Function For Transfer To The Sv Storage Device For The Pv In Manual Mode - Mitsubishi Electric MELSEC-Q series Programming Manual

Function for transfer to the SV storage device for the PV in
manual mode
When using the PID control instruction to perform PID control, execute the PID operation instruction also in the manual mode.
In the manual mode, it is possible to select whether the PV imported from the A/D converter module is transferred to the SV
storage device or not when the PID operation instruction is executed, depending on the ON/OFF status of the PID bumpless
processing flag (SM774, SM794).
PID Bumpless Processing Flag
SM794 (Incomplete
derivative)
OFF
ON
Mode switching from manual to automatic depending on ON/OFF of SM774 and SM794
There are the following differences in control when the manual mode is switched to the automatic mode.
• When SM774/SM794 is OFF, the PV is transferred to the SV storage device. Therefore, there is no difference between the
PV and SV when the manual mode is switched to the automatic mode. Hence, an abrupt change does not occur in MV at
the time of mode switching. Instead, since the SV after mode switching differs from the target value in the automatic mode,
the user should change the SV to the target value step by step in the sequence program.
• When SM774/SM794 is ON, the PV is not transferred to the SV storage device. Therefore, there is a difference between
the PV and SV when the manual mode is switched to the automatic mode. If the difference is large at the time of mode
switching, 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 the automatic mode can be executed immediately without the SV being changed step by
step in the sequence program.
The SV and PV are stored into the devices specified in the I/O data area with the PID operation instruction.
4 FUNCTIONS OF PID CONTROL
32
4.3 Other Functions
Operation
SM774 (Complete
derivative)
• The PV is transferred to the SV storage device when the PID operation instruction is executed.
• When the manual mode is switched to the automatic mode, the MV output in the manual mode is
continued.
• When the SV is changed after switching to the automatic mode, control is performed to achieve the SV,
starting from the MV output in the manual mode.
• The PV is not transferred to the SV storage device when the PID operation instruction is executed.
• When the manual mode is switched to the automatic mode, control is performed to achieve the SV,
starting from the MV output in the manual mode.
• Before switching to the automatic mode, store the SV into the SV storage device.