Carbon monoxide detector
A carbon monoxide detector or CO detector is a device that detects the presence of the carbon monoxide gas in order to prevent carbon monoxide poisoning. In the late 1990s Underwriters Laboratories changed their definition of a single station CO detector with a sound device in it to a carbon monoxide alarm; this applies to all CO safety alarms. CO is a colorless and odorless compound produced by incomplete combustion of carbon-containing materials, it is referred to as the "silent killer" because it is undetectable by humans without using detection technology and, in a study by Underwriters Laboratories, "Sixty percent of Americans could not identify any potential signs of a CO leak in the home". Elevated levels of CO can be dangerous to humans depending on the amount present and length of exposure. Smaller concentrations can be harmful over longer periods of time while increasing concentrations require diminishing exposure times to be harmful. CO detectors are designed to measure CO levels over time and sound an alarm before dangerous levels of CO accumulate in an environment, giving people adequate warning to safely ventilate the area or evacuate.
Some system-connected detectors alert a monitoring service that can dispatch emergency services if necessary. While CO detectors do not serve as smoke detectors and vice versa, dual smoke/CO detectors are sold. Smoke detectors warn of smoldering or flaming fires by detecting the smoke they generate, whereas CO detectors detect and warn people about dangerous CO buildup caused, for example, by a malfunctioning fuel-burning device. In the home, some common sources of CO include open flames, space heaters, water heaters, blocked chimneys or running a car or grill inside a garage; the devices, which retail for $15–$60 USD and are available, can either be battery-operated or AC powered. Battery lifetimes have been increasing as the technology has developed and certain battery-powered devices now advertise a battery lifetime of up to 10 years. All CO detectors have "test" buttons like smoke detectors. CO detectors can be placed near the ceiling or near the floor because CO is close to the same density as air.
Since CO is colorless and odorless, detection in a home environment is impossible without such a warning device. It is a toxic inhalant and attaches to the hemoglobin with an affinity 200x stronger than oxygen, producing inadequate amounts of oxygen traveling through the body; when carbon monoxide detectors were introduced into the market, they had a limited lifespan of 2 years. However technology developments have increased this and many now advertise up to 10 years. Newer models are designed to signal a need to be replaced after that time-span although there are many instances of detectors operating far beyond this point. According to the 2005 edition of the carbon monoxide guidelines, NFPA 720, published by the National Fire Protection Association, sections 22.214.171.124 and 126.96.36.199, all CO detectors “shall be centrally located outside of each separate sleeping area in the immediate vicinity of the bedrooms,” and each detector “shall be located on the wall, ceiling or other location as specified in the installation instructions that accompany the unit.”
According to the 2009 edition of the IRC, published by the International Code Council, section R315.1, "For new construction, an approved carbon monoxide alarm shall be installed outside of each separate sleeping area in the immediate vicinity of the bedrooms in dwelling units within which fuel-fired appliances are installed and in dwelling units that have attached garages", section 315.2, "Where work requiring a permit occurs in existing dwellings that have attached garages or in existing dwellings within which fuel-fired appliances exist, carbon monoxide alarms shall be provided in accordance with Section R315.1." Installation locations vary by manufacturer. Manufacturers’ recommendations differ to a certain degree based on research conducted with each one’s specific detector. Therefore, make sure to read the provided installation manual for each detector before installing. CO detectors are available as system-connected, monitored devices. System-connected detectors, which can be wired to either a security or fire panel, are monitored by a central station.
In case the residence is empty, the residents are sleeping or occupants are suffering from the effects of CO, the central station can be alerted to the high concentrations of CO gas and can send the proper authorities to investigate. The gas sensors in CO alarms have a limited and indeterminable life span two to five years; the test button on a CO alarm only tests the circuitry, not the sensor. CO alarms should be tested with an external source of calibrated test gas, as recommended by the latest version of NFPA 720. Alarms over five years old should be replaced but they should be checked on installation and at least annually during the manufacturers warranty period. Early designs were a white pad which would fade to a brownish or blackish color if carbon monoxide was present; such chemical detectors were cheap and were available, but only give a visual warning of a problem. As carbon monoxide related deaths increased during the 1990s, audible alarms became standard; the alarm points on carbon monoxide detectors are not a simple alarm level but are a concentration-time function.
