When the O2 sensors go bad what will the car do? Does it sputter or act like it's not getting gas?


When the oxygen sensor fails, the computer can no longer sense the air/fuel ratio, so it ends up guessing. Your car performs MORE?

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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. It was developed by the Robert Bosch GmbH company during the late 1960s under the supervision of Dr. 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. The planar-style sensor entered the market in 1998 (also pioneered by Bosch) 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 started 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. Divers also use a similar device to measure the partial pressure of oxygen in their breathing gas. 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.. Oxygen sensors are also used in hypoxic air fire prevention systems to monitor continuously the oxygen concentration inside the protected volumes. 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 methods. Each method has its own advantages and disadvantages. Automotive oxygen sensors, colloquially known as O2 sensors, make modern electronic fuel injection and emission control possible. They help determine, in real time, if the air–fuel ratio of a combustion engine is rich or lean. Since oxygen sensors are located in the exhaust stream, they do not directly measure the air or the fuel entering the engine but when information from oxygen sensors is coupled with information from other sources, it can be used to indirectly determine the air-fuel ratio. 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 enabling electronic fuel injection to work efficiently, this emissions control technique can reduce the amounts of both unburnt fuel and oxides of nitrogen entering the atmosphere. Unburnt fuel is pollution in the form of air-borne hydrocarbons, while oxides of nitrogen (NOx gases) are a result of combustion chamber temperatures exceeding 1,300 kelvin due to excess air in the fuel mixture and contribute to smog and acid rain. Volvo was the first automobile manufacturer to employ this technology in the late 1970s, along with the three-way catalyst used in the catalytic converter. The sensor does not actually measure oxygen concentration, but rather the difference between the amount of oxygen in the exhaust gas and the amount of oxygen in air. Rich mixture causes an oxygen demand. This demand causes a voltage to build up, due to transportation of oxygen ions through the sensor layer. Lean mixture causes low voltage, since there is an oxygen excess. Modern spark-ignited combustion engines use oxygen sensors and catalytic converters in order to reduce exhaust emissions. Information on oxygen concentration is sent to the engine management computer or engine control unit (ECU), which adjusts the amount of fuel injected into the engine to compensate for excess air or excess fuel. The ECU attempts to maintain, on average, a certain air–fuel ratio by interpreting the information it gains from the oxygen sensor. The primary goal is a compromise between power, fuel economy, and emissions, and in most cases is achieved by an air-fuel-ratio close to stoichiometric. For spark-ignition engines (such as those that burn gasoline, as opposed to diesel), the three types of emissions modern systems are concerned with are: hydrocarbons (which are released when the fuel is not burnt completely, such as when misfiring or running rich), carbon monoxide (which is the result of running slightly rich) and NOx (which dominate when the mixture is lean). Failure of these sensors, either through normal aging, the use of leaded fuels, or fuel contaminated with silicones or silicates, for example, can lead to damage of an automobile's catalytic converter and expensive repairs. 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 vehicle. 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 ECU and the oxygen sensor(s) in which the ECU adjusts the quantity of fuel and expects to see a resulting change in the response of the oxygen sensor. This loop forces the engine to operate both slightly lean and slightly rich on successive loops, as it attempts to maintain a mostly stoichiometric ratio on average. If modifications cause the engine to run moderately lean, there will be a slight increase in fuel economy, sometimes at the expense of increased NOx emissions, much higher exhaust gas temperatures, and sometimes a slight increase in power that can quickly turn into misfires and a drastic loss of power, as well as potential engine damage, at ultra-lean air-to-fuel ratios. If modifications cause the engine to run rich, then there will be a slight increase in power to a point (after which the engine starts flooding from too much unburned fuel), but at the cost of decreased fuel economy, and an increase in unburned hydrocarbons in the exhaust which causes overheating of the catalytic converter. Prolonged operation at rich mixtures can cause catastrophic failure of the catalytic converter (see backfire). The ECU also controls the spark engine timing along with the fuel injector pulse width, so modifications which alter the engine to operate either too lean or too rich may result in inefficient fuel consumption whenever fuel is ignited too soon or too late in the combustion cycle. When an internal combustion engine is under high load (e.g. wide open throttle), the output of the oxygen sensor is ignored, and the ECU automatically enriches the mixture to protect the engine, as misfires under load are much more likely to cause damage. This is referred to as an engine running in 'open-loop mode'. Any changes in the sensor output will be ignored in this state. In many cars (with the exception of some turbocharged models), inputs from the air flow meter are also ignored, as they 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. 