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An oxygen sensor, or lambda sensor, is an electronic device that measures the proportion of oxygen (O2) in the gas or liquid being analyzed. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the It was developed by Robert Bosch GmbH during the late 1960s under supervision by Dr. Robert Bosch GmbH is a German diversified technology-based corporation which was started in 1886 by Robert Bosch in Stuttgart Germany. Günter Bauman. The original sensing element is made with a thimble-shaped zirconia ceramic coated on both the exhaust and reference sides with a thin layer of platinum and comes in both heated and unheated forms. Zirconia redirects here For the Sailor Moon character see Dead Moon Circus. The word ceramic is derived from the Greek word κεραμικός ( keramikos) Platinum (ˈplætɪnəm is a Chemical element with the Atomic symbol Pt and an Atomic number of 78 The planar-style sensor entered the market in 1998 (also pioneered by Robert Bosch GmbH) and significantly reduced the mass of the ceramic sensing element as well as incorporating the heater within the ceramic structure. This resulted in a sensor that both started operating sooner and responded faster. The most common application is to measure the exhaust gas concentration of oxygen for internal combustion engines in automobiles and other vehicles. The internal combustion engine is an engine in which the Combustion of Fuel and an Oxidizer (typically air occurs in a confined space called a Divers also use a similar device to measure the partial pressure of oxygen in their breathing gas. Scuba diving is swimming underwater, or taking part in another activity while using a Scuba set. In a mixture of Ideal gases each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume Air is the most common and only natural breathing gas. Other artificial gases either pure gases or mixtures of gases are used in breathing equipment and enclosed habitats such
Scientists use oxygen sensors to measure respiration or production of oxygen and use a different approach. In Animal physiology, respiration is the transport of Oxygen from the outside air to the cells within tissues and the transport of Carbon dioxide Oxygen sensors are used in oxygen analyzers which find a lot of use in medical applications such as anesthesia monitors, respirators and oxygen concentrators. A respirator is a device designed to protect the wearer from inhaling harmful Dusts fumes vapors and/or Gases Respirators come in a wide range of types and sizes
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. Zirconia redirects here For the Sailor Moon character see Dead Moon Circus. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Not to be confused with Supersonic. Ultrasound is cyclic Sound pressure with a Frequency greater than the upper Each method has its own advantages and disadvantages.
Automotive applications
Automotive oxygen sensors, colloquially known as O2 sensors, make modern electronic fuel injection and emission control possible. They determine if the air fuel ratio exiting a gas-combustion engine is rich (with unburnt fuel vapor) or lean (with excess oxygen). Air-fuel ratio ( AFR) is the mass ratio of air to fuel present during combustion Closed-loop feedback-controlled fuel injection varies the fuel injector output according to real-time sensor data rather than operating with a predetermined (open-loop) fuel map. In addition to improving overall engine operation, they reduce the amounts of both unburnt fuel and oxides of nitrogen from entering the atmosphere. Unburnt fuel is pollution in the form of air-borne hydrocarbons, while oxides of nitrogen (NOx gases) are a result of excess air in the fuel mixture and cause smog and acid rain. The term nitrogen oxide typically refers to any Binary compound of Oxygen and Nitrogen, or to a mixture of such compounds Nitric Smog is a kind of Air pollution; the word "smog" is a Portmanteau of Smoke and Fog. Acid rain is Rain or any other form of precipitation that is unusually Acidic It has harmful effects on plants aquatic animals and infastructure Volvo was the first automobile manufacturer to employ this technology in the late 70s, along with the 3-way catalyst.
Information on oxygen concentration is sent to the engine management computer or ECU, which adjusts the mixture to give the engine the best possible fuel economy and lowest possible exhaust emissions. An engine control unit (ECU is an Electronic control unit which controls various aspects of an Internal combustion engine 's operation Fuel economy in automobiles is the amount of Fuel required to move the Automobile over a given Distance. Automobile emissions control covers all the technologies that are employed to reduce the Air pollution -causing emissions produced by Automobiles Exhaust emissions Failure of these sensors, either through normal aging, the use of leaded fuels, or fuel contamination with silicones or silicates, for example, can lead to damage of an automobile's catalytic converter and expensive repairs. Silicones are largely inert compounds with a wide variety of forms and uses For the Artificial intelligence Androids of the 1990s Science fiction series Space Above and Beyond, see Silicate (AI A catalytic converter (colloquially "cat" or "catcon" is a device used to reduce the toxicity of emissions from an Internal combustion engine.
