Ensure +5/-5 dual supply for chip TL062 IC3. Gnd is common ps ground, let grounds radiate from ground plane in one side of PCB. R3-R8 is an attenuator that may need to be designed or modified.
In output R23 is for protection from shorting of +5V supply, R23 can also go to an unregulated or external
supply upto 24V DC which is referenced to this circuits gnd. More voltage more distance.
Q2 is the current control device, and R22 50E is the shunt for taking a sample of current. 4-20mA in the output (provided suitable load is connected) means 200mV- 1000mV across 50E shunt. This is fed to close loop control system of IC3a inverting pin.
An opamp on this type of feedback tries to drive the output in such a way, so as to maintain both the inputs at same level.
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