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. The sensors were introduced in the US from about 1979, 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 (14.7:1 air:fuel by mass for gasoline) to ensure complete combustion. The sensor element is a ceramic cylinder plated inside and out with porous platinum electrodes; the whole assembly is protected by a metal gauze. 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 316 °C (600 °F), so most newer lambda probes have heating elements encased in the ceramic that bring the ceramic tip up to temperature quickly. Older probes, without heating elements, would eventually be heated by the exhaust, but there is a time lag between when the engine is started and when the components in the exhaust system come to a thermal equilibrium. The length of time required for the exhaust gases to bring the probe to temperature depends on the temperature of the ambient air and the geometry of the exhaust system. Without a heater, the process may take several minutes. There are pollution problems that are attributed to this slow start-up process, including a similar problem with the working temperature of a catalytic converter. 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. The zirconium dioxide, or zirconia, lambda sensor is based on a solid-state electrochemical fuel cell called the Nernst cell. 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" of fuel and oxygen, 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). An output voltage 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 setpoint is approximately 0.45 V (450 mV) DC. This is where the quantities of air and fuel are in the optimum ratio, which is ~0.5% lean of the stoichiometric point, such that the exhaust output contains minimal carbon monoxide. The voltage produced by the sensor is nonlinear with respect to oxygen concentration. The sensor is most sensitive near the stoichiometric point and less sensitive when either very lean or very rich. The ECU is a control system that uses feedback from the sensor to adjust the fuel/air mixture. As in all control systems, the time constant of the sensor is important; the ability of the ECU to control the fuel-air-ratio depends upon the response time of the sensor. An aging or fouled sensor tends to have a slower response time, which can degrade system performance. The shorter the time period, the higher the so-called "cross count" 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. A variation on the zirconia sensor, called the "wideband" sensor, was introduced by Robert Bosch in 1994, and has been widely used for car engine management systems in order to meet the ever-increasing demands for better fuel economy, lower emissions and better engine performance at the same time. 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. 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. The wideband zirconia sensor is used in stratified fuel injection systems, and can now also be used in diesel engines to satisfy the upcoming EURO and ULEV emission limits. Wideband sensors have three elements: The wiring diagram for the wideband sensor typically has six wires: A less common type of narrow-band lambda sensor has a ceramic element made of titania (titanium dioxide). This type does not generate its own voltage, but changes its electrical resistance in response to the oxygen concentration. 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 1/1000 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 (lower oxygen concentration) the resistance is low, and for fuel-lean exhaust (higher oxygen concentration) the resistance is high. The control unit feeds the sensor with a small electrical current and measures the resulting voltage drop across the sensor, which varies from near 0 volts to about 5 volts. Like the zirconia sensor, this type is nonlinear, such that it is sometimes simplistically described as a binary indicator, reading either "rich" or "lean". 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. The probe is typically screwed into a threaded hole in the exhaust system, located after the branch manifold of the exhaust system combines, and before the catalytic converter. 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. 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. Normally, the lifetime of an unheated sensor is about 30,000 to 50,000 miles (50,000 to 80,000 km). Heated sensor lifetime is typically 100,000 miles (160,000 km). 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. The probe then tends to report lean mixture, the ECU enriches the mixture, the exhaust gets rich with carbon monoxide and hydrocarbons, and the fuel economy 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). 