Gas Detector

A gas detector is a device which detects the presence of various gases within an area, usually as part of a system to warn about gases which might be harmful to humans or animals.

Gas detectors can be used to detect combustible, toxic, and oxygen and CO2 gases. This device may be used in firefighting.

A catalytic bead sensor is a type of sensor that is used for gas detection.

Principle:
The catalytic bead sensor consist of two coils of fine platinum wire each embedded in a bead of alumina, connected electrically in a Wheatstone bridge circuit. One of the pellistors is impregnated with a special catalyst which promotes oxidation whilst the other is treated to inhibit oxidation. Current is passed through the coils so that they reach a temperature at which oxidation of a gas readily occurs at the catalysed bead (500-550°C). Passing combustible gas raises the temperature further which increases the resistance of the platinum coil in the catalysed bead, leading to an imbalance of the bridge. This output change is linear, for most gases, up to and beyond 100% LEL, response time is a few seconds to detect alarm levels (around 20% LEL), at least 12% oxygen by volume is needed for the oxidation.

Catalyst poisoning - because of the direct contact of the gas with the catalytic surface it may be deactived in some circumstances.

Sensor drift - Decreased sensitivity may occur depending on operating and ambient conditions.

There are generally three types of toxic entities; chemical, biological, and physical:

• Chemicals include inorganic substances such as lead, mercury, asbestos, hydrofluoric acid, and chlorine gas, organic compounds such as methyl alcohol, most medications, and poisons from living things.
• Biological toxic entities include those bacteria and viruses that are able to induce disease in living organisms. Biological toxicity can be complicated to measure because the"threshold dose" may be a single organism. Theoretically one virus, bacterium or worm can reproduce to cause a serious infection. However, in a host with an intact immune system the inherent toxicity of the organism is balanced by the host's ability to fight back; the effective toxicity is then a combination of both parts of the relationship. A similar situation is also present with other types of toxic agents.
• Physically toxic entities include things not usually thought of under the heading of"toxic" by many people: direct blows, concussion, sound and vibration, heat and cold, non-ionizing electromagnetic radiation such as infrared and visible light, and ionizing radiation such as X-rays and alpha, beta, and gamma radiation

An oxygen sensor, or lambda sensor, is an electronic device that measures the proportion of oxygen (O2) in the gas or liquid being analyzed.

Scientists use oxygen sensors to measure respiration or production of oxygen and use a different approach. Oxygen sensors are used in oxygen analyzers which find a lot of use in medical applications such as anesthesia monitors, respirators and oxygen concentrators. There are many different ways of measuring oxygen and these include technologies such as zirconia, electrochemical (also known as Galvanic), infrared, ultrasonic and very recently laser. Each method has its own advantages and disadvantages.

There are many different ways of measuring oxygen and these include technologies such as zirconia, electrochemical (also known as Galvanic), infrared, ultrasonic and very recently laser. Each method has its own advantages and disadvantages.

A carbon dioxide sensor or CO2 sensor is an instrument for the measurement of carbon dioxide gas. The most common principles for CO2 sensors are infrared gas sensors (NDIR) and chemical gas sensors. Measuring carbon dioxide is important in monitoring Indoor air quality and many industrial processes.

Chemical CO2 Sensors
Chemical CO2 gas sensors with sensitive layers based on polymer- or heteropolysiloxane have the principal advantage of a very low energy consumption and can be reduced in size to fit into microelectronic-based systems. On the downside, short- and long term drift effects as well as a rather low overall lifetime are major obstacles when compared with the NDIR measurement principle.

Since the danger of fires comes mostly from its quickly spreading CO2 output, these sensors can be used to detect fire and certain other air related problems safely without false alarm.