Other Functions; Bumpless Changeover Function; Mv Upper/Lower Limit Control Function - Mitsubishi Electric MELSEC-Q series Programming Manual

4.3

Other Functions

During PID control using the PID control instructions, MV upper/lower limit control is automatically executed by the bumpless
changeover function explained below.

Bumpless changeover function

• This function controls the MV (manipulated value) continuously when the control mode is changed between manual and
automatic.
• When the mode is changed (between manual and automatic), data is transferred between the "MV area for automatic mode
(automatic MV)" and "MV area for manual mode (manual MV)" as described below. The control mode is changed in the I/O
data area ( Page 51 I/O Data).
Mode switching
Changing from the manual mode to the automatic mode
Changing from the automatic mode to the manual mode
Manual and automatic modes of PID control:
• Automatic mode: PID operation is executed with a PID control instruction. The control object is controlled
according to the calculated MV.
• Manual mode: PID operation is not executed. The MV is calculated by the user and the control object is
controlled according to the user-calculated MV.
The loop set in the manual mode stores the PV (process value) in the set value area every sampling cycle.

MV upper/lower limit control function

• The MV upper/lower limit control function controls the upper or lower limit of the MV calculated in the PID operation. This
function is only effective in the automatic mode. It cannot be executed in the manual mode.
• By setting the MV upper limit (MVHL) and the MV lower limit (MVLL), the MV calculated in the PID operation can be
controlled within the range between the limits.
• When the MV upper/lower limit control is used, the MV is controlled as illustrated above. A MVHL (MV upper limit) and
MVLL (MV lower limit) takes on a value between -50 and 2050 or a user-defined value (except the QnACPU). The following
are the default settings: The value set for the upper limit must not be smaller than the value set for the lower limit. An error
will occur if it is.
MV
Upper limit
Lower limit
Description
The MV in the manual mode is transmitted to the MV area for the automatic mode.
The MV in the automatic mode is transmitted to the MV area for the manual mode.
Default value
2000 (Or user-defined value)
0 (Or user-defined value)
4 FUNCTIONS OF PID CONTROL
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4.3 Other Functions
4