CTD profiler Model SD204


  • Compact & robust design
  • Long term stability sensors
  • High memory capacity
  • Sonar equipment compatibility
  • Year-long battery capacity
  • Depth to: 6000 meters
  • Windows based software
  • Output in physical units
  • Online plotting
  • Auto range for turbidity & fluorescence



CTD Instrument





Magkey, easy field operating



CTD profiler with optional sensors

Model SD204 as Multi-parameter CTD Instrument

The model SD204 is also called CTD profiler, STD profiler, Sound Velocity profiler, CTD Instrument and CTD Sonde.
The SD204 measures, calculates and records sea water conductivity, salinity, temperature, depth (pressure), sound velocity and water density. Therefor the SD204 is often referred as a Sound profiler.

Optional sensors can be added, f. example: dissolved oxygen, fluorescence and turbidity. For optional sensors with several sensitivity ranges, the SD204 has auto range capability. Data are recorded in physical units.

The accompanying software, SD200W, contains versatile functions for programming, post- and online data processing and presentations: - multigraph, online plotting, density and depth calculations (weighed profile). The program is continuously extended according to customer's requests. The programmed settings and calibration coefficients are maintained in nonvolatile eeprom, and will not be changed/lost if power is disconnected. Robustness and complete protection from leakage is obtained by vacuum molding the electronic and all other components in solid polyurethane.

On/Off-switching is by a magnetic key or from keyboard. A sealed battery compartment contains two replaceable C-cells. In practical operation the battery capacity is sufficient for continuous year-around operation with good margin.
The instrument is equipped with a mooring bar with a shackle at each end. Data are recorded in physical units and simultaneously transmitted via a serial (RS232) I/O watertight connector for on-line use.

Newer SD204 has built in radio transceiver and transmitter same as SD208,  read more about SD208 Here

For remote readout and monitoring(web based) and 2 way communication, the manufacturer offers several options:
Communication Unit CU801, Automatic ctd profiler system APB5 . Communication medium as LTE(4G) and satellite is used.


Conductivity: Inductive cell
Range: 0 to 70 mS/cm
Resolution: 0.01 mS/cm
Accuracy: +/- 0.02 mS/cm

Salinity: Calculated from C,T & D
Range: 0 to 40 ppt
Resolution: 0.01 ppt
Accuracy: +/- 0.02 ppt

Range: -2 to +40°C
Resolution: 0.001°C
Accuracy: +/- 0.01°C
Response time:  0.2 sec

Pressure: Specify desired depth range with order
Ranges: 500, 1000, 2000, -- 6000 m
Resolution: 0.01 dbar (m)
Accuracy: +/- 0.01% FS
Response time: 0.1 sec

Sound Velocity: Calculated from S,T & D
Range: 1300 to 1700 m/s
Resolution: 1cm/s
Accuracy: +/- 5 cm/s

Dissolved oxygen: (optional)
Sensor type: SAIV205
Range: 0 to 20 mg/l
Resolution: 0.01 mg/l
Accuracy: +/- 0.2 mg/l

Fluorescence: (optional)
Sensor type: Fluorescein/Chlorophyll/Rhodamine/CDOM
Ranges: 2.5, 7.5, 25, 75 ug/l selectable/autorange
Resolution: 0.03 µg/l

Turbidity: (optional)
Sensor type: Backscatter
Ranges: 12.5, 62.5, 250, 750 FTU selectable /autorange
Linearity: < 2%

Real time clock: +/- 2 sec/day

Modes: STD/CTD with/without sound velocity, oxygen and optional sensor.

Intervals: 1 sec to 180 min.

Capacity: 56000 data sets of STD/CTD

Data output: RS232 ASCII code.1200-9600 baud, 1 start, 7 data, 1 stop, even parity or
1 start, 8 data, 1 stop, no parity selectable via menu

Power: 2 ea. 3.6V lithium C-cells.
Recommended type: SAFT LSH14 (Sufficient for 1.500.000 data sets)
External: 10-30VDC

Material: Vacuum molded polyurethane and titanium
Dimension: Length 400 mm. Diameter 60 mm
Weight: In air: 2 kg. In water: 0.8 kg.

Packing: Suitcase (534x427x157 mm), Grossweight 5,5 kg

Accessories: (included) On/Off magnetic key, PC communication cable 2,5m,
MINISOFT SD200W program and Operating Manual

Warranty: Two years against faulty materials and workmanship

Download datasheet as PDF