Tampering with or modifying the signal that the oxygen sensor sends to the engine computer can be detrimental to emissions control and can even damage the engine. When the engine is under low-load conditions (such as when accelerating very gently, or maintaining a constant speed), it is operating in 'closed-loop mode'. This refers to a feedback loop between the fuel injectors and the oxygen sensor, to maintain stoichiometric ratio. If modifications cause the mixture to run lean, there will be a slight increase in fuel economy, but a great increase in nitrogen oxide emissions, and the risk of damaging the engine due to detonation and excessively high exhaust gas temperatures. Detonation is a process of Supersonic Combustion in which a Shock wave is propagated forward due to energy release in a reaction zone behind it If modifications cause the mixture to run rich, then there will be a slight increase in power, again at the risk of overheating and igniting the catalytic converter, while decreasing fuel economy and increasing hydrocarbon emissions.
When an internal combustion engine is under high load (such as when using wide-open throttle), the output of the oxygen sensor is ignored, and the engine automatically enriches the mixture to protect the engine. Any changes in the sensor output will be ignored in this state, as are changes from the air flow meter, which might otherwise lower engine performance due to the mixture being too rich or too lean, and increase the risk of engine damage due to detonation if the mixture is too lean. An air flow meter, also know as air consumption meter is a device that measures how much Air is flowing through a tube Detonation is a process of Supersonic Combustion in which a Shock wave is propagated forward due to energy release in a reaction zone behind it
Function of a lambda probe
Lambda probes are used to reduce vehicle emissions by ensuring that engines burn their fuel efficiently and cleanly. Robert Bosch GmbH introduced the first automotive lambda probe in 1976, and it was first used by Volvo and Saab in that year. Robert Bosch GmbH is a German diversified technology-based corporation which was started in 1886 by Robert Bosch in Stuttgart Germany. The sensors were introduced in the US from about 1980, and were required on all models of cars in many countries in Europe in 1993.
By measuring the proportion of oxygen in the remaining exhaust gas, and by knowing the volume and temperature of the air entering the cylinders amongst other things, an ECU can use look-up tables to determine the amount of fuel required to burn at the stoichiometric ratio (14. A cylinder is the central working part of a Reciprocating engine, the space in which a Piston travels 7:1 air:fuel by mass for gasoline) to ensure complete combustion.
The probe
The sensor element is a ceramic cylinder plated inside and out with porous platinum electrodes; the whole assembly is protected by a metal gauze. The word ceramic is derived from the Greek word κεραμικός ( keramikos) Platinum (ˈplætɪnəm is a Chemical element with the Atomic symbol Pt and an Atomic number of 78 It operates by measuring the difference in oxygen between the exhaust gas and the external air, and generates a voltage or changes its resistance depending on the difference between the two. The sensors only work effectively when heated to approximately 800°C, so most newer lambda probes have heating elements encased in the ceramic to bring the ceramic tip up to temperature quickly when the exhaust is cold. The probe typically has four wires attached to it: two for the lambda output, and two for the heater power, although some automakers use a common ground for the sensor element and heaters, resulting in three wires. Earlier non-electrically-heated sensors had one or two wires.
Operation of the probe
Zirconia sensor
The zirconium dioxide, or zirconia, lambda sensor is based on a solid-state electrochemical fuel cell called the Nernst cell. Zirconia redirects here For the Sailor Moon character see Dead Moon Circus. A fuel cell is an electrochemical conversion device It produces electricity from Fuel (on the Anode side and an oxidant (on the Its two electrodes provide an output voltage corresponding to the quantity of oxygen in the exhaust relative to that in the atmosphere. An output voltage of 0. 2 V (200 mV) DC represents a lean mixture. That is one where the amount of oxygen entering the cylinder is sufficient to fully oxidize the carbon monoxide (CO), produced in burning the air and fuel, into carbon dioxide (CO2). Carbon monoxide, with the chemical formula CO is a colorless odorless tasteless yet highly toxic Gas. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single A reading of 0. 8 V (800 mV) DC represents a rich mixture, one which is high in unburned fuel and low in remaining oxygen. The ideal point is 0. 45 V (450 mV) DC; this is where the quantities of air and fuel are in the optimum ratio, called the stoichiometric point, and the exhaust output mainly consists of fully oxidized CO2. Stoichiometry (sometimes called reaction stoichiometry to distinguish it from composition stoichiometry is the Calculation of Quantitative (measurable
The voltage produced by the sensor is so nonlinear with respect to oxygen concentration that it is impractical for the electronic control unit (ECU) to measure intermediate values - it merely registers "lean" or "rich", and periodically adjusts the fuel/air mixture to keep the output of the sensor alternating between these two states. The time period chosen by the ECU to monitor the sensor and adjust the fuel/air mixture creates an inevitable delay, which makes this system less responsive than one using a linear sensor (see below). The shorter the time period, the higher the so-called "cross count" [1] and the more responsive the system.
