CHE 185 – PROCESS CONTROL AND DYNAMICS CONTROL 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

STRUCTURE OF BATCH CONTROL THE ACTUAL PROGRAM IS DESIGNED USING A LADDER LOGIC DIAGRAM ( &TX_TTNEWS[TT_NEWS]=63761) &TX_TTNEWS[TT_NEWS]=63761 A TYPICAL FORMAT IS: /1753/PLC.HTML#II

STRUCTURE OF BATCH CONTROL 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

LADDER LOGIC EXAMPLE 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

LADDER LOGIC EXAMPLE 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

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

BASIC CONTROL AND INTERFACING TOOLS AND DEVICES 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

BASIC CONTROL AND INTERFACING TOOLS AND DEVICES CROSSING SIGNAL DIAGRAM

BASIC CONTROL AND INTERFACING TOOLS AND DEVICES 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.

DEVICE INTERFACES WITH THE PLC 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: html

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

DEVICE INTERFACES WITH THE PLC 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

DEVICE INTERFACES WITH THE PLC 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.

DEVICE INTERFACES WITH THE PLC 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

DEVICE INTERFACES WITH THE PLC 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

DEVICE INTERFACES WITH THE PLC 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

DEVICE INTERFACES WITH THE PLC 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

DEVICE INTERFACES WITH THE PLC 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

DEVICE INTERFACES WITH THE PLC 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

DEVICE INTERFACES WITH THE PLC 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

DEVICE INTERFACES WITH THE PLC 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 auto.com/loadcell_b elt_scale.htm

DEVICE INTERFACES WITH THE PLC FLOW METERING SYSTEMS BELT SCALES THE SPEED MEASUREMENT DEVICE IS MOUNTED SO THAT IT CONTACTS THE INNER SURFACE OF THE RETURN BELT.

DEVICE INTERFACES WITH THE PLC 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. TECH.COM.AU/LOSS2045.HTM) THESE UNITS CAN ALSO BE USED AS VOLUMETRIC FEEDER SYSTEMS

DEVICE INTERFACES WITH THE PLC 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

DEVICE INTERFACES WITH THE PLC 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.