U3 and LJTick-InAmp
Posted 12 July 2011 - 12:20 PM
Posted 12 July 2011 - 09:57 PM
What are you using for excitation voltage? 12V will be no good for the LJTIA. Rather you should use the 2.5V reference on the LJTIA:
Using 2.5V excitation, you will get 18.75 mV at rated pressure, so from the signal range tables you would use Voffset=0.4 and Gain=x51:
You will want to measure the actual offset of the applicable channel on your LJTIA, not just assume 0.40 volts. If the input is 0 to 18.75 mV, the output will be about 0.4 to 1.35625 volts, so sounds like you will need to change your software.
Posted 13 July 2011 - 08:27 AM
Posted 13 July 2011 - 08:41 AM
If you use Vexc=12V and connect the supply minus to U3 GND, you will have a common-mode voltage of 6 volts. From the LJTIA signal-range tables, and the AD623 calculator that is linked, you can see that is no good:
If you know the 12V supply is isolated from the LJTIA, you can not connect the supply minus to GND but rather connect signal minus to GND (also connected to IN-). This gets rid of the large common-mode voltage.
Posted 09 August 2012 - 12:49 PM
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