12 SFC programming i Training PLC Allen Bradley

DAY 3
SESSION 4

12-1

SEQUENTIAL FUNCTION CHART (SFC)
PROGRAMMING I

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010


WHAT IS SFC ?
• Stand for: SEQUENTIAL FUNCTION CHART
• SFC is similar to a flow-chart of your process

12-2

• SFC defines the steps or states through which your system
progresses

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010


12-3

SFC SCHEMA

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010


WHEN TO USE SFC ?
Use SFC to:
• Organize the functional specification for your system

12-4

• Program and control your system as a series of steps and
transitions

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010


SFC OVERVIEW
STEP
ACTION

TRANSITION

12-5

QUALIFIER

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010


SFC OVERVIEW

12-6

SIMULTANEOUS
BRANCH

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010


SFC OVERVIEW

SELECTION
BRANCH

TEXT BOX

12-7

STOP

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010

BASIC ELEMENTS IN SFC

12-8

STEP
• Represent a major function of process

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010


BASIC ELEMENTS IN SFC
STEP
• Contains the actions that occur at a particular time, phase, or
station.
• Executes continuously until a transition tells the SFC to go to the
next step.
ACTION

12-9

• One of the functions that a step performs.

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010

BASIC ELEMENTS IN SFC
TRANSITION

12-10

• Defines the physical conditions that must occur or change in order
to go to the next step.
• If true, go to the next step.
• If false, repeat the step above.

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010


BASIC ELEMENTS IN SFC
SELECTION BRANCH

12-11

• Only one path executes.
• Checks from left to right the transitions that start each path. It
takes the first true path.
• If no transitions are true, the SFC repeats the previous step.

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010

BASIC ELEMENTS IN SFC
SIMULTANEOUS BRANCH

12-12

• Execute 2 or more steps at the same time
• All paths must finish before continuing the SFC
• Checks the ending transition after the last step in each path has
executed at least once. If the transition is false, the SFC repeats
the previous step

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010


BASIC ELEMENTS IN SFC
LOOP BACK

12-13

• Loop back to a previous step
• Connect the wire to the step to which you want to go

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010

BASIC ELEMENTS IN SFC
TEXT BOX
• Lets you add descriptive text or notes to your SFC

QUALIFIER
• Determines when an action starts and stops

STOP

Sequential Function Chart (SFC) Programming I

12-14

• Lets you stop and wait for a command to restart

6 – 10 December 2010


BASIC ELEMENTS IN SFC
SEQUENCE

12-15

• A group of steps that execute one after the other.

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010

STEP STRUCTURE
• Each step uses a tag to provide information about the step

12-16

• Access this information via the Monitor Tags tab of the Tags
window

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010


STEP STRUCTURE
Property

Function

T

Determine how long a step has been active
(milliseconds)

X

Do something while the step is active (including first
and last scan)
Do something one time when the step becomes active

SA

Do something while the step is active, except on the
first and last scan

12-17

FS

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010


STEP STRUCTURE
Property

Function
Do something one time on the last scan of the step

TMax

Determine the maximum time that a step has been
active during any of its executions

Count

Determine how many times a step has become active

12-18

LS

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010


12-19

STEP STRUCTURE

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010


ACTION TYPE
NON BOOLEAN

12-20

• Contains the logic for the action
• Uses structured text to execute assignments and instructions
• Call a subroutine

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010

ACTION TYPE
Use structured text assignments, constructs, and instructions

12-21

Call a subroutine

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010


ACTION TYPE
BOOLEAN
• Contains no logic for the action
• It simply sets a bit in its tag (ACTION Structure)

12-22

• To do the action, other logic must monitor the bit and execute
when the bit is on

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010


ACTION STRUCTURE
• Use actions to divide a step into the different functions that the
step performs, such as commanding a motor, setting the state

of a valve

12-23

• Each action (non-boolean and boolean) uses a tag to provide
information about the action

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010


ACTION STRUCTURE
Property

Function

Q

Determine when the action is active

T

Determine how long a step has been active
(milliseconds)
Determine how many times a step has become active

12-24

Count

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010


QUALIFIER
• Each action (non-boolean and boolean) uses a qualifier to
determine when it starts and stops
• The default qualifier is Non-Stored

12-25

• The action starts when the step is activated and stops when
the step is deactivated

Sequential Function Chart (SFC) Programming I

6 – 10 December 2010