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INSTRUMENTATION & MEASUREMENTS EE-218

• INTRODUCTION
1- Feedback Control.
2- Levels of Control Engineering
3- Process-Control Principles
4- System Modelling.
• MAJOR SPECIFICATIONS OF MEASURING INSTRUMENTS.
2.1 - Introduction to Instrumentation.
2.2 - Units, Standard and Definitions.
• MEASUREMENT OF PRESSURE.
3.1 - Pressure Principles
3.2 - Pressure Units
3.3 - Absolute Pressure and Gauge pressure.
3.4 - Methods of Pressure Measurement.
• MEASUREMENT OF LEVEL.
4.1 - Methods of Level Measurement.
• MEASUREMENT OF TEMPERATURE.
5.1 - Units.
5.2 - Expansion Thermometers.
5.3 - Methods of Temperature Measurements.
• MEASUREMENT OF FLOW.
6.1 - Units.
6.2 - Methods of Flow Measurements.
• MEASUREMENT OF Displacement
• LABORATORY

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 ‫ﻣﺑﺎدئ اﻟﺗﺣﻛم ﻓﻲ اﻟﻌﻣﻠﯾﺎت‬.
1. Process-Control Principles (Johnson)
In process control, the basic objective (‫ ( الغرض الرئيسى‬is to regulate (‫) تنظيم‬
the value of some quantity. To regulate means to maintain (‫ )المحافظةعلى‬that
quantity at a desired value ( ‫ ) قيمة محددة‬regardless of external influences
( ‫) بغض النظر عن المؤثرات الخارجية‬. The desired value is called the set point
( ‫) القيمة المطلوبة‬.
The control process may be manual control or automatic control.

1.1 Manual Control (‫)تحكم يدوى‬

Consider the liquid level control process shows in figure (1), where the
objective is to regulate the level at a desired value, the set point H. The
level, is called the controlled variable.
The main parts of the process are:-
- A tank with sight glass S (‫) زجاجةبيان‬. ‫زﺟﺎج ﺷﻔﺎف‬
- A valve to change the output liquid flow (‫ )تدفق السائل‬by the human.

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The human measures the actual level h in the sight glass and compares
(‫ )مقارنة‬it with the set point H (the red horizontal cl=colored line).
If h > H, the human opens the valve to increase the output flow Qout the
water level h lowers till (‫ )حتى‬h =H.
If h < H, the human closes the valve to decrease the output flow Qout and
allow the level h to rise till h =H. So by continuous monitoring ( ‫) مرااقبة مستمرة‬
of the sight glass the human can bring (‫ )يستطيع جعل‬the water level h to the set
point H.

Qin

Sight glass (‫)زجاجة بيان‬

Qout

Figure (1) Manual level control 4

1.2 Automatic Control ‫ھذا اﻟﻣﻔﮭوم ﯾﻌﻧﻲ اﺳﺗﺧدام اﻟﮭواء اﻟﻣﺿﻐوط ﻛوﺳﯾﻠﺔ ﻟﻧﻘل‬
‫اﻹﺷﺎرات داﺧل ﻧظﺎم اﻟﺗﺣﻛم ﻓﻲ اﻟﻌﻣﻠﯾﺎت اﻟﺻﻧﺎﻋﯾﺔ‬
In modern controllers, we use electrical, hydraulic or pneumatic transmission (‫ )نقل‬of signals
to control the process.

To achieve automatic control (‫)لتنفيذ التحكم اآللى‬, the system in figure (1) is modified (‫ )تم تطويرها‬as
shown in figure (2), the human is replaced by (‫ )حل محله‬the following devices:-

- Sensor: To measure the water level and generates (‫ )يعطى‬a signal S that
represents (‫ )التى تعبرعن‬that level.
- Controller: It compares the set point H with the actual level h and generates
a control signal u to change the valve opening via an actuator.
- Actuator: Is connected to the valve by a mechanical link.

Qin

Sensor Controller

Actuator
H h

Qout
i

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Figure (2) Automatic level control
2. Process Control Block Diagram ( ‫)مخطط منظومة ا لتحكم‬

Each element (‫ )عنصر‬in the system is represented by a block as shown in figure (3).
The basic elements are:-

Process: The tank and the liquid.

Sensor: Measures the level and converts (‫ )يقوم بتحويلها‬it into an

electrical or pneumatic (‫ )هواء مضغوط‬signal.

Error detector: (‫ )كاشف ا لخطأ‬A part of the controller that compares the set
or comparator point H with the actual level h.

Controller: A decision making device, it generates a control signal.

Actuator: (‫ )ا لمنفذ‬The final control element, the device (‫ )ا لجهاز‬that

has a direct impact (‫ )تأثير مباشر‬on the process and
changes the controlled variable to bring it to ( ‫)حتى يساوى‬
the set point.
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 or comparator
Set Error
Control signal actuating signal actual output
point detector

Controller Actuator Process

Sensor
Feedback signal

Figure (3) Block Diagram of a Typical Feedback (closed-loop) Control system.