The zirconia sensor is of the 'narrow band' type, referring to the narrow range of fuel/air ratios to which it responds.
Wideband zirconia sensor
A variation on the zirconia sensor, called the 'wideband' sensor, was introduced by Robert Bosch in 1994 but is (as of 2006) used in only a few vehicles. Year 1994 ( MCMXCIV) was a Common year starting on Saturday (link will display full 1994 Gregorian calendar) Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. It is based on a planar zirconia element, but also incorporates an electrochemical gas pump. An electronic circuit containing a feedback loop controls the gas pump current to keep the output of the electrochemical cell constant, so that the pump current directly indicates the oxygen content of the exhaust gas. Feedback is a circular causal Process whereby some proportion of a system's output is returned (fed back to the Input. This sensor eliminates the lean-rich cycling inherent in narrow-band sensors, allowing the control unit to adjust the fuel delivery and ignition timing of the engine much more rapidly. In the automotive industry this sensor is also called a UEGO (for Universal Exhaust Gas Oxygen) sensor. UEGO sensors are also commonly used in aftermarket dyno tuning and high-performance driver air-fuel display equipment. For the dynamometer used in railroading see Dynamometer car. A dynamometer or "dyno" for short is a machine used to measure The wideband zirconia sensor is used in stratified fuel injection systems, and can now also be used in diesel engines to satisfy the forthcoming EURO and ULEV emission limits.
Titania sensor
A less common type of narrow-band lambda sensor has a ceramic element made of titanium dioxide (titania). Titanium dioxide, also known as titanium(IV oxide or titania, is the naturally occurring Oxide of Titanium, chemical formula Ti[[oxygen This type does not generate its own voltage, but changes its electrical resistance in response to the oxygen concentration. Electrical resistance is a ratio of the degree to which an object opposes an Electric current through it measured in Ohms Its reciprocal quantity is The resistance of the titania is a function of the oxygen partial pressure and the temperature. Therefore, some sensors are used with a gas temperature sensor to compensate for the resistance change due to temperature. The resistance value at any temperature is about 1/1000th the change in oxygen concentration. Luckily, at lambda = 1, there is a large change of oxygen, so the resistance change is typically 1000 times between rich and lean, depending on the temperature.
As titania is an N-type semiconductor with a structure TiO2-x, the x defects in the crystal lattice conduct the charge. So, for fuel-rich exhaust the resistance is low, and for fuel-lean exhaust the resistance is high. The control unit feeds the sensor with a small electrical current and measures the resulting voltage across the sensor, which varies from near 0 volts to about 5 volts. Like the zirconia sensor, this type is so nonlinear that in practice it is used simply as a binary "rich or lean" indicator. Titania sensors are more expensive than zirconia sensors, but they also respond faster.
In automotive applications the titania sensor, unlike the zirconia sensor, does not require a reference sample of atmospheric air to operate properly. This makes the sensor assembly easier to design against water contamination. While most automotive sensors are submersible, zirconia-based sensors require a very small supply of reference air from the atmosphere. In theory, the sensor wire harness and connector are sealed. Air that leaches through the wire harness to the sensor is assumed to come from an open point in the harness - usually the ECU which is housed in an enclosed space like the trunk or vehicle interior.
Location of the probe in a system
The probe is typically screwed into a tapped hole in the exhaust, located after the branch manifold of the exhaust system combines, and before the catalytic converter. A catalytic converter (colloquially "cat" or "catcon" is a device used to reduce the toxicity of emissions from an Internal combustion engine. New vehicles are required to have a sensor before and after the exhaust catalyst to meet U. S. regulations requiring that all emissions components be monitored for failure. Pre and post-catalyst signals are monitored to determine catalyst efficiency. Additionally, some catalyst systems require brief cycles of lean (oxygen-containing) gas to load the catalyst and promote additional oxidation reduction of undesirable exhaust components.
