A defect detector is a device used on railroads to detect axle and signal problems in passing trains. The detectors are integrated into the tracks and include sensors to detect several different kinds of problems that could occur. Defect detectors were one invention which enabled American railroads to eliminate the caboose at the rear of the train, as well as various station agents stationed along the route to detect unsafe conditions; the use of defect detectors has since spread to other overseas railroads. Before the advent of automated detectors, on-board train crew and track-side workers used to visually inspect trains for defects e.g. "hotboxes" would smoke or glow red. By the 1940s, automatic defect detectors included infrared sensors for hotboxes, wires outlining the clearance envelope to detect high and wide loads, "brittle bars" – frangible bars mounted between the rails – to detect dragging equipment; the detectors would transmit their data via wired links to remote read-outs in stations, offices or interlocking towers, where a stylus-and-cylinder gauge would record a reading for every axle.
The first computerized detectors had lights indicating the nature of defect and a numeric display of the associated axle number. Seaboard Air Line was the first railroad to install defect detectors which "spoke" their results over radios carried by train crew. Models allowed crews to interact with the detector using a touch tone function on their radios to recall the defect report. Today, defect detectors are part of the general monitoring platforms keeping track of train status. A Defect Detector Would Sound Like This: CSX Equipment Defect Detector Milepost 484.6 No Defects Repeat No Defects. Total Axle 721. Train Length 12,973. Track 1. Temperature 63. End Of Transmission; the sensors installed at defect detector locations can include and are explained: Hot boxes or Hot Bearing Detectors are used to measure the temperature of the journal bearings of a train. They consist of two infrared eyes on each side of the tracks looking up at the train's bearings, they register the radiation from every journal.
If a bearing reaches the maximum temperature for safe travel, the detector will flag and count it as a defect. A column of cones sits across the whole width of the railroad attached to a switch. Anything dragging from the train will hit this cone, it returns to its normal position to prepare for anything else that might be dragging under the train. The detector will register this flag it as a defect. Brittle bars are still used elsewhere, but still have to be repaired. Over time, dragging equipment detector's metal flaps need to be replaced because of extensive damage to them. Single use systems involve a frangible engagement bar or a stainless steel wire/braid strung between the rails and outside the rails as well, fastened to the sleepers. If the bar or braid is hit by something it breaks, the circuit break alerts that there is a dragging item. Auto-resetting systems involve a pivot pin system to allow the target to reset itself after a hit. Infrared beams are placed horizontally above the track or vertically next to the track.
Anything that breaks the beam will be counted as a defect. A high car detector is placed anywhere an excess height car could be routed onto a low clearance line. A shifted load detector is found on railroads where double-stack trains are prevalent as the containers may become misaligned and present a hazard to bridge trusses or tunnel walls. Wheel sensors along the tracks feel for flat spots on the train's wheels. Any flat wheel that becomes too dangerous to travel on will be counted as a defect; these systems utilize accelerometers, strain gauges, fiber optic methods, or the latest wheel impact phase detector. A wheel impact load detector measures impacts, but does not normalize these impact measurements against anything: the impact reading, they do not attempt to cater for differences in sprung mass, as they are measuring wheel defect impact rather than impact load. Therefore, the same wheel defect will register a much larger impact when a wagon is loaded, versus when it is empty. A wheel condition monitoring detector monitors the condition of the wheel independent of sprung mass – independent of load.
They do this by subtracting the wheel mass to get the normalized impact value. These systems are therefore better at detecting smaller defects with greater resolution. A length of side looking infrared detectors that can detect if a wheel has locked up and is sliding along the track or has had the brakes lock up causing the entire wheel to heat up; these detectors are a crude weighbridge and/or WILD system, as they are only concerned with measuring weight differentials. They do not have to be as accurate as proper weighbridge or WILD systems, but just accurate enough to be able to average the weight of bogies during a train pass to calculate the relative balance of wagons, to establish if one rail is loaded unacceptably greater than the other; this is not performed on empty wagons because of the significant percentage imbalances that can be caused by fluctuations in weight due to bogie tracking geometry or hunting issues, which in terms of weight differentials are accentuated compared to when a wagon is loaded.
