What is a dissolved oxygen meter
A dissolved oxygen meter actually measures the amount of oxygen dissolved in an aqueous solution. Oxygen is dissolved in water by the surrounding air, air movement and photosynthesis. Dissolved oxygen electrodes can be used to measure and monitor processes where oxygen levels can affect reaction rates, process efficiency, or the environment. The dissolved oxygen meter has the characteristics of easy installation, long calibration period (3~4 months), insensitivity to other substances, etc., and can monitor the use of the coating and internal electrolyte. Generally, the electrolyte and coating should be replaced every one to three years.
Proper dissolved oxygen is essential to good water quality and all life forms require oxygen. The natural stream purification process requires proper oxygen levels to supply aerobic life forms. If the oxygen content in the water is lower than 5.0mg/L, it will be difficult for aquatic organisms to survive, and the lower the concentration, the more difficult it will be. If the oxygen content is lower than 1-2mg/L and lasts for several hours, it will lead to the death of a large number of aquatic organisms.
Dissolved oxygen meter is divided into polarographic and fluorescence methods.
1. Polarographic dissolved oxygen meter.
Most of the dissolved oxygen meters on the market are polarographic analysis instruments, and the ppm-level ones can be widely used in the continuous monitoring of dissolved oxygen values in solutions such as chemical fertilizers, environmental protection, pharmaceuticals, biochemistry, food and tap water. The ppb level is specially designed for ppb level dissolved oxygen measurement in power plants, boiler feed water and condensate water, etc. It ensures the stability and accuracy at (ultra) low concentrations, and the current technologies are very good in terms of measurement performance and use environment. Big improvement.
Common dissolved oxygen meters mostly use diaphragm electrodes as transducers to convert dissolved oxygen concentration (actually oxygen partial pressure) into electrical signals, which are then amplified and adjusted (including salinity and temperature compensation), and then displayed by analog-to-digital conversion. .
There are two types of practical membrane electrodes for dissolved oxygen meters: polarographic (Polarography) and galvanic cell (Galvanic Cell). Polarography: In the electrode, a gold (Au) ring or a platinum (Pt) gold ring is used as the cathode; silver-silver chloride (or mercury-mercurous chloride) is used as the anode. The electrolyte is potassium chloride solution. The outer surface of the cathode is covered with an oxygen-permeable film. The film can adopt breathable materials such as polytetrafluoroethylene, polyvinyl chloride, polyethylene, silicone rubber, etc.
Second, the fluorescence dissolved oxygen meter.
The fluorescent dissolved oxygen meter is based on the principle of quenching active fluorescence by specific substances in physics.
The fluorescent substance at the front of the sensor is a special platinum metalloporphyrin compounded with a polyester foil that allows gas molecules to pass through, and the surface is coated with a layer of black light-shielding material to avoid interference from sunlight and other fluorescent substances in water. The sapphire light window is isolated from the red and blue light sources and photosensitive elements in the watertight titanium alloy shell. The modulated blue light shines on the fluorescent substance to excite and emit red light. Because oxygen molecules can take away energy (quenching effect), the time and intensity of red light excitation are inversely proportional to the concentration of oxygen molecules. We use the red light source synchronized with the blue light as a reference, measure the phase difference between the excited red light and the reference light, and compare it with the internal calibration value, so as to calculate the concentration of oxygen molecules, after linearization and temperature compensation , to output the final value.
Dissolved oxygen meters are also divided into several categories:
1. According to portability, it is divided into: portable dissolved oxygen meter, desktop dissolved oxygen meter and pen-type dissolved oxygen meter.
2. According to the purpose, it is divided into: laboratory dissolved oxygen meter, industrial online dissolved oxygen meter, etc.
3. According to the advanced level, it is divided into: economical dissolved oxygen meter, intelligent dissolved oxygen meter, precision dissolved oxygen meter or pointer type dissolved oxygen meter, digital display dissolved oxygen meter.
4. The pen-type dissolved oxygen meter is generally made into a single range and has a narrow measurement range. It is a special and simple instrument.
