Why does it hase a power supply for the rs232 to rs422?
It really depends on which end of the run the converter is on. If you place it near the PC, so that the 100m run is RS-422, then a converter powered by the PC's serial port (no external supply) will probably work fine. If you want to place the converter near the sensor, so that the 100m run is RS-232, then it would probably be wise to use one that has an external supply.