQmx VIs, LabVIEW will allow you to choose any channel from the drop-down. However, if you are selecting a non-differential channel number with a differential configuration, you will get an error.

I threw a VI together to show how you could choose the 16 differential channels and the configuration of the DAQmx Create Channel VI. I hope this helps.

[lmd2]

thanx,
as they say, 'a picture is worth a thousand words'
it is always much clearer to see an example
thanks a lot