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. Some sensors have an air inlet to the sensor in the lead, so contamination from the lead caused by water or oil leaks can be sucked into the sensor and cause failure. Symptoms of a failing oxygen sensor includes: The diving type of oxygen sensor, which is sometimes called an oxygen analyser or ppO2 meter, is used in scuba diving. They are used to measure the oxygen concentration of breathing gas mixes such as nitrox and trimix. They are also used within the oxygen control mechanisms of closed-circuit rebreathers to keep the partial pressure of oxygen within safe limits. This type of sensor operates by measuring the electricity generated by a small electro-galvanic fuel cell. In soil respiration studies oxygen sensors can be used in conjunction with carbon dioxide sensors to help improve the characterization of soil respiration. Typically, soil oxygen sensors use a galvanic cell to produce a current flow that is proportional to the oxygen concentration being measured. These sensors are buried at various depths to monitor oxygen depletion over time, which is then used to predict soil respiration rates. Generally, these soil sensors are equipped with a built-in heater to prevent condensation from forming on the permeable membrane, as relative humidity can reach 100% in soil. 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. The traditional way of measuring oxygen concentration in a water sample has been to use wet chemistry techniques e.g. the Winkler titration method. 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). The Clark-type electrode is the most used oxygen sensor for measuring oxygen dissolved in a liquid. The basic principle is that there is a cathode and an anode submersed in an electrolyte. Oxygen enters the sensor through a permeable membrane by diffusion, and is reduced at the cathode, creating a measurable electrical current. 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. 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. An oxygen optode is a sensor based on optical measurement of the oxygen concentration. 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 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. 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. That is, the sensitivity decreases as oxygen concentration increases following the Stern–Volmer relationship. 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. 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. These type of electrode sensors can be used for insitu and realtime monitoring of Oxygen production in water splitting reactions. The platinized electrodes can accomplish the real time monitoring of Hydrogen production in water splitting device. Calzaferri and his co workers employed this type of electrodes very extensively for photoelectrochemical water splitting research.][
A throttle position sensor (TPS) is a sensor used to monitor the position of the throttle in an internal combustion engine. The sensor is usually located on the butterfly spindle/shaft so that it can directly monitor the position of the throttle. More advanced forms of the sensor are also used, for example an extra closed throttle position sensor (CTPS) may be employed to indicate that the throttle is completely closed. Some engine control units (ECUs) also control the throttle position electronic throttle control (ETC) or "drive by wire" systems and if that is done the position sensor is used in a feedback loop to enable that control. Related to the TPS are accelerator pedal sensors, which often include a wide open throttle (WOT) sensor. The accelerator pedal sensors are used in electronic throttle control (ETC) or "drive by wire" systems, and the most common use of a wide open throttle sensor is for the kick-down function on automatic transmissions. Modern day sensors are non contact type. These modern non contact TPS include Hall effect sensors, Inductive sensors, magnetoresistive and others. In the potentiometric type sensors, a multi-finger metal brush/rake is in contact with a resistive strip, while the butterfly valve is turned from the lower mechanical stop (minimum air position) to WOT, there is a change in the resistance and this change in resistance is given as the input to the ECU. Non contact type TPS work on the principle of Hall effect or Inductive sensors, or magnetoresistive technologies, wherein generally the magnet or inductive loop is the dynamic part which is mounted on the butterfly valve throttle spindle/shaft gear and the sensor & signal processing circuit board is mounted within the ETC gear box cover and is stationary. When the magnet/inductive loop mounted on the spindle which is rotated from the lower mechanical stop to WOT, there is a change in the magnetic field for the sensor. The change in the magnetic field is sensed by the sensor and the voltage generated is given as the input to the ECU. Normally a two pole rare earth magnet is used for the TPS due to their high Curie temperatures required in the under-hood vehicle environment. The magnet may be of diametrical type, ring type, rectangular or segment type. The magnet is defined to have a certain magnetic field that does not vary significantly with time or temperature. In case of failure of the TPS operation the CHECK ENGINE light remains illuminated even if there is no problem or error in the ECU. It cannot be corrected by clearing ECU errors by running diagnostic software. In order to rectify the malfunction the TPS needs to be replaced by a new one.
