APPLICATION NOTE NO. 11 S

Using Biospherical Surface PAR Light Sensor with SBE 11plus Deck Unit
Revised March 2006

Application note in pdf format

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):

Notes:

• 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, and QCP-2300L underwater PAR sensors.
• See Application Note 11 QSP-PD for details on the QSP-200PD, QSP-2200 (PD) and QCP-2200 (PD) underwater PAR sensors.

SEASOFT-DOS Versions 4.021 and later, and all versions of SEASOFT-Win32, fully support the acquisition and display of the data from these surface reference PAR sensors and the corresponding underwater PAR sensor.

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.

2. 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.

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

Set up the configuration (.con) file for the SBE 9plus CTD. Enable the recording of the surface PAR sensor by selecting Surface PAR voltage added. This alters the display by adding two additional external voltages. The highest numbered voltage is labeled SPAR/surface irradiance. Enter the surface light conversion factor and the ratio multiplier in the .con file.

Note: The CTD configuration (.con) file is edited using the Configure menu (in SEASAVE or SBE Data Processing in our SEASOFT-Win32 suite of programs) or SEACON (in SEASOFT-DOS).

SEASOFT calculates surface light as:

surface light (μEinstein/m^2.sec) = volts * conversion factor

To compute the conversion factor, calculate the output of the surface PAR sensor in μEinstein/m^2.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/cm^2.sec:
Conversion factor = (0.01384 μEinsteins/cm^2.sec) * (10000 cm²/m²) / 0.0856 volts = 1617 μEinsteins/m^2.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/m^2.sec light level plot as 1000 μEinsteins/m^2.sec. The ratio multiplier should be set to 1 for normal operations.

Notes:

• 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/m^2.sec, 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.

Last modified: 06-Apr-2007

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