I think you're setting up the linearization function properly (though X1 & X2 should be 819 & 4095, respectively, but that is inconsequential to this problem). If you can see the actual analog raw value changing appropriately and you have the linearization function set up properly, then the problem must be that the linearization function is not being called for some reason. Make sure the program is downloaded to the PLC and make sure the function is not in a subroutine that's not being called. If you post your program here, someone will try to help troubleshoot your code.