there is no particular list of 4 & 2 wires instruments.
The rule is 2 wires instruments are low power consuming that's why they use the 2 wires both for loop power supply and for signal transmission. so they are loop powered from the control system.
where is 4 wires instruments need more power than the loop can supply thats why they need 2 wires for in independent power supply and 2 others for signal transmission to the control system. Electromagnetic flowmeters are most likely to be 4 wires instruments.
there is also 3 wires instruments which share 1 common as ground, 1 wire for + power supply and 1 wire for signal transmission.