Speedometer and Odometer

8/6/2019 Speedometer and Odometer

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Speedometer and Odometer

Dials and guages on the automobilesdashboards provide crucial information to the

driver. The speedometer displays the speedat which the vehicle is moving. The odometershows the total number of miles the car hastraveled and is useful for tracking wear andscheduling vehicle maintenance.

Abdul jabbar5/17/2011


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Speedometer and OdometerDials and gauges on the automobile dashboard provide crucial informationto the driver. The speedometer displays the speed at which the vehicle is

moving, measuring either the rotation rate of a drum connected to the car'stransmission or the frequency of electrical pulses that vary according to thecar's speed. The odometer shows the total number of miles the car hastraveled and is useful for tracking wear and scheduling vehicle maintenance.


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Inventor of the speedometer

Babbage's Difference EngineConsidered by many to be a direct forerunner of the modern computer, theDifference Engine was able to compute mathematical tables. This woodcutshows a small portion of the ingenious machine, which was designed by

Charles Babbage in the 1820s. Although the device did not have a memory,Babbages later idea for the Analytical Engine would have been a true,

programmable computer if the technology of his time had been able to buildit.


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Speedometer:

Speedometer, device for measuring the speed of a vehicle. This is usually

done either by measuring the number of revolutions over a known timeinterval, or by devising an instrument that measures revolutions per minute(rpm) directly. An example of such a device is the automobile speedometer,in which a flexible cable attached to the drive rotates a permanent magnet inthe instrument. This induces a magnetic field on a surrounding drum,tending to drag the drum around with it. The drum is restrained by a spring,to which a pointer is connected. The higher the speed of the engine, thehigher will be the drag induced, and with it the deflection of the pointer.Increasingly, modern automobile speedometers are not linked mechanicallyto the transmission. Instead, a device located in the transmission produces a

series of electrical pulses whose frequency varies in proportion to thevehicle's speed; the electrical pulses are sent to a calibrated device thattranslates the pulses into the speed of the automobile. This information issent to a device that displays the vehicle's speed to the driver, in the form ofeither a deflected speedometer needle, or a digital readout. Otherspeedometers are operated by centrifugal force, driving a set of revolvingflyball weights outward as speed is increased (see Centrifuge). Theseweights are connected through a linkage to a spring, which is compressed asthe speed increases, and to which a pointer is connected. This type of device

first found wide application when the Scottish engineer and inventor JamesWatt introduced it as a governor to control steam engines.

An airplane speedometer, or airspeed indicator, depends on the measurementof dynamic pressure. A so-called pitot tube, named after the French physicistand engineer Henri Pitot, is a U-shaped tube with two openings; one openingis oriented into the direction of the airflow of the moving plane, and theother opening is oriented perpendicular to the direction of the airflow.Between the openings, in the curved part of the tube, is liquid mercury.When the plane is stationary, the pressure at each of the openings is the

same, and there is an equal amount of mercury on each side of the U-shapedtube. When the plane is moving, increased air pressure in the side of the tubethat has the opening oriented into the airflow pushes the mercury towardsthe other side of the U-shaped tube; the degree to which the mercury isdisplaced is used to indicate the airspeed. The speed of a craft in water isfrequently measured by a towed instrument, consisting of a small propeller,


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the rotational speed of which increases with forward speed, actuating acalibrated dial aboard the craft.

The term tachometeris usually applied to an instrument used to measureangular speed, such as that of a shaft, in revolutions per minute. Today manyautomobiles have tachometers that measure the rate of revolution of theautomobile's driveshaft.

Tachometer: Tachometer, measuring device that indicates rotational(angular) speed in revolutions per minute (rpm). In motor vehicles, atachometer measures the speed of the engine crankshaft as it rotates anddisplays the results on a gauge to inform the driver. The word tachometer isa combination of the Greek words tachos, meaning speed, and metria,meaning measure.

There are many different types of tachometers, beyond the familiardashboard gauge. These vary in appearance, operation, and application.Automotive technicians, for example, use handheld tachometers duringsome engine service procedures or exhaust emissions testing. In addition,there are many industrial uses for tachometers on a variety of types ofequipment.

Spring

Spring (mechanics), in mechanics, device made of an elastic material thatundergoes a significant change in shape, or deformation, under an appliedload. Springs are used in spring balances for weighing (see Weight) and forthe storage of mechanical energy, as in watch and clock springs or door-closing springs. Springs are also used to absorb impact, as in coil or leafsprings used for automobile suspensions, and to reduce vibration by the useof rubber blocks. The specific form of a spring depends on its use. A

weighing spring, for example, is normally wound as a helix, and itselongation is proportional to the applied force, so that the spring can becalibrated to measure this force. Watch springs are wound as spiral coils,and sets of flat bars or leaves, superimposed on one another to formlaminations, are used as leaf springs in automobile suspensions


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Centrifuge

Centrifuge, mechanical device using the principle of centrifugal force toseparate substances of different densities. A common centrifuge is a

container that is spun rapidly. The only limit to the centifugal force is thestrength of the metal of which the device is made. Centrifugal forces may bethousands of times as great as the force of gravity.


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Odometer:

Odometer, instrument that displays the distance traveled by a vehicle. Itmeasures the distance in either miles or kilometers. An odometer countscontinuously upward, but many cars have a second odometer that can bereset to zero to measure the distance of individual trips. Automobileodometers are located in a central instrument display near the speedometer.

