Connecting 2 low-voltage sensors to LabJack U3-HV | LabJack
 

Connecting 2 low-voltage sensors to LabJack U3-HV

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nnguyen
ngoc_nguyen1711's picture
Connecting 2 low-voltage sensors to LabJack U3-HV

Hello, 

I want to connect a pressure transducer to FIO6 and an oxygen sensor to FIO5 of the LJ U3-HV. The pressure transducer (15 PSI-D-CGRADE-MV) has a max output signal of 90mV, and the oxygen sensor ( has a max output signal of 400µA.

My question is: Since the output range of the sensors are very low, would the U3 alone work just fine or do I need an LJTick? 

I have attached the specsheets of both sensors, along with the simplified connections diagram that I am planning to go with. Could you review them and help me with this, please? I would really appreciate it. 

Thank you!

LabJack Support
LabJack Support's picture
For your oxygen sensor, the

For your oxygen sensor, the stuff to the left of the transimpedance amplifier in your diagram does not matter much to us.  What we need to know is what sort of voltage signal will the transimpedance amp be sending to the U3.

 

For your pressure sensor, start here:

https://labjack.com/support/app-notes/pressure-sensors

You have a raw bridge sensor, so continue here:

https://labjack.com/support/app-notes/bridge-circuits

A bridge circuit provides a differential signal, but as long as your power supply is isolated your single-ended connection (FIO6 & GND) should be okay.  The resolution of the low voltage analog input is about 0.6 mV, which does not give you a lot of steps but you will see your signal change.  Another issue is that you might not be able to measure the lower output voltages from your bridge:

https://labjack.com/support/datasheets/u3/hardware-description/ain/analo...

The simplest solution would be an LJTick-InAmp.