che 185 – process control and dynamics control of batch processes

CHE 185 – PROCESS CONTROL AND

DYNAMICSCONTROL OF BATCH

PROCESSES

STRUCTURE OF BATCH CONTROL

• THE BATCH RECIPE IS KNOWN AS STRUCTURED BATCH LOGIC

• IT CAN BE A RECIPE TO PROGRAM AN ENTIRE CYCLE OF OPERATION

• IT CAN BE A RECIPE FOR A SINGLE STEP• IT IS NORMALLY IMPLEMENTED USING A

PROGRAMMABLE LOGIC CONTROLLER


• THE ACTUAL PROGRAM IS DESIGNED USING A LADDER LOGIC DIAGRAM (HTTP://WWW.CONTROLENG.COM/INDEX.PHP?ID=483&CHASH=081010&TX_TTNEWS[TT_NEWS]=63761)

• A TYPICAL FORMAT IS:• HTTP://WWW.GEOCITIES

.COM/RESEARCHTRIANGLE

/1753/PLC.HTML#II

http://www.controleng.com/index.php?id=483&cHash=081010&tx_ttnews%5Btt_news%5D=63761

http://www.controleng.com/index.php?id=483&cHash=081010&tx_ttnews%5Btt_news%5D=63761

http://www.geocities.com/ResearchTriangle/1753/plc.html








• THE SYMBOLS USED IN THIS DIAGRAM INCLUDE:

LADDER LOGIC DIAGRAM

• MOST OF THE TIME THIS DIAGRAM IS USED– TO DESIGN THE PROGRAM FOR THE PLC– AS A BASIS FOR THE ONE-LINE ELECTRICAL

DIAGRAM FOR THE CIRCUIT

LADDER LOGIC DIAGRAM

• DURING A CYCLE (OPERATIONS PHASES), THE RECIPE NEEDS TO

• CONTROL THE DESIRED ACTION• IMPLEMENT EACH STEP BY• RUN THE INITIATION PROGRAM TO CONFIRM THE

PROCESS IS READY FOR THE STEP• START THE ACTION PROGRAM• CONFIRM EACH STEP HAS OCCURRED PRIOR TO

STARTING THE NEXT STEP• TAKE APPROPRIATE ACTION IF THE PROCESS DOES

NOT FOLLOW THE RECIPE (EXCEPTION)

LADDER LOGIC EXAMPLE

• CONSIDER THE SEQUENCE OF SHUTTING DOWN A CAR

• THE INITIAL STEP IS TO TURN THE KEY TO THE OFF POSITION, OR PUSH THE BUTTON FOR A KEYLESS IGNITION

• THIS STEP REQUIRES THE KEY TO BE IN THE IGNITION OR THE REMOTE TO BE PRESENT

• IT IS POSSIBLE TO DO THIS WHILE THE CAR IS MOVING, FOR UNANTICIPATED EMERGENCIES


• WHEN THE KEY IS REMOVED OR THE BUTTON PUSHED

• AN ALARM MAY SOUND IF THE LIGHTS ARE STILL ON

• THIS ALARM IS ACTIVATED BY THE KEY BEING REMOVED FROM THE IGNITION AND IS POWERED BY THE BATTERY


• FOR THIS LIGHTS-ON ALARM TO FUNCTION THE FOLLOWING MUST BE TRUE:

• THE LIGHTS MUST BE IN AN ON POSITION• THE KEY MUST BE OUT OF THE IGNITION OR

THE POWER OFF BUTTON PUSHED• THE BATTERY MUST BE CHARGED• THE ALARM MUST BE FUNCTIONAL

LADDER LOGIC EXAMPLE• ONE-LINE DIAGRAM FOR THE PROCESS MIGHT

RESEMBLE:

• THIS ALARM SHOULD NOT GO ON WHEN THE LIGHTS ARE TURNED ON WITHOUT THE KEY BEING IN THE IGNITION

POWERSOURCE(Battery,notalternator)

GROUND

CLOSEDIf LightsAre ON(Includedin lightswitch)

CLOSEDIf Key isNot intheIgnition(Includedinignitionswitch)

HARD-WIRED VERSION OF CIRCUIT

ALARM ISALWAYSON (Can beaudialand/orvisual)

