3212 Jos Ee Instr_S108 06 Kecepatan

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Sistem Instrumentasi

Sensor Gerakan (posisi dan kecepatan)

Ir. Jos Pramudijanto, M.Eng.Jurusan Teknik Elektro FTI ITS

Telp. 5947302 Fax.5931237Email: [email protected]

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PengantarObjektif:

Macam sensor posisi dan sensor kecepatanMetode pengukuran dengan sensor posisi dan kecepatan

Definisi:Suatu sensor yang mengkonversikan perubahan gerakan suatu objek menjadi energi listrikSuatu perubahan kecepatan bisa didapatkan dari perubahan posisi

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Sensor PosisiResistive

Potentiometers

InductiveLinear Variable Differential Transformers (LVDTs)Synchros, Resolvers, and Inductosyn

Electro-opticalOptical encoders

Capacitive, piezo-electric, ultrasonic, magnetostrictive, etc.

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PotensiometerSensor analog yang bekerja seperti divider

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Potensiometer dan Proximity

Potensiometer (rotary and linear)

Proximity switch (mechanical)

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Potensiometer untuk posisi

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Linear-Variable Differential Transformer

LVDT

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Konstruksi LVDT

LVDT terdiri dari magnetic core yang bergerak dalam silinder.

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Prinsip Kerja LVDT

Inti berada di tengah-tengah maka :Flux S1 = S2Tegangan induksi E1 = E2Enetto = 0

Inti bergerak ke arah S1 maka :Flux S1 > S2tegangan induksi E1 > E2, Enetto = E1 - E2

Inti bergerak ke arah S2 maka :Flux S1 < S2Tegangan induksi E1 < E2Enetto = E2 – E1

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Synchro

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Rangkaian Synchro

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Synchro to Digital Converter

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Resolver

Sin

Cosine

Reference

Uses an AC signal to excite the rotor winding.Stator has two windings at 90 degrees to each other.As the rotor turns the coupling to the two windings will change

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Rangkaian Resolver

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Inductosyn

Similar to a resolver but made in two planes.The Inductosyn has many pole pairs, +50The output will repeat ones for each pole pair.Each cycle can be decoded to +14 bitsRequire very precise alignment, and high quality amplifiers.Analog Encoders offer similar solution at a lower cost.

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Konstruksi Inductosyn

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Optical Encoder

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Sinyal Output Optical Encoder

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Increment EncoderGenerally Have two picks up that are 90 degrees out of Phase (A and B) This allows you to determine the direction of rotation and thus count up or downBy using the rising and falling edges of both A and B we can get 4 times the number of slots.May have one or more index marks for homing.

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Absolute Encoder

Gray Code Vs BinaryGray Code only changes by one bit per transition.At least one sensor per track.

0111

01 00

0111

00 10

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Pengukuran dg Encoder Absolute

! Shaft Encoder convert position into binary equivalent. This system use 8 bit shaft encoder. So, the resolution of shaft encoder is :

!The linear displacement is :

oresolution 41,12

3608 ==

ranglentdisplacemelinear o π2360

Χ=

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Konstruksi Encoder Increment

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Konstruksi Encoder Increment

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Konstruksi Encoder Absolut

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Perbandingan Sensor Posisi

TypeResolution

BitsIncremental or Absolute

Signal Type Signals

Electrical Imunity

Number of Wires

Electrical Interface

Encoder Incremental

12 Incremental Digital A, B, Index

Very Good

4-8 None

Encoder Absolute

16 Absolute Digital Binary Very Good

20+ None

Sinusoidal Encoders

22 Absolute Analog Sin, Cos, Index

Fair 6-10 Interpolator

Resolver14 Absolute Analog

Volts RMSSin,Cos Good 6 R/D Converter

Inductosyn24 Incremental Analog

millivoltsSin, Cos Fair 6 Amp +Converter

Capacitive24 Either

Analog millivolts Sin, Cos Fair 6-10 Converter

Inductive 24 Either Analog millivolts

Sin, Cos Fair 6-10 Converter

Incremental Encoder dan Resolver paling populer

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Sensor KecepatanInductive

tachogeneratorslinear sensors

GyroscopesDifferentiation of position

analogdigital

Integration of acceleration

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Tachogenerator

Sensor ini konstruksinya mirip motor DC magnet permanen.Tegangan keluaran yang dihasilkan berupa tegangan DC.

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Increment EncoderEncoder yang digunakan untuk pengukuran kecepatan menggunakan encoder dengan output A, B, dan ZOutput A dan B berbeda phase sebesar 90 derajat. Sedang output Z untuk zero index (untuk kecepatan tinggi).

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Accelerometer

Accelerometer bahan piezo-electric.Pengukuran kecepatan dengan membuat rangkaian integrator.

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Capacitive and Inductive Sensors

Operate similar to analog encoders.Patterns are placed on the rotor and stator. Rotor and stator can be made of low cost materialsTechnology similar to printed circuit board fabrication.Capable of very low power operation. This would allow for battery baked operation.Resolution similar to analog encoders and InductosynsElectronics utilize Digital to Analog converters and DSPs or PLDs.