A Hall effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications. In its simplest form, the sensor operates as an analog transducer, directly returning a voltage. With a known magnetic field, its distance from the Hall plate can be determined. Using groups of sensors, the relative position of the magnet can be deduced. Electricity carried through a conductor will produce a magnetic field that varies with current, and a Hall sensor can be used to measure the current without interrupting the circuit. Typically, the sensor is integrated with a wound core or permanent magnet that surrounds the conductor to be measured. Frequently, a Hall sensor is combined with circuitry that allows the device to act in a digital (on/off) mode, and may be called a switch in this configuration. Commonly seen in industrial applications such as the pictured pneumatic cylinder, they are also used in consumer equipment; for example some computer printers use them to detect missing paper and open covers. When high reliability is required, they are used in keyboards. A wheel topped with two magnets that pass by a Hall effect sensor Hall sensors are commonly used to time the speed of wheels and shafts, such as for internal combustion engine ignition timing, tachometers and anti-lock braking systems. They are used in brushless DC electric motors to detect the position of the permanent magnet. In the pictured wheel with two equally spaced magnets, the voltage from the sensor will peak twice for each revolution. This arrangement is commonly used to regulate the speed of disk drives. A Hall probe contains an indium compound semiconductor crystal such as indium antimonide, mounted on an aluminum backing plate, and encapsulated in the probe head. The plane of the crystal is perpendicular to the probe handle. Connecting leads from the crystal are brought down through the handle to the circuit box. When the Hall probe is held so that the magnetic field lines are passing at right angles through the sensor of the probe, the meter gives a reading of the value of magnetic flux density (B). A current is passed through the crystal which, when placed in a magnetic field has a “Hall effect” voltage developed across it. The Hall effect is seen when a conductor is passed through a uniform magnetic field. The natural electron drift of the charge carriers causes the magnetic field to apply a Lorentz force (the force exerted on a charged particle in an electromagnetic field) to these charge carriers. The result is what is seen as a charge separation, with a build up of either positive or negative charges on the bottom or on the top of the plate. The crystal measures 5 mm square. The probe handle, being made of a non-ferrous material, has no disturbing effect on the field. A Hall probe can be used to measure the Earth's magnetic field. It must be held so that the Earth's field lines are passing directly through it. It is then rotated quickly so the field lines pass through the sensor in the opposite direction. The change in the flux density reading is double the Earth's magnetic flux density. A Hall probe must first be calibrated against a known value of magnetic field strength. For a solenoid the Hall probe is placed in the center. Hall effect sensors may require analog circuitry to be interfaced to microprocessors. These interfaces may include input diagnostics, fault protection for transient conditions, and short/open circuit detection. It may also provide and monitor the current to the hall effect sensor itself. There are precision IC products available to handle these features.
A sensor (also called detector) is a converter that measures a physical quantity and converts it into a signal which can be read by an observer or by an (today mostly electronic) instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated glass tube. A thermocouple converts temperature to an output voltage which can be read by a voltmeter. For accuracy, most sensors are calibrated against known standards. Sensors are used in everyday objects such as touch-sensitive elevator buttons (tactile sensor) and lamps which dim or brighten by touching the base. There are also innumerable applications for sensors of which most people are never aware. Applications include cars, machines, aerospace, medicine, manufacturing and robotics. A sensor is a device which receives and responds to a signal when touched. A sensor's sensitivity indicates how much the sensor's output changes when the measured quantity changes. For instance, if the mercury in a thermometer moves 1 cm when the temperature changes by 1 °C, the sensitivity is 1 cm/°C (it is basically the slope Dy/Dx assuming a linear characteristic). Sensors that measure very small changes must have very high sensitivities. Sensors also have an impact on what they measure; for instance, a room temperature thermometer inserted into a hot cup of liquid cools the liquid while the liquid heats the thermometer. Sensors need to be designed to have a small effect on what is measured; making the sensor smaller often improves this and may introduce other advantages. Technological progress allows more and more sensors to be manufactured on a microscopic scale as microsensors using MEMS technology. In most cases, a microsensor reaches a significantly higher speed and sensitivity compared with macroscopic approaches. A good sensor obeys the following rules: Ideal sensors are designed to be linear or linear to some simple mathematical function of the measurement, typically logarithmic. The output of such a sensor is an analog signal and linearly proportional to the value or simple function of the measured property. The sensitivity is then defined as the ratio between output signal and measured property. For example, if a sensor measures temperature and has a voltage output, the sensitivity is a constant with the unit [V/K]; this sensor is linear because the ratio is constant at all points of measurement. For an analog sensor signal to be processed, or used in digital equimpent, it needs to be converted to a digital signal, using an analog-to-digital converter. If the sensor is not ideal, several types of deviations can be observed: All these deviations can be classified as systematic errors or random errors. Systematic errors can sometimes be compensated for by means of some kind of calibration strategy. Noise is a random error that can be reduced by signal processing, such as filtering, usually at the expense of the dynamic behavior of the sensor. The resolution of a sensor is the smallest change it can detect in the quantity that it is measuring. Often in a digital display, the least significant digit will fluctuate, indicating that changes of that magnitude are only just resolved. The resolution is related to the precision with which the measurement is made. For example, a scanning tunneling probe (a fine tip near a surface collects an electron tunneling current) can resolve atoms and molecules. All living organisms contain biological sensors with functions similar to those of the mechanical devices described. Most of these are specialized cells that are sensitive to: In biomedicine and biotechnology, sensors which detect analytes thanks to a biological component, such as cells, protein, nucleic acid or biomimetic polymers, are called biosensors. Whereas a non-biological sensor, even organic (=carbon chemistry), for biological analytes is referred to as sensor or nanosensor (such a microcantilevers). This terminology applies for both in vitro and in vivo applications. The encapsulation of the biological component in biosensors, presents a slightly different problem that ordinary sensors; this can either be done by means of a semipermeable barrier, such as a dialysis membrane or a hydrogel, or a 3D polymer matrix, which either physically constrains the sensing macromolecule or chemically constrains the macromolecule by bounding it to the scaffold.
