Online Water pH Sensor

I. Product Overview

The HD-DJ3 online pH sensor is intended for environmental water quality monitoring and for water samples of high or low ionic strength. It satisfies the requirements of most industrial and environmental applications for continuous online pH measurement. The sensor provides an RS485 (MODBUS-RTU) output and a 4–20 mA current output.

II. Key Features

1. Low-impedance pH-sensitive glass membrane with internal signal isolation for strong interference immunity.

2. Good reproducibility, thermal stability and low drift, with a compact body and fast response.

3. 3/4 NPT pipe thread for simple immersion mounting or installation in pipelines and tanks.

4. Stable performance and long service life, with an IP68 waterproof rating.

5. Automatic temperature compensation over the whole measuring range.

III. Technical Parameters

IV. Installation and Wiring

Do not install the sensor upside down or horizontally; install it at an angle of at least 15° to the horizontal.

The cable is a 5-core shielded cable: brown - power supply (12–24 VDC), black - ground (GND), green - RS485-B, yellow - RS485-A. Check the wiring order carefully before powering on, to avoid unnecessary losses caused by incorrect connection. Cable colours may differ slightly between production batches; the colour print on the cable always prevails.

V. Maintenance and Care

Before first use, or when reusing a sensor that has been stored for a long time, soak the sensitive bulb and the reference junction in 3.3 mol/L KCl solution for more than 2 hours. Rinse with deionised (or distilled) water and dry before use so that impurities are not carried into the sample, and immerse at least one third of the sensor in the liquid under test. Keep the terminal block clean and dry; when the sensor is not in use, clean it and fit the protective cap filled with 3.3 mol/L KCl solution, or store the sensor in a container of the same solution. If the terminal block is soiled, wipe it with anhydrous alcohol and let it dry. Avoid prolonged immersion in deionised water, protein solutions, strong acids, strong alkalis or acidic fluoride solutions, and keep the sensor away from silicone grease. A sensor in long service may develop a semi-transparent glass membrane or deposits, which can be washed with dilute hydrochloric acid and then rinsed with water. When measurement error appears, recalibrate the sensor with a host instrument; if maintenance no longer restores calibration and measurement, replace the sensor.