Ocean Seven 304 Plus CTD Logger


The OCEAN SEVEN 304Plus CTD completes the line of high quality and accuracy IDRONAUT OCEAN SEVEN CTDs, fulfilling the demand of a high performance CTD probe with very small diameter and very low power consumption.
This CTD can be easily integrated/adapted to third-party systems like floating profilers and/or oceanographic moorings, ROVs and AUVs.
IDRONAUT prides itself on the design of its full ocean depth, pump-free, low-maintenance sensors. Central to which is the high accuracy seven-platinum-ring quartz conductivity cell (patented) which can be cleaned in the field without the need for re-calibration.
This unique quartz cell employs a large diameter (8 mm) and a short length (46mm) to guarantee self-flushing.
The OS304Plus does not require pumps or any other external device to flush the sensors, which minimizes its power consumption and allows the use in Arctica and Antarctica. The OS304Plus CTD standard interface is RS232C.
Other optional interfaces are: TTL and wireless Bluetooth®.
The OS304Plus communicates at a speed up to 115k2 bps, thus reducing data uploading time to a minimum.
The OS304Plus can be manufactured with a 316 grade L stainless steel housing or a white POM housing or a titanium housing allowing deployment to depths of 1000 dbar or 2000 dbar or 7000 dbar respectively.


  • Up to 8 Hz CTD simultaneous sampling.
  • Very low power consumption.
  • Expandable: pH, O2, Turbidity and other sensor interfaces, available upon request.
  • Large memory (2GByte) 60.000.000 data sets.
  • High-speed data uploading.

A UV-LED (Ultraviolet, 250..300 nm @500μW, Light-Emitting Diode) is integrated into the conductivity sensor quartz cell (patent pending).
The UV-LED sterilizes the early growth of biofouling, thus eliminating environmental drift in the conductivity sensor.

The OCEAN SEVEN 304Plus is equipped with the MCBH series of wet-pluggable connector.

The OS304Plus CTD is equipped with a 2-Gbyte internal non-volatile FLASH memory which allows the storing of about 60,000,000 data sets each one being composed of the reading of: CTD sensors plus the acquisition date and time.
Different types of battery can be installed in the CTD housing:

  • 2 x size "AA" Alkaline 1.5V battery assembled in a single pack 3.0V
  • 1 x size "AA" Lithium non rechargeable battery 3.6V, 2.4Ah
  • 1 x size “C” Lithium non rechargeable battery 3.6V, 8.4Ah
  • 1 x NiMH rechargeable IDRONAUT custom battery pack (3x1.2 AA) 3.6V, 2.6Ah

The NiMh rechargeable battery pack allows up to 50 hours of continuous operation, while the “C” size Lithium non rechargeable battery allows up to 168 hours of continuous operation.
Whenever the OS304Plus operates in Timed, Burst and Conditional modes, the battery endurance is considerably extended because the OS304Plus enters a deep sleep mode between acquisitions and drains only 8µAh from the battery.
For instance, by monitoring every hour, the OS304Plus will run, in theory, for 12 years on a single Lithium size “C” cell.

The OS310 multiparameter CTD can be equipped with the following sensors to measure:

(1) Other standard pressure transducers, immediately available, have: 10, 40, 100, 200, 500, 2000, 4000, 6000, 7000 dbar ranges.
(2) By reducing the range to 0..70 mS/cm, the resolution becomes 0.0002 mS/cm.
(3) At 1 m/second flow rate.
The fundamental properties of seawater like: Salinity, Sound Speed, Water Density, Oxygen ppm are obtained using the algorithms described in the UNESCO “Technical papers in marine science no.44 – Algorithms for computation of fundamental properties of sea water”.
The fresh water properties like: TDS (Total Dissolved Solids), Fresh Water Conductivity corrected at 20°C and 25°C are automatically calculated.

The OS 304Plus CTD can be optionally equipped with the IDRONAUT Highly Accurate Precise (0.01%FS) pressure transducer, the IDRONAUT OEM Turbidity Meter and the IDONAUT dissolved oxygen sensor.

(1) From nitrogen to air.
(2) Accuracy and resolution are referred to 750 FTU scale.

Idronaut programmes operating under all Windows versions allow the operator to configure the OS304Plus data acquisition and logger functions and upload data from the memory. They are:

It is also available a shorter AUV version (total length 435 mm for 1000 and 7000 dbar).
Please contact Idronaut for further information.