Chapter 14 Pid Control/Process Control Function; Pid Control Function - Mitsubishi Electric MELSEC iQ-R-R00CPU User Manual

14
PID CONTROL/PROCESS CONTROL
FUNCTION
This chapter describes the PID control/process control function.
14.1

PID Control Function

RnPCPU
RnCPU RnENCPU
(Process)
PID control is applicable to process control in which factors such as flow rate, velocity, air flow volume, temperature, tension,
and mixing ratio must be controlled. The control for maintaining the control object at the preset value is shown in the diagram
below: PID control via the PID control instructions is implemented by combining the CPU module with the A/D converter
module and D/A converter module.
Set value SV
PV
*1 SV: Set value
*2 PV: Process value
*3 MV: Manipulated value
In the PID control, the PID operation is executed to compare the value set beforehand (SV) with the digital value (process
value (PV)) in which the analog value measured by a sensor is read from the A/D converter module.
PID operation utilizes proportional operation (P), integral operation (I), and derivative operation (D) in combination, thereby
calculating the manipulated value (MV) quickly and accurately so that a process value (PV) is to be equivalent to a set value
(SV). A larger difference between the process value (PV) and set value (SV) results in a faster speed to reach the set value
(SV) quickly by increasing the manipulated value (MV) and a smaller difference between the process value (PV) and set value
(SV) results in a slower speed to reach the set value (SV) accurately by decreasing the manipulated value (MV). The
calculated manipulated value (MV) is written to the D/A converter module and output to the external device.
For the PID control, use the PID operation instruction. To execute the same PID control as that of the
MELSEC-Q series and MELSEC-L series, use the PID control instructions.
For details on the comparison between the PID operation instruction and PID control instructions, instruction
specifications, PID control, and programming, refer to the following.
 MELSEC iQ-R Programming Manual (CPU Module Instructions, Standard Functions/Function Blocks)
14 PID CONTROL/PROCESS CONTROL FUNCTION
262
14.1 PID Control Function
RnPCPU RnPSFCPU RnPSFCPU RnSFCPU RnSFCPU
(Redundant) (Standard) (Safety) (Standard)
Inside the CPU module
PID control instruction
*1
PID operation
*2
(Safety)
Manual MV
Automatic MV
Automatic/manual
switching
*3
MV
D/A converter module
*2
PV
A/D converter module
Controlled
system
Sensor