Carbon dioxide sensor

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, the function of the lungs in the form of a capnograph device, and many industrial processes.

Nondispersive Infrared (NDIR) CO2 Sensors

NDIR sensors are spectroscopic sensors to detect CO2 in a gaseous environment by its characteristic absorption. The key components are an infrared source, a light tube, an interference (wavelength) filter, and an infrared detector. The gas is pumped or diffuses into the light tube, and the electronics measure the absorption of the characteristic wavelength of light. NDIR sensors are most often used for measuring carbon dioxide.[1] The best of these have sensitivities of 20–50 PPM.[1] Typical NDIR sensors cost in the (US) $100 to $1000 range.

New developments include using microelectromechanical systems to bring down the costs of this sensor and to create smaller devices (for example for use in air conditioning applications). NDIR CO2 sensors are also used for dissolved CO2 for applications such as beverage carbonation, pharmaceutical fermentation and CO2 sequestration applications. In this case they are mated to an ATR (attenuated total reflection) optic and measure the gas in situ.

Another method (Henry's Law) can be also be used to measure the amount of dissolved CO2 in a liquid, if the amount of foreign gases is insignificant.

Chemical CO2 sensors

Chemical CO2 gas sensors with sensitive layers based on polymer- or heteropolysiloxane have the principle advantage of a very low energy consumption, and that they 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.[2] Most CO₂ sensors are fully calibrated prior to shipping from the factory. Over time, the zero point of the sensor needs to be calibrated to maintain the long term stability of the sensor.[3]


See also


  1. ^ a b Carbonate Based CO2 Sensors with High Performance, Th. Lang, H.-D. Wiemhöfer and W. Göpel, Conf.Proc.Eurosensors IX, Stockholm (S) (1995); Sensors and Actuators B, 34, 1996, 383–387.
  2. ^ Reliable CO2 Sensors Based with Silicon-based Polymers on Quartz Microbalance Transducers, R. Zhou, S. Vaihinger, K.E. Geckeler and W. Göpel, Conf.Proc.Eurosensors VII, Budapest (H) (1993); Sensors and Actuators B, 18–19, 1994, 415–420.
  3. ^ Co2 Auto-Calibration Guide "Archived copy" (PDF). Archived from the original (PDF) on 2014-08-19. Retrieved 2014-08-19.CS1 maint: Archived copy as title (link)
  4. ^ Arief-Ang, I.B.; Hamilton, M.; Salim, F. (2018-06-01). "RUP: Large Room Utilisation Prediction with carbon dioxide sensor". Pervasive and Mobile Computing. 46: 49–72. doi:10.1016/j.pmcj.2018.03.001. ISSN 1873-1589.
  5. ^ Arief-Ang, I.B.; Salim, F.D.; Hamilton, M. (2018-04-14). Data Mining [SD-HOC: Seasonal Decomposition Algorithm for Mining Lagged Time Series]. Springer, Singapore. pp. 125–143. doi:10.1007/978-981-13-0292-3_8. ISBN 978-981-13-0291-6.
  6. ^ KMC Controls. (2013). Demand Control Ventilation Benefits for Your Building. Retrieved 25 March 2013, from
Alarm sensor

In telecommunication, the term alarm sensor has the following meanings:

1. In communications systems, a device that can sense an abnormal condition within the system and provide a signal indicating the presence or nature of the abnormality to either a local or remote alarm indicator, and (b) may detect events ranging from a simple contact opening or closure to a time-phased automatic shutdown and restart cycle.

2. In a physical security system, an approved device used to indicate a change in the physical environment of a facility or a part thereof.

3. In electronic security systems, a physical device or change/presence of any electronic signal/logic which causes trigger to electronic circuit to perform application specific operation. In electronic alarm systems the use of this trigger event done by such devices is to turn on the alarm or siren producing sound and/or perform a security calling through telephone lines.

Note: Alarm sensors may also be redundant or chained, such as when one alarm sensor is used to protect the housing, cabling, or power protected by another alarm sensor.

