Sequential Control Functions
CS1000/3000 Fundamental Course Textbook
PART-E Sequential Control Functions
E-1 Sequential Control Blocks
E-2 Sequence Table Blocks
E-3 Timer and Soft-counter Block
E-4 Types of Contact Output
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Sequential Control Positioning
The function blocks that execute the sequential control are referred
to as sequential control blocks. The positioning of the sequential
control blocks is shown blow:
FCS
Basic control
Software I/O
I/O interfaces
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Types of Sequential Control
Definition of sequential control:
Sequential control executes in sequence each control step following the
pre-defined conditions or orders.
The sequential control can be divided into following two types:
Condition control (Monitoring)
Monitors process status and controls according to the pre-defined conditions.
Programmed control (Phase steps)
Controls according to the pre-defined programs (phases).
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Sequential Control Description
Sequence table block:
The conditions and operations are arranged in the decision table format and
specifies which operation is performed by the combination of conditions. This table
is suitable for describing the both types of sequence.
Logic chart block:
The logic chart block aligns each condition and operation, and the combination of
conditions is described with logic elements to specify the operation performed. This is
suitable for describing the condition control type such as an interlock sequence.
SFC (Sequential Function Chart ) block:
The SFC is a graphical programming language suitable for describing a process control
sequence. It is standardized by the international standard, IEC SC65A/WG6.
It is used for relatively large-scaled sequential controls and device controls. The SFC block defines
the flow of an entire sequence. Each step in the SFC is described with sequence tables or SEBOL
(Sequence and Batch Oriented Language).
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Types of Sequential Control Blocks
Sequence table block:
The sequence table block realizes a sequential control by operating other function
blocks and/or process I/O or software I/O.
Logic chart block:
The logic chart block realizes an interlock
sequence with the logic chart diagram using
logic elements.
SFC block:
The SFC block executes the sequential control
program described with SFC.
Sequence auxiliary blocks:
Switch instrument blocks:
Valve pattern monitors: (optional)
See Supplement V. Function Block List.
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Sequence Table Block (ST16)
32 rules
Condition signals
Total 32 (default)
Action signals
Total 32 (default)
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Condition rules
Input
connection
information
Condition
specification
Output
connection
information
Action
specification
I/O signals
Total 64
(fixed)
Action rules
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Sequence Table Block
Processing timing
Scan period
Step label
Condition
signal
comment
Action
signal
comment
Next step label
Rule expansion destination tag name
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Example of Sequence Description
An example of descriptions of the fundamental logic circuits, AND,
OR and NOT.
%SW0200
ON
Rule
%Z011101
ON
%SW0201
ON
Step
C01
.
.
.
%SW0200.PV ON Y
%SW0201.PV ON Y
%SW0202.PV ON
%SW0203.PV ON
C32 (Condition signals)
AND logic circuit
%SW0202
ON
A01 %Z011101.PV H
.
%Z011102.PV H
.
%SW0200.PV H
.
A32 (Action signals)
%Z011102
ON
%SW0203
ON
OR logic circuit
%SW0200
OFF
01 02 03 . . . . . . . . . . 32
N
Y
Y
Y
Y Y
Y
THEN
ELSE
%SW0200
ON
NOT logic circuit
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Non-step Type Sequence Table
Non-step type sequence table tests all rules at every control
period.
Rule
Basic operation 1:
01 02 03 . . . . . . . . . . 32
Step
(1) As for condition testing, in the
same rule number when all
conditions (Y or N) are satisfied, the
condition of the rule is true.
(2) Rule columns for the same
rule number are all blank are
considered true unconditionally.
C01
.
.
.
%SW0200
Y
%SW0201
Y
%SW0202
%SW0203
C32 (Condition signals)
A01
.
.
.
A32
%Z011101
%Z011102
%Z011103
N
N
Y
Y
Y
(Action signals)
THEN
ELSE
%SW0200 and %SW0201 are ON and then %Z011101 turns ON.
%SW0201 and %SW0202 are OFF and then %Z011102 turns ON.
%Z011103 turns ON unconditionally.
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Non-step Type Sequence Table
Basic operation 2:
When multiple action signals exist in
a condition satisfied rule, the actions
are executed from top to down.
Rule
01 02 03 . . . . . . . . . . 32
Step
C01
%SW0200
Y
%SW0201
Y
.
%SW0202
.
.
%SW0203
C32 (Condition signals)
A01
.
.
.
A32
%Z011101
%Z011102
%Z011103
Y
Y
N
(Action signals)
THEN
ELSE
Actions are executed in order of %Z011101, %Z011102, %Z011103.
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Execution and Output Timing
Execution timing
A sequence table block and a logic chart block have the
following four types of execution timing:
Periodic execution (T):
Repeatedly executed in a preset cycle.
One-shot execution (O):
Executed once when invoked by other function blocks.
Initial execution/Restart execution (I):
Executed when the FCS performs a cold or a restart.
Initial execution (B):
Executed when the FCS performs a restart.
Output timing
A sequence table block has two types of output timing:
Output only when conditions change (C)
Output each time conditions are satisfied (E)
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Output Timing
Output only when conditions change (C):
The action is executed only once when the condition is switched from false to
true. However, if the non-latched output is specified for the action signal, the
action changes when the condition is switched from true to false.
Output each time conditions are satisfied (E):
The action is executed each control period as long as the condition remains
true.
