PROCESS CONTROL For Operators BY Eng AHMED SABRY

PROCESS CONTROL For Operators BY Eng. AHMED SABRY 2004 February Ahmed Sabry 1

Basic Instrument Loops 2004 February Ahmed Sabry 2

Data Acquisition Loops Process Sensor DAQ ------- XMTR OR • OR Primary Element Switch Indicate • Record • Alarm Control Room Field 2004 February Ahmed Sabry 3

Data Acquisition Loops For data acquisition there must be: • Sensor and / or transmitter to measure the variable and generate a proportional signal that represents the instant value of the variable. • A receiver instrument (indicator, recorder, or alarm annunciator) that receives an input signal from the sensor and / or transmitter and present it to the operators and other plant teams in the proper form. • Signal transmission medium (e. g. cables) to transmit the measurement signal from sensor and / or transmitter to the receivers. All data acquisition loops are open loops in which the data flows in one direction only, i. e. from sensor and / or transmitter to the receiver. 2004 February Ahmed Sabry 4

Open Control Loops Final Control Element Process Sensor XMTR Indicator • Valve Data • V. Speed Motor • Louvers SP • Turbine Operator decision and action 2004 February Ahmed Sabry 5

Open Control Loops << In the open loop control, the operator plays the role of the controller, as seen from the previous side >>. • He receives the data (value of the measured variable) from the indicator • He knows the required S. P. value • He compares the data with the S. P. and takes the decision (direction and amount of the required correction) • He carries-out the necessary action using, e. g. , the valve handwheel, a manual control station or a pressure regulator to generate an output signal to the valve, … etc. 2004 February Ahmed Sabry 6

Open Control Loops Manual Control Station XMTR PV Indication 0% Data to operator 100% O/P decrease by operator O/P Increase by operator O/P to the control valve Valve opening 0% 2004 February 100% Ahmed Sabry 7

Open Control Loops Control Valve Manual Adjustment Using Pressure Regulator Pressure Gage Signal Pressure Adjustment wheel Manual signal to control valve Instrument Air Supply Pressure Regulator 2004 February Ahmed Sabry 8

Simple Feedback Control Loops Final Control Element Process Sensor • Valve • V. Speed Motor XMTR Set Point Controller • Louvers • Turbine Output Signal Field 2004 February Control Room Ahmed Sabry 9

The Controller Set Point by Operator SP PV signal O/P TO Final Control Element 2004 February Ahmed Sabry Comparator Error Signal E= PV-SP XMTR Controller O/P Calculation 10

Typical Electronic Controller Faceplate Local / Remote Set Point Switch LSP Increase LSP Decrease Automatic Mode Manual Mode Man. O/P decrease 2004 February Man. O/P Increase Valve % open indication Ahmed Sabry 11

Interlock System Final Control Element Process Sensor Solenoid OR XMTR OR Switch Local Panel Interlock System MCC DCS Field 2004 February Ahmed Sabry Control Room 12

Typical Control Loops 2004 February Ahmed Sabry 13

Simple Feedback Control Loop XMTR PV Process I/P OR Positioner O/P Controller Set Point 2004 February Ahmed Sabry 14

Cascade Control Loop FT XMTR-2 HE Steam Hot Water PV-2 I/P OR Positioner TT XMTR-1 O/P Slave Controller RSP Master Controller PV-1 SP 2004 February Ahmed Sabry 15

Split Range Control Loop Set Point PV XMTR Controller Process CV 1 CV 2 3 -9 psi Positioner-1 9 -15 psi 2004 February O/P Positioner-2 Ahmed Sabry 16

Ratio Control Loop Ratio Setting PV-1 XMTR-1 X Fuel Air SP PV-2 XMTR-2 Controller Air Positioner 2004 February O/P 4 -20 ma Ahmed Sabry 17