Setup discrepancies between traditional Daq and DAQmx with SCXI1120D module and SCXI1327 terminal block?

[CJW1800]

Hi,

I posted previously about setting up a SCXI 1120D module in DAQmx (http://forums.ni.com/t5/LabVIEW/SCXI-1120D-setup-using-DAQ-assistant/m-p/2412476#M745405) and I have recently come back onto this project. I am now trying to complete the process of converting existing Traditional DAQ code into DAQmx code.

I can now read the signal from the SCXI 1120D using Traditional DAQ and DAQmx, but they are not reading the same value. I'm pretty sure I have the setup the same for both acquisition types, see details below, the only parameter I'm unsure of is whether setting the Accessory Config. Attenuation to 100 is the same as setting the Terminal Block Gain to 0.01?

SCXI 1120D Module with SCXI 1327 terminal block

Traditional system setup

Gain = 0.5
Filter 4500Hz
Terminal Block Gain = 0.01

Reading = 20.6v

DAQmx system setup

Gain = 0.5
Filter = 4500Hz

Accessory Config.

Attenuation = 100

Reading = 9.99v

If I set the Accessory Config. Attenuation to 1, I get a reading of 0.205v, approximately 100 times less than the Traditional DAQ reading.

Can anyone suggest anything to try?

Cheers

Chris

[Supreeth.K]

Hi CJW1800,

The attenuation setting is the same as the terminal block gain setting as shown in the document here: http://digital.ni.com/public.nsf/allkb/0271A75DFB30BD0586256F3300567984?OpenDocument . But, it is important to make sure that you match this setting in the hardware (scxi-1327)

What is the gain setting that you have mentioned? Is it the software channel gain setting for the 1120D in MAX? If so, have you made sure that the gain calculated from stage 1 and stage 2 gain settings of your jumpers on the 1120D match the software gain setting? The formula for the gain can be found on pg 2-11 in this document: http://www.ni.com/pdf/manuals/320425d.pdf

Thanks and Regards 

[CJW1800]

Hi Supreeth,

Thanks for your reply and apologies for the delay in mine.

I'm not sure why I need to worry about anything to do with the hardware? I am not making any changes to the hardware, all I'm doing is replacing the Traditional DAQ with DAQmx. Everything works perfectly with the old Traditional DAQ, but when I read from the same channel using the MAX setup as in my previous post it doesn't.

The gain setting that I mentioned is the gain drop down box in the configuration pop up for the module.

Thanks

Chris

[CJW1800]

Good morning,

I've made a bit of progress on this, but could do with some explanation of what's going on.

Some additional information about the channel setup, the max and min limits that I have used when configuring the channel is 10v and 0v respectively.

With my traditional setup as described in my first post (and the additional info above), my raw readings range from 10v - 52.5v, which I can't explain if my input range is 0-10v?

I'm now able to read via my DAQmx setup by changing the input range of the channel from 0-10v to 0-55v.

Can anyone help explain what is going on?

Thanks

Chris