Density

Water density is the mass of water per unit volume, and it changes with the water's temperature and the salts dissolved in it. On this platform it is one of the conductivity-family values a multiparameter water-quality instrument reports alongside conductivity, specific conductance, salinity, and TDS, rather than something measured on its own.

Two instrument families in the sensor catalog report it. The In-Situ Aqua TROLL conductivity loggers and sondes (the Aqua TROLL 100 and 200 CTD loggers and the Aqua TROLL 400, 500, and 600 multiparameter instruments) report density in g/cm³ with the rest of their conductivity set. The Level TROLL and BaroTROLL loggers and the RDO probes do not. The Spectra Scientific Spectra Litmus configurable sondes (Litmus 6 and Litmus 4) report it in g/L.

Both families are read by a Thiamis gateway over Modbus RS-485. An In-Situ instrument first reports its model and serial number, then its parameter registers are polled each interval; fixed instruments such as the Aqua TROLL 100 and 200 return a set list, while the Aqua TROLL 600 is scanned so that whichever smart sensors are installed are discovered automatically. The Spectra Litmus is polled over Modbus RS-485 at 9600 baud; because it is a configurable smart-sensor sonde, the values that return depend on the sensors fitted to that unit. The Spectra Litmus has since been withdrawn from the vendor's catalog in favor of resold YSI EXO sondes.