The Thelma Biotel depth sensor transmitter is a versatile tool for wireless depth and pressure measurements under different conditions. The standard sensor offers high – resolution data down to either a standard of 290 meters water depth or a deep water version down to 1000 meters water depth.


  • Available in all transmitter sizes 6, 7, 9, 13 and 16
  • Long operational lifetime ~ 3 months – > 10 years

The Thelma Biotel depth sensor transmitter measures the pressure of the liquid above the sensor and the atmospheric pressure to achieve depth values. The pressure sensor is located at the face of the transmitter, and measurements are taken through a small hole that transfers the pressure through the casting and onto the pressure sensor membrane.

Thelma Biotel offers the smallest depth sensor acoustic transmitters on the market. It can be delivered down to 6 mm in combination with other sensors, such as temperature and acceleration, with several months of operational lifetime.

The pressure sensor cast into the face of the transmitter.


The depth sensors are extremely versatile and suitable for use in tracking many different aquatic species, and for deployment control of oceanographic instruments and infrastructures like mooring lines, fishing gear, nets, sinker tubes and cage weights in aquaculture facilities.


The standard measurement for pressure is a point measurement taken right before the data is transmitted. This means that the measurement frequency will be linked to the transmit interval. Always check your delivery note to ensure you apply the correct calculation when converting measurement data to the unit of choice. The method may vary due to different data ranges and setups.


There is a variation of measurement modes available upon request. Some of these include higher resolution down to cm in water depth, average depth measurements to remove bias from wave disturbance, proportion of last day the measurements have been more shallow or deep than a baseline, or Max / Min / average for last day.

Do not hesitate to contact us for more information regarding your project.


The depth sensor can be produced with a set of different depth range alternatives to match the required maximum depth. Most sensor data transmit protocols have 8 bits or 0-255 points resolution, so these point of resolution needs to be distributed over the relevant depths to be measured. See the table below for available standard depth spans and resulting resolution. The OPs protocol carries a data value of 0-4095 points span, so it can be delivered as 0.1 resolution all the way from 0 to 290 meters. This is currently handled as special production and will require some added production time. 

If the depth range exceeds that of the standard sensor scope, the 1K sensor can offer a greater maximum measured depth.


The pressure sensor is located at the top of the transmitter, and measurements are taken through a small port in the epoxy casting. Pressure beyond maximum absolute pressure (Max survival depth) may rupture and damage the sensor.


The sensor is well protected for normal use and handling, but we propose to avoid long immersion in solvents. 70% ethanol dip and wipe is the preferred disinfection procedure.