Chapter 21 Pid Control/Process Control Function; Pid Control Function - Mitsubishi Electric MELSEC iQ-R Series User Manual

21
PID CONTROL/PROCESS CONTROL
FUNCTION
This chapter describes the PID control/process control function.
21.1

PID Control Function

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.
*1
Set value SV
*2
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.
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 instruction specifications, PID control, and programming, refer to the following.
 MELSEC iQ-R Programming Manual (CPU Module Instructions, Standard Functions/Function Blocks)
Inside the CPU module
PID control instruction
Automatic MV
PID operation
Manual MV
*3
MV
D/A converter module
Automatic/manual
switching
*2
PV
A/D converter module
21 PID CONTROL/PROCESS CONTROL FUNCTION
Controlled
system
Sensor
305
21.1 PID Control Function
21