Mysterious curcuits with amplifier?

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Astrid

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Several times I came across the following circuit, unfortunately I do not understand how it works.
We will advise you what circuit is used




Edit:
To complement a line with a fuse F1 is input for current measurements in a multimeter and leads to shunt
 
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I've never seen that before, but it looks like those diodes are some kind of input protection. At first glance it looks like a bridge rectifier, but if you redraw the circuit, you will have two anti-parallel diodes at the two input resistors, and two anti-parallel diodes from the inverting-input resistor to ground.

To summarize, I don't quite know WHAT you've got there.
 

looking like a small signal voltage follower with floating analog inputs not connecting to the OPAMP ground..

Small signal only possible because if the input is more than 1.4V it will be short circuited by the diodes..
 

i think this circuit is a kind of full wave bridge rectifier amplifier.

This works as full wave rectifier. Here(in your circuit) instead of resistance you are using voltage difference between point 1 and 4 as input to amplifier.In your circuit this rectifier is used to as full wave rectifier and yeah it used to avoid damage to amplifier.
 


Sorry, but that's not the way it's connected.
 

To complement a line with a fuse F1 is input for current measurements in a multimeter and leads to current shunt (resistor 100m Ohm or 5 Ohm)
 

I think that when one of the top diode conduct the current then forces to op- amps output to conduct current via R15, so loads the diodes. The bits that are missing from the diagram are the return for the input signal and the PSU common line.
Frank
 

The diodes are definitively in antiparallel and most likely are a protection device, clamping the voltage to a safe level.

The opamp...well it has 100% feedback so it must be a unity gain follower.
 

I'm fairly confident this is just a voltage follower with protection on the input. Part of the problem is that this is not a complete schematic. What the heck is "AGND0"? Is that the return of the opamp power supplies? Is it also the return of the input signal?
 

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