LSIS XBE-DC08A, User Manual

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asi
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Chapter 6 Built-in PID Function
6-2
The built-in PID control functions of ultimate performance XGB feature as follows.
(1) Since operations are executed within CPU part, it can be controlled by PID parameters and PLC program without
PID module.
(2) A variety of controls can be selected
▪ That is, a user can easily select P operation, PI operation and PID operation.
(3) Precise control operation
▪ It can make precise PID control operations possible through floating point operations.
(4) PWM (Pulse Width Modulation) output available.
▪ It outputs control operation results to the output contact point designated by a user through PWM.
(5) Improving convenience of control settings and monitoring
▪ Through parameter setting method and K area flag, it maximizes control parameter settings during operation and
convenience of monitoring
(6) Freely selectable operation direction
▪ Forward, reverse and mixed forward/reverse operations are available
(7) Cascade operation realizing quick and precise PID control
▪ It can increase quickness of response to disturbance through cascade loop.
(8) Various additional functions
▪ PID control can be achieved by various methods a user wishes because set value ramp, the present value follow-up,
limiting change of values and types of alarm functions are provided.
6.2 Basic Theory of PID Control
Here describes basic theory of PID control and how to configure PID control.
(1) Terms
Terms used in this user manual are as follows.
▪ PV: status of plant detected by sensor (Process value)
▪ SV: Target value (Set Value) to control plant, if control is done normally, PV should follow the SV.
▪ E: error between SV and PV. It can be expressed as (SV-PV).
▪ Kp: proportional coefficient
▪ Ti: Integral time constant. Sometimes called integral time
▪ Td: Derivative time constant. Sometimes called derivative time
▪ MV: Control input or control device output. The input to plant to make PV follow the V
▪ Ts: Sampling time, a cycle of operation to execute PID control
(2) PID operation expression
Basic PID operation expressions are as follows.
PV SV E
− =
E K MV
P P
=
∫
=
Edt
T
K
MV
i
P
i
dt
dE
T K MV
d P d
=
d i P
MV MV MV MV
+ + =
(6.2.1)
(6.2.2)
(6.2.3)
(6.2.4)
(6.2.5)