Trying to connect FT sensor to Arduino Mega using RX TX
The Serial RX and TX pins of an Arduino are not RS-232 compatible without using some type of circuit to give you the proper voltage levels.

**RS-232 logic and voltage levels**
0 (space)   Asserted    +3 to +15 V
1 (mark)    Deasserted  −15 to −3 V 


Connecting the RX/TX pins of an Arduino directly to an RS-232 device may fry your Arduino in addition to just not working for communication.  This circuit given below is an example what you'll need.  There are pre-made adapter boards available for a few dollars.