Problem about set-up for multi-channel pressure data collection

[hanwei]

Hi all:

I am a beginner of NI DAQ.

Now i meet some problems about pressure signal collection (power supplier for pressure transducer is 24v).

firstly, I use 500ohm resistor to transfer the current signal(4mA-20mA) to voltage signal, and then i want to use SCXI1002 and PCI6040E to test these voltage signals.

because the voltage signal cross the resisors are floating signal, so I use two bias-resistors.

But the problem is :

  when I collect one channel pressure signal, everthing is fine,

  but when I want test 2 or more channel pressure signal, the voltage is wrong! (too high).    (I build another 2 bias-resistor for 2nd channel),

 does everybody knows how to set-up multi-channel bias-resistor ?? or is there any problems in my system??

 the electriccal schematic drawing is attached here, anybody knows how big of bias resistor that I should use for multi-channel?? it is very weird, because when I try to change the value of bias resistor, the corresponding voltage is also changed,

[RT4CY]

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