Sensor surveillance
The air-fuel ratio and naturally, the status of the sensor, can be monitored by means of using an air-fuel ratio meter that displays the read output voltage of the sensor. Air-fuel ratio ( AFR) is the mass ratio of air to fuel present during combustion An air-fuel ratio meter monitors the Air-fuel ratio of an Internal combustion engine. Electrical tension (or voltage after its SI unit, the Volt) is the difference of electrical potential between two points of an electrical
Sensor failures
Normally, the lifetime of an unheated sensor is about 30,000 to 50,000 miles. Heated sensor lifetime is typically 100,000 miles. Failure of an unheated sensor is usually caused by the buildup of soot on the ceramic element, which lengthens its response time and may cause total loss of ability to sense oxygen. For heated sensors, normal deposits are burned off during operation and failure occurs due to catalyst depletion, similar to the reason a battery stops producing current. The probe then tends to report lean mixture, the ECU enriches the mixture, the exhaust gets rich with carbon monoxide and hydrocarbons, and the mileage worsens.
Leaded gasoline contaminates the oxygen sensors and catalytic converters. Most oxygen sensors are rated for some service life in the presence of leaded gasoline but sensor life will be shortened to as little as 15,000 miles depending on the lead concentration. Lead-damaged sensors typically have their tips discolored light rusty.
Another common cause of premature failure of lambda probes is contamination of fuel with silicones (used in some sealings and greases) or silicates (used as corrosion inhibitors in some antifreezes). Silicones are largely inert compounds with a wide variety of forms and uses Although the word grease originally described the rendered fat of animals the term is now applied more broadly to mean a Lubricant of higher initial Viscosity For the Artificial intelligence Androids of the 1990s Science fiction series Space Above and Beyond, see Silicate (AI A corrosion inhibitor is a chemical compound that when added to a fluid or gas decreases the corrosion rate of a Metal or an Alloy. Antifreeze is a Cryoprotectant used in Internal combustion engines and for many other heat transfer applications such as electronics cooling and Chillers In this case, the deposits on the sensor are colored between shiny white and grainy light gray.
Leaks of oil into the engine may cover the probe tip with an oily black deposit, with associated loss of response.
An overly rich mixture causes buildup of black powdery deposit on the probe. This may be caused by failure of the probe itself, or by a problem elsewhere in the fuel rationing system.
Applying an external voltage to the zirconia sensors, e. g. by checking them with some types of ohmmeter, may damage them. An ohmmeter is an electrical instrument that measures Electrical resistance, the opposition to an Electric current. [1]
Diving applications
The diving type of oxygen sensor, which is sometimes called an oxygen analyser or ppO2 meter, is used in scuba diving. An electro-galvanic fuel cell is an electrical device used to measure the concentration of Oxygen gas in Scuba diving and Medical equipment Scuba diving is swimming underwater, or taking part in another activity while using a Scuba set. They are used to measure the oxygen concentration of breathing gas mixes such as nitrox and trimix. Air is the most common and only natural breathing gas. Other artificial gases either pure gases or mixtures of gases are used in breathing equipment and enclosed habitats such Nitrox refers to any gas mixture composed (excluding trace gases of nitrogen and oxygen this includes normal Air which is approximately 78% Nitrogen They are also used within the oxygen control mechanisms of closed-circuit rebreathers to keep the partial pressure of oxygen within safe limits. A rebreather is a type of Breathing set that provides a Breathing gas containing Oxygen and recycled exhaled gas In a mixture of Ideal gases each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume This type of sensor operates by measuring the electricity generated by a small electro-galvanic fuel cell. An electro-galvanic fuel cell is an electrical device used to measure the concentration of Oxygen gas in Scuba diving and Medical equipment
A company based out of the United Kingdom and Russia performed a 6 year study of oxygen sensors and their performance in the diving industry related to safety and reliability: http://www.deeplife.co.uk/or_files/DV_O2_cell_study_070329.pdf
Scientific applications
In marine biology or limnology oxygen measurements are usually done in order to measure respiration of a community or an organism, but have also been used to measure primary production of algae. Marine biology is the scientific study of living Organisms in the Ocean or other marine or Brackish bodies of water Limnology (from Greek Λίμνη limne, "lake" and λόγος logos, "knowledge" is the division of Hydrology that studies inland Algae ( sing. alga are a large and diverse group of simple typically Autotrophic organisms ranging from Unicellular to Multicellular forms The traditional way of measuring oxygen concentration in a water sample has been to use wet chemistry techniques e. g. the Winkler titration method. The Winkler test is used to determine the level of dissolved Oxygen in water samples There are however commercially available oxygen sensors that measure the oxygen concentration in liquids with great accuracy. There are two types of oxygen sensors available: electrodes (electrochemical sensors) and optodes (optical sensors).