The AFR sensor is an air-fuel ratio sensor that is slowly replacing (or supplementing) the Zirconium oxygen sensor (O2 sensor) in modern motor vehicles.][ The early introduction of the oxygen sensor came about in the late 1970s. Since then Zirconia has been the material of choice for its construction. The Zirconia O2 sensor produces its own voltage, which makes it a type of generator. The varying voltage will display on a scope as a waveform somewhat resembling a sine wave when in closed loop control. The actual voltage that is generated is a measure of the oxygen that is needed to complete the combustion of the CO and HC present at the sensor tip. The stoichiometric air-fuel ratio mixture ratio for gasoline engine is the theoretical air -to- fuel ratio at which all of the fuel will react with all of the available oxygen resulting in complete combustion. At or near this ratio, the combustion process produces the best balance between power and low emissions. At the stoichiometric air-fuel ratio, the generated O2 sensor voltage is about 450 mV. The Engine Control Module (ECM) recognizes a rich condition above the 450 mV level, and a lean condition below it, but does not detect the extent of the richness or leanness. It is for this reason that the Zirconium O2 sensor is called a “narrow-band” O2 sensor. The Titanium O2 sensor was used throughout the late 1980s and early 1990s on a limited basis. This sensor’s semiconductor construction makes its operation different from that of the Zirconium O2 sensor. Instead of generating its own voltage, the Titanium O2 sensor’s electrical resistance changes according to the exhaust oxygen content. When the air/fuel ratio is rich, the resistance of the sensor is around 950 Ohms and more than 21 Kilohms when the mixture is lean. As with the Zirconium sensor, the Titanium O2 sensor is also considered a narrow-band O2 sensor. As mentioned before, the main problem with any narrow-band O2 sensor is that the ECM only detects that the mixture is slightly richer or leaner than the stoichiometric ratio. The ECM does not measure the operating air-fuel ratio outside the stoichiometric range. In effect it only detects that the mixture is richer or leaner than stoichiometry. An O2 sensor voltage that goes lower than 450 mV will cause a widening of injector pulse and vice-versa. The resulting changing or cycling fuel control (closed-loop) O2 signal is what the technician sees on the scope when probing at the O2 sensor signal wire. The newer “wide-band” O2 sensor solves the narrow sensing problem of the previous Zirconium sensors. These sensors are often called by different names such as, continuous lambda sensors (lambda representing air-fuel ratio), AFR (air-fuel ratio sensors), LAF (lean air-fuel sensor) and wide-band O2 sensor. Regardless of the name, the principle is the same, which is to put the ECM in a better position to control the air/fuel mixture. In effect, the wide-band O2 sensor can detect the exhaust’s O2 content way below or above the perfect air/fuel ratio. Such control is needed on new lean burning engines with extremely low emission output levels. Tighter emission regulations and demands for better fuel economy are driving this newer fuel control technology. The wide-band O2 sensor looks similar in appearance to the regular Zirconium O2 sensor. Its inner construction and operation are totally different, however. The Wide-band O2 sensor is composed of a dual inner layer called “Reference cell” and “Pump cell”. The ECM’s AFR sensor circuitry always tries to keep a perfect air/fuel ratio inside a special monitoring chamber (Diffusion Chamber or pump-cell circuit) by way of controlling its current. The AFR sensor uses dedicated electronic circuitry to set a pumping current in the sensor’s pump cell. In other words, if the air/fuel mixture is lean, the pump cell circuit voltage momentarily goes low and the ECM immediately regulates the current going through it in order to maintain a set voltage value or stoichiometric ratio inside the diffusion chamber. The pump cell then discharges the excess oxygen through the diffusion gap by means of the current created in the pump-cell circuit. The ECM senses the current and widens injector pulsation accordingly to add fuel. If on the other hand the air/fuel mixture goes rich, the pump cell circuit voltage rapidly climbs high and the ECM immediately reverses the current polarity to readjust the pump cell circuit voltage to its set stable value. The pump-cell then pumps oxygen into the monitoring chamber by way of the reversed current in the ECM’s AFR pump-cell circuit. The ECM detects the reversed current and an injector pulsation-reduction command is issued bringing the mixture back to lean. Since the current in the pump cell circuit is also proportional to the oxygen concentration or deficiency in the exhaust, it serves as an index of the air/fuel ratio. The ECM is constantly monitoring the pump cell current circuitry, which it always tries to keep at a set voltage. For