A Roman engineer, Vitruvius, described the concept of an odometer in the1st century BC. Around AD 1500, Italian inventor Leonardo da Vinci designeda device that used stones to indicate distance traveled. Da Vinci devised acontainer that had a hole in the bottom just big enough for certain stones tofall through. The container, loaded with stones, was attached so that rotation

of one of the vehicles wheels caused a plate or drum to rotate around thecontainer of stones. This plate had a single hole about the same size as thehole in the container. After the wheel rotated a certain number of times, thetwo holes lined up and a stone fell through the opening into a box. Distancetraveled could be estimated by the number of stones in the box.


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In modern odometers, the motion of either the vehicles wheels or itstransmission gears is relayed, usually by a cable and a series of gears, tosmall drums or dials inside the odometer. As each drum rotates, it displays aseries of numbers from zero to nine. The instrument is calibrated so thateither one mile or one kilometer produces a complete rotation of the drumthat indicates single units of distance. Ten rotations of that drum causes thedrum to the left of it to advance one number. In that manner, the displaychanges from 19 to 20, for example, with the passage of the 20th mile. This

process is repeated for the remaining dials, so that three, four, or more dialswill turn as the distance traveled by the vehicle mounts. Odometers usuallydisplay a maximum of 999,999 miles or kilometers before coming aroundfull circle to the beginning number 000,000.


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Limit Switches

A limit switch is a device that can sense a process or environmentalparameter such as temperature or pressure and close a switch contact orchange an electrical parameter based on a measurement of that parameterversus the limit switch.Defination: Limit switches are a type of sensor that detectpresence and absence. Specifically, mechanical limit switchesare switches that are mechanically activated, meaning thatthey have some sort of arm, lever, knob, plunger, etc., whichis

physicallyor mechanicallyactivated by making contactwith another object. As the object makes contact with theactuator of the switch, it eventually moves the actuator to itslimit where the contacts change state. Other varieties ofsensors/switches exist, including proximity sensors, lightsensors, electric switches, among others.In its simplest form, a limit switch is a switch that can bemounted into remote locations so that it is actuated by anobject other than a human operator. Some basic functions of

limit switches are: Detecting presence/absence Counting Detecting range of movement Detecting positioning & travel limit Breaking a live circuit when unsafe conditions arise Detecting speed and hundreds of other applicationsLimit switches are a problem-solving product. There is oftenno right answer as to which switch can be used in any

given situation. Usually product choice is left to the user todetermine how he can best utilize the switch. Because of thischaracteristic, limit switches can be fun to sell a funproductthey are the solution to a brainteaser game!Mechanical limit switches can be found in anyindustrial orcommercial application where detection or safety is needed.


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Strengths & weaknessesLimit switches are a practical solution for sensing in mostsituations. There are, however, a few disadvantages to usinglimit switches. Some of the strengths and weaknesses of thelimit switches are listed below:

Applications:Limit switches are very commonly used devices. Think about

these simple applications: What keeps the microwave from starting without the doorbeing shut first? What turns the light off when the refrigerator door isclosed? Why do your cars dome lights come on when you open thedoor? What stops the washing machine when a load becomesunbalanced?

Industrial Application Examples

Case 1: Packaging. Boxes of paper approach the end of thepackaging line, ready to be stacked onto pallets 6 boxeshigh. A palletizer with suction-cup grippers picks up a boxand swings around to a waiting pallet. How does the unitknow it has reached the sixth


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layer of boxes? When the pivot arm reaches the top of itsvertical travel, the arm hits a limit switch. The switch signalsthe system to send the full pallet down line and sets up anempty pallet to restart the process.

Case 2: Working where people cannot. Inside a sawmill, a high-speed saw quickly reduces logs into construction beams. Inthe process, chips and dust float in the air. Breathing isimpossible in the area without a mask. Even with goggles, itwould beimpossible to inspect the cutting. The production department

devised a system of limit switches to do the inspectingautomatically. A remote operator can configure the switchesto allow the log to be cut to the desired dimensions.


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Case 3: Food and beverage. At a frozen food processor, anautomatic pallet stacking system is used. This system uses awobble stick limit switch to detect when the palletshave been loaded to their desired level. The switch then

signals the conveyor to send the load through an automaticvertical rise door into the freezer for quick freezing.

Case 4: Fire safety. In a manufacturing plant, rooms need to beclosed off quickly in case of contamination or fire. To helpfacilitate this process, high-speed doors have beendeveloped. These doors may move as quickly as six feet persecond. At such speeds,

the door would destroy itself quickly, if not for the use oflimit switches. The limit switches are used to slow the door

just before it is fully opened or fully closed.

Some of many industries with limit switch needs: Material handling packaging, moving, warehousing,distribution Food & beverage packaging, distribution


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Manufacturing automotive/heavy equipment, machining,marine/aviation, glass & plastics Metals mining, refining, processing, forming Commercial applications

Control cabinets Many, many more!

References: http://www05.abb.com/global/scot/scot260.nsf/veritydisplay/8bb7f20

332ba74d5852575d20063da5a/$file/1sxu141184x0201.pdf Microsoft Encarta 2009 [DVD]. Redmond, WA: Microsoft

Corporation, 2008
http://www05.abb.com/global/scot/scot260.nsf/veritydisplay/8bb7f20332ba74d5852575d20063da5a/$file/1sxu141184x0201.pdfhttp://www05.abb.com/global/scot/scot260.nsf/veritydisplay/8bb7f20332ba74d5852575d20063da5a/$file/1sxu141184x0201.pdfhttp://www05.abb.com/global/scot/scot260.nsf/veritydisplay/8bb7f20332ba74d5852575d20063da5a/$file/1sxu141184x0201.pdfhttp://www05.abb.com/global/scot/scot260.nsf/veritydisplay/8bb7f20332ba74d5852575d20063da5a/$file/1sxu141184x0201.pdf

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Speedometer and Odometer