For the new bicolor vertical channels of the JET Far Infrared interferometer, CEA developed analogue and digital electronics to measure by time delay counting the variation of phase of the two wavelength beams that have crossed the plasma. Algorithms to simultaneously correct, at the time scale of the period of the sine signals, the possible fringe jumps of the two wavelength signals are embedded in a FPGA processor. Laboratory tests to validate the fringe jump corrections are reported and the first results of the phase measurements on plasmas are analyzed and compared with the data that are produced by the existing JET electronics.