APPLICATION NOTE NO. 13-5

Modifying SBE 13 Oxygen Sensor for 5 Volt Output
Revised May 2007 

Application note in pdf format

Note: This Application Note does not apply to the SBE 43 Dissolved Oxygen Sensor (see Application Notes 64, 64-1, 64-2, and 64-3).

The original SBE 13 Dissolved Oxygen Sensor produces two output signals: an oxygen-dependent output in the range of 0 to + 5 volts, and a temperature-dependent output in the range of -5 to + 5 volts. For the SBE 911plus CTD as well as other applications requiring that both signals be in the 0 to +5 volt range, the sensor electronics may be easily modified as follows:

1. Disassemble the sensor by unthreading the end cap.
2. Disconnect the yellow and orange (anode and cathode) wires from PC Board 10044 (this is the board with the orange capacitor and green transformer; see drawing 40117 ).
3. Remove the 3 screws holding PCB 10044 to the aluminum interboard spacers.
4. Separate PCB 10044 from the other PCB (it will be hinged by 4 yellow wires).
5. Referring to annotated drawing 40115, remove R22b from PCB 10045 and connect a jumper wire in its place.
6. Remove R27b from PCB 10045 and connect a jumper wire in its place.
7. Change PCB 10045 resistor R22a to 976K 1%.
8. Change PCB 10045 resistor R27a to 442K 1%.
9. Reassemble the boards and reconnect the anode and cathode wires.
10. Run SEASOFT and enter the new values for K and C (9.0 and -6.7 respectively) in the CTD configuration (.con) file.
    NOTE: In our SEASOFT-Win32 suite of programs, edit the CTD configuration (.con) file using the Configure Inputs menu in Seasave V7 (real-time data acquisition software) or the Configure menu in SBE Data Processing (data processing software).

The new resistors can be standard 1% types, which should be available from any reasonably well-stocked electronics supplier. Sea-Bird can supply these resistors if necessary.

The calibration values shown are nominal, but should give sufficient accuracy for the intended purpose of temperature compensating the membrane current. The coefficients can be more exactly defined if desired by comparing the DO temperature readout with the temperature of a controlled bath (be sure to let the sensor fully equilibrate thermally). Calculate the adjusted coefficients as follows:

K = (T_hi - T_lo)/(V_hi - V_lo)

C = T_hi - KV_hi

drawing 40115 (click on thumbnail to view full size)

drawing 40117 (click on thumbnail to view full size)

Application Note 13-1: SBE 13, 23, 30 Dissolved Oxygen Sensor Calibration & Deployment

Application Note 13-2: Dissolved Oxygen Sensor Disassembly & Reassembly Instructions

Application Note 13-3: SBE Dissolved Oxygen Sensor Calibration Note (new value for the Pcor coefficient)

Application Note 13-4: SBE 13, 23, & 30 Dissolved Oxygen Sensor Life Expectancy

Last modified: 30-Jun-2009

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