Op-amp circuit of an electronic card for a turbine flow meter (m3 Counter)

[Dadou]

Hi!
This circuit is part of an electronic card used as an interface in a flow meter. An inductive sensor which operate without being powered counts the rotations of the turbine; then transmits the signal to the pins 24,pin25 and shield of the circuit (Refer to the picture). The output of the op-amp drives a "Nand" Cmos gate. Note that there are two similar circuits as there are two sensorsne on the x-axis and the other to the y-axis. Each sensor is connected to a separate circuit similar to the one shown.
I whould like to know if the circuit is a linear or a non-liear op-amp application and the operation of this circuit?
Thank you in advance for your time and consideration.

 

[duke37]

There is no DC connection to the op-amp -input so the output could be anything.

 

[kellys_eye]

Yes there is.

The components at the bottom of the (poorly drawn) schematic are effectively across the op-amp inputs and there is a connection to Vcc through R5

 

[duke37]

Yes there is.

The components at the bottom of the (poorly drawn) schematic are effectively across the op-amp inputs and there is a connection to Vcc through R5

As I see it, C3 blocks any DC connection.

D1 and D2 are back to back diodes, presumably to limit the differential voltage across the op-amp input, but they are not connected there.

Agree with a very poor schematic layout.