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Inventory of four common carbon monoxide sensors

by:Rika Sensors     2021-11-29
Inventory of four common carbon monoxide sensors
Carbon monoxide sensor is a chemical sensor. The chemical sensor is mainly composed of two parts: the conduction or conversion system. CO gas detection sensor based on carbon monoxide gas detection. It can detect the concentration of the dangerous gas CO exposed to the environment, and clearly read the gas concentration, peak value, and high and low concentration alarm levels. If the current high and low gas concentration values u200bu200bexceed the preset limit values, the alarm will alert the user through sound and light alarms.

Currently, the sensors for detecting carbon monoxide are mainly divided into semiconductor type, electrochemical type, infrared type and catalytic combustion type according to the detection principle. The main working principles and advantages and disadvantages of the sensors are as follows:

1. The sensitivity of the type

semiconductor sensor to gas depends on the temperature at which the sensitive element is heated. For the detection of carbon monoxide, the ## temperature at which the sensitive element is heated is below 100'C. This temperature is much lower than the detection temperature for other gases (such as butane, methane, hydrogen, ethanol vapor, etc.). However, in this case At low temperatures, the response speed of carbon monoxide decreases, and its sensitive characteristics are easily affected by water vapor in the atmosphere.

In order to solve this problem, the sensitive components are heated alternately from high temperature to low temperature. Vapor and other mixed gases are removed from the surface of the sensitive element. During the low temperature period, the sensitive unit can detect carbon monoxide well, and has excellent sensitivity and reproducibility.

Advantages: low price and excellent performance.

Disadvantages: high power consumption, not suitable for battery-powered use, easily affected by temperature, humidity, airflow, etc., poor anti-cross interference ability, high false alarm rate.

2, electrochemical type

(1) Working principle and characteristic curve

When a fixed voltage is applied to the positive and negative electrodes of the electrolytic cell, reactions occur on the active electrode and the counter electrode respectively. Taking the carbon monoxide sensor as an example, the chemical reaction formula is:

This reversible oxidation-reduction reaction always occurs between the working electrode and the counter electrode, and a potential difference is generated between the electrodes. However, the reactions that occur on both electrodes will polarize the electrodes, which makes it difficult to maintain the potential between the electrodes. Constant, which also limits the detectable range of carbon monoxide concentration.

The total reaction is that carbon monoxide is oxidized to carbon dioxide, and the flow of electrons forms an external current. The charge balance is completed by the flow of carriers in the electrolyte.

p>The biggest feature of the electrochemical gas sensor is that the current is completely proportional to the carbon monoxide concentration, and the output signal has a good linear relationship with the gas concentration, so the signal processing and display are very convenient. Another feature is that because it is a normal temperature reaction, it does not need The heater, therefore, the voltage between the electrodes can use dry batteries, does not require commercial power, and is convenient to carry the carbon monoxide alarm.

Advantages: small size, zero power consumption, high sensitivity, good stability, good linearity, repeatability Better, the effect speed is fast, the resolution can generally reach 1ppm, and the life is longer.

Disadvantages: The price, performance, craftsmanship, anti-interference performance, temperature and humidity changes among brands vary greatly.

p>3. Infrared type

The detection principle of infrared sensor is: molecules composed of two different types of atoms have the so-called dipole moment (the product of the length of the dipole and the amount of charge on one end of the dipole). After irradiating infrared light, it will absorb light of a specific wavelength determined by the molecular structure of the gas.

The type of gas can be determined from the absorption wavelength of the absorption spectrum, and the concentration of the gas can be determined from the intensity of absorption. This kind of sensor has very high sensitivity, selectivity, especially precision, and is often used in meters, but its structure is complex and costly, and it is rarely used in alarms.

Advantages: wide range, high accuracy, good selectivity, High reliability, no adsorption effect, no poisoning, no oxygen dependence, less environmental interference, and long life.

Disadvantages: high price, difficult maintenance, physical The product is too large to be used in portable instruments, the detection accuracy of low concentration needs to be improved, and it is not suitable for long-term power supply use.

4. The catalytic combustion type

sensor has a pair of catalytic combustion detection elements. One element is very sensitive to carbon monoxide gas. The element is coated with multiple layers of catalyst and the other element is insensitive to compensate for changes in ambient temperature. This pair of detection elements and another pair of high-precision resistors form a Wheatstone bridge.

Advantages: accurate measurement, fast response, and long life.

Disadvantages: within the range of flammable gas, no selectivity. Working in the dark, there is a danger of ignition and explosion. Most elemental organic vapors are poisonous to the sensor.

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