CONTROL OF BATCH PROCESSESx

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14 Νοε 2013 (πριν από 3 χρόνια και 9 μήνες)

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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
(
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

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

POWER
SOURCE
(Battery,
not
alternator)
GROUND
CLOSED
If Lights
Are ON
(Included
in light
switch)
CLOSED
If Key is
Not in
the
Ignition
(Included
in
ignition
switch)
HARD-WIRED VERSION OF CIRCUIT
ALARM IS
ALWAYS
ON (Can be
audial
and/or
visual)
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

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:

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

http://www.process
-
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.HTTP
://WWW.WEB
-
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

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

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.