YSI ProDSS [626905] Nitrate Sensor with Module. YSI ProDSS sensors are smart, user-replaceable units that that can be connected in any port and are automatically recognized by the handheld while retaining the calibration data. For highest accuracy, always install a conductivity/temperature sensor to compensate all measurement data for temperature and dissolved oxygen data for conductivity. Up to four sensors can be installed on a single cable assembly.