NI 9208 multichannel reading issue

[hrwang]

I have two sensors give 4-20mA signal. They share same 24V power supply, I wired 24V to vsuply of NI 9208, connected the positive of the sensors to vsuply as well, negetive to the channels and commen of the power supply to the commen of the card. I don't see anything wrong with the wiring. I choose one measurement on demand.

Here is the strange part. I can read two sensors correctely if I read them one by one, say, you test the currents using NI Max one channel a time, the readings are correct. However, if you choose to read them by using ONE DAQ assistent block, both current became same values. But if you choose to read them by two DAQ in consective frames, the values are right.

Any explanations?   

Thanks,

[hrwang]

If I read two channels separately, they read 8.7 and 12.6 mA respectively. If I read them together, they read same, 8.7mA. 

No replies?

[Spicy_Mystery]

Hi hrwang,

I think you may need to use the Select Signals Express VI, or a Split Signals node, to divide the outputs from the DAQ Assistant.  Is this pertinent?  If not, then please help me get a better idea of what is going on.  Feel free to include a picture of your code.