A gas sensor is a type of converter that transforms the volumetric fraction of a given gas into a corresponding electrical signal.
The probe conditions the gas sample through the gas sensor, typically involving the removal of impurities and interfering gases, as well as drying or cooling treatment of the display portion of the instrument.
It is a device that converts gas component information, concentration and other data into information that can be used by personnel, instruments, computers and more!
Gas sensors are generally categorized as a type of chemical sensor, although this classification may not be entirely scientific.
I. Types of gas sensors
Following are the types of gas sensors:
1. Thermopile gas sensor
The thermopile gas sensor is one of the first gas sensors developed, capable of detecting various gases such as carbon dioxide, methane, oxygen, etc.
It consists of a thermopile probe and a circuit board; The thermopile probe detects the gas concentration and the circuit board transmits these signals to the display for the user to view the detection results.
2. Optical gas sensor
The optical gas sensor is one of the newest gas sensors, also capable of detecting various gases such as carbon dioxide, methane, oxygen, etc.
The optical sensor comprises an optical probe and a circuit board; the optical probe detects the gas concentration, transmitting signals to the circuit board for the user to view the detection results.
3. Electrochemical gas sensor
Electrochemical gas sensor is a common type of gas sensor that can detect various gases such as carbon dioxide, methane, oxygen, etc.
It consists of an electrochemical probe and a circuit board; the electrochemical probe detects the gas concentration, and the circuit board transmits these signals to the display for users to examine the detection results.
4. Metallic gas sensor
Metal gas sensor is another common type of gas sensor, capable of detecting various gases such as carbon dioxide, methane, oxygen, etc.
It consists of a metal probe and a circuit board; the metal probe detects the gas concentration and the circuit board transmits these signals to the display for users to view the detection results.
5. Infrared gas sensor
Infrared gas sensor is a new type of gas sensor, capable of detecting various gases such as carbon dioxide, methane, oxygen, etc.
It consists of an infrared probe and a circuit board; the infrared probe detects the gas concentration and the circuit board transmits these signals to the display for the user to view the detection results.
II. Gas sensor selection principles
A gas sensor is a device that converts the volume fraction of a given gas into a corresponding electrical signal. Below we will provide a detailed introduction to the principles of gas sensor selection.
1. Determination of sensor type based on measurement object and environment
For a specific measurement task, one must first consider which type of gas sensor to use, which can only be determined after analyzing several factors. Even when measuring the same physical quantity, there are several types of sensors to choose from.
The suitability of a sensor depends on the characteristics of the measured object and the conditions of use of the sensor, including factors such as range size, volume requirements of the sensor at the measurement location, whether the measurement is contact or non-contact. , signal output method, sensor source and cost.
After considering these factors, you can determine the type of sensor to be used and then consider its specific performance indicators.
2. Choosing Sensitivity
Generally, within the linear range of a sensor, higher sensitivity is preferred. High sensitivity results in larger output signals corresponding to changes in the measured variable, which facilitates signal processing.
However, a sensor with high sensitivity can also easily pick up noise unrelated to the measurement, which can be amplified and affect measurement accuracy. Therefore, the sensor must have a high signal-to-noise ratio to minimize disturbances from the outside world.
The sensitivity of a sensor is directional. If the measured object is a unidirectional quantity and its directionality is important, a sensor with low sensitivity in other directions should be chosen.
If the measured object is a multidimensional vector, a sensor with lower cross sensitivity is preferable.
3. Frequency response characteristics
The frequency response characteristics of a sensor determine the frequency range of the measurement. It must maintain distortion-free measurement conditions within the permitted frequency range.
In practice, the sensor response always has a delay, and it is desirable that this delay is as short as possible. A sensor with high frequency response can measure a wide range of signal frequencies.
Due to the structural characteristics of mechanical systems, which often have large inertia, low-frequency sensors are more suitable for measuring low-frequency signals.
In dynamic measurements, the response characteristics must match the signal characteristics (steady state, transient, random, etc.) to avoid excessive errors.
4. Linear Range
The linear range of a sensor refers to the range in which the output is proportional to the input. Theoretically, within this range, sensitivity remains constant. A wider linear range indicates a larger measuring range and guarantees a certain measurement accuracy.
When selecting a sensor, you must first check whether its range meets the requirements once its type has been determined.
However, in reality, no sensor can guarantee excellent linearity, and linearity is relative.
When the required measurement accuracy is relatively low, within a certain range, sensors with small nonlinear errors can be approximated as linear, which greatly simplifies the measurement process.
5. Stability
Stability refers to the ability of a sensor to maintain its performance unchanged after a period of use.
Factors that affect the long-term stability of a sensor include not only the structure of the sensor itself, but also its usage environment. Therefore, a gas sensor must have strong environmental adaptability to ensure good stability.
Before choosing a sensor, you should investigate your operating environment and choose a suitable sensor or take appropriate measures to reduce environmental influences based on this environment. The stability of a sensor has quantitative indicators.
After exceeding the usage period, the sensor should be recalibrated before use to determine if its performance has changed.
In situations where the sensor needs to be used for a long period of time and cannot be easily replaced or calibrated, the selected sensor must have stricter stability requirements and be able to withstand long-term testing.
6. Accuracy
Accuracy is an important performance indicator of a sensor and a critical factor that affects the measurement accuracy of the entire measurement system. The higher the accuracy of the sensor, the more expensive it will be.
Therefore, the accuracy of the sensor only needs to meet the accuracy requirements of the entire measurement system, and there is no need to choose excessively high accuracy.
This way, you can choose a cheaper and simpler sensor among many sensors that can serve the same measurement purpose.
If the objective of the measurement is qualitative analysis, a sensor with high repeatability should be chosen, and it is not necessary to choose one with excellent quantitative precision.
If the objective is quantitative analysis and precise measurement values are required, a sensor with an accuracy level that meets the requirements must be chosen.