Source: from Federal Standard 1037C and from MIL-STD-188 and from TRISHAM Software Systems

Carbon monoxide detector

A carbon monoxide detector or CO detector is a device that detects the presence of the carbon monoxide (CO) gas in order to prevent carbon monoxide poisoning. In the late 1990s Underwriters Laboratories changed their definition of a single station CO detector with a sound device in it to a carbon monoxide (CO) alarm. This applies to all CO safety alarms that meet UL 2034 standard; however for passive indicators and system devices that meet UL 2075, UL refers to these as carbon monoxide detectors.

CO is a colorless, tasteless and odorless compound produced by incomplete combustion of carbon-containing materials. It is often referred to as the "silent killer" because it is virtually undetectable by humans without using detection technology and, in a study by Underwriters Laboratories, "Sixty percent of Americans could not identify any potential signs of a CO leak in the home". Elevated levels of CO can be dangerous to humans depending on the amount present and length of exposure. Smaller concentrations can be harmful over longer periods of time while increasing concentrations require diminishing exposure times to be harmful.CO detectors are designed to measure CO levels over time and sound an alarm before dangerous levels of CO accumulate in an environment, giving people adequate warning to safely ventilate the area or evacuate. Some system-connected detectors also alert a monitoring service that can dispatch emergency services if necessary.

While CO detectors do not serve as smoke detectors and vice versa, dual smoke/CO detectors are also sold. Smoke detectors warn of smoldering or flaming fires by detecting the smoke they generate, whereas CO detectors detect and warn people about dangerous CO buildup caused, for example, by a malfunctioning fuel-burning device. In the home, some common sources of CO include open flames, space heaters, water heaters, blocked chimneys or running a car or grill inside a garage.

Carbon paste electrode

A carbon-paste electrode (CPE) is made from a mixture of conducting graphite powder and a pasting liquid. These electrodes are simple to make and offer an easily renewable surface for electron exchange. Carbon paste electrodes belong to a special group of heterogeneous carbon electrodes. These electrodes are widely used mainly for voltammetric measurements; however, carbon paste-based sensors are also applicable in coulometry (both amperometry and potentiometry).

Catadioptric sensor

A catadioptric sensor is a visual sensor that contains mirrors (catoptrics) and lenses (dioptrics), a combined catadioptric system. These are panoramic sensors created by pointing a camera at a curved mirror.

Catalytic bead sensor

A catalytic bead sensor is a type of sensor that is used for combustible gas detection from the family of gas sensors known as pellistors.

Displacement receiver

A displacement receiver is a device that responds to or is sensitive to directed distance (displacement).

Examples of displacement receivers include carbon microphones, strain gauges, and pressure sensors or force sensors, which, to within an appropriate scale factor, respond to distance.

In music, certain music keyboards can be considered displacement receivers in the sense that they respond to displacement, rather than velocity (as is more commonly the case).

Examples of displacement-responding sensors include the mechanical action of tracker organs, as well as the force-sensing resistors found in music keyboards that had polyphonic aftertouch capability. Polyphonic aftertouch is no longer a feature of presently manufactured keyboards, but certain older models such as the Roland A50 featured a pressure sensing resistor, similar in principle-of-operation to a carbon microphone, in each key.

Electromechanical film

Electromechanical Film is a thin membrane whose thickness is related to an electric voltage. It can be used as a pressure sensor, microphone, or a speaker. It can also convert electrical energy to vibration, functioning as an actuator.


A humistor is a type of variable resistor whose resistance varies based on humidity.

Infrared point sensor

An infrared point sensor is a point gas detector based on the nondispersive infrared sensor technology.

Intelligent sensor

An intelligent sensor is a sensor that takes some predefined action when it senses the appropriate input (light, heat, sound, motion, touch, etc.).

List of sensors

This is a list of sensors sorted by sensor type.

Occupancy sensor

An occupancy sensor is an indoor motion detecting devices used to detect the presence of a person to automatically control lights or temperature or ventilation systems. The sensors use infrared, ultrasonic, microwave, or other technology. The term encompasses devices as different as PIR sensors, hotel room keycard locks and smart meters. Occupancy sensors are typically used to save energy, provide automatic control, and comply with building codes.