this reason, the techniques used to test and diagnose the regular Zirconium O2 sensor can not be used to test the wide-band AFR sensor. These sensors are current devices and do not have a cycling voltage waveform. The testing procedures, which will be discussed later, are quite different from the older O2 sensors. The AFR sensor operation can be thought of as being similar to the hot wire Mass airflow sensor (MAF). But, instead of an MAF hot wire, the ECM tries to keep a perfectly stoichiometric air/fuel ratio inside the monitoring chamber by varying the pump cell circuit current. The sensing part, at the tip of the sensor, is always held at a constant voltage (depending on manufacturer). If the mixture goes rich, the ECM will adjust the current flowing through the sensing tip or pump cell circuit until the constant operating voltage level is achieved again. The voltage change happens very fast. The current through the pump circuit also pushes along the oxygen atoms either into, or out of, the diffusion chamber (monitoring chamber) which restores the monitoring chamber’s air/fuel ratio to stoichiometry. Although the ECM varies the current, it tries to maintain the pump circuit at a constant voltage potential. As the ECM monitors the varying current, a special circuit (also inside the PCM (Power-train Control Module) converts the current into a voltage value and passes it on to the serial data stream as a scanner PID. This is why the best way to test an AFR sensor’s signal is by monitoring the voltage conversion circuitry, which the ECM sends out as an AFR-voltage PID. It is possible to monitor the actual AFR sensor varying current, but the changes are very small (in the low milliamp range) and difficult to monitor. A second drawback to a manual AFR current test is that the signal wire has to be cut or broken to connect the ammeter in series with the pump circuit. Today’s average clamp-on ammeter is not accurate enough at such a small scale. For this reason, the easiest (but not the only) way to test an AFR sensor is with the scanner. By using a scanner to communicate with the ECM, one can view AFR sensor activity. This data is typically displayed as WRAF, A/F, or AFR sensor voltage. However, on some vehicles and scanners it will show up as "lambda" or "equivalence ratio." If the PID displays a voltage reading, it should be equal to the sensor's reference voltage when the air/fuel mixture is ideal. The reference voltage varies from car to car, but is often 3.3v or 2.6v. When the fuel mixture becomes richer (on a sudden, quick acceleration), the voltage should decrease. Under lean conditions (such as deceleration) the voltage should increase. If the scanner PID displays a "lambda" or "equivalence ratio," the reading should be 1.0 under stoichiometric conditions. Numbers above 1.0 indicate a lean condition while numbers below 1.0 indicate rich mixtures. The ECM uses the information from the sensors to adjust the amount of fuel being injected into the engine, so corresponding changes in the short-term fuel trim PID(s) should also be seen. Lean mixture readings from the AFR sensor will prompt the ECM to add fuel, which will manifest itself as a positive (or more positive) short-term fuel trim percentage. Some technicians will force the engine to run lean by creating a vacuum leak downstream from the mass airflow sensor, and then watch scanner PIDs for a response. The engine can be forced rich by adding a metered amount of propane to the incoming airflow. In either case, if the sensor does not respond, it likely has a problem. However, these tests do not rule out other circuitry problems or ECM issues. Because an AFR sensor can be relatively expensive (up to $400 U.S dollars), a professional diagnosis is recommended. Another major difference between the wide-band AFR sensor and a Zirconium O2 sensor is that it has an operating temperature above 1200°F (649°C). On these units the temperature is very critical and for this reason a special pulse-width controlled heater circuit is employed to control the heater temperature precisely. The ECM controls the heater circuit. The wide operating range coupled with the inherent fast acting operation of the AFR sensor puts the system always at stoichiometry, which reduces a great deal of emissions. With this type of fuel control, the air/fuel ratio is always hovering close to 14.7:1. If the mixture goes slightly rich the ECM adjusts the pump circuit’s current to maintain the set operating voltage. The current is detected by the ECM’s detection circuit, with the result of a command for a reduction in injector pulsation being issued. As soon as the air-fuel mixture changes back to stoichiometry, because of the reduction in injector pulsation, the ECM will adjust the current respectively. The end result is no current (0.00 amperes) at 14.7:1 air-fuel ratio. In this case a light negative hump is seen on the ammeter with the reading returning to 0.00 almost immediately. The fuel correction happens very quickly.
