Power a current loop from two sources (Sensor Tap)

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Hi everyone!

So I’m working on a project and I think I’m done with one part of it, measuring a 4-20mA signal and powering the circuit while there is potentially another power source. If another power supply is detected then it would use it and disconnect the internal power supply and if no other power supply is detected it will use the internal power supply. It would be some sort of 4-20 mA signal tap!
Normally I check with my friends but they are off on vacation so I’m turning to you guys!

I’ve tried this circuit design in LTSpice and designed it in Eagle (schematic and PCB) and it seems to work in the spice simulator but I’m not too sure if it’s something to work in practice (my gut says no).

Would appreciate if somebody could just give some feedback on the Ida/design! (I’m just a student so don’t bash my Eagle skills )

Thanks in advanced!

Files posted:
    Theory of operation (Hand drawn picture of how I wish it would operate)
    LTSpice simulator (Screenshot of a simplified schematic with output)
    Eagle schematic (PDF of non-simplified schematic)