3.3 Theory of operation
The sensor irradiates the freshwater with orange light (590 nm). The blue-green algae in the water
absorbs the orange light energy and gives red light (650 nm). The sensor directly measures the
quantity of red light in the water to determine the concentration of blue-green algae. The reading is
0 to 40,000 ppb (or 0 to 5 V).
3.4 Calibration
Chemical exposure hazard. Obey laboratory safety procedures and wear all of the personal protective
equipment appropriate to the chemicals that are handled. Refer to the current safety data sheets
(MSDS/SDS) for safety protocols.
Chemical exposure hazard. Dispose of chemicals and wastes in accordance with local, regional and
national regulations.
Calibrate the sensors before initial use, at regular intervals and after sensor maintenance or
modifications. Periodically, do a calibration check to make sure that measurements are still within
tolerance range.
Refer to the Hydrolab Operating Software Manual for instructions on how to do the tasks that follow:
• Start a sensor calibration.
• Start a sensor calibration check.
• Set the calibration mode.
• Select the measurement units shown during calibration and calibration checks.
• Look at the calibration history.
To look at the Hydrolab Operating Software Manual, start the Hydrolab Operating Software, click
Help and select Hydrolab Operating Software Help.
When a calibration or a calibration check is started, the step-by-step instructions for the sensor show
on the display.
3.4.1 Use a solid secondary standard
Use a solid secondary standard to verify the calibration of the sensor when a calibration check is
done. Refer to Accessories for ordering information.
Use a solid secondary standard only to verify the calibration of the sensor on which the value is set.
Set the value of the solid secondary standard as follows:
1. Make sure that the optical surface of the sensor is clean and dry.
2. Put the sensor into a sample with a known concentration or a Rhodamine Calibration Dye
Solution.
3. Record the sensor output voltage (0 to 5 V).
4. Clean and dry the sensor.
5. Put the solid secondary standard on the optical end of the sensor.
6. Turn the solid secondary standard until it is aligned with the indexing mark on the sensor. A
clicking sound is heard when the solid secondary standard is correctly aligned.
7. Use the supplied screwdriver to turn the screw located on the side of the solid secondary
standard. Turn the screw until the sensor output voltage is the same as the value recorded.
Note: Turn the screw clockwise to increase the voltage. Turn the screw counter-clockwise to decrease the
voltage.
C A U T I O N
C A U T I O N
English 9