CHE 185 – PROCESS CONTROL AND DYNAMICS DCS AND PLC FUNDAMENTALS

PNEUMATIC CONTROLLER INSTALLATION

DISTRIBUTED CONTROL SYSTEMS –OPERATING OBJECTIVES INCLUDE PROCESS AND MANAGEMENT CONTROL –MAY BE DESCRIBED AS SUPERVISORY CONTROL AND DATA ACQUISITION (SCADA) SYSTEMS –DISTRIBUTED CONTROL MEANS LOCALIZED CONTROLLERS AND CONTROL COMPUTERS LINKED WITH SUPERVISORY COMPUTERS

DCS ARCHITECTURE

HISTORY OF COMPUTER CONTROL IN PROCESSES ANALOG COMPUTERS - ATTEMPTED TO REPLACE THE CONTROLLERS WITH ANALOG PROGRAMS –SYSTEMS WERE VERY COMPLEX –ONLY CUSTOM COMPONENTS –FAILED TO WIN ACCEPTANCE ON A LARGE SCALE miconductor/timeline/1964- Hybrid.html

HISTORY OF COMPUTER CONTROL IN PROCESSES MICROELECTRONIC ANALOG CONTROLLERS –ELECTRONIC CONTROLLERS THAT REPLACED LARGER PNEUMATIC UNITS –SOME COULD BE LINKED TOGETHER (HARDWIRED) TO PROVIDE CONTROL SYSTEMS

HISTORY OF COMPUTER CONTROL IN PROCESSES DIGITAL CONTROLLERS –LOCAL CONTROL UNITS –COULD BE PROGRAMED WITH NUMEROUS FUNCTIONS –COULD RECEIVE AN EXTERNAL SETPOINT FROM ANOTHER SYSTEM –CONNECTED TO A SINGLE CENTRALIZED CONTROL ROOM COMPUTER AR-MODEL-828-DIGITAL- PROCESS-CONTROLLER- /

HISTORY OF COMPUTER CONTROL IN PROCESSES EARLY DCS SYSTEMS –CONTROL LOOPS WERE BASED ON LOCAL CONTROLLERS –DATA HIGHWAY INTRODUCED TO PROVIDE CONNECTIVITY –DATA LOGGING BECOMES POSSIBLE –USED CUSTOM PROGRAMMING AND MOST COMPONENTS WERE SPECIALIZED

HISTORY OF COMPUTER CONTROL IN PROCESSES LATER DCS SYSTEMS –PARALLEL COMPUTING DESIGN –EACH LOOP CONTROL UNIT CAN OPERATE INDEPENDENTLY –SMART COMPONENTS ALLOW FOR SELF CHECKS AND AUTOMATIC SWITCHING TO REDUNDANT CONTROLLERS

HISTORY OF COMPUTER CONTROL IN PROCESSES

HISTORY OF COMPUTER CONTROL IN PROCESSES LATER DCS SYSTEMS –INCORPORATE INTERACTIONS WITH –PROGRAMMABLE LOGIC CONTROLLERS –CAN BE USED FOR SUPERVISORY MANAGEMENT –OPERATE WITH CONVENTIONAL SYSTEMS NETWORKING SYSTEMS (INCLUDING THE INTERNET) OPERATING SYSTEMS EMPLOY MORE STANDARDIZED PROGRAMMING

HISTORY OF COMPUTER CONTROL IN PROCESSES LATER DCS SYSTEMS –ALLOWS USE OF FIELDBUS TECHNOLOGY –SMART CONTROL COMPONENTS THAT CAN SELF CHECK FOR CORRECT OPERATION –REDUCES THE NUMBER OF DIRECT CONTROL CONNECTIONS TO THE CONTROL ROOM

HISTORY OF COMPUTER CONTROL IN PROCESSES OPTIMIZATION OF FACILITY OPERATION CAN BE AUTOMATED ON EXTERNAL COMPUTERS THAT RECEIVE DATA FROM THE DCS AND RETURN IMPROVED SETPOINTS

