Engineering Course
SEQUENCE CONTROL (SEQUENCE TABLE)
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TYPES OF SEQUENCE CONTROL BLOCKS
The following function blocks are catagorized as sequence control blocks: 1.Sequence Table Blocks 2.Logic Chart Block 3.Sequential Function Chart Block 4.Switch Instrument Blocks 5.Sequence Element Blocks 6.Valve Monitoring Block
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TYPES OF SEQUENCE CONTROL BLOCKS (1/2)
Sequence Table Blocks This function blocks realizes sequence control by operating other function blocks and/or process or software I/O. There are two basic type of Sequence Table blocks: • Sequence Table Block ST16 • Rule Extension Block ST16E On top of the basic types above, there are also other types such as Sequence Table Block M_ST16 (Number of condition signals: 32 to 64, number of action signals: 32 to 64 / Total 96) Rule Extension Block M_ST16 Sequence Table Block L_ST16 (Number of condition signals: 64, number of action signals: 64 / Total 128) Rule Extension Block L_ST16 The conditions & operations are arranged in the table format & specifies which operation is performed by the combination of conditions.
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SEQUENCE TABLE BLOCK (ST16, ST16E) Sequence Table block (ST16, ST16E) is a decision table type function block that describes the relationship between input signal and output signal in a Y/N (Yes/No) fashion.
The ST16 block has a sequence control function that handles a total of 64 I/O signals and 32 rules. The I/O signals can also be redistributed in the 8-signal unit. The rule extension block (ST16E) is used for extending the rules of ST16 block. It connects to an ST16 block and only allows connection to a step-type ST16 block. Hence, it cannot be used/activated independently.
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SEQUENCE TABLE BLOCK (ST16, ST16E) I/O connection is set by describing connection information & data in the input connection information setting area, condition setting area, output connection information setting area & operation specification setting area of the sequence table.
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SEQUENCE TABLE BLOCK (ST16, ST16E) When the phase step sequence table is used, the number of processes (number of steps) may be insuficient depending on the process that is being performed. Solution: use the rule expansion format sequence table block (ST16E) to expand the number of rules.
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SEQUENCE TABLE BLOCK (ST16, ST16E) Complete Sequence Table Configuration •Condition Signal
Enter the element symbol in the Tag Name Data Item column (eg. FC002.ALRM) and condition specification in the Data column (eg. HI).
•Action Signal
Enter the element symbol in the Tag Name Data Item column (eg. %AN0010.PV) and action specification in the Data column (eg. H).
•Rule Number
Up to 32 rules per block may be used. The output is based on each rule condition and condition testing result.
•Condition Rule
Use Y/N pattern (in combination) to condition rule. If the testing result of condition signal corresponds with the Y/N pattern, the condition is then said satisfied.
•Action Rule
Use Y/N pattern (in combination) to action rule. If the the testing result of condition signal is satisfied, action rule will be manipulated according to the Y/N pattern.
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SEQUENCE TABLE BLOCK (ST16, ST16E) Complete Sequence Table Configuration •Step Label
Step labels are used for phase indication when performing step sequence control in the Sequence Table. The labels are character strings that combine two or less alphanumeric characters (A to Z, 0 to 9).
•Next Step Label
THEN Execute the next step label when the corresponding rule condition status is true or satisfied & after the manipulated output is completed. ELSE Execute the next step label when the corresponding rule status is false.
•Tag Name.Data Item
Describe the connection information of the condition and action signal (eg. FC001.MODE, FC001.PSW, TIMER001.OP, etc).
•Data
Describe the specification of condition and action signal (eg. AUT, HI, L, H, STOP, RUN, etc).
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SEQUENCE TABLE BLOCK (ST16, ST16E) Complete Sequence Table Configuration •Comment
Comments are defined by user to describe the meaning of symbols & contents of status manipulation of condition & action rules.
•Processing Timing
There ara two processing timings: Start/Execution Timing It refers to the timing at which control algorithms are executed when receiving input signals. Select one of the following type - Periodic Execution (T) - One-Shot Processing (O) - Startup at Initial Cold Start/Restart of FCS (I) - Restricted Initial Execution (B) Output Timing It indicates the condition or behaviour of action signals in conjunction with the condition rule status change (applicable with T & O type of Start Timing only). Select either - Output Only When Condition Change (C) or - Output Each Time Conditions Are Satisfied (E)
•Scan Period
Sequence table with periodic execution type (T) is activated at defined scan period. There are three types of scan periods: - Basic Scan (1 second – fixed) - Medium Speed Scan ( 200 & 500 milliseconds) 50, 100, 250 milliseconds are also applicable. - High Speed Scan (200 & 500 milliseconds) 50, 100, 250 milliseconds are also applicable.
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SEQUENCE TABLE BLOCK (ST16, ST16E) Start / Execution Timing
Periodic Execution (T) The periodic execution means that the sequence control block is repeatedly executed in a preset cycle.
