Measurement SystemsProf. Ahmed A. Al-Rajihy

University of BabylonCollege of Engineering-Almussyieb

Department of Automobiles Engineering

Text: Measurement Systems, Application and Design by Ernest O. Doebelin.

INTRODUCTION

WHY STUDY

MEASUREMENTS ?

TYPES OF MEASUREMENT APLICATIONS

- Monitoring of Measured Variables and operations, eg; monitoring temperature

and humidity, in hospital rooms.- Control of processes and operations, eg;

control of oven temperature.- Experimental engineering analysis, eg;

experimental investigations.

Ruler

Vernier

Micrometer

Common measured variables.

Displacement Velocity Acceleration Elasticity Viscosity Composition Force/Weight Pressure TorqueTemperature Humidity pHVolume Mass Density Voltage Current Power Volume Flow rate Level

Controller or

Observer

Measurementof Strain Calculate stressValue

The Generalized Measurement SystemMost measurement systems may be divided into three parts (stages);1‐ A detector –transducer* stage, which detects the physical variable and perform either a mechanical or electrical transformation to convert the signal into a more usable form. *The transducer is a device that transforms   one physical effect into another.

2- Some intermediate stage, which modifies the direct signal by amplification, filtering or any other means so that a desirable output is available.

3- The final or terminating stage, which acts to indicate, record or control the variable being measured.

Examples:

Functional Elements of a Measurement System (structure of

measurement systems):The primary and/or secondary transducergives an output which is a function of themeasurand (the input applied to it) such asliquid in glass thermometer, thermocouple,strain gauge, …..

Signal conditioning element;The output of the primary transducer isoften in inconvenient form, and it hasto be converted into a more convenientone. For example the output of a straingauge is a varying resistance, this isconverted to a voltage by a bridgecircuit.

The signal processing element is represented by;-Electronic amplifier,-Analogue-to-digital converter (ADC) which converts a voltage into a digital form for input to a computer,-Computer which calculates the measured value of the variable from the incoming digital data.

*Signal transmission element is usedto transmit data (signal) from oneelement to another.

*Signal utilization may takes theform either of a signal presentationunit or of a signal recordingelement.

Ex; Temperature Measurement System (Primary Sensing Element)

Ex; Force Measurement System (Primary + Secondary Sensing Element)

Standard Inputs:1‐ Step Input2‐ Impulse Input3‐ Ramp Input4‐ Terminated Ramp5‐ periodic Input

Thank You For Listening