Freshwater CTD XR-420/620

RBR's freshwater CTD (conductivity, temperature and depth), the XR-420CTDf (freshwater) is a small, autonomous data logger (sonde, recorder) designed to monitor conductivity, temperature and pressure. Specific conductivity, salinity, depth and speed of sound are derived through post-processing using RBR software supplied with the instrument. 

RBR's Profiling CTD, the XR-620CTDfF is designed for profiling freshwater water columns, it has the same features as the XR-420 along with a very fast response thermistor, to provide synchronous measurement with conductivity, and a sampling rate of at up to 6Hz. It also has a software wet-switch that turns off the sampling when the logger is out of the water, to save batteries and memory between casts.

Both models are available in delrin polymer or titanium pressure cases, allowing deployment to 740m or 2000m respectively. If required, external connectors can be selected for data and power connections underwater. Additional sensors can also be fitted (see XR420/620 multi-channel for up to six channels and the XRX series for up to ten channels).  Pressure sensors are optional.

Conductivity - Uses a 3-electrode sensor suitable for deployment in water with conductivity in the range 0 to 2 mS/cm. The circuitry features an extremely low noise which allows measurement of conductivity with a resolution of less than 0.02µS/cm

Temperature - The sensor probe is built and calibrated in-house using a low-drift thermistor. Internal or external placement are offered, depending on the intended conditions, and standard or fast time constants (3 seconds or <100 milliseconds for external types). Standard range is -5 to +35 °C, though this can be extended on request.

Pressure - (optional) Measured with a piezo-resistive transducer with Hastelloy diaphragm to avoid corrosion. Accuracy is 0.05% of the full scale rating and achievable resolution is 0.0001%. See the data sheet for possible sensor ratings.

	Datasheet
	Data Logger User Manual