Gas and Contaminant Detectors
What Are They?
A gas / contaminant detector measures and indicates the concentration of certain gases or contaminants in the air via different technologies. Typically they are employed to prevent toxic exposure to occupants and fire. They can also be used as part of demand control ventilation systems. Detectors can be portable or fixed. They can be stand alone or be part of a combined protection system.
Types of Gas Detector Technologies:
Gas detectors are categorized by the type of gas they detect: combustible or toxic. Within this broad categorization, they are further defined by the technology they use: catalytic and infrared. These sensors detect combustible gases and electrochemical and metal oxide semiconductor technologies generally detect toxic gases.
Measurement of Toxic Gases
Electrochemical sensors or cells are most commonly used in the detection of toxic gases like carbon monoxide, chlorine and nitrogen oxides. They function via electrodes signals when a gas is detected. Generally, these types of detectors are highly sensitive and give off warning signals via electrical currents. Various manufacturers produce these detectors with a digital display.
Metal Oxide Semiconductors, or MOS, are also used for detecting toxic gases (commonly carbon monoxide) and work via a gas sensitive film that is composed of tin or tungsten oxides. The sensitive film reacts with gases, triggering the device when toxic levels are present. Generally, metal oxide sensors are considered efficient due their ability to operate in low-humidity ranges. In addition, they are able to detect a range of gases, including combustibles.
Measurement of Combustible Gases
Catalytic sensors represent a large number of gas detector devices that are manufactured today. This technology is used to detect combustible gases such as hydrocarbon, and works via catalytic oxidation. The sensors of this type of detector are typically constructed from a platinum treated wire coil. As a combustible gas comes into contact with the catalytic surface, it is oxidized and the wiring resistance is changed by heat that is released. A bridge circuit is typically used to indicate the resistance change.
Infrared sensors or IR detectors work via a system of transmitters and receivers to detect combustible gases, specifically hydrocarbon vapors. Typically, the transmitters are light sources and receivers are light detectors. If a gas is present in the optical path, it will interfere with the power of the light transmission between the transmitter and receiver. The altered state of light determines if and what type of gas is present.
What to know when selecting detection equipment?
The application drives everything in this environment. How big is the area that needs to be monitored? How many different things need to be sensed in the area? What needs to happen when the sensor is triggered in an area? The answers to these questions will steer you into the correct products and systems.