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AN08: Sea-Bird Universal Opto-isolated Junction Box

Document Number: 
Publication Date: 
Friday, March 7, 2008
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The SBE 28 Opto-Isolated Junction Box is a multi-purpose accessory that provides a convenient power and/or data interface between many Sea-Bird instruments and the user's computer serial port. The opto box is AC powered, and configured for either 115 VAC operation (PN 90123) or 230 VAC operation (PN 90124). The interface box provides an optically coupled RS-232C standard interface and supplies an isolated +15 volt DC power supply to permit working without interference from shipboard power circuits and grounds.

The SBE 28 is intended to optically isolate a user's AC-powered computer from an SBE 16, 19, 20, 21, or 26 and provide power, up to 1 ampere, to a CTD or other real-time instrument and associated auxiliary sensors, without relying on internal batteries. The maximum cable length will be limited by the voltage drop due to the cable's resistance and the operating current requirement. SeaCATs with the internal opto-isolated line driver option for real-time telemetry over long cables cannot be powered by the SBE 28 opto box due to there being no connection between internal and external ground. Internal opto-isolation is a standard feature in the SBE 25 Sealogger CTD.

Instruments not equipped with the internal opto-isolated line driver option can receive external power through a data I/O connector with an external power pin which is diode-OR'd with the internal battery supply. Since the 15 volts from the opto box is greater than the normal battery voltage, the instrument will automatically draw power from the SBE 28, not its internal batteries. The Thermosalinograph does not have batteries, so it is always powered from the opto box.

Four cables are supplied when the SBE 28 is ordered:

  1. PN 80437, 2.5 m (8.2 ft) cable with 4-pin MS3106A-14S-2P connector to 4-pin RMG-4FS underwater connector used to connect the instrument directly to the opto box. A 10 m (33 ft) long cable PN 80438 is supplied with the SBE 21. (Drawing 31063B)
  2. PN 80073, 1.5 m (4.9 ft) cable with DB-25P to DB-25S for connecting the opto box to the serial interface port of the computer.
  3. PN 17130, 0.3 m (1 ft) cable with DB-25P to DB9S adapter is supplied for use with 'AT' and laptop computers.
  4. PN 17015, 2 m (6.6 ft) AC mains power cable. The AC power cable should be connected white to NEUTRAL, black to LINE, and green to EARTH (ground).


To operate your instrument with the SBE 28

  1. Connect the instrument to the opto box using cable PN 80437 or PN 80438.
  2. Connect the opto box to the computer serial port using cable PN 80073; use cable PN 17130 if necessary.
  3. Connect the AC power cord PN 17150 from the opto box to the power source.

SBE 28 opto box PN 90123 is configured for a power source of 115 VAC.
SBE 28 opto box PN 90124 is configured for a power source of 230 VAC.


  1. Turn the opto box power ON with the toggle switch. The red LED should light up when the switch is flipped to the 'ON' position.
  2. Run the terminal program that is appropriate for your instrument and communicate with the instrument via the computer keyboard. When communication is being received from the CTD, the yellow LED will flash. The green LED will flash when communication from the computer is being sent to the CTD.


Drawing 40410: SBE 28 Unibox PCB Assembly

Drawing 31058: Universal Opto Box

Drawing 40415: Unibox Assembly 230 VAC

Drawing 31071: Unibox Wiring, 115 VAC

Drawing 31089: Unibox Wiring, 230 VAC

Drawing 31063: Unioptobox Data Cable Assembly


Application Note Revision History

Date Description
October 2000 Initial release. Covers both Sea Tech fluorometer and WET Labs Flash Lamp fluorometer.
September 2008 - Incorporate Seasave V7.
- Previously said that software does not list WET Labs FLF, but it was updated in 2000 to include it.


Applies To