SEACAT Thermosalinograph
SBE 21

Print version     Current Manual - SBE 21 & Interface Box (for older manuals, click here)      Configuration options & accessories

DESCRIPTION

The SBE 21 accurately determines sea surface temperature and conductivity from underway vessels. Data is simultaneously stored in memory and transmitted to a computer serial port, allowing independent data logging and real-time data acquisition. Typically mounted near the ship's seawater intake, the SBE 21 is connected to an AC-powered interface box positioned near the computer. The interface box provides power and an isolated data interface, and contains a NMEA 0183 port for appending navigation information to the data stream.

For corrosion resistance, only plastic, titanium, and the glass/platinum cell are exposed to seawater. Valves control seawater circulation and fresh water flushing. The sensor assembly is easily removed for cleaning and calibration.

TEMPERATURE & CONDUCTIVITY SENSORS

The sensors are mounted in a PVC water jacket assembly:

• The platinum-electrode glass conductivity cell's unique internal-field geometry eliminates proximity effects; this feature is critically important for thermosalinographs, where the cell operates in a water jacket's confined volume. The internal-field cell makes possible the use of expendable anti-foulant devices (supplied). The same conductivity sensor and stable interface electronics have been used on thousands of SBE 16 / 16plus / 16plus V2 (moored) and SBE 19 / 19plus /  19plus V2 (profiling) SEACATs in use around the world today.
• The thermistor temperature sensor is stable and immune to shock and vibration. The interface electronics are the same as used in the SBE 16plus / 16plus V2 and 19plus / 19plus V2 SEACATs.

AUXILIARY SENSORS

Bulkhead connectors are provided (standard) for optional auxiliary sensors:

• RS-232 interface allows an optional SBE 38 temperature sensor to interface with the SBE 21. The SBE 38, installed at the seawater intake (ideally located near the bow), measures sea surface temperature with minimal thermal contamination from the ship's hull.
• Four 0-5 volt A/D input channels allow optional auxiliary sensors to interface with the SBE 21. The channels are configured for four single-ended (standard) or two differential (optional) 0-5 volt inputs.

Acquisition and display of auxiliary sensor data is fully supported in our software.

OPERATION

The SBE 21 samples using one of the following user-programmable schemes:

• Continuously at 4 Hz: At pre-programmed 3- to 600-second intervals, the SBE 21 averages the sample data, stores the average in memory, and sends the average to the computer.
• At pre-programmed intervals: At pre-programmed 3- to 600-second intervals, the SBE 21 takes one sample, stores the sample in memory, and sends the data to the computer.

When the SBE 21 memory fills, real-time output continues after internal recording stops. When a computer cannot be dedicated to data logging, the SBE 21's internal memory permits autonomous operation with periodic downloading.

Firmware upgrades can be downloaded through the communications port by the user, without opening the electronics.

SOFTWARE

SEASOFT^© V2, our complete Windows 2000/XP software package, is included at no charge. Its modular programs include:

• Seaterm^© — communication and data upload from memory
• Seasave^© — real-time data acquisition, display, and plotting of CT and auxiliary sensor data and derived variables (salinity, density, sound velocity, etc.)
• SBE Data Processing^© — filtering, averaging, and plotting of CT and auxiliary sensor data and derived variables

MECHANICAL INSTALLATION

The PVC base or back plate may be drilled for mounting to the ship. Seawater connections (for normal use) and fresh water connections (for cleaning) are PVC pipes with 1-inch (25.4-mm) U.S. standard NPT threads. Mating female fittings are provided, and can easily be adapted to locally available pipe sizes. A stainless steel and plastic in-line pipe mount is available for safe below-waterline installation of the remote temperature sensor.

MEMORY & DATA FORMAT

The SBE 21 has a 64 Mbyte FLASH RAM memory. Each sample of temperature and conductivity uses 6 bytes. Remote temperature (if enabled) adds 3 bytes per sample, and each optional A/D voltage adds 2 bytes. Inter-record headers, written each 10,000 samples, contain sample numbers, data pointers, and time/date from the SBE 21's internal real-time clock.

PN 90488 SEACAT/SEALOGGER RS-232 & NAVIGATION INTERFACE BOX

A 100-250 VAC-powered interface box supplies isolated DC power, provides an optically-coupled RS-232 standard interface to the user's computer, and permits the appending of navigation data via a NMEA 0183 interface port. Each sample (including primary and remote temperature, conductivity, and analog voltages) is transmitted via the interface box, where navigation information (converted to a uniform format from a wide range of receiver types) is appended prior to transfer to the computer. A 10-meter cable for connecting the SBE 21 to the interface box, AC power cord, and 1.5-meter cable for connecting the interface box to the computer are also supplied.

SPECIFICATIONS

ADDITIONAL INFORMATION / LINKS:

Documentation -- manual, photos, technical papers, application notes, etc.

• Current product manual --  SBE 21 and Interface Box (for older manuals, click here)
• Photo Gallery
• Print version of this specification sheet / brochure
• Application Notes:
  - 2D: Instructions for Care and Cleaning of Conductivity Cells
  - 6: Determination of Sound Velocity from CTD Data
  - 10: Compressibility Compensation of Sea-Bird Conductivity Sensors
  - 14: 1978 Practical Salinity Scale
  - 34: Conductivity Cell Filling and Storage Device P/N 50087
  - 42: ITS-90 Temperature Scale
  - 67: Editing Sea-Bird .hex Data Files
  - 68: Using USB Ports to Communicate with Sea-Bird Instruments
  - 70: Installing Anti-Foulant Device Mount Kit on SBE 4, 16, 19, and 21 Conductivity Cells
  - 71: Desiccant Use and Regeneration (drying)
  - 73: Using Instruments with Pressure Sensors at Elevations Above Sea Level
  - 90: Absolute Salinity and TEOS-10: Sea-Bird's Implementation Plans

Sales Information -- options, accessories, cables, mount kits, spares, etc.

• Configuration options & accessories:
  - Details for SBE 21
  - Listing for all products
• Cables
• Mount kits
• Spare parts
• Other -- De-bubbler (produced by the State University of New York, Ocean Instrument Laboratory; information provided for reference only)
  Availability Update: The University had suspended production of the de-bubbler in 2010. In December 2010, we were informed that they have begun production again.

Software -- components of Seasoft V2

• Seaterm -- description, download
• Seasave V7 -- description, download
• SBE Data Processing -- description, download

Links to Other Instruments of Interest

• SBE 38 -- remote temperature sensor for use with SBE 21
• SBE 45 MicroTSG Thermosalinograph -- lower cost, compact thermosalinograph
• Other SEACATs -- SBE 16plus V2 (RS-232 or RS-485) and 16plus-IM V2 (Inductive Modem) for moored applications, SBE 19plus V2 for profiling or moored applications

Specifications are subject to change without notice.  

Last modified: 26-Apr-2011

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