Sensors play a key role in monitoring combustible gas and vapor, including catalytic sensors and infrared (IR) sensors. The environment, response time and temperature range are only factors to consider when deciding which technology is the best to use.

So, what is the difference between catalytic sensor and infrared (IR) sensor? Why do these two technologies have their own advantages and disadvantages, and how to know which method is most suitable for different environments?

infrared sensor

Infrared sensor technology is based on the following principle: a specific wavelength of infrared (IR) light will be absorbed by the target gas. Generally, there are two emitters in the sensor, which generate infrared beams: the measurement beam with the wavelength to be absorbed by the target gas and the reference beam that will not be absorbed. Each beam has the same intensity and is deflected to the light receiver through a mirror inside the sensor. In the presence of target gas, the intensity difference between the reference beam and the measurement beam will be used to measure the presence of gas concentration.

In many cases, infrared (IR) sensor technology has many advantages over catalytic combustion technology, or is more reliable in aspects that may damage the performance of catalytic combustion sensor, including low oxygen and inert environment. Only the infrared beam interacts with the surrounding gas molecules, so that the sensor does not face the threat of poisoning or suppression. Infrared technology provides fail safe testing. This means that if the infrared beam fails, the user will be informed of the failure.

Infrared sensors are very suitable for the oil and gas industry, which can detect methane, pentane or propane in explosive low oxygen environment, and the catalytic combustion sensors in these environments may encounter difficulties.

However, IR sensors are not perfect because they can only output target gas linearly. If the infrared sensor responds to other flammable gases, the target gas will be nonlinear. Just as the catalytic combustion sensor is prone to poisoning, IR sensor is also vulnerable to severe mechanical and high temperature impact, and also strongly affected by pressure changes.

In addition, infrared sensors can not be used to detect hydrogen, so we recommend using catalytic combustion or semiconductor sensors in this case. The primary goal of safety is to choose the appropriate detection technology to minimize the hazards in the workplace. We hope that by clearly identifying the differences between the two sensors, we can improve people’s understanding of how to maintain safety in various industries and hazardous environments.

  

Comparison between infrared sensor and catalytic combustion sensor

Catalytic combustion sensor

Catalytic combustion gas sensor is a kind of equipment used to detect combustible gas or vapor in the explosion range to warn the rise of gas concentration level.

The working principle of the sensor is a circle of platinum wire with catalyst inside to form a small active bead, which can reduce the ignition temperature of the gas around it. In the presence of combustible gas, the temperature and resistance of the bead increase relative to that of the inert reference bead. The resistance difference is measured so that the existing gas concentration can be measured. Because of the existence of catalyst and bead, catalytic combustion sensor is also called catalytic or catalytic bead sensor.

The catalytic sensor was first created by British scientist and inventor Alan Baker in the 1960s, while the catalytic combustion sensor was originally designed for long-term use of flame safety lamp and Canary technology. Today it is used in industrial and underground applications such as mines or tunnels, refineries and oil rigs.

Compared with IR sensors, the cost of catalytic combustion sensors is relatively low due to the difference of technical level, but they may need to be replaced more frequently. When the linear output corresponds to the gas concentration, the correction factor can be used to calculate the approximate response of the catalyst to other flammable gases. When there are many flammable gases, the catalyst can be a good choice.

The fixed detector probe with built-in catalytic sensor outputs MV bridge signal, which is very suitable for installation in inaccessible areas; It can be debugged and calibrated through the controller panel. On the other hand, catalytic combustion needs oxygen in the working process, so it is difficult to cope with the environment with low or little oxygen content. For this reason, confined space instruments containing catalytic combustion combustible gas alarms usually also need to include detectors for measuring oxygen. In the environment of compounds containing silicon, lead, sulfur and phosphate, sensors are prone to poisoning (irreversible sensitivity reduction) or inhibition (reversible sensitivity reduction), which may cause harm to people in the workplace. If exposed to high concentration gas, the catalytic combustion sensor may be damaged. In this case, catalytic combustion is not “fail safe”, which means that no notification will be given when gas is detected and the instrument fails. Any failure can only be determined by bump test before each use to ensure that the performance will not degrade.

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