The Thelma Biotel Acoustic Depth Transmitters were originally developed for manual tracking of migrating Atlantic salmon smolt. The transmitter is capable of measuring 0 to 290 m water depth (0-30 bar). These transmitters have been used for tracking of migrating Atlantic salmon post-smolt down to 23 cm length. With the new and smaller depth tags available now, these tags can be used for even smaller fish. The depth sensors are extremely versatile and suitable for use in tracking of many different fish species, for deployment control of oceanographic instruments and infrastructures like the sinker tubes or cage weights in aquaculture facilites. The sensors are available in 7.3 mm, 9 mm, 13 mm and 16 mm sizes with different battery packs to suit the needs of different applications. Many different combinations of battery packs etc is possible, you are welcome to ask even though you don't immediately find what you looking for in the product lists. 

A larger housing with a threaded body  is also available. This enables battery replacement and reprogramming in cases where the tags can be retreived. These tags are especially well suited for ultra long deployments of several years and for wireless measurements on equipment etc. 

ID and Depth transmitter

The transmitter is predominantly used as a coded transmitter (ID and depth), transmitting with fixed or random intervals. A coded transmitter’s battery life will be independent of the fish’s swimming depth. 

Manual tracker transmitters

We have developed a special dual frequency manual tracker version of the depth tag where sensor data is sent on one frequency, like the 69 kHz. A second frequency is used to transmit a continous ping signal at a fixed ping rate. This way manual tracking can be done efficiently at one frequency with a fixed pulse rate. At the same time, data on depth and temperature (optional) is automatically logged on a second frequency as standard R-coded transmits. This solution gives you the option of using standalone loggers as well as multichannel receivers to back up and enhance data reception in your manual tracking set-up.    

Time delay transmitter (discontinued)

Measured depth can also be continuously encoded as the time delay between two acoustic pulses. A delay of 1000 ms corresponds to 0 m, increasing with 100 ms per meter. The resolution is 10 cm, corresponding to 10 ms. The correspondence between depth and time delay can easily be changed on request from customers, e.g. 10 ms per feet. This type of tag is perfect if you only have one tag in your system at the time and you want continous information of the measured depth. For manual tracking, use in aquariums etc.  


Depth transmitter technical data

  D-LP7  D-MP9  D-LP9L D-LP13  D-MP13  D-HP16
Length [mm] 22.5 26.9 27.5 31


 Diameter [mm]  7.3  9 12.7  16
 Weight in air [g] 2.1  4.5  4.3 9.7  12.0  29.4
 Weight in water [g] 1.2  2.8  2.6 5.6  7.2 15.4
 Power output [dB re 1µPa@1m] 139  146  146 150  153 158
 Measurement range [m] 0-290 
Resolution/accuracy Sensitive for down to 10 mm depth changes / maximum offset error +/- 50 cm depth


Typical battery life

(90 seconds between transmits)

Transmitter  Typical battery life 
D-LP7 6 months
D-LP9 20 months
D-MP9 10 months

17 months

D-LP13 35 months
D-MP13 31 months
D-HP16 >4 years