Amplifier for sensor signal

I'm viewing the photo of the board (which doesn't match the schematic).

However I think its run its course.

In review of the board the BNC connector carries the output signal, not the sensor signal. In so far it's a fair choice.

In all of those situations, the shield of the connector is the chassis ground (though the scopes may allow that not to be connected to mains ground.)

Apparently not the case (sic.) here. :roll_eyes:

It was not stated, however I would expect the barrel of the BNC is connected to the 5V common. As close to ground as you get in this circuit.

The separate power socket allows for ground loops with the BNC output. Only one GND connection should exists between the module and the Arduino.

The circuit assumes a p-channel depletion mode FET in that position, hence the p-channel JFET J177. The FET needs to be switched off during measurements and on when the sensor is idle, so its gate is basically a logic signal you control, LOW for on, HIGH for off.
MOSFETs are almost universally enhancement mode, not depletion mode, and the chances of sourcing a p-channel depletion mode MOSFET are slim.

Also the low voltages involve constrain which JFETs will be usable here, and I think you'll need to find a surface-mount equivalent to the J177 as this seems to be discontinued in through-hole (that's very common these days).

It might be easier to use a different circuit to short the sensor when idle, a reed-relay perhaps.

current input, voltage output. The feedback resistor VR1 maps the input current to a voltage.

A synthetic signal ground rail like this is commonly called a virtual ground, which is confusing as there's another meaning for virtual ground, being a node in the circuit kept at ground potential by negative feedback (but not connected to ground).
Call it signal ground perhaps?

The inverting input of the opamp is kept at virtual ground (in the second sense).

Not very commonly, I think. That would normally be referred to as a reference voltage. Underscored by the fact that it's often annotated "Vref". The fact that it is also usually a virtual ground by way of being tied to the virtual ground at the inverting input of an input follower, is only circumstantial.

I see it commonly, quick search:

https://tangentsoft.net/elec/vgrounds.html
https://medium.com/supplyframe-hardware/designing-with-op-amps-the-virtual-ground-1bf84b6ee13c

I suspects the issue might be semantics. IMHO the output signal reference is what I would call ground. In this case the output reference (aka common) is: U2 pin -Vs and U1 anode.