These detectors can use a variety of sensors, but they are a safety curta
An oxygen sensor is an electronic device that measures the proportion of oxygen in the gas or liquid being analysed. It was developed by Robert Bosch GmbH 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 1990 and reduced the mass of the ceramic sensing element, as well as incorporating the heater within the ceramic structure; this resulted in a sensor that responded faster. The most common application is to measure the exhaust-gas concentration of oxygen for internal combustion engines in automobiles and other vehicles in order to calculate and, if required, dynamically adjust the air-fuel ratio so that catalytic converters can work optimally, determine whether the converter is performing properly or not. Divers 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 extensive use in medical applications such as anesthesia monitors and oxygen concentrator so. Oxygen sensors are used in hypoxic air fire prevention systems to continuously monitor the oxygen concentration inside the protected volumes. There are many different ways of measuring oxygen; these include technologies such as zirconia, infrared, ultrasonic and recently, laser methods. Automotive oxygen sensors, colloquially known as O2 sensors, make modern electronic fuel injection and emission control possible, they help determine, in real time, whether 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 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 are a result of combustion chamber temperatures exceeding 1300 kelvins, due to excess air in the fuel mixture therefore 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 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. 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, 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 gained from the oxygen sensor. The primary goal is a compromise between power, fuel economy, emissions, in most cases is achieved by an air–fuel ratio close to stoichiometric. For spark-ignition engines, the three types of emissions modern systems are concerned with are: hydrocarbons, carbon monoxide and NOx. 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 damage the vehicle.
When the engine is under low-load conditions, it is operating in "closed-loop mode". This refers to a feedback loop between the ECU and the oxygen sensor 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 lean and rich on successive loops, as it attempts to maintain a stoichiometric ratio on average. If modifications cause the engine to run moderately lean, there will be a slight increase in fuel efficiency, sometimes at the expense of increased NOx emissions, much higher exhaust gas temperatures, sometimes a slight increase in power that can turn into misfires and a drastic loss of power, as well as potential engine and catalytic-converter damage, at ultra-lean air–fuel ratios. If modifications cause the engine to run rich there will be a slight increase in power to a point (after which the engine starts flooding from too mu
A yaw rotation is a movement around the yaw axis of a rigid body that changes the direction it is pointing, to the left or right of its direction of motion. The yaw rate or yaw velocity of a car, projectile or other rigid body is the angular velocity of this rotation, or rate of change of the heading angle when the aircraft is horizontal, it is measured in degrees per second or radians per second. Another important concept is the yaw moment, or yawing moment, the component of a torque about the yaw axis. Yaw velocity can be measured by measuring the ground velocity at two geometrically separated points on the body, or by a gyroscope, or it can be synthesized from accelerometers and the like, it is the primary measure of. It is important in electronic stabilized vehicles; the yaw rate is directly related to the lateral acceleration of the vehicle turning at constant speed around a constant radius, by the relationship tangential speed*yaw velocity = lateral acceleration = tangential speed^2/radius of turn, in appropriate unitsThe sign convention can be established by rigorous attention to coordinate systems.
In a more general manoeuvre where the radius is varying, and/or the speed is varying, the above relationship no longer holds. The yaw rate can be measured with accelerometers in the vertical axis. Any device intended to measure the yaw rate is called a yaw rate sensor. Studying the stability of a road vehicle requires a reasonable approximation to the equations of motion; the diagram illustrates a four-wheel vehicle, in which the front axle is located a metres ahead of the centre of gravity and the rear axle is b metres towards the rear from the center of gravity. The body of the car is pointing in a direction θ while it is travelling in a direction ψ. In general, these are not the same; the tyre treads at the region of contact point in the direction of travel, but the hubs are aligned with the vehicle body, with the steering held central. The tyres distort as they rotate to accommodate this mis-alignment, generate side forces as a consequence. From directional stability study, denoting the angular velocity ω, the equations of motion are: d ω d t = 2 k I β − 2 k V I ω d β d t = − 4 k M V β + M V 2 ω The coefficient of d β d t will be called the'damping' by analogy with a mass-spring-damper which has a similar equation of motion.
By the same analogy, the coefficient of β will be called the'stiffness', as its function is to return the system to zero deflection, in the same manner as a spring. The form of the solution depends only on the signs of the damping and stiffness terms; the four possible solution types are presented in the figure. The only satisfactory solution requires both damping to be positive. If the centre of gravity is ahead of the centre of the wheelbase (, this will always be positive, the vehicle will be stable at all speeds. However, if it lies further aft, the term has the potential of becoming negative above a speed given by: V 2 = 2 k 2 M Above this speed, the vehicle will be directionally unstable. Corrections for relative effect of front and rear tyres and steering forces are available in the main article; these rotations are intrinsic rotations and the calculus behind them is similar to the Frenet-Serret formulas. Performing a rotation in an intrinsic reference frame is equivalent to right-multiply its characteristic matrix by the matrix of the rotation.
