Electrochemical sensor working principle and matters needing attention
Published:2012-7-3   Views:3367
Working principle
Oxygen sensor
The working principle of the oxygen sensor diaphragm galvanic cell. These sensors typically include precious metal cathode with catalytic activity, easy polarization of the active metal anode, acid, alkali, salt solution, or other ion conductor electrolyte, closed shell, pin etc.. Oxygen sensor shell is a closed container and the container is filled with electrolyte, the top has a capillary pores, allow oxygen through and enters the working electrode. The oxygen sensor is in internal electrolysis, cause conductive ions within sensor changes. Variation of oxygen concentration in the environment can be accurately perceived by electrolytic current flowing through the two electrode measurement. In the proper range, the electrolytic current has a good linear relation with the concentration of oxygen.
The electrochemical process of oxygen in the sensor is described as: when the oxygen to the working electrode, such as immediately as the reaction (1) is reduced to hydroxyl ions:
O2+2H2O+4e, 4OH- (1)
These hydroxyl ions through the electrolyte to reach the anode (lead), the oxidation reaction with lead (2), to generate the corresponding metal hydroxide.
The 2Pb+4OH- → 2Pb (OH) 2+4e (2)
The total cell reaction:
O2+2Pb+2H2O=2Pb (OH) 2 (3)
The reaction of the current size depending on the oxygen diffusion, diffusion rate of oxygen depends on the oxygen partial pressure and capillary pore size. Can be connected with a known resistance to measure the resulting voltage, which can accurately measure the concentration of oxygen.
The electrochemical reaction, the active metal lead to being consumed and passivation in oxidation reaction, so that the sensor has a certain use period, when all of the available active metal lead completely oxidized or passivation, the sensor will stop working. Life expectancy is usually oxygen sensor for 1-2 years, but also by the amount of oxygen content or restrict access to the anode lead to prolong life. The selectivity of the sensor:
This kind of sensor has a high sensitivity of the gas to be detected, but the sensitivity to other interference gases can be very good resolution, selectivity is achieved in the following way:
1 different reaction, using different catalysts for the preparation of catalytic electrodes.
2 since each gas has a best response potential respectively, by selectively improve sensors to regulate the working electrode and the reference electrode bias voltage can be better.
According to the interference gas selectivity of 3 physical and chemical properties of the filter layer of suitable can also improve sensor.
When using the matters needing attention
Please use the specifications allow range;
Determination of 1 gas sensitivity, please in clean atmosphere;
2 directly to the ventilation measurement of gas on sensor surface strongly blowing condition determination, will be on the gas sensitivity is very high. The gas sensitivity of determination, should avoid the determination of gas from the front;
Ventilation face dont 3 gas blocking, not pollution, sometimes pore blocking is the cause of low sensitivity;
4 not excessive shock or vibration;
The use of long time gas environment of high concentration of 5 in recovery to the initial state is slow;
6 sensors to avoid contact with organic solvents, coatings, chemicals, Oils and high concentration gas;
7 electrolyte leakage will damage, please do not arbitrarily open sensor;
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