Liquid EC meter amplifier. Need help understanding schematic.

[anthonyone]

Hi guys,
im trying to understand the amplifier configuration circled in red. I was probing around an off the shelf EC meter for arduino since it died due to short in the caps. I tried making a schematic by probing the pcb and i couldn't understand the amplifier config circled in red.
Any help is appreciated.
Thanks.
 

[TimFox]

I didn't analyze the circuit carefully, but it looks like a precision rectifier or absolute value analog computation circuit, where the diodes only switch current and their voltage drop does not contribute an error.
Books on op amp applications usually discuss these circuits.

[eblc1388]

As TimFox has mentioned, the circuit is a form of precision rectifier circuits using 5 resistor of equal value. It is the same topology(albeit reversed output polarity because of the diodes) as the blue square marked circuit shown below.

For its complete theory of operation, you can take a look at the following link:
https://www.electronics-tutorial.net/analog-integrated-circuits/precision-rectifier/modified-precision-full-wave-rectifier/

Please also take note of  possible mistakes in the schematic:
1. the part number of another IC. The IC should be CD4060BM instead.
2. the EC_OUT polarity is negative w.r.t. circuit GND. This is in conflict with output diode D6 unless output level never exceed -0.6V. Please confirm polarity of diodes D8 & D9

[anthonyone]

2. the EC_OUT polarity is negative w.r.t. circuit GND. This is in conflict with output diode D6 unless output level never exceed -0.6V. Please confirm polarity of diodes D8 & D9

eblc1388 thanks a ton the polarity of the diodes D8 and D9 was the issue. I built the entire circuit on a breadboard and it works!!!

I didn't analyze the circuit carefully, but it looks like a precision rectifier or absolute value analog computation circuit, where the diodes only switch current and their voltage drop does not contribute an error.
Books on op amp applications usually discuss these circuits.

Thanks TimFox i started learning about full wave precision rectifiers. Is there any book in particular which is noob friendly?

[TimFox]

A classic is Jung's "IC Op-amp Cookbook", which has gone through several conditions.
 https://www.abebooks.com/IC-op-amp-cookbook-Jung-Walter-G/30081731328/bd?cm_mmc=ggl-_-US_Shopp_Trade-_-used-_-naa&gclid=EAIaIQobChMI046D68aa6gIVC77ACh3vzAtdEAYYAiABEgJH7fD_BwE