APPLICATION NOTE NO.
9
Calculating Calibration Coefficients for Sea Tech Fluorometer & WET Labs
Flash Lamp Fluorometer (FLF)
Revised September 2008
Some Sea-Bird CTDs can be equipped with a Sea Tech or WET Labs Flash Lamp Fluorometer. For these fluorometers, the CTD configuration file requires the scale factor and offset to enable the software to calculate the concentration:
Concentration = (voltage * scale factor / 5) + offset
These fluorometers have internal, switch-selectable ranges. The scale factor is dependent on the fluorometer range:
Fluorometer | Range (milligrams/cubic meter) | Scale Factor |
Sea Tech | 0 - 3 | 3 |
0 - 10 (factory-set default) | 10 | |
0 - 30 | 30 | |
0 - 100 | 100 | |
0 - 300 | 300 | |
0 - 1000 | 1000 | |
WET Labs FLF | 0 - 100 | 100 |
0 - 300 (factory-set default) | 300 | |
0 - 1000 | 1000 | |
The offset can be calculated by measuring the fluorometer voltage output when its light sensor is completely blocked from the strobe light by an opaque substance such as heavy black rubber:
offset = (-scale factor * output voltage ) / 5
Note: Scale factor and offset can be adjusted to fit a linear regression of fluorometer responses to known chlorophyll a concentrations.
- Double click on the voltage channel used by the fluorometer from the list of available voltage numbers (see CTD Configuration Sheet at beginning of CTD manual for voltage channel assignments as shipped from the factory).
- Modify other fixed display setup parameters (such as seconds between updates, font size, etc.) as desired.
- Click OK.
- CTDs that start logging by command (such as SBE 16) ‑ Use a terminal program to send the command to start logging. Disconnect from the terminal program to free up the COMM port.
- CTDs that start logging with a magnetic switch (such as SBE 19 and 25) – Move the switch to the On position.
- SBE 9plus starts logging automatically when you start real-time data acquisition in Seasave V7 (Step 6A).
- Click Start to start real-time data acquisition.
- Record the fluorometer voltage and use this value in the equation to calculate the offset.
- In the Real-Time Data menu, select Stop.
Sea-Bird Home Phone: (+1) 425-643-9866 Fax: (+1) 425-643-9954 E-mail: seabird@seabird.com