Water Chlorophyll Sensor

I. Working Principle

The HD-DJ15S online chlorophyll sensor is designed to determine chlorophyll content. Its working principle is based on the fluorescence and light-absorption characteristics of chlorophyll.

Under natural light or illumination at a specific wavelength, chlorophyll absorbs light energy and emits fluorescence. The intensity of this fluorescence is proportional to the chlorophyll content, so the content can be estimated by measuring the fluorescence intensity.

The sensor measures chlorophyll in real time, quickly and non-destructively. It is used for rivers, lakes, ponds, marine surveys, aquaculture, drinking water sources, and the study, survey and monitoring of algae and phytoplankton.

II. Key Features

1. Fluorescence method with a measuring range of 0–400 µg/L and a resolution of 0.01 µg/L.

2. Linearity R² > 0.999 with automatic temperature compensation.

3. Built-in automatic cleaner prevents biological attachment and optical window fouling; cleaning time and cycle count are configurable (0.7 W).

4. RS485 output with the Modbus-RTU protocol.

5. 316L stainless steel housing with IP68 protection for long-term immersion.

6. 3/4 NPT thread for fixed immersion mounting; installation in a drag chain is not permitted.

7. Two-point calibration with low power consumption of 0.4 W at 12 V.

III. Technical Parameters

IV. Installation and Wiring

Choose 3/4 NPT threaded fixing, a mounting bracket, or any other method that holds the sensor firmly in place. Fixed installation is preferred; installation on a drag chain is not permitted.

Take full account of water flow and level variation so that the water crosses the optical path, and keep the sensor at least 10 cm below the water surface.

Keep at least 3 cm from the side wall and 10 cm from the bottom.

The cable is a 4-core shielded cable: red - power supply (12–24 V), black - ground (GND), green - RS485-B, yellow - RS485-A.

V. Maintenance and Care

Maintenance schedule: clean the sensor every 0.5–3 days (without brush) or every 4–8 weeks (with brush); inspect the sensor every 6 months; replace the O-ring every 1–2 years.

Check the outer surface and rinse it with clean water. If dirt remains, wipe with a soft damp cloth; for stubborn deposits, add a little household detergent to the water.

Check the cable sheath for cracks; the cable should not be taut during normal operation.

Check the measuring window for contamination and wipe it with a lint-free cloth.

Calibrate the sensor with the host software, or by sending MODBUS commands directly over RS485.

VI. Calibration

Zero-point calibration: measure an appropriate volume of distilled water into a brown beaker and place the sensor vertically in the solution, with its front end at least 10 cm from the bottom. After 3–5 minutes, when the value is stable, perform zero-point calibration.

Slope calibration: place the sensor in the standard solution under the same positioning conditions. After 3–5 minutes, when the value is stable, perform slope calibration.