The first aircraft to demonstrate active control about all three axes was the Wright brothers' 1902 glider. Adverse yaw Aircraft principal axes Coriolis acceleration Directional stability Flight dynamics Six degrees of freedom Vehicle dynamics Yaw rate sensor
Mass flow sensor
A mass flow sensor is a sensor used to determine the mass flow rate of air entering a fuel-injected internal combustion engine. The air mass information is necessary for the engine control unit to balance and deliver the correct fuel mass to the engine. Air changes its density with pressure. In automotive applications, air density varies with the ambient temperature and the use of forced induction, which means that mass flow sensors are more appropriate than volumetric flow sensors for determining the quantity of intake air in each cylinder. There are two common types of mass airflow sensors in use on automotive engines; these are the hot wire. Neither design employs technology. However, with additional sensors and inputs, an engine's ECU can determine the mass flow rate of intake air. Both approaches are used exclusively on electronic fuel injection engines. Both sensor designs output a 0.0–5.0 volt or a pulse-width modulation signal, proportional to the air mass flow rate, both sensors have an intake air temperature sensor incorporated into their housings for most post on-board diagnostics vehicles.
Vehicles prior to 1996 could have MAF without an IAT. An example is 1994 Infiniti Q45; when a MAF sensor is used in conjunction with an oxygen sensor, the engine's air/fuel ratio can be controlled accurately. The MAF sensor provides the open-loop controller predicted air flow information to the ECU, the oxygen sensor provides closed-loop feedback in order to make minor corrections to the predicted air mass. See manifold absolute pressure sensor; the VAF sensor measures the air flow into the engine with a spring-loaded air vane attached to a variable resistor. The vane moves in proportion to the airflow. A voltage is applied to the potentiometer and a proportional voltage appears on the output terminal of the potentiometer in proportion to the angle the vane rotates, or the movement of the vane may directly regulate the amount of fuel injected, as in the K-Jetronic system. Many VAF sensors have an air-fuel adjustment screw, which opens or closes a small air passage on the side of the VAF sensor.
This screw controls the air-fuel mixture by letting a metered amount of air flow past the air flap, thereby leaning or richening the mixture. By turning the screw clockwise the mixture is counterclockwise the mixture is leaned; the vane moves because of the drag force of the air flow against it. The drag force depends on air velocity and the shape of the vane, see drag equation; some VAF sensors include an additional intake air temperature sensor to allow the engines ECU to calculate the density of the air, the fuel delivery accordingly. The vane meter approach has some drawbacks: it restricts airflow which limits engine output its moving electrical or mechanical contacts can wear finding a suitable mounting location within a confined engine compartment is problematic the vane has to be oriented with respect to gravity. In some manufacturers fuel pump control was part on the VAF internal wiring. A hot wire mass airflow sensor determines the mass of air flowing into the engine’s air intake system.
The theory of operation of the hot wire mass airflow sensor is similar to that of the hot wire anemometer. This is achieved by heating a wire suspended in the engine’s air stream, like a toaster wire, with either a constant voltage over the wire or a constant current through the wire; the wire's electrical resistance increases as the wire’s temperature increases, which varies the electrical current flowing through the circuit, according to Ohm's law. When air flows past the wire, the wire cools, decreasing its resistance, which in turn allows more current to flow through the circuit, since the supply voltage is a constant; as more current flows, the wire’s temperature increases until the resistance reaches equilibrium again. The current increase or decrease is proportional to the mass of air flowing past the wire; the integrated electronic circuit converts the proportional measurement into a calibrated signal, sent to the ECU. If air density increases due to pressure increase or temperature drop, but the air volume remains constant, the denser air will remove more heat from the wire indicating a higher mass airflow.
Unlike the vane meter's paddle sensing element, the hot wire responds directly to air density. This sensor's capabilities are well suited to support the gasoline combustion process which fundamentally responds to air mass, not air volume; this sensor sometimes employs a mixture screw, but this screw is electronic and uses a variable resistor instead of an air bypass screw. The screw needs more turns to achieve the desired results. A hot wire burn-off cleaning circuit is employed on some of these sensors. A burn-off relay applies a high current through the platinum hot wire after the vehicle is turned off for a second or so, thereby burning or vaporizing any contaminants that have stuck to the platinum hot wire element; the hot film MAF sensor works somewhat similar to the hot wire MAF sensor, but instead it outputs a frequency signal. This sensor uses a hot film-grid instead of a hot wire, it is found in late 80’s early 90’s fuel-injected vehicles. The output frequency is directly proportional to the air mass entering the engine.