A

LADDER LOGIC EXAMPLE• EXAMPLE IF THE KEY IS NOT REMOVED

WHEN THE DRIVER EXIT• AN ALARM WILL SOUND IF THE DRIVER’S

DOOR IS OPENED TO ALERT THE DRIVER THAT THE KEY IS STILL IN THE IGNITION

• FOR THIS SEQUENCE TO WORK, ALL THE FOLLOWING MUST BE TRUE:– THE KEY MUST BE IN THE IGNITION– THE KEY MUST BE IN THE OFF POSITION– THE DOOR MUST BE OPEN– THE BATTERY MUST BE CHARGED TO POWER THE

ALARM

LADDER LOGIC EXAMPLE• NOTE - IT IS STILL POSSIBLE TO LOCK THE

KEYS IN THE CAR WITH THE LIGHTS ON• MANY CARS ALSO HAVE A STEERING

COLUMN LOCK THAT IS ACTIVATED WHEN THE KEY IS REMOVED FROM THE IGNITION, BUT THIS IS NORMALLY A MECHANICAL RATHER THAN ELECTRICAL PROCESS.

BASIC CONTROL AND INTERFACING TOOLS AND DEVICES

• THE PLC IS A COMPUTER USED TO PROGRAM RELAYS AND OTHER COMPONENTS AS SOFT DEVICES

• AN OUTLINE OF THE SKILLS USED FOR IMPLEMENTING PLC CONTROL IS AT: HTTP://WWW.PACONTROL.COM/PLC.HTML

• THE PLC PROGRAM REPRESENTS THE CONNECTION BETWEEN THE LOGIC AND HARDWARE IN THE SYSTEM

http://www.pacontrol.com/PLC.html


• CONSIDER THE FOLLOWING EXAMPLE OF A WALK / DON'T WALK SIGN AT A PEDESTRIAN CROSSING WITH PLC CONTROL

• ACTION IS INITIATED BY A PEDESTRIAN UPON ARRIVING AT THE CROSSING PUSHES THE WALK BUTTON

• THIS STARTS A 15 SECOND DELAY, FOR THE SEQUENCE TO STOP TRAFFIC.

• AFTER THIS DELAY, THE WALK SIGN WILL BE DISPLAYED FOR 10 SECONDS. (ALL OTHER TIMES THE DON'T WALK SIGN IS DISPLAYED.

• THE MNEMONIC CODE LISTING AND LADDER DIAGRAM ARE ON THE NEXT PAGE


CROSSING SIGNAL DIAGRAM


• CROSSING SIGNAL EXAMPLE • THE FIRST STEP IN THE SEQUENCE

INVOLVES CLOSING A CIRCUIT WITH PUSH BUTTON 100

• THE SYSTEM RESETS AT THE END OF THE CYCLE

DEVICE INTERFACES WITH THE PLC

• SEVERAL SPECIFIC TYPES OF UNITS HAVE BEEN DEVELOPED

• LOAD CELLS ARE USED FOR MEASUREMENT OF AMOUNTS

• THE PRINCIPLE OF THE LOAD CELL IS A CHANGE IN A MEASURABLE VARIABLE DUE TO AN INDUCED LOAD

• LOAD CELL OUTPUT SIGNALS CAN BE INDUCED MECHANICALLY, PNEUMATICALLY OR ELECTRONICALLY

• THEY CAN MEASURE WEIGHTS DUE TO COMPRESSION, SHEAR, TENSION, OR BENDING.


• THE LOAD CELL SIGNAL IS READ THROUGH A WHEATSTONE BRIDGE:

DEVICE INTERFACES WITH THE PLC• LOAD CELLS CAN WEIGH ITEMS AS SMALL AS A PILL OR AS

LARGE AS A LOADED RAIL CAR• EXAMPLES OF RANGES FOR UTILIZATION ARE:

DEVICE INTERFACES WITH THE PLC• EXAMPLES OF RANGES FOR UTILIZATION

ARE:

http://www.omega.com/literature/transactions/volume3/load.html

DEVICE INTERFACES WITH THE PLC• EXAMPLES OF RANGES FOR UTILIZATION ARE:


