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11 PROCESS CONTROL INSTRUCTIONS
11.1 Overview
Execution condition switching
Loop RUN/STOP
If any loop component such as a detector or operation terminal other than the programmable controller fails, each loop can be
run and stopped independently for the purpose of maintenance. SPA of the alarm detection (ALM) is used to run/stop the
applicable loop.
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Basic operation to stop a loop
• Output status is retained. (Example: Output of S.2PID instruction = 0)
• No alarm is detected.
• The control mode is MAN.
Tracking
Tracking refers to making a certain signal follow and match another signal.
Tracking function
The tracking function used by process control instructions includes the bumpless function and output limiter processing
function.
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Bumpless function
The bumpless function prevents manipulated value (MV) output stepping changes when switching from the automatic mode
to manual mode, and continuously and smoothly controls MV output.
■
Output limiter processing function
The output limiter processing function limits the upper or lower limit of the manipulated value (MV) output by the PID operation
in automatic mode. This output limiter processing function is only valid in automatic mode and is not executed in manual
mode. The output limiter processing function is not executed either even in automatic mode if the tracking bit (TRK) is set to 0
(Disable tracking).
Cascade loop tracking
The process control loops making up a cascade loop use the manipulated value (MV) of a primary loop (Loop 0) as the set
value (SV) of a secondary loop (Loop 1). Tracking is performed to prevent a sudden change in the set value (SV) when the
control mode of the secondary loop (Loop1) is changed.
Cascade loop tracking processing is outlined below.
In cascade operation, the manipulated value (MV) of Loop 0 is transferred to the set value (SV) of Loop 1. When cascade
operation is not performed, the set value (SV) of Loop 1 is transferred to the manipulated value (MV) of Loop 0. (Tracking to
the source specified as the input terminal of the set value (SV) of Loop 1)
Tracking is performed when the control mode is switched to one other than CAS, CSV, or CCB.
PID
PID
SV
SV
MV
MV
PV1
PV2
Loop 0
Loop 1
Transferring data
Tracking bit (TRK: 1)
Содержание MELSEC iQ-R Series
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Страница 1795: ...25 TYPE CONVERSION FUNCTIONS 25 1 Converting BOOL to WORD 1793 25 Operation error There is no operation error ...
Страница 1805: ...25 TYPE CONVERSION FUNCTIONS 25 10 Converting WORD to DINT 1803 25 Operation error There is no operation error ...
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Страница 2067: ...APPX Appendix 5 PID Control Program Examples 2065 A 252 Set PID control data for loop 2 ...
Страница 2082: ...2080 APPX Appendix 6 Process Control Program Examples 129 Set the default value of the loop tag ...
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