So as mass flow increases so does frequency. These sensors tend to cause intermittent problems due to internal electrical failures; the use of an oscilloscope is recommended to check the outp
Catalytic bead sensor
A catalytic bead sensor is a type of sensor, used for combustible gas detection from the family of gas sensors known as pellistors. The catalytic bead sensor consists of two coils of fine platinum wire each embedded in a bead of alumina, connected electrically in a Wheatstone bridge circuit. One of the pellistors is impregnated with a special catalyst which promotes oxidation whilst the other is treated to inhibit oxidation. Current is passed through the coils so that they reach a temperature at which oxidation of a gas occurs at the catalysed bead. Passing combustible gas raises the temperature further which increases the resistance of the platinum coil in the catalysed bead, leading to an imbalance of the bridge; this output change is linear, for most gases, up to and beyond 100% LEL, response time is a few seconds to detect alarm levels, at least 12% oxygen by volume is needed for the oxidation. Catalyst poisoning - because of the direct contact of the gas with the catalytic surface it may be deactivated in some circumstances.
Sensor drift - Decreased sensitivity may occur depending on operating and ambient conditions. Modes of failure - which include poisoning and sinter blockage, they become apparent during routine maintenance checking. List of sensors
Variable reluctance sensor
A variable reluctance sensor is a transducer that measures changes in magnetic reluctance. When combined with basic electronic circuitry, the sensor detects the change in presence or proximity of ferrous objects. With more complex circuitry and the addition of software and specific mechanical hardware, a VR sensor can provide measurements of linear velocity, angular velocity and torque. A VR sensor used as a simple proximity sensor can determine the position of a mechanical link in a piece of industrial equipment. A Crankshaft position sensor is used to provide the angular position of the crankshaft to the Engine control unit; the Engine control unit can calculate engine speed. Speed sensors used in automobile transmissions, are used to measure the rotational speed of shafts within the transmission; the Engine control unit or Transmission control unit uses these sensors to determine when to shift from one gear to the next. A pickup used in an electric guitar detect vibrations of the metallic "strings".
See Pickup for details of this application. This sensor consists of a permanent magnet, a ferromagnetic pole piece, coil of wire. VR sensor interface circuits VR sensors need waveform shaping for their output to be digitally readable; the normal output of a VR sensor is an analog signal, shaped much like a sine wave. The frequency and amplitude of the analog signal is proportional to the target's velocity; this waveform needs to be squared up, flattened off by a comparator like electronic chip to be digitally readable. While discrete VR sensor interface circuits can be implemented, the semiconductor industry offers integrated solutions. Examples are the MAX9924 to MAX9927 VR sensor interface IC from Maxim Integrated products, LM1815 VR sensor amplifier from National Semiconductor and NCV1124 from ON semiconductor. An integrated VR sensor interface circuit like the MAX9924 features a differential input stage to provide enhanced noise immunity, Precision Amplifier and Comparator with user enabled Internal Adaptive Peak Threshold or user programmed external threshold to provide a wide dynamic range and zero-crossing detection circuit to provide accurate phase Information.
To measure angular position or rotational speed of a shaft, a toothed ring made of ferrous material can be attached to the shaft. As the teeth of the rotating wheel pass by the face of the magnet, the amount of magnetic flux passing through the magnet and the coil varies; when the gear tooth is close to the sensor, the flux is at a maximum. When the tooth is further away, the flux drops off; the moving target results in a time-varying flux. Subsequent electronics are used to process this signal to get a waveform that can be more counted and timed; this system has been employed in ABS braking. By attaching two reluctor rings to a shaft, the torque can be measured; the tooth spacing on reluctor rings may be uneven. Although VR sensors are based on mature technology, they still offer several significant advantages; the first is low cost - coils of wire and magnets are inexpensive. The low cost of the transducer is offset by the cost of the additional signal-processing circuitry needed to recover a useful signal.