Electrodes
The Clark-type electrode is the most used oxygen sensor for measuring oxygen dissolved in a liquid. The Clark electrode is an Electrode that measures Oxygen on a catalytic Platinum surface using the reaction O2 + 2 e− The basic principle is that there is a cathode and an anode submersed in an electrolyte. A cathode is an Electrode through which (positive Electric current flows out of a polarized electrical device An anode is an Electrode through which Electric current flows into a polarized electrical device An electrolyte is any substance containing free Ions that behaves as an electrically conductive medium Oxygen enters the sensor through a permeable membrane by diffusion, and is reduced at the cathode, creating a measurable electrical current. Diffusion is the net movement of particles (typically molecules from an area of high concentration to an area of low concentration by uncoordinated random movement
There is a linear relationship between the oxygen concentration and the electrical current. With a two-point calibration (0% and 100% air saturation), it is possible to measure oxygen in the sample.
One drawback to this approach is that oxygen is consumed during the measurement with a rate equal to the diffusion in the sensor. This means that the sensor must be stirred in order to get the correct measurement and avoid stagnant water. Water stagnation occurs when Water stops flowing Stagnant water can be a major Environmental hazard. With an increasing sensor size, the oxygen consumption increases and so does the stirring sensitivity. In large sensors there tend to also be a drift in the signal over time due to consumption of the electrolyte. However, Clark-type sensors can be made very small with a tip size of 10 µm. The oxygen consumption of such a microsensor is so small that it is practically insensitive to stirring and can be used in stagnant media such as sediments or inside plant tissue.
Optodes
An oxygen optode is a sensor based on optical measurement of the oxygen concentration. An optode or optrode is an optical Sensor device that optically measures a specific substance usually with the aid of a chemical Transducer. A chemical film is glued to the tip of an optical cable and the fluorescence properties of this film depend on the oxygen concentration. Fluorescence is a Luminescence that is mostly found as an Fluorescence is at a maximum when there is no oxygen present. When an O2 molecule comes along it collides with the film and this quenches the photoluminescence. A quench refers to a rapid Cooling. In Polymer chemistry and Materials science, quenching is used to prevent low-temperature processes such as phase Photoluminescence (abbreviated as PL) is a process in which a substance absorbs Photons (electromagnetic radiation and then re-radiates photons In a given oxygen concentration there will be a specific number of O2 molecules colliding with the film at any given time, and the fluorescence properties will be stable.
The signal (fluorescence) to oxygen ratio is not linear, and an optode is most sensitive at low oxygen concentration. The sensitivity of an electronic device such as a Communications system receiver or Detection device such as a PIN diode, is the minimum magnitude That is, the sensitivity decreases as oxygen concentration increases following the Stern-Volmer relationship. The Stern-Volmer relationship named after Otto Stern and Max Volmer, allows us to explore the kinetics of a photophysical intermolecular deactivation process The optode sensors can, however, work in the whole region 0% to 100% oxygen saturation in water, and the calibration is done the same way as with the Clark type sensor. In Chemistry, saturation has five different meanings In Physical chemistry, saturation is the point at which a Solution of a substance No oxygen is consumed and hence the sensor is insensitive to stirring, but the signal will stabilize more quickly if the sensor is stirred after being put in the sample.
See also
References
A pulse oximeter is a Medical device that indirectly measures the oxygen saturation of a patient's Blood (as opposed to measuring oxygen saturation directly through Oxygen saturation is a relative measure of the amount of Oxygen that is Dissolved or carried in a given medium Pulse oximetry is a non-invasive method allowing the monitoring of the Oxygenation of a patient's Hemoglobin. Accelerometer Touch sensor Active pixel sensor Air flow meter Alarm sensorDapyx Software network: MP3 Explorer | Ebook Manager | Zenithic