INTRODUCTION

BASIC CONCEPTS OF MEASUREMENT and

TRANDUCER CLASSIFICATION

BASIC CONCEPT

• Measurement: describing natural phenomena in quantitive terms

»Express in numbers

weight = 1 kg

Measurement System :

TRANDUCER SIGNAL CONDITIONING

DISPLAY/READOUT DEVICE/

CONTROL SYSTEM

POWER SUPPLY

INPUT MEASURAND

Tranducer

• Convert the measurand into a usable electrical output

=> “ A device capable of being actuated by an energizing input from one or more transmission media and in turn, generating a related signal to one or more transmission system or media “

=> Energy is one form of information

Signal Conditioning :

• Convert transducer output into electrical quantity suitable for display or next control system– Amplifiers– Signal Generation– Filtering– Converting

Display and Power Supply

• Display/readout/next control system– Analog Display– Digital Display

• Power Supply : provides the requires excitation

Tranducer Classification• Mechanical Tranducer

– Operate without any external power supply

– Posses high accuracy– Low cost– Requirement of large forces =>

mechanical friction– Incompability with other sensing

element– Not suitable for long distance

measurement• example : dial gauge, barometer

Dial Gauge

Barometer

Tranducer Classification (2)• Electrical Tranducer :

– Output can be amplified to any desired level – Output can be indicated and recordes remotely at

a distance– Output can be modified to meet requirement of

display, or controlling other device (sinyal -> tegangan atau arus, analog -> frekuensi atau pulsa)

– The signal can be conditioned or mixed to obtain any combination output

Disadvantates : less reliable => precision problem

Tranduser Elektrik• Suatu device yang dapat melakukan ‘sensing’

terhadap suatu besaran fisik, mekanik dan optikal yang diukur, dan mengubahnya menjadi nilai tegangan atau arus yang proporsional dengan masukan yang diukur

Klasifikasi Tranduser Elektrik :

• Tranduser Aktif

• Tranduser Pasif

Tranduser Aktif

• ‘self generating device’ , bekerja menurut hukum konversi energi

• Dapat membangkitkan sinyal output listrik yang ekivalen tanpa adanya sumber energi luar– Contoh : tekanan ke arus, temperatur ke

tegangan

Tranduser Aktif

PiezoelectricSolar Cell

Tranduser Pasif

• Bekerja berdasarkan prinsip pengontrolan energi

• Bergantung pada perubahan parameter listrik (resistansi, induktansi, kapasitansi)

• Diperlukan penggerak dari luar– Contoh : strain gauge ; digerakan sumber DC

Tranduser Pasif

Tabel 1 : Klasifikasi Tranduser Elektrik

Tabel 2 : Dimentional relationship between parameter

Basic Quantity Measured Parameter

Linear Displacement Length, width, tickness, position, level, surface quality, strain, velocity accelaration

Angular Displacement Altitude, angle of incidence, angle of flow, angle of vibration

Linear Velocity Speed, rate of flow, momentum, vibration

Angular velocity Angular speed, rate of turn, angular momentum, vibration

Linear acceleration Vibration, impact, motion

Angular acceleration Torque, angular vibration, angular impact, moment of inertia

Basic Quantity Measured Parameter

Force Weight, thrust, density, stress, torque, vibration, acceleration, pressure, flow, fluid velocity, sound intensity

Temperature Gas & Liquid expansion, heat flow, heat conductivity, fluid flow, surface temperature, radiation pressure, gas velocity, turbulence

Light Light Flux & density, temperature, length, force, torque, frequency

Time Frequency, number of events, statistical distributin

Electromagnetic radiation Wavelength, power, field strength

Dimentional relationship between parameter (2)

Keperluan dasar Tranduser

• Ruggedness (kokoh) : kemampuan pada overload

• Linearity : menghasilkan hubungan input – output yang linear

• Repeatibility : menghasilkan sinyal output yang tepat sama bila dilakukan pengukuran berulang

• S/N (signal to noise ) rasio yg cukup besar => SNR = Psignal / Pnoise

Keperluan dasar Tranduser (2)

• Stabilitas dan Keandalan (Stability and Reliability) : respon hasil pengukuran terhadap keadaan lingkungan

• Dynamic Response : perbandingan yang baik antara input dan output terhadap fungsi waktu

Contoh Spesifikasi : Pressure Tranduser

References :1. Rangan, C.S., "Instrumentation, Device and Systems",

Tata McGraw-Hill Publishing Company Limited, New Delhi, 1987.

2. Hall, Douglas V., "Microprocessor and Interfacing", McGraw-Hill Book Company, Singapore, 1986.

3. William D. Cooper “Instrumentasi Elektronika dan Teknik Pengukuran” Penerbit : Erlangga 1993

4. Wobschall, Darold., “ Circuit Design for Electronic Instrumentation”, McGraw-Hill, 1987

5. Internet