The HMP35A Temperature and RH probe was replaced with the HMP35C; the HMP35C was eventually replaced with the HMP45C-L. Initially, the HMP35A was Vaisala's production line model that had a Platinum Resistance Thermometer (PRT) for measuring temperature and a HUMICAP-H sensor for measuring relative humidity. It required continuous 12 V power; no switching circuit was included.
Campbell Scientific eventually modified the HMP35A to include a 107 for measuring temperature. For about a month, Campbell Scientific continued to call the modified probe, the HMP35A. Eventually, Campbell Scientific renamed the modified probe the HMP35C.