OPTIMIZATION OF FACILITY POWER PLANT EXAMPLE –NO x CONTROL –OVERALL EFFICIENCY – WATER CONSUMPTION ISA HAS DEVELOPED A RANGE OF STANDARDS TO FACILITATE DEVELOPMENT OF DCS

THE FUTURE OF DCS WIRELESS SEEMS TO BE THE NEXT MAJOR STEP COULD ELIMINATE MOST WIRED CONNECTIONS SYSTEM IS MORE PHYSICALLY SECURE THAN ONE WHICH RELIES ON HARDWIRING HACKERS ARE A MAJOR HAZARD

PROGRAMMABLE LOGIC CONTROLLERS USES FOR PLC’s BATCH OPERATIONS RELAY PANEL OPERATIONS UNITS ARE PROGRAMMED TO PROVIDE FUNCTIONS PROGRAMS ARE TYPICALLY WRITTEN IN A FORM THAT STATES IF CONDITION “X” OCCURS, THEN PROCEED TO CONDITION “Y” THE SUBSEQUENT CONDITION MAY INVOLVE TRANSFER OF SIGNALS OR STARTING A TIMER.

PROGRAMMABLE LOGIC CONTROLLERS TYPICAL PLC PROGRAM SEQUENCE

COMPONENTS IN PLC’s CONNECTIONS TO THE OUTSIDE – INPUTS –OUTPUTS PROGRAMMED COMPONENTS –TIMERS –COUNTERS –DATA STORAGE –CIRCUITS

PROGRAMMABLE LOGIC CONTROLLERS PROGRAMS FOLLOW THE FORM USED FOR CIRCUIT LOGIC CALLED LADDER DIAGRAMS

PROGRAMMABLE LOGIC CONTROLLERS EXAMPLE OF A PLC LADDER DIAGRAM FOR FILLING A PROCESS TANK

PROGRAMMABLE LOGIC CONTROLLERS PROCESS CRITERIA START TRANSFER PUMP WHEN LOW LEVEL IS REACHED STOP TRANSFER PUMP WHEN HIGH LEVEL IS REACHED

PROGRAMMABLE LOGIC CONTROLLERS LADDER DIAGRAM FOR THIS SYSTEM LOW AND HIGH LEVEL INPUTS ARE LABELED 01 AND 02, RESPECTIVELY OUTPUT 500 IS TO THE MOTOR RELAY 1001 IS THE PROGRAMMED CIRCUIT - CLOSES WHEN 01 AND 02 ARE CLOSED.

PROGRAMMABLE LOGIC CONTROLLERS OPERATION SEQUENCE –WHEN TANK IS EMPTY, 01 AND 02 ARE BOTH CLOSED, SO THE PUMP IS ON. THE LOGIC PATH IS THROUGH , AS 1001 IS CLOSED –WHEN THE LOW LEVEL IS ACHIEVED, INPUT 01 OPENS, BUT THE PUMP STILL RUNS BECAUSE THE LOGIC PATH IS THROUGH

PROGRAMMABLE LOGIC CONTROLLERS OPERATION SEQUENCE –WHEN THE HIGH LEVEL IS ACHIEVED, INPUT 02 OPENS AND THE LOGIC PATH IS BROKEN, SO 1001 OPENS AND THE PUMP SHUTS OFF. –WHEN THE LEVEL DROPS BELOW HIGH, 02 CLOSES, BUT THE PUMP DOES NOT RESTART BECAUSE 1001 IS STILL OPEN. –WHEN THE PUMP DROPS BELOW LOW, 02 CLOSES, SO 1001 CLOSES AND THE PUMP RESTARTS

PROGRAMMABLE LOGIC CONTROLLERS OTHER COMPONENTS COUNTERS - ALLOW SUMMATION OF STEPS TO DETERMINE WHEN A TOTAL HAS BEEN REACHED TIMERS - CHECK ON THE DURATION OF A STEP

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.

FIELDBUS ARCHITECTURE