• LOAD CELL SPECIFIC APPLICATIONS FOR BATCHI OPERATIONS– ADDING AMOUNTS OF MATERIALS TO

BATCH PROCESSES,– MEASUREMENT OF PRODUCT INTO

FINISHED GOODS CONTAINERS– DISCRETE DEVICES TWO-STATE DEVICES;

LIMIT SWITCHES; DEVICE STATES


• CONTACT POSITION SENSORS (LIMIT SWITCHES) ARE ELECTROMECHANICAL DEVICES– THEY ARE OPEN & CLOSED BY THE

MOVEMENT OF A LEVER ARM THAT IS IN CONTACT WITH A MATERIAL.

– THE POSITION SWITCH HAS TWO POSITIONS WHICH RELATE TO A BINARY SIGNAL, SO THEY WORK WELL WITH THE PLC TYPE OF PROGRAM.


• CONTACT POSITION SENSORS TYPICAL APPLICATIONS– VALVE POSITION - WHEN MOUNTED ON

THE ACTUATOR OR VALVE SHAFT– POSITIONING WHEN A UNIT IS LOCATED

CORRECTLY– ON A CONVEYOR BELT, TO ASSURE THE

BELT IS ON TRACK


• NON-CONTACT POSITION SENSORS• PHOTOELECTRIC DEVICES -

– THE LEVER ARM IN THE LIMIT SWITCH IS REPLACED WITH A LIGHT BEAM (FROM AN LED) AND A PHOTOCELL

– THESE CAN BE VERY SENSITIVE BUT THAT ALSO CAN LIMIT THEIR APPLICATION TO VERY CLEAN SYSTEMS


• NON-CONTACT POSITION SENSORS• ULTRASONIC DEVICES -

– THESE CAN BE EITHER ANALOG OR DIGITAL

– THEY HAVE A WIDE RANGE OF APPLICATION THOUGH THEY WILL NOT WORK WITH MATERIALS THAT ARE SOUND ABSORBING


• NON-CONTACT POSITION SENSORS• CAPACITANCE DEVICES

– MEASURE THE PRESENCE OF A MATERIAL IN A FIELD• SENSITIVITY DEPENDS ON DIELECTRIC

CHARACTERISTICS OF THE TARGET• SENSITIVITY INCREASES WITH DIELECTRIC

CONSTANT• MATERIALS WITH RELATIVELY HIGH

DIELECTRIC CONSTANTS CAN BE DETECTED INSIDE CONTAINERS WITH LOW DIELECTRICS CONSTANTS, E.G., WATER IN A GLASS CONTAINER


• NON-CONTACT POSITION SENSORS• INDUCTION DEVICES• DEVICES THAT USE

ELECTROMAGNETIC EDDY FIELDS GENERATED BY METALLIC COMPONENTS IN MOTION

• USED FOR NON-CONTACT OPERATIONS SUCH AS VIBRATION SENSORS ON ROTATING SHAFTS


• NON-CONTACT POSITION SENSORS• INDUCTION DEVICES• SENSITIVITY IS HIGH FOR METALS AND

LOW FOR NON-METALS, SO THESES ARE NOT AFFECTED BY OIL AND GREASE

• THESE DEVICES CAN BE ANALOG OR DIGITAL IN CONFIGURATION


• FLOW METERING SYSTEMS• FLOW CAN BE CONTROLLED BY

DIRECT MEASUREMENT OR LOSS-OF-WEIGHT METHODS

• DIRECT MEASUREMENT USES SOME TYPE OF DIRECT MEASUREMENT OF THE FLOW

• THESE ARE THE IN-PIPE DEVICES


• FLOW METERING SYSTEMS• BELT SCALES USE THE COMBINATION OF LOAD

CELLS WITH SPEED SENSORS TO MEASURE MATERIAL FLOW ON A BELT. THIS SHOWS THE LOAD CELLS INSTALLED FOR A CONVEYOR BELT IDLER. THEY MEASURE THE LOAD ON THE IDLERS

http://www.process-auto.com/loadcell_belt_scale.htm


• FLOW METERING SYSTEMS• BELT SCALES • THE SPEED MEASUREMENT DEVICE IS MOUNTED SO

THAT IT CONTACTS THE INNER SURFACE OF THE RETURN BELT.