A pellistor is a solid-state device used to detect gases which are either combustible or which have a significant difference in thermal conductivity to that of air. The word "pellistor" is a combination of pellet and resistor.

Position sensor

A position sensor is any device that permits position measurement. It can either be an absolute position sensor or a relative one (displacement sensor). Position sensors can be linear, angular, or multi-axis.

Some position sensors available today:

Capacitive transducer

Capacitive displacement sensor

Eddy-current sensor

Ultrasonic sensor

Grating sensor

Hall effect sensor

Inductive non-contact position sensors

Laser Doppler vibrometer (optical)

Linear variable differential transformer (LVDT)

Multi-axis displacement transducer

Photodiode array

Piezo-electric transducer (piezo-electric)


Proximity sensor (optical)

Rotary encoder (angular)

Seismic displacement pick-up

String potentiometer (also known as string pot., string encoder, cable position transducer)

Confocal chromatic sensor

Potentiometric sensor

A potentiometric sensor is a type of chemical sensor that may be used to determine the analytical concentration of some components of the analyte gas or solution. These sensors measure the electrical potential of an electrode when no current is present.

Velocity receiver

A velocity receiver (velocity sensor) is a sensor that responds to velocity rather than absolute position. For example, dynamic microphones are velocity receivers. Likewise, many electronic keyboards used for music are velocity sensitive, and may be said to possess a velocity receiver in each key. Most of these function by measuring the time difference between switch closures at two different positions along the travel of each key.

There are two types of velocity receivers, moving coil and piezoelectric. The former contains a coil supported by springs and a permanently fixed magnet and require no output signal amplifiers. Movement causes the coil to move relative to the magnet, which in turn generates a voltage that is proportional to the velocity of that movement.

Piezoelectric sensor velocity receivers are similar to a piezoelectric accelerometer, except that the output of the device is proportional to the velocity of the transducer. Unlike the moving coil variety, piezoelectric sensors will likely require an amplifier due to the small generated signal.

Water sensor

The Water in Fuel Sensor or WiF sensor indicates the presence of water in the fuel. It is installed in the fuel filter and when the water level in the water separator reaches the warning level, the Wif sends an electrical signal to the ECU or to dashboard (lamp).

The WiF is used especially in the Common Rail engines to avoid the Fuel injector damage.

The WiF sensor uses the difference of electric conductivity through water and diesel fuel by 2 electrodes.

First generation WiF sensors use a potting resin to isolate the electronic circuit, while the latest generation of Wif sensors (the WS3 sensor in Surface-mount technology) are made totally without leakage using an innovative co-moulding process.

The latest generation of WiF sensors have a high resistance to vibrations and to thermal excursion cycles.

The main automotive WiF designer and producer is SMP Poland.

Wavefront sensor

A wavefront sensor is a device for measuring the aberrations of an optical wavefront. Although an amplitude splitting interferometer such as the Michelson interferometer could be called a wavefront sensor, the term is normally applied to instruments that do not require an unaberrated reference beam to interfere with. They are commonly used in adaptive optics systems, lens testing and increasingly in ophthalmology.

There are several types of wavefront sensors, including:

Shack–Hartmann wavefront sensor

Phase-shifting Schlieren technique

Wavefront curvature sensor

Pyramid wavefront sensor

Common-path interferometer

Foucault knife-edge test

Multilateral shearing interferometer

Ronchi tester

Shearing interferometer

Yaw-rate sensor

A yaw-rate sensor is a gyroscopic device that measures a vehicle’s angular velocity around its vertical axis. The angle between the vehicle's heading and vehicle actual movement direction is called slip angle, which is related to the yaw rate.

Acoustic, sound, vibration
Automotive, transportation
Electric, magnetic, radio
Environment, weather,
Flow, fluid velocity
Ionising radiation,
subatomic particles
Navigation instruments
Position, angle,
Optical, light, imaging
Force, density, level
Thermal, heat,
Proximity, presence
Sensor technology
Fundamental concepts
and control
Professions, trades,
and services
Industry organizations
Health and safety
See also

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