Pressure

The available depth ranges for an RBR depth sensor are: 10/20/50/100/200/500/740/1000/2000/4000/6000/10000* m (dBar)

The maximum depth rating for loggers with Delrin® housing is 740m (740dBar),

* note that the DR-1050 and TDR-2050 can be deployed to 10,000 m, XR series loggers are limited to 6000m.

Measurement resolution is <0.001% full scale, and accuracy is 0.05% full scale.

The XR-series, the TDR-2050 and DR-1050, all use an internal Keller piezo-resistive strain gauge sensors.The sensors are absolute pressure sensors. Atmospheric pressure (nominally 10.1325 dbar at sea level) must be subtracted from the absolute pressure to obtain water depth. An alternate pressure gauge available for the XR-series instruments is the 8CDP series from Paroscientific. These offer an accuracy of 0.015% and a resolution approaching 1 part in 10-8.

The standard depth sensors are calibrated at RBR to better than ±0.05% full scale using an NIST traceable deadweight pressure generator. Using reliable semiconductor technology and a 316 stainless steel housing, the depth sensors are developed for long-term stability in harsh environments. This is also reflected in their operating temperature range of -40°C to 125°C. Typical depth hysteresis of the depth sensor is ±0.015%FS, and it has a response time of 0.1 ms.

A Druck Pressurements hydraulic deadweight tester is used to give a direct NIST traceable standard. Pressures throughout the range of 0 to 4000PSI (0 to 2700m depth) are available to an accuracy of 0.015%. For each pressure range offered, an eight point calibration is carried out and a cubic fit to the data is used to give the sensor characteristic. The gauges used are all absolute pressure. The conversion from absolute pressure to depth requires a knowledge of the local atmospheric pressure and water density. These may be entered into the logger software at the time of download of data to give water depth. Depths beyond this range are calibrated against a Paroscientific 10,000dBar gauge which has an accuracy of 0.01% full scale.