At lower concentrations the detector will not sound an alarm for many tens of minutes. At 400 parts per million, the alarm will so
A computer is a device that can be instructed to carry out sequences of arithmetic or logical operations automatically via computer programming. Modern computers have the ability to follow generalized sets of called programs; these programs enable computers to perform an wide range of tasks. A "complete" computer including the hardware, the operating system, peripheral equipment required and used for "full" operation can be referred to as a computer system; this term may as well be used for a group of computers that are connected and work together, in particular a computer network or computer cluster. Computers are used as control systems for a wide variety of industrial and consumer devices; this includes simple special purpose devices like microwave ovens and remote controls, factory devices such as industrial robots and computer-aided design, general purpose devices like personal computers and mobile devices such as smartphones. The Internet is run on computers and it connects hundreds of millions of other computers and their users.
Early computers were only conceived as calculating devices. Since ancient times, simple manual devices like the abacus aided people in doing calculations. Early in the Industrial Revolution, some mechanical devices were built to automate long tedious tasks, such as guiding patterns for looms. More sophisticated electrical machines did specialized analog calculations in the early 20th century; the first digital electronic calculating machines were developed during World War II. The speed and versatility of computers have been increasing ever since then. Conventionally, a modern computer consists of at least one processing element a central processing unit, some form of memory; the processing element carries out arithmetic and logical operations, a sequencing and control unit can change the order of operations in response to stored information. Peripheral devices include input devices, output devices, input/output devices that perform both functions. Peripheral devices allow information to be retrieved from an external source and they enable the result of operations to be saved and retrieved.
According to the Oxford English Dictionary, the first known use of the word "computer" was in 1613 in a book called The Yong Mans Gleanings by English writer Richard Braithwait: "I haue read the truest computer of Times, the best Arithmetician that euer breathed, he reduceth thy dayes into a short number." This usage of the term referred to a human computer, a person who carried out calculations or computations. The word continued with the same meaning until the middle of the 20th century. During the latter part of this period women were hired as computers because they could be paid less than their male counterparts. By 1943, most human computers were women. From the end of the 19th century the word began to take on its more familiar meaning, a machine that carries out computations; the Online Etymology Dictionary gives the first attested use of "computer" in the 1640s, meaning "one who calculates". The Online Etymology Dictionary states that the use of the term to mean "'calculating machine' is from 1897."
The Online Etymology Dictionary indicates that the "modern use" of the term, to mean "programmable digital electronic computer" dates from "1945 under this name. Devices have been used to aid computation for thousands of years using one-to-one correspondence with fingers; the earliest counting device was a form of tally stick. Record keeping aids throughout the Fertile Crescent included calculi which represented counts of items livestock or grains, sealed in hollow unbaked clay containers; the use of counting rods is one example. The abacus was used for arithmetic tasks; the Roman abacus was developed from devices used in Babylonia as early as 2400 BC. Since many other forms of reckoning boards or tables have been invented. In a medieval European counting house, a checkered cloth would be placed on a table, markers moved around on it according to certain rules, as an aid to calculating sums of money; the Antikythera mechanism is believed to be the earliest mechanical analog "computer", according to Derek J. de Solla Price.
It was designed to calculate astronomical positions. It was discovered in 1901 in the Antikythera wreck off the Greek island of Antikythera, between Kythera and Crete, has been dated to c. 100 BC. Devices of a level of complexity comparable to that of the Antikythera mechanism would not reappear until a thousand years later. Many mechanical aids to calculation and measurement were constructed for astronomical and navigation use; the planisphere was a star chart invented by Abū Rayhān al-Bīrūnī in the early 11th century. The astrolabe was invented in the Hellenistic world in either the 1st or 2nd centuries BC and is attributed to Hipparchus. A combination of the planisphere and dioptra, the astrolabe was an analog computer capable of working out several different kinds of problems in spherical astronomy. An astrolabe incorporating a mechanical calendar computer and gear-wheels was invented by Abi Bakr of Isfahan, Persia in 1235. Abū Rayhān al-Bīrūnī invented the first mechanical geared lunisolar calendar astrolabe, an early fixed-wired knowledge processing machine with a gear train and gear-wheels, c. 1000 AD.
