KFDO300 Online Fluorescence Dissolved Oxygen Sensor Water Quality Sensor

Characteristics

Integrated design, anti-electromagnetic interference

Built-in temperature sensor, real-time temperature compensation Support salinity and air pressure compensation

Stainless steel case, IP68 waterproof grade, suitable for various working conditions

RS485 signal output, Standard Modbus protocol, easy integration, networking

Technical Specifications

General Knowledge of Dissolved Oxygen

Tips:Polarographic Dissolved Oxygen Sensors

A polarographic DO sensor is an electrochemical sensor that consists of a silver anode and a noble metal (such as gold, platinum or infrequently, silver) cathode in a potassium chloride (KCl) solution. When the instrument is turned on, it requires a 5-60 minute warm-up period to polarize the electrodes before calibrating or measuring. The electrodes are polarized by a constant voltage (between 0.4 V and 1.2 V is required to reduce oxygen) from the cathode to the anode). As electrons travel in the opposite direction of a current, the anode becomes positively polarized and the cathode becomes negatively polarized. This polarization occurs as electrons travel from the anode to the cathode via an internal wire circuit. When oxygen diffuses across the membrane, the molecules are reduced at the cathode, increasing the electrical signal. The polarizing potential is held constant while the sensor detects changes in the current caused by the dissolved oxygen reduction. The more oxygen that passes the the membrane and is reduced, the greater the electrical current read by the polarographic DO sensor.

This is a two-part reaction – the oxidation of the silver anode and the reduction of the dissolved oxygen. These reactions occur as follows:

Ag – silver anode
KCl and H₂O – potassium chloride solution
Au/Pt – gold or platinum cathode *inert electrode – does not participate*

Silver Anode Reaction and Oxidation
4Ag —-> 4Ag⁺ +4e^–
4Ag⁺ 4KCl —-> 4AgCl + 4K⁺

Gold Cathode Reaction and Oxygen Reduction
*The Au/Pt cathode is inert and only passes electrons; it does not participate in the reaction* 
O₂ + 4e^– + 2H₂O —-> 4OH^–
4OH^– + 4K⁺ —-> 4KOH

Overall Reaction
O₂ + 2H₂O + 4KCl + 4Ag —-> 4AgCl + 4KOH
The gold/platinum cathode is left out of the reaction equation as it does not interfere with nor participate in the reaction. In a polarographic dissolved oxygen sensor, the role of the cathode is to accept and pass on electrons from the anode to the oxygen molecules. In order for oxygen to acquire the electrons, the oxygen reduction reaction must occur at the cathode’s surface. The electrons passed from the silver anode to the cathode via an internal circuit are used to reduce the oxygen molecules to hydroxide ions at the cathode’s surface, producing a current. This current is proportional to oxygen consumed, and thus to the partial pressure of oxygen in the sample.

The silver anode is oxidized during this process as it gives up its electrons to the reduction reaction, but the oxidation only occurs when measurements are being taken. This reaction is noticeable as the anode darkens (AgCl coating). As the oxidized coating accumulates, the sensor’s performance will degrade. This will be clear not only visually when looking at the electrode, but when using the dissolved oxygen sensor. Readings will be unusually low, will not stabilize, or the sensor will not calibrate. When this occurs, the electrodes can be cleaned to restore sensor performance. Electrode maintenance should be far less frequent than membrane replacement, which is based on application.

Contact Information

Phone +86-17719566736

Email sales@kacise.com

Location Tangyan South Road, High-tech Zone, Xi'an City, Shaanxi Province, China