sensor & actuator

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  • 7/24/2019 Sensor & Actuator


    INTRODUCTIONGeneral defnition o sensor & actuator

    The main components o industrial automation are sensor, actuator and

    controller. Our main discussion here is limited to sensor and actuator only. What

    is exactly sensor and actuator? As the name implies, sensors are devices that

    sense the presence or absence o obects.

    !i"ure # $ensor %$ource ?????'!rom the f"ure above (e )no( that sensor is a device that receive input si"nal,

    process it and "enerates output. While American *ational $tandards +nstitute

    says that sensor is a device (hich provides a usable output in response to a

    specifed measure.$o (e can say that sensor is sophisticated device that are reuently used

    to detect and respond to electrical or optical si"nals by converts the physical

    parameter %or example temperature, blood pressure, humidity, speed, etc.' into

    a si"nal (hich can be measured electrically. $ensor capable o convertin" any

    physical uantity to be measured into a si"nal (hich can be read, displayed,

    stored or used to control some other uantity. This si"nal produced by the sensor

    is euivalent to the uantity to be measured. $ensors are used to measure a

    particular characteristic o any obect or device. !or example a thermocouple, a

    thermocouple (ill sense heat ener"y %temperature' at one o its unction andproduce euivalent output volta"e(hich can be measured by a voltmeter. -ore

    the temperature rise, hi"her the volta"eread by the voltmeter. All sensors need

    to be calibrated (ith respect (ith some reerence value or standard device or

    accurate measurement.-ean(hile, actuator is a type o motor or movin" or controllin" a

    mechanism or system. +t is operated by a source o ener"y, typically electric

    current, hydraulic uid pressure, or pneumatic pressure, and converts that

    ener"y into motion. An actuator is the mechanism by (hich a control system acts

    upon an environment. An actuator is somethin" that converts ener"y into motion.

    +t also can be used to apply a orce. An actuator typically is a mechanical devicethat ta)es ener"y / usually ener"y that is created by air, electricity or liuid /

    and converts it into some )ind o motion. That motion can be in virtually any

    orm, such as bloc)in", clampin" or eectin". Actuators typically are used in

    manuacturin" or industrial applications and mi"ht be used in devices such as

    motors, pumps, s(itches and valves.0xplain the types o sensor & actuator 1 examples2ased on the properties here are several types o sensor as listed belo(.

    3roximity sensor

    This type o sensor uses an electronic feld to detect (hen an obect

    is near. There is no physical contact bet(een the obect and the sensor.+nductive proximity sensors detect only metal obects. 4apacitive proximity

    sensors can sense both metallic and non5metallic obects. Thin) o a
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    manuacturin" process (here the ali"nment o a part is critical. A proximity

    sensor can be used to ma)e sure the part is ali"ned (ithin a certain

    tolerance. + the part is not properly ali"ned, the proximity sensor (ill be

    tri""ered. This type o sensor is "enerally used to sense at distances less

    than one inch.3roximity sensors are used in a variety o applications. 4onsider

    these 3roximity sensors can be used to detect the end o travel on apositionin" table, to determine speed by countin" a "ear6s teeth, or be

    used to chec) i a valve is ully opened or closed. 3roximity sensors can be

    used to detect the presence or absence o a metallic (or) piece or metallic

    pallets on conveyor lines. When a robot arm s(in"s around or a pic) and

    place operation, a proximity sensor ma)es sure the arm actually has a part

    in its "rippers.

    Photoelectric sensor

    This type o sensor uses li"ht to detect the presence or absence o

    an obect. A Thru52eam photoelectric sensor uses t(o devices %a li"ht

    source and a detector' acin" each other. 7etection occurs (hen an obectbloc)s or brea)s the beam o li"ht passin" bet(een them. A 8etro5

    8eective %8eex' sensor emits a li"ht beam that is reected bac) to the

    sensor rom a retro reector as sho(n in f"ure 9. When an obect bloc)s

    the beam bet(een the sensor and the retro reector, detection occurs. A

    7i:use 8eective sensor emits a li"ht beam that must be reected bac) to

    it by the tar"et obect itsel or detection to occur %f"ure ;'.-ost electric "ara"e door openers include a photoelectric sensor or

    saety reasons. + the photoelectric sensor6s beam is bro)en as the door is

    "oin" do(n, the sensor si"nals the door opener to reverse the direction o

    the door. While environmental actors can a:ect photoelectric sensors,these devices have a lon" sensin" ran"e. The obects they detect can be o

    any material.

