Process Control Priyatmadi 2005 Pengantar Pengendalian Proses Priyatmadi Jurusan teknik Elektro FT UGM 1

Overall Course Objectives • Develop the skills necessary to function as an industrial process control engineer.

– Skills • Tuning loops • Control loop design •

Control loop troubleshooting

• Command of the terminology – Fundamental understanding • Process dynamics • Feedback control Process Control Priyatmadi 2005 2

Control Relevant Aspects of Control Loop Hardware • Necessary for control loop troubleshooting: – To determine if each subsystem (control computer, actuator system, and sensor system) is functioning properly – To understand the proper design and operation of all the components that make-up each of the subsystems of a control loop Process Control Priyatmadi 2005 3

Process Control Classification • Manual Control • Automatic Control • Feedback Control • Feed forward Control • Analog Control • Digital Control Process Control Priyatmadi 2005 4

Manual Control Process Control Priyatmadi 2005 5

Automatic Control Cold water in steam in hot water out 3-15psi Set point I/P Set point + e(t) 4-20 mA TIC Controller m(t) 4-20 mA Plant Sensor Process Control Priyatmadi 2005 TT c(t) 6

F 1 T 1

Control Diagram of a Typical Control Loop

Actuator System F 2 T 2 Sensor System Controller TC T TT

Process Control Priyatmadi 2005 7

Components and Signals of a Typical Control Loop

F T Air 1 1 Console 3-15 psig I/P Operator T 4-20 ma sp D/A DCS Control Computer F 2 T 2 Thermowell T Thermocouple millivolt signal A/D 4-20 ma Transmitter

Process Control Priyatmadi 2005 8

Controller Development • Pneumatic controllers • Electronic analog controllers • Supervisory control computers • Distributed Control Systems (DCS) • Fieldbus technology Process Control Priyatmadi 2005 9

Pneumatic Controllers - Phase I • Introduced in the 1920’s • Installed in the field next to the valve • Use bellows, baffles, and nozzles with an air supply to implement PID action.

• Provided automatic control and replaced manual control for many loops Process Control Priyatmadi 2005 10

Pneumatic Controllers - Phase II • Transmitter type pneumatic controllers began to replace field mounted controllers in the late 1930’s.

• Controller located in control room with pneumatic transmission from sensors to control room and back to the valve.

• Allowed operators to address a number of controllers from a centralized control room.

Process Control Priyatmadi 2005 11

Pneumatic Controller Installation

F 1 T 1

Process Control Priyatmadi 2005

3-15 psig Air T sp Pneumatic Controller 3-15 psig F 2 T 2 Thermowell T Thermocouple millivolt signal Air Transmitter

12

Electronic Analog Controllers • Became available in the late 1950’s.

• Replaced the pneumatic tubing with wires.

• Used resistors, capacitors, and transistors based amplifiers to implement PID action.

• Outsold pneumatic controllers by 1970.

• Allowed for advanced PID control: ratio, feedforward, etc.

Process Control Priyatmadi 2005 13

Electronic Controller Installation

F 1 T 1 Air 3-15 psig I/P 4-20 ma T sp Electronic Analog Controller

Process Control Priyatmadi 2005

F 2 T 2 Thermowell T Thermocouple millivolt signal 4-20 ma Transmitter

14

Computer Control System • Based upon a mainframe digital computer.

• Offered the ability to use data storage and retrieval, alarm functions, and process optimization.

• First installed on a refinery in 1959.

• Had reliability limitations.

Process Control Priyatmadi 2005 15

Supervisory Control Computer

Video Display Unit Alarming Functions Printer Supervisory Control Computer

Process Control Priyatmadi 2005

Analog Control Subsytem

...

Interfacing Hardware Data Storage Acquisition System

16

Distributed Control System- DCS • Introduced in the late 1970’s.

• Based upon redundant microprocessors for performing control functions for a part of the plant. SUPERIOR RELIABILITY • Less expensive per loop for large plants.

• Less expensive to expand.

• Facilitates the use of advanced control.

Process Control Priyatmadi 2005 17

Process Control Priyatmadi 2005

System Consoles

DCS Architecture

Host Computer Data Storage Unit PLC Data Highway (Shared Communication Facilities) Local Console Local Control Local

..............

Unit Unit Local Console Process Transmitters and Actuators

18

DCS and Troubleshooting • The data storage and trending capability of a DCS greatly facilitate troubleshooting control problems. That is, the sources of process upsets can many times be tracked down through the process by trending a group of process measurements until the source of the process upset is located.

Process Control Priyatmadi 2005 19

Control Relevant Aspects of a DCS • The most important control aspect of a DCS is the cycle time for controller calls. The shortest cycles times are typically around 0.2 seconds while most loops can be executed every 0.5 to 1.0 seconds. These cycle times affect flow control loops and other fast control loops.

Process Control Priyatmadi 2005 20

Fieldbus Technology • Based upon smart valves, smart sensors and controllers installed in the field.

• Uses data highway to replace wires from sensor to DCS and to the control valves.

• Less expensive installations and better reliability.

• Can mix different sources (vendors) of sensors, transmitters, and control valves.

• Now commercially available and should begin to replace DCSs.

Process Control Priyatmadi 2005 21

Fieldbus Architecture

Plant-Wide Network Local Area Network

.................

Local Area Network Smart Sensors Smart Control Valves and Controllers

Process Control Priyatmadi 2005

Fieldbus Network a Smart Sensors Smart Control Valves and Controllers Fieldbus Network

22