Output only when conditions change (C)
Output each time conditions are satisfied (E)
ON
Condition
ON
OFF
Condition
OFF
Non-latched type
(L type)
Output
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Output
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Processing Timing
Execution timing and output timing can be used in combination.
The table below shows the combination of timings for ST16 and
ST16E.
Default
For the LC64, logic chart block, output timing (C) can not be specified.
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Step Type Sequence Table
Step type sequence table tests only rules in the current step at
every control period.
Basic operation 1:
Rule
Step
For the step type sequence table,
the next execution step label must
be described in the THEN/ ELSE
column in order to advance the
steps.
C01
%SW0200
%SW0201
.
%SW0202
.
.
%SW0203
C32 (Condition signals)
The step will not advance if both next
step labels in the THEN/ ELSE are
blank. The same step is executed
each time.
A01
.
.
.
A32
%Z011101
%Z011102
%Z011103
04
05
08
Y
Y
Y
Y
Y
Y
Y
(Action signals)
THEN
ELSE
05
08
Step label
Tested rules
Next step label (THEN label)
Next step label (ELSE label)
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Step Type Sequence Table
Basic operation 2:
Rule
The next step specified in the
THEN column is the step to
advance when the condition test
result is true.
After all actions for the
corresponding rules are
executed, the step proceeds to
the next step.
Step
C01
.
.
.
%SW0200
%SW0201
%SW0202
%SW0203
C32 (Condition signals)
A01
.
.
.
A32
%Z011101
%Z011102
%Z011103
04
05
08
Y
Y
Y
Y
Y
Y
Y
(Action signals)
THEN
ELSE
05
08
When the condition of the rule in step
04 is satisfied, the step advances to 05.
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Step Type Sequence Table
Basic operation 3:
Rule
The next step specified in the
ELSE column is the step to
advance when the condition test
result is false.
When conditions for the
corresponding rules are not
satisfied, the step proceeds to
the next step without executing
the actions.
Step
C01
.
.
.
%SW0200
%SW0201
%SW0202
%SW0203
C32 (Condition signals)
A01
.
.
.
A32
%Z011101
%Z011102
%Z011103
04
05
08
Y
Y
Y
Y
Y
Y
Y
(Action signals)
THEN
ELSE
05
08
When the condition of the rule in step 04 is
not satisfied, the step advances to 08.
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Step Type Sequence Table
Rule
Basic operation 4:
When a step advances to a
next step, the next step is
executed at the next scan
period.
When a step advances, the
conditions of each rule are
initialized once.
Step
02
01
C01
%SW0200
%SW0201
.
%SW0202
.
.
%SW0203
C32 (Condition signals)
Y
Y
A01
.
.
.
A32
%Z011101
%Z011102
03
04
%Z011103
(Action signals)
THEN
02
03
04
ELSE
The step sequence executes only a single step at each scan period.
In this example, it may take 2 seconds or more to turn %Z011103 OFF,
after the step 01 was executed.
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Step Type Sequence Table
Rule
Basic operation 5:
Step
Step label 00 is executed at
each period. The step 00 can be
described only at the head of a
sequence table group.
C01
.
.
.
* 1. The step 00 cannot be
described as a next step label.
A01
.
.
.
A32
* 2. The step 00 cannot be described
on an extended sequence table.
00
01 02
03
%SW0200
Y
%SW0201
Y
%SW0202
Y
%SW0203
C32 (Condition signals)
%Z011101
%Z011102
%Z011103
04
Y
N
N
(Action signals)
THEN
02
03
04
ELSE
The step 00 as well as the current step 03,
conditions are tested. If conditions of step 00
are satisfied, actions are executed.
Current step
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Timer Block (TM)
The sequence auxiliary blocks are provided such as a timer, a softcounter and so on.
The timer block (TM) measures time
in the unit of second or minute.
Timer start switch
An example of the timer block operation.
Processing Timing: TC
Y
%SW0500.PV
ON
TM100.BSTS
CTUP
TM100.OP
START
%SW0500.PV
Timer count-up
Timer start/stop
Start switch off
BSTS: Block status
CTUP: Count-up
OP: Operation
START: Start/stop action
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Start command
19
Stop command
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Software Counter Block (CTS)
The software counter block (CTS) counts a number of times that
the condition is satisfied.
An example of the soft-counter block operation.
Processing Timing: TE
Stop switch
%SW0501.PV ON
Update switch
%SW0502.PV ON
Counter count-up
CT100.BSTS
CTUP
Counter update
CT100.ACT
ON
Counter stop
CT100.ACT
OFF
%SW0501.PV
%SW0502.PV
BSTS: Block status
CTUP: Count-up
ACT: Action
ON: Update, OFF: Stop
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Stop command
20
Y
Y
Y
Update command
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Types of Contact Output
Latched (H) type output:
The latched type output holds the current output status until ON or OFF
operation is executed.
e.g. %SW0501.PV.H
The latched and non-latched type output can also be applied for internal
switches, annunciator message outputs and so on.
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Types of Contact Output
Non-latched (L) type output:
The non-latched type output turns ON when logical computation result
becomes true and turns OFF when becomes not true.
e.g. %SW0501.PV.L
OFF action is not effective for the non-latched type output.
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Types of Contact Output
Flashing (F) type output:
The flashing type output starts flashing when ON operation is executed and
stops flashing when OFF operation is executed. In order to turn off the
current state, OFF operation as H type is required.
e.g. %Z011101.PV.F
The flashing type output can not be applied for internal switches,
annunciator message outputs and so on.
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