    !i"ure < 3hotoelectric sensor mechanism %source ????'

    $ome types o actuators are sho(n belo( =ydraulic %rotary' actuator

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    This type o actuator o:ers the beneft o a lon" lie. =ydraulic actuators

    consist o a cylinder or uid motor that utili>es hydraulic po(er to acilitate

    mechanical process. The mechanical motion "ives an output in terms o linear,

    rotary or oscillatory motion. The hydraulic actuator also allo(s or very precise

    control o the movement produced. +n linear hydraulic actuators, a typical set5up

    is made up o a hollo( cylinder that contains a liuid, usually oil, and a piston

    that is inserted in it. When pressure is applied onto the piston, obects can bemoved by the orce produced.

    =ydraulic actuators can be operated manually, such as a hydraulic car

    ac), or they can be operated throu"h a hydraulic pump, (hich can be seen in

    construction euipment such as cranes or excavators.

    3neumatic actuators

    This actuator (or) on the same concept as hydraulic actuators except

    compressed "as is used instead o liuid. 0ner"y, in the orm o compressed "as,

    is converted into linear or rotary motion, dependin" on the type o actuator.

    3neumatic ener"y is more desirable or main en"ine controls because it can

    uic)ly respond in startin" and stoppin" as the po(er source does not need to bestored in reserve or operation. Also, pneumatic actuators are preerred in places

    (here cleanliness is important, since the uid in hydraulic actuators mi"ht lea)

    and contaminate the surroundin"s. =o(ever, pneumatic actuators are still li)ely

    to lea), ma)in" them less ecient compared to mechanical actuators. Another

    do(nside is that they ta)e up a lot o space, create a lot o noise and are dicult

    to transport once installed in a place.

    !i"ure @ 3neumatic actuator %source (((.marineinsi"'

    The most common example is main en"ine pneumatic actuator or chan"in" o

    roller position over cam shat or reversin". 0lectric actuators0lectric actuators are devices po(ered by motors that convert electrical

    ener"y to mechanical torue. The electrical ener"y is used to create motion in

    euipment that reuires multi5turn valves li)e "ate or "lobe valves. $ince no oil is

    involved, electrical actuators are considered to be one o the cleanest and readily

    available orms o actuators. 0lectric actuators are typically installed in en"ines,

    (here they open and close di:erent valves. There are many desi"ns o electric

    actuators and this depends on their unction in the en"ine that they are installed

    in. One o its application is in electrical motor operated valve and ma"netic valve

    actuator or solenoid valve.

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    !i"ure 9 0lectric actuator %source (((.marineinsi"'

    -echanical actuators

    +t unctions throu"h convertin" rotary motion to linear motion. 7evices

    such as "ears, rails, pulley, chain and others are used to help convert the motion.

    $ome o the simple mechanisms used to convert motion are scre(s, (here the

    rotation o the actuators nut causes the scre( shat to move in a strai"ht line,

    the (heel and axle, (here the rotatin" motion o a (heel causes a belt or

    somethin" similar to move in a linear motion.


    !i"ure B -echanical actuator %source (((.marineinsi"'

    2asic example o mechanical actuator is chain bloc) hoistin" (ei"ht in (hich

    mechanical motion o chain over the sproc)et is utili>ed to lit a rated load.

    3lun"er actuator

    A typical plun"er actuator unctions somethin" li)e this a cam or plate hits

    the end o the plun"er, (hich is pressed in and operates the contacts in the

    s(itch. A plun"er actuator is the best choice to monitor short, controlled machine

    movements, or (here space or mountin" restrictions (ill not permit the use o a

    lever actuator.

    !i"ure ; 3lun"er types %source ?????'

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    2ut then (e are (onderin", ho( to choose an appropriate sensor? There are

    some considerations that should be made. Table belo( sho( some actors that

    (e should consider.

    Table # 4hoosin" sensor %source ?????'2asically, a "ood sensor should have the ollo(in" characteristics

    #' =i"h $ensitivity$ensitivity indicates ho( much the output o the device chan"es (ith unit

    chan"e in input %uantity to be measured'.e, mea

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