Online Dissolved oxygen sensor can be divided into three forms according to the principle, namely: primary battery type, polarographic type, and fluorescence method. Today we will introduce the polarographic type and fluorescence method, we can compare them from the following aspects.
1.working principles of dissolved oxygen sensor:
(1).The working principle of polarographic dissolved oxygen sensor:
Two electrodes made of different metals are immersed in the electrolyte. When a polarization voltage of 0.6-0.8V is applied to the electrodes of the dissolved oxygen sensor, oxygen diffuses through the membrane into the electrolyte and forms a measurement circuit with the gold and silver electrodes. The cathode releases electrons and the anode accepts electrons, creating an electric current. The resulting current (or voltage) is proportional to the concentration of dissolved oxygen entering the electrode system.
(2). The working principle of the fluorescent dissolved oxygen sensor:
The fluorescence dissolved oxygen sensor is based on the principle of fluorescence quenching. The blue light irradiates the fluorescent material to excite the fluorescent material and emit red light. Since oxygen molecules can take away energy (quenching effect), the time and intensity of the excited red light are inversely proportional to the concentration of oxygen molecules. By measuring the phase difference between the excitation red light and the reference light and comparing it with the internal calibration value, the concentration of oxygen molecules can be calculated.
- Dissolved oxygen online sensor electrode composition:
Electrode composition of polarographic : silver anode; precious metal cathode, covered with semi-permeable membrane; electrolyte;
Electrode composition of fluorescent : sensor, optical element, electronic element, probe.
- Comparison of application scope of dissolved oxygen online sensor:
Polarographic application range: wide application range, can measure ppb trace level and ppm level;
Scope of application of fluorescence :
Since the optical dissolved oxygen sensor adopts a nonlinear calculation method (the fluorescence quenching time interval and dissolved oxygen concentration have a nonlinear relationship), only single-point verification and process calibration can be performed; it is recommended to use measurement The range is 0.05-20mg/L.
- Contrast of use conditions of dissolved oxygen online sensor:
there is a minimum flow rate requirement for the measurement medium;
there is no minimum flow rate requirement for the measurement medium.
- Comparison of interference factors of three dissolved oxygen online sensor:
Interference factors of polarographic :
PH, medium conductivity, oil, sulfide, iron, ferrous, carbonate and algae in the medium; if the electrolyte is polluted, it will cause the battery potential to decrease drift, resulting in measurement errors;
Interference factors of fluorescent:
strong anti-interference ability, in addition to high concentration of chlorine dioxide, it is not easy to be affected by other interfering substances, but the probe should avoid direct sunlight; the fluorescent cap is scratched or partially polluted It retains its accuracy in any condition and is easy to clean.
- Comparison of maintenance amount of dissolved oxygen online sensor:
Maintenance amount of polarographic sensor: a good electrode needs maintenance such as replenishing the electrolyte, replacing the diaphragm, cleaning the electrode, etc. for about half a year;
Maintenance amount of fluorescent sensor: low maintenance amount, no need to calibrate, replace electrolyte and permeable membrane, replace fluorescent cap every 2~3 years.
To sum up, it is recommended to choose a fluorescent dissolved oxygen sensor on site, which is not only easy to use, but also convenient. Desun Uniwill supplies fluorescent dissolved oxygen sensor, portable dissolved oxygen meter with factory price!
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