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EVAL-ADuCM355QSPZ - 2 Wire Impedance Conductivity

Category: Software
Product Number: EVAL-ADuCM355QSPZ

Hi all - Help needed

I am trying to do a 2 wire impedance measurement to read conductivity. 

I am using pins CE0 and AIN1 with M355_Impedance example code. This example code uses AC voltage correct? It works well when my resistance is below 60k but anything above that, the impedance reading is incorrect (Ex: 1Meg showing as 500k).

I know that I have to adjust TIA and the PGA to not saturate the ADC and get incorrect impedance reading. How do I do that and how do I know what to set it to? Does this mean I have to manually change these before measuring different conductivity liquids? Does it not do it automatically (see below CN 0428 circuit note)? Also in this example code - how do I change the AC frequency and dacvolt peak to peak value?

Thanks in advance