Dissolved oxygen online analyzer measurement basic application principle

(1) Membrane electrode method

Membrane electrode method is one of the most commonly used methods for continuous determination of dissolved oxygen. The membrane electrode is also known as Clark oxygen electrode. This electrode utilizes the principle that membrane is permeable to oxygen but cannot penetrate water and organic and inorganic solutes. The protective electrode does not The reducing substance is in close contact, so that the sensitivity of the sensor is not affected. The semipermeable membrane is usually composed of a material such as polytetrafluoroethylene fiber or polyethylene.

The membrane electrode method dissolves the oxygen sensor by a gold electrode (cathode) and a silver electrode (anode) and a potassium chloride or potassium hydroxide electrolyte. The oxygen diffuses through the membrane into the electrolyte and forms a measurement loop with the gold electrode and the silver electrode. When a polarization voltage of 0.6 to 0.8 V is applied to the electrode of the dissolved oxygen analyzer, oxygen diffuses through the membrane, the cathode releases electrons, and the anode receives electrons, generating an electric current. The entire reaction process is:

Anode reaction: 4Ag4Cl-→4AgCl4e-

Cathodic reaction: O22H2O4e-→4OH-

According to Faraday's law: When the electrode structure is fixed, at a certain temperature, the magnitude of the diffusion current is only proportional to the oxygen concentration of the sample, and the current value is measured to know the concentration of oxygen in the sample to be tested.

(2) Membrane-free electrode method

The sensor consists of a special silver alloy electrode (cathode) and an iron electrode (anode). There is no cover film and a special electrolyte. There is no polarization between the two poles. It uses the solution to be tested as an electrolyte, and the two poles form a primary battery and generate a current. The reaction formula is as follows:

Anode reaction: 2Fe→2Fe24e-

Cathodic reaction: O22H2O4e-→4OH-

The magnitude of this current is proportional to the number of oxygen molecules being measured in the solution. The signal is sent to the transmitter together with the temperature signal measured by the thermal resistance of the sensor, and the oxygen content in the water is calculated by using the relationship between the oxygen content stored in the sensor and the oxygen partial pressure and temperature, and then converted into a standard signal. Output.

(3) Fluorescence method

Dissolved oxygen online analyzer

Dissolved oxygen transmitter features:

1. The system has password protection, output hold, output delay, analog output, relay output (optional) and real-time analog function.

2. There are two calibration methods: 1-point calibration (online) and air (offline) calibration. In order to improve the accuracy of the sensor, the system will automatically detect important parameters such as temperature before accepting the calibration data.

3. The system has complete self-diagnosis information: When the measuring electrode is damaged, the sensor seal is damaged, and the temperature sensor is damaged, it will automatically alarm.

4. The transmitter can customize the scale.

5. High reliability, good stability, simple operation and convenience.

6. Completely electrically isolated.

7. Dissolved oxygen is the measurement of oxygen content in aqueous solution. Its measuring range is 0~40ppm, and it adopts two-wire DC 24V power input, which can output 4~20mA analog quantity. The length of power cable can reach 914m. The distance to the sensor can reach 305 meters.

Dissolved oxygen sensor features:

1. The sensor material has good mechanical strength and chemical resistance, and can adapt to a variety of harsh environments.

2. The three reaction electrodes are mounted in an easily replaceable reaction chamber, and the oxygen electrode is easily exchanged.

a. The sensor is easy to regenerate and saves operating costs.

b. The output current of the three current sensors is proportional to the O2 pressure.

c. The cathode material is Jinyang and the polar material is silver pole. The reference electrode material is silver or silver bromide.

d. The reference electrode is used to stabilize the polarization potential. Guarantee the accuracy of the measurement.

3. The built-in preamplifier improves the stability of the sensor. The cable from the sensor to the transmitter can be lengthened up to 305 meters.

4. When the measurement sensor is damaged, the built-in temperature sensor is damaged, the reaction chamber membrane is damaged, and the self-diagnosis system will return an alarm signal.

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