Mitsubishi Electric MELSEC FX2N-2LC, User Manual

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5
Introduction of Functions 5
5-1
5. Introduction of Functions
This section introduces the functions of the FX
2N
-2LC.
For setting of each function, refer to the description on buffer memories (BFM) later.
5.1 PID control
5.1.1 Easy PID control with two degrees of freedom
PID control is a control method to obtain stable control result by setting each of the constants
"P (proportional band)", "I (integral time)" and "D (derivative time)".
However, if each PID constant is so set that the "response to setting" becomes good, the
"response to disturbance" becomes deteriorated in PID control. On the contrary, if each PID
constant is so set that the "response to disturbance" becomes good, the "response to setting"
becomes deteriorated.
The FX
2N
-2LC performs easy PID control with two degrees of freedom in which PID constants
realizing good response to disturbance are adopted and the shape of the "response to setting"
can be selected as either "fast", "medium" or "slow".
Setting of PID constants and selection of the "response to setting" can be performed using
buffer memories.
Conventional PID control
When PID constants are set so that the response to changes in set value becomes good
Response to changes in set value Response to disturbance
Set value
(SV) Set value
(SV)
When PID constants are so set that the response to disturbance becomes good
Response to changes in set value Response to disturbance
Set value
(SV)
Set value
(SV)
Easy PID control with two degrees of freedom
Response to changes in set value Response to disturbance
Set value
(SV) Set value
(SV)
Fast
Medium
Slow
FX2N-2LC Temperature Control Block