User`s manual

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MELSEC-Q
1 OVERVIEW
1.2 PID Control Overview
PID control is applied to the process control of flow rate, speed, air volume, temperature, tension,
compounding or like.
In a configuration shown in Fig. 1.1, PID control maintains the object to be controlled at a preset
value.
Process control instructions
are used
SV
PV
PID
operation
Automatic
MV
D/A
converter
module
Controlled
system
Sensor
Set value
Manual
MV
MV
A/D
converter
module
Subdivided (micro-blocked) processings
of PID control
Fig. 1.1 Example of application to process control
PID control compares the value measured in the detection section (process value: PV) with the
preset value (set value: SV) and adjust the output value (manipulated value: MV) to eliminate the
difference between the process value and set value.
In PID control, proportional operation (P), integral operation (I) and derivative operation (D) are
combined to calculate the manipulated value that will make the process value equal to the set
value fast and precisely.
• If the difference between the process value and set value is large, the manipulated value is
increased to make it close to the set value fast.
• When the difference between the process value and set value has reduced, the manipulated
value is decreased to make it equal to the set value slowly and precisely.