One-Shot Execution (O) When execution timing of a function block is defined as one-shot type, the block is executed only when it is invoked by other function block. A one-shot function block can invoke another one-shot function block. However, such succession is limited to seven blocks. Invocation can only be initiated from the same FCS. Invocation signal ACT.ON
Invoking function block
ACT.OFF Sequence process execution Executing
One-shot type function block
Idle One-Shot Processing Conceptual Diagram
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SEQUENCE TABLE BLOCK (ST16, ST16E) Start / Execution Timing
Initial Execution/Restart Execution (I) In this execution type, the sequence block executes its process when the FCS performs a cold start or a restart.
Restricted Initial Execution (B) In restricted initial execution, the sequence control block executes only when the FCS performs a cold start, not include restart.
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SEQUENCE TABLE BLOCK (ST16, ST16E) Output Timing
Output Only When Conditions Are Changed (C) The sequence table blocks output an operation/action signal only at the timing when the judged conditions are changed from false to true. This is applicable only with periodic execution (T) or one-shot start (O) start timing. Condition detection (a change from false to true state) True Condition rule change
False Action change/interuption is possible eventhough the conditions rule are satisfied True
Action rule change
False “Output Only When Conditions Are Changed” Conceptual Figure
Note: Note However, if non-latched output is specified for the action signal, the operation changes when the condition is switched from true to false. PT YOKOGAWA INDONESIA Training Center – Technical Support Group
SEQUENCE TABLE BLOCK (ST16, ST16E) Output Timing
Output Each Time Conditions Are Satisfied (E) The sequence table blocks output its operation/action signal every scan period as long as the judged conditions are satisfied. Condition detection (false or true state) True Condition rule change
False Action change/interuption is not possible as long as the condition remains satisfied. True
Action rule change
False “Output Each Time Conditions Are Satisfied” Conceptual Figure
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SEQUENCE TABLE BLOCK (ST16, ST16E) Execution & Output Timing Combination
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SEQUENCE TABLE BLOCK (ST16, ST16E) Sequence Description Example (AND Gate)
The basic logical AND gate can be configured in a Sequence Table as follow:
In the example above, only when all conditions signals are satisfied the action/output operation may be performed. PT YOKOGAWA INDONESIA Training Center – Technical Support Group
SEQUENCE TABLE BLOCK (ST16, ST16E) Sequence Description Example (OR Gate)
The basic logical OR gate can be configured in a Sequence Table as follow:
In the example above, when any of conditions signals is satisfied the action/output operation may be performed. PT YOKOGAWA INDONESIA Training Center – Technical Support Group
SEQUENCE TABLE BLOCK (ST16, ST16E) Operation Of Non-Step Sequence In a non step sequence table, all 32 rules are subject to condition testing and the output operation is performed according to the conditions. As for condition testing, a condition is satisfied when all conditions (Y/N) for the same rule number are true. Rule column that is blank is considered true unconditionally. Operations/actions are executed according to the operation contents of Y/N patterned for the rule number whose conditions are satisfied. When the conditions of multiple rules are satisfied simultaneously with respect to the same action signal, if request for both Y/N are detected as the resultant operations, the request for Y takes precedence and the operation for N will not be executed.
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SEQUENCE TABLE BLOCK (ST16, ST16E) Operation Of Non-Step Sequence (Example) Here is an example of the sequence that normally monitors operation to prevent the buffer tank in the processing piping system from overflow. The sequence table below monitors the conditions in rule numbers 01 to 04 simultaneously. If any condition becomes true, the action/operation in the same rule will be executed. The monitoring continues after the execution.
LAHH100.PV LAH100.PV LAL100.PV LALL100.PV
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SEQUENCE TABLE BLOCK (ST16, ST16E) Operation Of Step Sequence In a step sequence table, the process control sequence of a phase-step process is divided into the smallest phase units (steps) on the condition monitoring and operation, then these steps are executed one by one. Only step label 00 and the rule corresponding to the Only the step currently being executed is subject to condition testing. Only the actions for the rules whose conditions are satisfied in the step currently being executed, are in operation.
current step number are subject to condition testing & operation. Step label 00 is executed during each period & it may only be used at the head of a sequence table group. So it cannot be used as a next step label. The next execution step label must be described in THEN/ELSE part in order to advance the next step. If both are left blank the same step is executed each time & will not advance. The next step specified in THEN part is the step to advance when the condition test result is satisfied (true state). The next step specified in ELSE part is the step to advance when the condition test result is unsatisfied (false state). It will proceeds to the next step without executing the action/operation rules. If there are multiple requests for step transition in the same step, the step advances to the next step label with the smallest rule number. The next step execution is done during the next scan period.
