Conductivity meter, salinity, temperature sensor and depth logger, CTD

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DST CTD miniature salinity, temperature & depth logger

Small and cost effective CTD


Key features

  • Designed to be attached to fish and marine animals for migration studies
  • Cost effective CTD for use on nets and moorings
  • Smallest CTD on the market, dimensions only 50 mm x 15 mm
  • High pressure survival, various depth calibration ranges available up to 2400 m
  • Selection of different conductivity ranges up to 63 mS/cm


DST CTD is the smallest salinity logger on the market that measures and records salinity (conductivity), temperature and depth. Recorded data is stored in the logger‘s internal memory with a real-time clock reference for each measurement.

The DST CTD is supported by the SeaStar software and the Communication Box which serves as an interface between the logger and a PC. Communication between the logger and the Communication Box is wireless.

In SeaStar, the user sets the start time, start date and sampling interval before starting the recorder. Up to seven different intervals can be set for the same measurement sequence. This is especially useful when more frequent measurements are needed at a certain time period. One interval for the whole measurement sequence is more commonly used though.

After recovering the DST data logger, recorded data is uploaded to SeaStar where results are displayed both in graphic and tabular form. After retrieving the data, the logger can be re-programmed and reused as long as the battery lasts.

A set of Communication Box and SeaStar software needs to be purchased with the first order.

Recommended accessories

Star-Oddi offers a plastic protective housing for use under harsh environmental conditions and for mounting to buoys, deploymnet lines, moorings or underwater gear.

For fish tagging projects Star-Oddi can provide a special tag holder kit for fastening the DST externally on fish.

For more information about accessories please click here.

Features on Request

Logic Feature
The optional logic feature allows users to choose a depth limit where the logger starts and stops recording. The logger is not storing measurements while outside the predetermined depth, saving memory and battery life. The user can choose in the SeaStar software at what depth limit the recordings should start at. This can be especially useful when used on fishing gear, or on animals that spend their time both in and out of water.

Real-time salinity monitoring
The CTD logger is available with an online feature, allowing the researcher to receive the data in real time from the logger. The DST CTD is then delivered with four external wires (power, ground, Tx and Rx) for connecting to the user’s own embedded system. When connected to the embedded system, data can be polled by the user (RS232 communication) and viewed in SeaStar. If you have a specific application where you need online monitoring of salinity then contact us for more details.


Examples of Application

The DST CTD is suitable for various studies:

  • Fish and marine animal tagging (externally)
  • Oceanography
  • Fisheries / fishing gear
  • Marine biology
  • Hydrology
  • Ecosystems research
  • Freshwater pollution

You can read more about research studies and scientific papers here.

Conductivity ranges

Type I (3-37 mS/cm)

Type II (13-50 mS/cm)

Type L (0.5-5 mS/cm)

The type II range can be extended to 13-63 mS/cm. You can calculate the most suitable conductivity range for your study with the free SalCalc conductivity calculator software.

Conductivity is a combination of salinity and temperature. The DST CTD is basically a conductivity recorder from which the salinity is calculated. To view the graphical display of the connection between conductivity, salinity and temperature for each conductivity type, click on the type names above.

For sensor types I and II the conductivity accuracy is defined as 4%  Full Scale (FS). The low conductivity sensor, type-L, has conductivity accuracy defined as 6% FS. Salinity is a calculated value where the dominating accuracy parameter is the conductivity, thus the salinity accuracy follows the conductivity, i.e. 4% FS for sensor types I and II, and 6% FS for type-L. As the salinity range varies with temperature so does the accuracy unit values (psu).

The variation of salinity range and accuracy unit value with temperature can be seen for each type below:

Type I

Type II
Type L


Please note that the conductivity sensors are sensitive and measurement accuracy can be affected by biofouling. The warranty does not cover issues concerning biofouling causing offset in salinity measurents, if not traceable to a production fault. In the SeaStar software it is possible to put in an offset value for salinity sensor, correcting salinity offsets.

Technical Specifications

SensorsConductivity (salinity), temperature, pressure
Size (diameter x length)15 mm x 50 mm
Housing materialAlumina (Ceramic)
Weight (in air/in water)in air: 21g
in water: 13g
Memory typeNon-volatile EEPROM
Memory capacity87,217 measurements per sensor
Memory capacity bytes392,478 bytes / conductivity-temperature-depth 4.5 bytes
Memory managementCustom programming
Data resolution12 bits
Temperature resolution0.032°C (0.058°F)
Temperature accuracy +/-0.1°C (0.18°F)
Temperature range -1°C to +40°C (30°F to 104°F)
Temperature response timeTime constant (63%) reached in 20 sec.
Standard depth ranges1m-100m
Depth resolution0.03% of selected range
Depth accuracy+/-0.6% of selected range
Depth response time Immediate
Conductivity ranges0.3 to 5 mS/cm
3 to 37 mS/cm
13 to 50 mS/cm
13 to 63 mS/cm
Conductivity resolution0.01 mS/cm (average)
Conductivity accuracy +/-1.5 mS/cm
Salinity rangeDepends on conductivity and temperature range
Salinity resolution0.02 PSU (average)
Salinity accuracy+/-1 (PSU)*
Data retention25 years
ClockReal time clock
Accuracy +/-1 min/month
Sampling intervalIn second(s), minute(s) or hour(s)
Number of different sampling intervals1 to 7 within same measurement sequence
CommunicationsCommunication Box, RS-232C 9 pin serial or USB
Attachment hole0.9 mm (in diameter)
Battery life4 years**
* Based on conductivity full scale accuracy at 24°C
** For sampling interval of 10 minutes; salinity, temperature and pressure recorded simultaneously.
Specifications may change without notice.

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