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AN11S: Using Biospherical Surface PAR Light Sensor with SBE 11plus Deck Unit

Document Number: 
Publication Date: 
Wednesday, July 26, 2017
PDF icon appnote11SJul17.pdf380.78 KB


If the SBE 11plus Deck Unit is configured with the A/D converter, it can acquire the output of a Biospherical Instruments Surface PAR sensor and integrate this into the CTD data stream. The A/D converter is standard in all V2 Deck Units (serial number 489 and greater) and optional in V1 Deck Units (serial number 488 and lower). This application note applies to the following Surface PAR sensors (the corresponding underwater PAR sensor, mounted on the SBE 9plus CTD or cage, is also shown):

Surface PAR Sensor Corresponding Underwater PAR Sensor
  If underwater PAR sensor connected
directly to CTD A/D voltage channel
If underwater PAR sensor interfacing to
PN 90310 Log Amp Module,
which is connected to CTD A/D voltage channel
QSR-240 or QSR-2200 QSP-200L, QSP-2300L, or QSP-2350L QSP-200(PD) or QSP 2200(PD)
QCR-240 or QCR-2200 QCP-200L, QCP-2300L, or QCP-2300L-HP QCP 2200(PD)


  • QSR-240, QCR-240, QSP-200L, QSP-200PD, and QCP-200L are no longer in production by Biospherical.
  • See Application Note 11 QSP-L for details on the QSP-200L, QCP-200L, QSP-2300L, QSP-2350L, QCP-2300L, and QCP-2300L-HP underwater PAR sensors.
  • See Application Note 11 QSP-PD for details on the QSP-200(PD), QSP-2200(PD), and QCP-2200(PD) underwater PAR sensors.

Our Seasoft V2 software fully supports the acquisition and display of the data from these surface reference PAR sensors and the corresponding underwater PAR sensor.


SBE 11plus Deck Unit Configuration

  1. Configure as follows to add the surface PAR voltage to the CTD data stream (increasing the number of words in the system by 1):
  • SBE 11plus V1: Set DIP switch S3 position 8 to OFF. The surface PAR voltage will be displayed at thumbwheel position B (or position 11 if your Deck Unit thumbwheel is labeled 0 - 15).
  • SBE 11plus V2: Refer to the SBE 11plus manual (V2) to send the appropriate commands. The surface PAR voltage will be displayed on the Deck Unit LED when the thumbwheel is set to position 9.
  1. Plug the cable connected to the surface PAR sensor into the 4-pin MS connector labeled Surface PAR on the back of the Deck Unit. A spare 4-pin MS style connector (MS3106A14S-2P) was supplied if a cable was not provided. The surface PAR bulkhead connector on the back panel of the SBE 11plus is an MS3102A14S-2S.
Deck Unit Function Surface PAR Sensor
with Switchcraft Connector
pin A Signal (gnd) pin 3
pin B Power (+12 volts) pin 4
pin C Power (ground) — Deck Units with Digital PCB Assembly 40937C or greater use Pin C.
All previous versions do not use Pin C. 
pin 1
pin D Signal pin 2
pin 5

Note: Biospherical sold the Surface PAR sensor with other connector types in the past. See the appropriate drawing for pinout details if your sensor does not have a Switchcraft connector.

  1. To convert to actual voltage, divide the number displayed on the Deck Unit LED by 819:
    Voltage = displayed number / 819.


Software Configuration

Note: In our Seasoft V2 suite of programs, edit the CTD configuration (.con or .xmlcon) 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).

Set up the configuration (.con or .xmlcon) file for the SBE 9plus CTD.

  1. Enable the surface PAR sensor by selecting Surface PAR voltage added.
  2. The Select Surface PAR Voltage Sensor dialog appears. Select SPAR/Biospherical/Licor, and click OK.

    This alters the display by adding two additional external voltages. The highest numbered voltage is labeled SPAR, Biospherical/Licor, as shown below.
  3. Double click on SPAR, Biospherical/Licor in the Channel/Sensor display. The calibration coefficient dialog box appears.


  1. Select the conversion units (which appears in the data file header; this selection does not modify the calculated values) and enter the surface light conversion factor corresponding to the desired units (see Application Note 11General).
  2. Enter the ratio multiplier.
  3. Click OK.



Seasoft calculates surface light as:

surface light (μEinstein/m2•sec) = volts * conversion factor

To compute the conversion factor, calculate the output of the surface PAR sensor in μEinstein/m2•sec/volt using the data from the Surface PAR calibration sheet that was provided by Biospherical (located in the CTD manual).

Conversion factor = Output in Air / Probe Net Response

For example, if Probe Net Response = 85.6 mV (0.0856 volts) and Output in Air = 0.01384 μEinsteins/cm2•sec:
Conversion factor = (0.01384 μEinsteins/cm2•sec) * (10000 cm2/m2) / 0.0856 volts = 1617 μEinsteins/m2•sec/volt

Seasoft calculates corrected PAR as:

corrected PAR = 100 * ratio multiplier * underwater light / surface light
     (underwater light is the calculated light output from the underwater sensor)

To compare the shape of data sets taken at disparate light levels, the ratio multiplier can be used to scale the data. For example, a ratio multiplier of 10 would make a 100 μEinsteins/m2•sec light level plot as 1000 μEinsteins/m2•sec. The ratio multiplier should be set to 1 for normal operations.


  • Do not enter the Calibration factor from the Biospherical calibration sheet as the Conversion factor in Seasoft.
  • To output Surface PAR in units other than μEinsteins/m2sec, multiply the calculated Conversion factor to obtain the desired units. See Application Note 11General to convert units.
  • See Application Note 11 QSP-L or 11 QSP-PD, as applicable, for instructions on entering the underwater PAR sensor coefficients.


Application Note Revision History

Date Description
  Initial release.
September 2001 Previously referred to SEACON in discussions of .con files. Add references to modifying .con file using Configure menu in Seasave or SBE Data Processing in Windows software.
October 2004 - Update with new (2003) Biospherical PAR sensor part numbers.
- Update Surface PAR sensor connector information.
- Expand / rewrite / reorganize.
June 2005 Provide output in microEinsteins/m2 sec, and refer to Application Note 11 General for conversion to other units.
May 2007 Incorporate Seasave V7, and eliminate discussion of Seasoft-DOS.
February 2010 - Add information on QSP-2350L and QCP-2300L-HP, which are on current price list.
- Change Seasoft-Win32 to Seasoft V2.
- Add information on .xmlcon files.
- Update address.
July 2017 - Update for Seasave and SBE Data Processing versions 7.26.7 and later: Add selection of Conversion units in PAR calibration coefficients dialog.
- Add software screen captures.
- New template.


Applies To