Circuit Explanation

[Vikky]

Hi all,

I am debuging a pH sensor. But while doing the same i could not understand what to the particular section of the circuit does. This has been maked in Red rectangle in the attached file.

The input of the sensor is -413 mv to +413 mv. As far as i understand, the first two op-amp just buffer the signal from the sensor. The measuring electode is been buffered with respect to the voltage at the reference point or the reference voltage of the sensor.

The second upper part takes the difference of it and since an another voltage is been appled (600 mv) for the offset, it would act a non-inverting summer to create a offset. But what does the lower part do?? If i remove it, the circuit doesn't work. Requesting the help.

 

[Ubergeek63]

it is a filtered reference level. when you take it out whatever offset it was canceling out gets amplified 10x

 

[Vikky]

Can you explain in detail. Also how the amplification of 10x is happening ?

What can i understand that, it is behaving like a votlage divider generating 600 mv at junction of R14 and R8.

The same amount of the votlage will be generated by V2. Acutally it is the DAC output which will be comming to V2 and by the microcontoller we can adjust the offset or change the calibration point.

Regards
Vikas