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2.1 Advantages of Automation

a- Cost reduction “due to efficient operation” (‫)توفيرالطاقة نظرا لكفائة التشغيل‬.

b- Reduced maintenance, because of efficient operation and timely

warning of defects.
(‫)تقليل الصيانة نظرا لكفائة التشغيل واالنذار بحدوث األعطال‬.

c- Personal saving, less number of individual (‫ )األفراد‬is required

(‫) توفيرالعمالة‬.

d- Improved environment ( ‫)ظروف تشغيل جيدة‬, watch keeping in a

comfortable ( ‫ ) مريحة‬control rooms.

e- Increased safety, the degree of human error is less

‫زيادة األما ن حيث أن الخطأ البشرى أقل‬
..

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2.2 Disadvantages of Automation
Increase Initial costs.( ‫) زيادة التكاليف األولية‬
a- Extra components ( ‫)مكونات زيادة‬.
b- More sophisticated ( ‫) متخصصة‬, reliable (‫ )قليل األعطال‬but expensive
(‫ )غالى‬components and devices (‫ )أجهزة‬are employed (‫)استخدام‬.
c- Skilled persons ( ‫ ) عماال مها ة‬are required to design, install ( ‫) ت كيا‬
and test ( ‫ )اختبا‬the components.

Increased running costs( ‫) زيادة مصاريف التشغيل‬, as extra

( ‫ )زيادة‬costs are involved to provide ( ‫)أضيفت لتحقق‬
a- Power required to operate the controls.
b- Staff education costs (‫)تكاليف تعليم‬.
c- Extra and more complex maintenance(‫ )صيييانة ضافييافية‬may be
required.
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 ....☺‫دا ﻋﻧوان ﺟدﯾد‬
3. Levels of Control Engineering

Application of control engineering in marine field has increased

steadily (‫ )زادت زييادة مسيتمرة‬during the last few years. The levels vary
between very simple system to complicated (‫ )معقيةة‬and sophisticated
systems (‫)أنظمةمتخصصة‬. These levels are:

1- Centralized (‫ )مركزية‬instrumentation in the engine room.(Display)

2- Data logging and alarm systems (ON -OFF Control)
3- Remote automatic control.
4- Fully Automated control system.

‫وﻗﻔﻧﺎ ﻟﺣد ھﻧﺎ‬ 10

3.1 Centralized Instrumentation in the Engine Room.
Initially (‫ )بةايية‬instruments were distributed (‫ )ييتم تززييع األجةي ة‬all around the
engine room. Watch keeping engineers (‫ – )مةنةسيي الزرديية‬besides attending
(‫ )التزاجية ة‬the maneuvering platform (‫ )أثنياض المنيارر‬- had to do a periodic round
to check the operation of various machinery (‫)المعةات المختلفة‬.

3.2 Data Logging and Alarm Systems.

The next logic step is to put these instruments in a separate air
conditioned control room (‫)غ فة تحكم مكيفة‬.
Centralized display.
The system provides (‫)تحقق‬:-
Recoding.
Alarming
Remote control
Important variable (‫ )المتغيرات الةامية‬such as temperature, pressure, level etc.
are scanned and monitored (‫)يتم اختيارها رقراضتةا‬.
ON -OFF normal operation is indicated by an alarm system which gives
visual and audible (‫ )مرئيية رمسيمز ة‬signal in the important parts of the ship
such as the bridge, control room, engineer's accommodation (‫) أماكن اال اشة‬,
etc
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3.3 Automatic Control
Fully automated engine rooms are developed (‫ )طزرت‬to reduce (‫ )تقليل‬the
number of crew. In a so called “unmanned watch". The night watches are
completely unattended. In the day work the crew carries the maintenance
work. The crew is considered (‫ )يعتبر‬as stand-by (‫ )احتياطى‬in case of an
emergency (‫)للطزارئ‬.

3.4 Fully Automated System for Ship Applications (‫)تطبيقات‬

A modern automation and control system is a fully integrated system

that covers many aspects of the ship operation such as:
• The engine room
• Power management and energy efficiency
• Cargo handling (‫)تداول الشحنة‬
• Navigation ( ‫)االبحا‬ 12
 References
1. A K Sawhney, (1985), “Electrical and Electronic
Measurements and Instrumentation”, Dhanpat
Rai& Sons.

2. J B Gupta (2005), “ Electronic and Electrical

Measurements and Instrumentation”, S K Kataria
& Sons.

3. David A. Bell, (2012), “ Electronic

Instrumentation
and Measurements” , Prentice Hall, 3 rd edition.

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Thanks

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