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SEQUENCE TABLE BLOCK (ST16, ST16E) Operation Of Step Sequence (Example) Sequence Specification 1. Push the start button Valve A opens to fill the tank with water. 2. When the tank is full Switch A becomes ON. Valve A is closed. 3. Push the start button again (with the tank full of water) Valve B opens to drain the tank. 4. When the tank level becomes low Switch B becomes ON Valve B is closed
Water injection processing (Step label A1)
Water drain processing (Step label A2)
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SEQUENCE TABLE BLOCK (ST16, ST16E) Operation Of Step Sequence (Example)
Water injection processing (Step label A1)
Water drain processing (Step label A2)
In the above sequence table, rules number 01 & 02 are step A1. Rules number 03 & up are step A2. Rules number o5 and beyond do not have any Y/N pattern for the condition rule or action rule or move-destination step label, so they are not subject to condition testing nor action execution. Step A1 monitors the conditions for rules number 01 & 02 simultaneously. Whichever the condition is satisfied will be executed. Executing the action of rule 01 does not advance the step since there is no designation in the movedestination step label. After executing the action, A1 resumes monitoring rules number 01& 02 again. When rule number 02 conditions become true, the action of rule 02 is executed & the step advances to A2 as stated in the move-destination step label.
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SEQUENCE TABLE BLOCK (ST16, ST16E) Number Of Condition & Action Signal By default, sequence table ST16 has 32 condition signals and 32 action/operation signals. However, this allocation of condition & action signal can be changed on 8-signal unit basis.
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SEQUENCE TABLE BLOCK (ST16, ST16E) Number Of Condition & Action Signal Table : Combination of Condition & Action Signal Counts Number Of Condition Signal
Number Of Action Signal
8
56
16
48
24
40
32 (default)
32 (default)
40
24
48
16
56
8
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SEQUENCE TABLE BLOCK (ST16, ST16E) Rule Extension The number of rules in one sequence table is fixed at 32 & cannot be modified. However, if the number of rules in a sequence table is not enough to describe one phase unit, it can be extended in the 32-rule unit by connecting to another sequence table. The number of rules can be extended for a step-type sequence table.
Type the tag number of the extended sequence table in the NEXT box of the first/extending sequence table.
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Function Blocks and I/O Data) Function blocks that can be processed in a sequence table are shown below.
Switch Instrument Block
Valve Monitoring Block (VLVM)
Timer Block (TM)
Regulatory Control Blocks
Software Counter Block (CTS)
Calculation Blocks
Pulse Train Input Counter Block (CTP)
Faceplate Blocks
Code Input Block (CI)
SFC Blocks
Code Output Block (CO)
Unit Instrument Blocks
Relational Expression Block (RL)
Sequence Table Blocks
Resource Scheduler Block (RS)
Logic Chart Block
I/O data that can be processed in a sequence table are shown below.
Processing I/O (Digital Input/Output) Software I/O (Internal Switch, Annunciator, Global Switch) Communication I/O
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Switch Instrument & Enhanced Switch Instrument Blocks) 1/2
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Switch Instrument & Enhanced Switch Instrument Blocks) 2/2
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Timer Block [TM])
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Software Counter Block [CTS])
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Pulse Train Input [CTP])
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Code Input Block [CI])
Condition Signal Description (Code Output Block [CO])
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Relational Expression Block [RL])
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Resource Scheduler Block [RS])
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Valve Monitoring Block [VLVM])
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Regulatory Control Block) 1/4
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Regulatory Control Block) 2/4
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Regulatory Control Block) 3/4
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Regulatory Control Block) 4/4
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Calculation Block) 1/4
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Calculation Block) 2/4
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Calculation Block) 3/4
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Calculation Block) 4/4 The table lists the calculation blocks that can be referenced in the condition signal as oneshot operation. The format is: TAGNAME.ACT.ON
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Faceplate Block)
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Sequential Function Chart Block) The following lists the data items of SFC block that can describe data values in condition specifications and their setting ranges: STEPNO:
1 to 99
SWCR[5]: 0 to 15 SWST[5]: 0,1 SWOP[5]: -15 to 15
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Unit Supervision Block)
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Processing I/O Block)
Condition Signal Description (Global Switch)
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Software / Common Switch)
Condition Signal Description (Communication I/O)
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SEQUENCE TABLE BLOCK (ST16, ST16E) Condition Signal Description (Annunciator Message)
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LABORATORY WORKS Create a logic sequence from these control narratives: Case 1 In a cascade loop, if the process variable of the slave controller is HighHigh alarm then the slave controller mode will have to switch to CASCADE mode and the master controller mode will have to switch to AUTO mode. However, the operator is allowed to change the mode of slave controller to MANUAL or AUTO mode even tough the process variable is still in High-High alarm state. Case 2 In a cascade loop, if the process variable of the slave controller is HighHigh alarm then the slave controller mode will have to switch to CASCADE mode and the master controller mode will have to switch to AUTO mode. The control mode of the slave controller cannot be changed until the alarm vanishes (process variable is in normal state). PT YOKOGAWA INDONESIA Training Center – Technical Support Group
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