The sector, a calculating instrument used for solving problems in proportion, trigonometry and division, for various functions, such as squares and cube roots, was developed in
Curb feelers or curb finders are springs or wires installed on a vehicle which act as "whiskers" to alert drivers when they are at the right distance from the curb while parking. The devices are fitted low on the body, close to the wheels; as the vehicle approaches the curb, the protruding feelers scrape against the curb, making a noise and alerting the driver in time to avoid damaging the wheels or hubcaps. The feelers do not break easily. Curb feelers are still used on some hot rods, they are popular for cars with whitewall tires, which lose their white coating when scraped against the curb. Sometimes curb feelers are found only on the passenger side of the car, since, most near the curb when parking. Sometimes they are added only next to the front wheels; some curb feelers have a single wire or spring, while others have two to increase the area that can be protected. Any particular car may have just one curb feeler installed or more if attached near the front and rear, as well as on both sides of the vehicle.
Recreational vehicles sometimes have rubber feelers or metal, antenna-like rods mounted on the lower part of the body that act as feelers so that drivers are warned if they are approaching a curb or other obstruction, thus reducing the chances of gouging or cutting the tire sidewalls and increasing the safety of vehicle operation. Buses are sometimes fitted with curb feelers, which can assist the driver in ensuring that the bus is close enough to the curb to allow passengers to step to and from the curb easily. Today, the U. S. Department of Labor Mine Safety and Health Administration mentions that users of heavy equipment can benefit from an analogous accessory: In the 1950s, cars were equipped with curb feelers... Using a piece of 48 inches conveyor belt, 4-to-5-foot long by 4 to 6 inches wide and a couple of pieces of angle iron, you can make a pinch-point feeler, a warning device for the corners of a continuous miner; this will give a warning nudge to anyone in the danger area, giving him or her about a two-foot running start to stop the machine or to yell at the operator to stop.
The belting is stiff enough to hold its shape but flexible enough to give if it runs into a miner or vice versa. The flexibility allows this "curb feeler" to drag against the rib or be smacked by a shuttle car with little or no damage. A little spray from a can of reflective paint will make the belt a visual warning device as well. One or two on each corner will put as many as you want. Curb feelers based on optical technology are designed to function the same way but work in the proximity of an obstruction rather than having to come into physical contact with it; as described by one United States patent: An electronic curb feeler system uses two pairs of optical sensor units to detect an object located near the front end of a vehicle during parking. One pair of optical sensor units detects an object directly in front of a left portion of the front end of the vehicle while another pair of optical sensors detects an object directly in front of a right portion of the front end of the vehicle. By supplying the operator of the vehicle with the location of the object as well as the exact distance the object is from the front end of the vehicle the operator can avoid hitting the object while parking close to the object.
Devices such as this, simpler electronic devices similar to the original wire curb feelers used on cars, are used in the design of various mobile robotic devices. One robotics company that does work for the United States Department of Defense uses laser-assisted curb feeler technology. Fender skirts
Hall effect sensor
A Hall effect sensor is a device, used to measure the magnitude of a magnetic field. Its output voltage is directly proportional to the magnetic field strength through it. Hall effect sensors are used for proximity sensing, speed detection, current sensing applications. A Hall sensor is combined with threshold detection so that it acts as and is called a switch. Seen in industrial applications such as the pictured pneumatic cylinder, they are used in consumer equipment, they can be used in computer keyboards, an application that requires ultra-high reliability. Hall sensors are used to time the speed of wheels and shafts, such as for internal combustion engine ignition timing 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 spaced magnets, the voltage from the sensor will peak twice for each revolution; this arrangement is 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, encapsulated in the probe head.
The plane of the crystal is perpendicular to the probe handle. Connecting leads from the crystal is 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. 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. The natural electron drift of the charge carriers causes the magnetic field to apply a Lorentz force to these charge carriers; the result is what is seen as charge separation, with a buildup 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 should be calibrated against a known value of magnetic field strength. For a solenoid the Hall probe is placed in the center.
In a Hall effect sensor, a thin strip of metal has a current applied along it. In the presence of a magnetic field, the electrons in the metal strip are deflected toward one edge, producing a voltage gradient across the short side of the strip. Hall effect sensors have an advantage over inductive sensors in that, while inductive sensors respond to a changing magnetic field which induces current in a coil of wire and produces voltage at its output, Hall effect sensors can detect static magnetic fields. 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; when a beam of charged particles passes through a magnetic field, forces act on the particles and the beam is deflected from a straight path. The flow of electrons through a conductor form a beam of charged carriers; when an conductor is placed in a magnetic field perpendicular to the direction of the electrons, they will be deflected from a straight path.