And because the magnitude of the signal developed by the VR sensor is proportional to target speed, it is difficult to design circuitry to accommodate very-low-speed signals. A given VR-sensing system has a definite limit as to how slow the target can move and still develop a usable signal. An alternative but more expensive technology is Hall effect sensor. Hall effect sensors are true zero-rpm sensors and supply information when there's no transmission motion at all. One area in which VR sensors excel, however, is in high-temperature applications; because operating temperature is limited by the characteristics of the materials used in the device, with appropriate construction VR sensors can be made to operate at temperatures in excess of 300 °C. An example of such an extreme application is sensing the turbine speed of a jet engine or engine cam shaft and crankshaft position control in an automobile
Internal combustion engine cooling
Internal combustion engine cooling uses either air or liquid to remove the waste heat from an internal combustion engine. For small or special purpose engines, cooling using air from the atmosphere makes for a lightweight and simple system. Watercraft can use water directly from the surrounding environment to cool their engines. For water-cooled engines on aircraft and surface vehicles, waste heat is transferred from a closed loop of water pumped through the engine to the surrounding atmosphere by a radiator. Water has a higher heat capacity than air, can thus move heat more away from the engine, but a radiator and pumping system add weight and cost. Higher-power engines generate more waste heat, but can move more weight, meaning they are water-cooled. Radial engines allow air to flow around each cylinder directly, giving them an advantage for air cooling over straight engines, flat engines, V engines. Rotary engines have a similar configuration, but the cylinders continually rotate, creating an air flow when the vehicle is stationary.
Aircraft design more favors lower weight and air-cooled designs. Rotary engines were popular on aircraft until the end of World War I, but had serious stability and efficiency problems. Radial engines were popular until the end of World War II, until gas turbine engines replaced them. Modern propeller-driven aircraft with internal-combustion engines are still air-cooled. Modern cars favor power over weight, have water-cooled engines. Modern motorcycles are lighter than cars, both cooling fluids are common; some sport motorcycles were cooled with both oil. Heat engines generate mechanical power by extracting energy from heat flows, much as a water wheel extracts mechanical power from a flow of mass falling through a distance. Engines are inefficient, so more. Internal combustion engines remove waste heat through cool intake air, hot exhaust gases, explicit engine cooling. Engines with higher efficiency less as waste heat; some waste heat is essential: it guides heat through the engine, much as a water wheel works only if there is some exit velocity in the waste water to carry it away and make room for more water.
Thus, all heat engines need cooling to operate. Cooling is needed because high temperatures damage engine materials and lubricants and becomes more important in hot climates. Internal-combustion engines burn fuel hotter than the melting temperature of engine materials, hot enough to set fire to lubricants. Engine cooling removes energy fast enough to keep temperatures low; some high-efficiency engines run without explicit cooling and with only incidental heat loss, a design called adiabatic. Such engines can achieve high efficiency but compromise power output, duty cycle, engine weight and emissions. Most internal combustion engines are fluid cooled using either air or a liquid coolant run through a heat exchanger cooled by air. Marine engines and some stationary engines have ready access to a large volume of water at a suitable temperature; the water may be used directly to cool the engine, but has sediment, which can clog coolant passages, or chemicals, such as salt, that can chemically damage the engine.
Thus, engine coolant may be run through a heat exchanger, cooled by the body of water. Most liquid-cooled engines use a mixture of water and chemicals such as antifreeze and rust inhibitors; the industry term for the antifreeze mixture is engine coolant. Some antifreezes use no water at all, instead using a liquid with different properties, such as propylene glycol or a combination of propylene glycol and ethylene glycol. Most "air-cooled" engines use some liquid oil cooling, to maintain acceptable temperatures for both critical engine parts and the oil itself. Most "liquid-cooled" engines use some air cooling, with the intake stroke of air cooling the combustion chamber. An exception is Wankel engines, where some parts of the combustion chamber are never cooled by intake, requiring extra effort for successful operation. There are many demands on a cooling system. One key requirement is to adequately serve the entire engine, as the whole engine fails if just one part overheats. Therefore, it is vital.
Liquid-cooled engines are able to vary the size of their passageways through the engine block so that coolant flow may be tailored to the needs of each area. Locations with either high peak temperatures or high heat flow may require generous cooling; this reduces the occurrence of hot spots. Air-cooled engines may vary their cooling capacity by using more spaced cooling fins in that area, but this can make their manufacture difficult and expensive. Only the fixed parts of the engine, such as the block and head, are cooled directly by the main coolant system. Moving parts such as the pistons, to a lesser extent the crank and rods, must rely on the lubrication oil as a coolant, or to a limited amount of conduction into the block and thence the main coolant. High performance engines have additional oil, beyond the amount needed for lubrication, sprayed upwards onto the bottom of the piston just for extra cooling. Air-cooled motorcycles rely on oil-cooling in addition to air-cooling of the cylinder barrels.
Liquid-cooled engines have a circulation pump. The first engines relied