A hydrogen sensor is a gas detector that detects the presence of hydrogen. They contain micro-fabricated point-contact hydrogen sensors and are used to locate leaks. They are considered low-cost, compact, durable, and easy to maintain as compared to conventional gas detecting instruments. There are five key issues with hydrogen detectors: There are various types of hydrogen microsensors, which use different mechanisms to detect the gas. Palladium is used in many of these, because it selectively absorbs hydrogen gas and forms the compound palladium hydride. Palladium-based sensors have a strong temperature dependence which makes their response time too large at very low temperatures. Palladium sensors have to be protected against carbon monoxide, sulfur dioxide and hydrogen sulfide. Several types of optical fibre surface plasmon resonance (SPR) sensor are used for the point-contact detection of hydrogen: Sensors are typically calibrated at the manufacturing factory and are valid for the service life of the unit. Siloxane enhances the sensitivity and reaction time of hydrogen sensors. Detection of hydrogen levels as low as 25 ppm can be achieved; far below hydrogen's lower explosive limit of around 40,000 ppm.
An air–fuel ratio meter monitors the air–fuel ratio of an internal combustion engine. Also called air–fuel ratio gauge, air–fuel meter, or air–fuel gauge. It reads the voltage output of an oxygen sensor, sometimes also called lambda sensor, whether it be from a narrow band or wide band oxygen sensor. The original narrow-band oxygen sensors became factory installed standard in the late 1970s and early 80s. In recent years, a newer and much more accurate wide-band sensor, though more expensive, has become available. Most stand-alone narrow-band meters have 10 LEDs and some have more. Also common, narrow band meters in round housings with the standard mounting 2 1/16" and 2 5/8" diameters, as other types of car 'gauges'. These usually have 10 or 20 LEDs. Analogue 'needle' style gauges are also available. As stated above, there are wide-band meters that stand alone or are mounted in housings. Nearly all of these show the air–fuel ratio on a numeric display, since the wide-band sensors provide a much more accurate reading. And since they use more accurate electronics, these meters are more expensive. Lean mixtures improve the fuel economy but also cause sharp rises in the amount of nitrogen oxides (NOX). If the mixture becomes too lean, the engine may fail to ignite, causing misfire and a large increase in unburned hydrocarbon (HC) emissions. Lean mixtures burn hotter and may cause rough idle, hard starting and stalling, and can even damage the catalytic converter, or burn valves in the engine. The risk of spark knock/engine knocking (detonation) is also increased when the engine is under load. Mixtures that are richer than stoichiometric allow for greater peak engine power when using vapourized liquid fuels, due to the cooling effect of the evaporating fuel. This increases the intake oxygen density, allowing for more fuel to be combusted and more power developed. The ideal mixture in this type of operation depends on the individual engine. For example, engines with forced induction such as turbochargers and superchargers typically require a richer mixture under wide open throttle than naturally aspirated engines. Forced induction engines can be catastrophically damaged by burning too lean for too long. The leaner the air–fuel mixture, the higher the combustion temperature is inside the cylinder. Too high a temperature will destroy an engine – melting the pistons and valves. This can happen if you port the head and/or manifolds or increase boost without compensating by installing larger or more injectors, and/or increasing the fuel pressure to a sufficient level. Conversely, engine performance can be lessened by increasing fuelling without increasing air flow into the engine. Cold engines also typically require more fuel and a richer mixture when first started (see: cold start injector), because fuel does not vaporize as well when cold and therefore requires more fuel to properly "saturate" the air. Rich mixtures also burn slower and decrease the risk of spark knock/engine knocking (detonation) when the engine is under load. However, rich mixtures sharply increase carbon monoxide (CO) emissions. Oxygen sensors are installed in the exhaust system of the vehicle, attached to the engine's exhaust manifold, the sensor measures the ratio of the air–fuel mixture. As mentioned above, there are two types of sensors available; narrow band and wide band. Narrow-band sensors were the first to be introduced. The wide-band sensor was introduced much later. A narrow-band sensor has a nonlinear output, and switches between the thresholds of lean (ca 100–200 mV) and rich (ca 650–800 mV) areas very steeply. Narrow-band sensors are temperature-dependent. If the exhaust gases become warmer, the output voltage in the lean area will rise, and in the rich area it will be lowered. Consequently, a sensor, without pre-heating, has a lower lean-output