10 PID CONTROL INSTRUCTIONS
10.1 Overview
1157
10
Transferring PV to SV in manual mode
This function executes the PIDCONT instruction even in manual mode. In manual mode, whether transferring the process
value (PV) input from the A/D converter module to the set value (SV) storage area during execution of the PIDCONT
instruction or not can be selected by turning on or off SM792 or SM794. SM792 and SM794 are set to off by default. The PV
and SV are stored in the specified device or label in the I/O data area by using the PIDCONT instruction.
Depending on the on/off status of SM792 or SM794, the following differences apply when switching manual
mode to automatic mode.
• When SM792 or SM794 is off, the PV is transferred to the SV storage device or label. Therefore, there is no
difference between the PV and SV and an abrupt change does not occur in MV when the mode is switched.
Note, however, that since the SV after the mode is switched differs from the target value in automatic mode,
the user needs to change the SV step by step in the program so that it matches the target value.
• When SM792 or SM794 is on, the PV is not transferred to the SV storage device or label. Therefore, a
difference exists between the PV and SV when the mode is switched. If the difference is large when the
mode is switched, an abrupt change may occur in MV. Use this method in a system where the mode is
switched when the PV has fully neared the SV. PID control in automatic mode can be executed immediately
without the SV being changed step by step in the program.
Changing the setting range of PID control data and I/O data
The setting range of PID control data and I/O data can be changed as desired.
To change the range, turn on the bit corresponding to the target loop in SD792, SD793, SD794, and SD795.
0: PID limit restricted (default)
1: PID limit not restricted
SM792, SM794 Operation
Off • The PV is transferred to the SV storage device or label during execution of the PIDCONT instruction.
• When the mode is switched to automatic mode, the MV output in manual mode is continued.
• If the SV is changed after the mode is switched to automatic mode, control from the MV output to the SV is enabled.
On • The PV is not transferred to the SV storage device or label during execution of the PIDCONT instruction.
• When the mode is switched to automatic mode, control from the MV output in manual mode to the SV is enabled.
• Before switching to automatic mode, store the SV to the SV storage device or label.
Inexact
differential
Exact
differential
Operation
SD794 SD792
b0: Loop 1
b1: Loop 2
b14: Loop 15
b15: Loop 16
SD795 SD793
b0: Loop 17
b1: Loop 18
b14: Loop 31
b15: Loop 32
1/0
b15
1/0
b14 b13 b12 b11 b10 b9 b8 b7 b6 b5 b4 b3 b2
1/0
b1
1/0
b0
1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0
1/0
b15
1/0
b14 b13 b12 b11 b10 b9 b8 b7 b6 b5 b4 b3 b2
1/0
b1
1/0
b0
1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0
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