• FLOW METERING SYSTEMS

• LOSS-OF-WEIGHT CAN BE USED TO MEASURE MATERIAL FLOWS FROM A DEVICE MOUNTED ON A WEIGH SCALE AND USING LOAD CELLS, THE RATE OF DISCHARGE IS CONTROLLED BY THE ROTATION RATE FOR THE DISCHARGE AUGER (SCREW). THE SCREW IS LOCATED AT THE BASED OF THE HOPPER OR BIN. LOAD CELLS ARE USED TO DETERMINE THE RATE OF WEIGHT (LOSS.HTTP://WWW.WEB-TECH.COM.AU/LOSS2045.HTM)

• THESE UNITS CAN ALSO BE USED AS VOLUMETRIC FEEDER SYSTEMS


• FLOW METERING SYSTEMS

• DRIBBLE FLOW FEEDERS ARE ACTUALLY USED FOR LOADING INTO PACKAGES

• FIXED AMOUNTS OF MATERIAL ARE LOADED INTO WEIGH HOPPERS AND THEN LOADED INTO CONTAINERS

http://www.fischbein.com/americas/products.php?cat=1332


• FLOW METERING SYSTEMS• DRIBBLE FLOW FEEDERS EXAMPLE

SEQUENCE CONTROL

• THE NATURE OF BATCH CONTROL• BATCHES REQUIRE DISCRETE QUANTITIES OF RAW

MATERIALS• BATCH PROCESSES NEED TO HAVE TRACKING OF

PRODUCTS IN PROCESS• SOME BATCH PROCESSES HAVE MORE THAN ONE

PRODUCT IN PROCESS SIMULTANEOUSLY

SEQUENCE CONTROL

• THE NATURE OF BATCH CONTROL• INTERMEDIATE BATCH PRODUCTS ARE MOVED

FROM ONE OPERATION TO THE NEXT IN DISCRETE AMOUNTS

• SOME PROCESSES INCLUDE CONTINUOUS PROCESSING INTEGRATED WITH BATCH OPERATIONS

• THE NATURE OF BATCH PROCESSES MAKES THEM MORE COMPLEX THAN CONTINUOUS OPERATIONS

SEQUENCE CONTROL

• THE NATURE OF BATCH CONTROL• EACH STEP IN A BATCH PROCESS HAS A POTENTIAL

FOR FAILURE, SO FAILURE MODES NEED TO BE MORE COMPLEX THAN FOR CONTINUOUS OPERATIONS

• EACH STEP IN A BATCH PROCESS NEEDS TO BE CONFIRMED FOR COMPLETION

• MOST STEPS IN BATCH PROCESSES NEED TO GO TO COMPLETION ONCE THEY ARE STARTED.

SEQUENCE CONTROL

• INPUT/OUTPUT FOR BATCH SYSTEM CONTROL

• I/O MUST PROVIDE CONTINUOUS STATUS OF A BATCH PROCESS

• CONTROL SYSTEM SHOULD ALLOW CONTINUOUS MONITORS AND CONTROLS FOR SOME PARTS OF THE PROCESS.

PROGRAMMING FOR BATCH OPERATIONS

• EACH OPERATION IN BATCH SYSTEMS NEEDS TO BE PROGRAMMED INDEPENDENTLY, BUT STILL BE COMPATIBLE WITH THE OVERALL PROCESS CONTROL

• THE CONTROL SYSTEM MUST AUTOMATICALLY DETECT PROCESS UPSETS AND EQUIPMENT FAILURE

PROGRAMMING FOR BATCH OPERATIONS

• THE BATCH PROCESS MAY BE USED FOR MORE THAN ONE TYPE OF PRODUCT, SO NEEDS TO BE EASILY REPROGRAMMED.

• SOME PROCESSES, ESPECIALLY BIOTECH, MAY USE THE SAME EQUIPMENT FOR MORE THAN ONE STEP, WHICH LEADS TO MORE COMPLEX CONTROL SYSTEMS.

che 185 – process control and dynamics control of batch processes

Documents

ignition slide

alarm slide

ladder logic example

ladder logic diagram

battery slide

ladder logic example

circuit slide

functional slide