As a consequence, one plane of the conductor will become negatively charged and the opposite side will become positively charged. The voltage between these planes is called the Hall voltage; when the force on the charged particles from the electric field balances the force produced by magnetic field, the separation of them will stop. If the current is not changing the Hall voltage is a measure of the magnetic flux density. There are two kinds of Hall effect sensors. One is linear; the key factor determining sensitivity of Hall effect sensors is high electron mobility. As a result, the following materials are suitable for Hall effect sensors: gallium arsenide indium arsenide indium phosphide indium antimonide graphene Hall effect sensors are linear transducers; as a result, such sensors require a linear circuit for processing of the sensor's output signal. Such a linear circuit: provides a constant driving current to the sensors amplifies the output signalIn some cases the linear circuit may cancel the offset voltage of Hall effect sensors.
Moreover, AC modulation of the driving current may reduce the influence of this offset voltage. Hall effect sensors with linear transducers are integrated with digital electronics; this enables advanced corrections to the sensor's characteristics and digital interfacing to microprocessor systems. In some solutions of IC Hall effect sensors a DSP is used, which provides for more choices among processing techniques; the Hall effect sensor interfaces may include input diagnostics, fault protection for transient conditions, short/open circuit detection. It may provide and monitor the current to the Hall effect sensor itself. There are precision IC products available to handle these features. A Hall effect sensor may operate as an electronic switch; such a switch is much more reliable. It can be operated at higher frequencies than a mechanical switch, it does not suffer from contact bounce because a solid state
Nondispersive infrared sensor
A nondispersive infrared sensor is a simple spectroscopic sensor used as a gas detector. It is nondispersive in the sense of optical dispersion since the infrared energy is allowed to pass through the atmospheric sampling chamber without deformation; the main components of an NDIR sensor are an infrared source, a sample chamber or light tube, a light filter and an infrared detector. The IR light is directed through the sample chamber towards the detector. In parallel there is another chamber with an enclosed reference gas nitrogen; the gas in the sample chamber causes absorption of specific wavelengths according to the Beer–Lambert law, the attenuation of these wavelengths is measured by the detector to determine the gas concentration. The detector has an optical filter in front of it that eliminates all light except the wavelength that the selected gas molecules can absorb. Ideally other gas molecules do not absorb light at this wavelength, do not affect the amount of light reaching the detector however some cross-sensitivity is inevitable.
For instance, many measurements in the IR area are cross sensitive to H2O so gases like CO2, SO2 and NO2 initiate cross sensitivity in low concentrations. Part 1065.350 states that H2O can interfere with an NDIR analyzer's response to CO2. The IR signal from the source is chopped or modulated so that thermal background signals can be offset from the desired signal. NDIR sensors for carbon dioxide are encountered in HVAC units. Configurations with multiple filters, either on individual sensors or on a rotating wheel, allow simultaneous measurement at several chosen wavelengths. FTIR, a more complex technology, scans a wide part of the spectrum, measuring many absorbing species simultaneously. O2 - 0.763 µm CO2 - 4.26 µm, 2.7 µm, about 13 µm carbon monoxide - 4.67 µm, 1.55 µm, 2.33 µm, 4.6 µm, 4.8 µm, 5.9 µm NO - 5.3 µm, NO2 has to be reduced to NO and they are measured together as NOx.
A pellistor is a solid-state device used to detect gases which are either combustible or which have a significant difference in thermal conductivity to that of air. The word "pellistor" is a combination of resistor; the detecting element consist of small "pellets" of catalyst loaded ceramic whose resistance changes in the presence of gas. Many of them require to be heated in use, so they may be four terminal devices with two connections for a small heating element and two to the sensor itself. To avoid any risk of explosion, the sensitive element is enclosed in a wire mesh housing. More robust sensors for use in high risk environments may have solid steel housing with a gas port of sintered metal granules. Both of these work in a manner similar to the Davy safety lamp; the pellistor was developed in the early 1960s for use in mining operations as the successor of the flame safety lamp and the canary. It was invented by English scientist Alan Baker; the catalytic pellistor as used in the catalytic bead sensor works by burning the target gas.
