The TDL always gives 0.01 ppmv for a mixing ratio value. Looking at the Com 1 output using PCAnywhere indicates that the TDL starts up fine with measurements after the 30 second warm up period. The output shows a beerfactor of about 1.8 which would seem to indicate that it is getting a reasonable humidity measurement. When investing, it was noticed that the board stack was not very well connected to the bottom of the instrument. 2 of the 4 screws were missing and the other 2 were only in about half way. Maybe something got shorted out on the boards.

Asked Randy May for help.