and a higher rich-output, possibly even exceeding 1 Volt. The influence of temperature to voltage is smaller in the lean mode than in the rich mode. A "cold" engine makes the sensor switch the output voltage between ca 100 and 850/900 mV and after a while the sensor may output a switch voltage between ca 200 and 700/750mV, for turbocharged cars even less. The engine control unit (ECU) when operating in "closed loop" tend to maintain 0 oxygen (thus a stoichiometric balance), wherein the air–fuel mixture is approximately 14.7 times the mass of air to fuel for gasoline. This ratio maintains a "neutral" engine performance (lower fuel consumption yet decent engine power and minimal pollution). The average level of the sensor is near to 450 mV. Since narrow band sensors cannot output a fixed voltage level between the lean and the rich areas, the ECU controls the engine by providing the mixture between lean (and rich) in such a sufficiently fast manner by means of shorter (or longer)time of signal to injectors, so the average level becomes as said ca 450 mV. A wide-band sensor, on the other hand, has a very linear output, 0–5 V, and is not temperature dependent. If the purpose of the air–fuel ratio meter is to detect also an existing or possible problem with the sensor above of checking the general mixture and performance, a narrow band air-fuel ratio meter is sufficient. In high-performance tuning applications, the wide-band system is desirable.

Diving equipment is equipment used by underwater divers to make diving activities possible, easier, safer and/or more comfortable. This may be equipment primarily intended for this purpose, or equipment intended for other purposes which is found to be suitable for diving use.

Equipment which is used for underwater work or other activities which is not directly related to the activity of diving, or which has not been designed or modified specifically for underwater use by divers is excluded.

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

It was developed by the Robert Bosch GmbH company during the late 1960s under the supervision of Dr. 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. The planar-style sensor entered the market in 1998 (also pioneered by Bosch) 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 started sooner and responded faster.

Air–fuel ratio (AFR) is the mass ratio of air to fuel present in an internal combustion engine. The AFR can also refer to the volume ratio for combustion carried out in industrial furnaces. If exactly enough air is provided to completely burn all of the fuel, the ratio is known as the stoichiometric mixture, often abbreviated to stoich. For precise AFR calculations, the oxygen content of combustion air should be specified because of possible dilution by ambient water vapor, or enrichment by oxygen additions. The AFR is an important measure for anti-pollution and performance-tuning reasons. The lower the AFR, the "richer" the flame.


OBD-II PIDs (On-board diagnostics Parameter IDs) are codes used to request data from a vehicle, used as a diagnostic tool. SAE standard J/1979 defines many PIDs, but manufacturers also define many more PIDs specific to their vehicles. All light duty vehicles (i.e. less than 8,500 pounds) sold in North America since 1996, as well as medium duty vehicles (i.e. 8,500-14,000 pounds) beginning in 2005, and heavy duty vehicles (i.e. greater than 14,000 pounds) beginning in 2010]citation needed[, are required to support OBD-II diagnostics, using a standardized data link connector, and a subset of the SAE J/1979 defined PIDs (or SAE J/1939 as applicable for medium/heavy duty vehicles), primarily for state mandated emissions inspections.

Typically, an automotive technician will use PIDs with a scan tool connected to the vehicle's OBD-II connector.

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The periodic table is a tabular arrangement of the chemical elements, organized on the basis of their atomic numbers, electron configurations, and recurring chemical properties. Elements are presented in order of increasing atomic number (the number of protons in the nucleus). The standard form of the table consists of a grid of elements laid out in 18 columns and 7 rows, with a double row of elements below that. The table can also be deconstructed into four rectangular blocks: the s-block to the left, the p-block to the right, the d-block in the middle, and the f-block below that.

The rows of the table are called periods; the columns are called groups, with some of these having names such as halogens or noble gases. Since, by definition, a periodic table incorporates recurring trends, any such table can be used to derive relationships between the properties of the elements and predict the properties of new, yet to be discovered or synthesized, elements. As a result, a periodic table—whether in the standard form or some other variant—provides a useful framework for analyzing chemical behavior, and such tables are widely used in chemistry and other sciences.

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