The thermal conductivity pellistor works by measuring the change in heat loss of the detecting element in the presence of the target gas. List of portmanteaus List of sensors
A speedometer or a speed meter is a gauge that measures and displays the instantaneous speed of a vehicle. Now universally fitted to motor vehicles, they started to be available as options in the 1900s, as standard equipment from about 1910 onwards. Speedometers for other vehicles use other means of sensing speed. For a boat, this is a pit log. For an aircraft, this is an airspeed indicator. Charles Babbage is credited with creating an early type of a speedometer, fitted to locomotives; the electric speedometer was invented by the Croatian Josip Belušić in 1888 and was called a velocimeter. Patented by Otto Schultze on 7 October 1902, it uses a rotating flexible cable driven by gearing linked to the output of the vehicle's transmission; the early Volkswagen Beetle and many motorcycles, use a cable driven from a front wheel. When the vehicle is in motion, a speedometer gear assembly turns a speedometer cable, which turns the speedometer mechanism itself. A small permanent magnet affixed to the speedometer cable interacts with a small aluminum cup attached to the shaft of the pointer on the analogue speedometer instrument.
As the magnet rotates near the cup, the changing magnetic field produces eddy currents in the cup, which themselves produce another magnetic field. The effect is that the magnet exerts a torque on the cup, "dragging" it, thus the speedometer pointer, in the direction of its rotation with no mechanical connection between them; the pointer shaft is held toward zero by a fine torsion spring. The torque on the cup increases with the speed of rotation of the magnet, thus an increase in the speed of the car will twist the cup and speedometer pointer against the spring. The cup and pointer will turn until the torque of the eddy currents on the cup are balanced by the opposing torque of the spring, stop. Given the torque on the cup is proportional to the car's speed, the spring's deflection is proportional to the torque, the angle of the pointer is proportional to the speed, so that spaced markers on the dial can be used for gaps in speed. At a given speed, the pointer will remain motionless and pointing to the appropriate number on the speedometer's dial.
The return spring is calibrated such that a given revolution speed of the cable corresponds to a specific speed indication on the speedometer. This calibration must take into account several factors, including ratios of the tailshaft gears that drive the flexible cable, the final drive ratio in the differential, the diameter of the driven tires. One of the key disadvantages of the eddy current speedometer is that it cannot show the vehicle speed when running in reverse gear since the cup would turn in the opposite direction - in this scenario the needle would be driven against its mechanical stop pin on the zero position. Many modern speedometers are electronic. In designs derived from earlier eddy-current models, a rotation sensor mounted in the transmission delivers a series of electronic pulses whose frequency corresponds to the rotational speed of the driveshaft, therefore the vehicle's speed, assuming the wheels have full traction; the sensor is a set of one or more magnets mounted on the output shaft or differential crownwheel, or a toothed metal disk positioned between a magnet and a magnetic field sensor.
As the part in question turns, the magnets or teeth pass beneath the sensor, each time producing a pulse in the sensor as they affect the strength of the magnetic field it is measuring. Alternatively,particularly in vehicles with multiplex wiring, some manufacturers use the pulses coming from the ABS wheel sensors which communicate to the instrument panel via the CAN Bus. Most modern electronic speedometers have the additional ability over the eddy current type to show the vehicle speed when moving in reverse gear. A computer converts the pulses to a speed and displays this speed on an electronically controlled, analog-style needle or a digital display. Pulse information is used for a variety of other purposes by the ECU or full-vehicle control system, e.g. triggering ABS or traction control, calculating average trip speed, or to increment the odometer in place of it being turned directly by the speedometer cable. Another early form of electronic speedometer relies upon the interaction between a precision watch mechanism and a mechanical pulsator driven by the car's wheel or transmission.
The watch mechanism endeavors to push the speedometer pointer toward zero, while the vehicle-driven pulsator tries to push it toward infinity. The position of the speedometer pointer reflects the relative magnitudes of the outputs of the two mechanisms. Typical bicycle speedometers measure the time between each wheel revolution, give a readout on a small, handlebar-mounted digital display; the sensor is mounted on the bike at a fixed location, pulsing when the spoke-mounted magnet passes by. In this way, it is analogous to an electronic car speedometer using pulses from an ABS sensor, but with a much cruder time/distance resolution - one pulse/display update per revolution, or as as once every 2–3 seconds at low speed with a 26-inch wheel. However, this is a critical problem, the system provides frequent updates at higher road speeds where the information is of more importance; the low pulse frequency has little impact on measurement accuracy, as these digital devices can be programmed by wheel size, or additionally by wheel or tire circumference in order to make distance measurements more accurate and precise than a typical motor vehicle gauge.
However these devices carry some minor disadvantage in requiring power from batteries that must be replaced every so in the rec