7

s FUNCTIONS

(1) Fuzzy feedback control

Fuzzy feedback control expresses the basic actions of

PID control in fuzzy rules and has a nonlinear characteristic

in order to straighten out the problem inherent to PID

control (i.e., overshoot occurs when improving response

or instability arises due to a change in system even when

optimum PID parameters are assigned).

• Comparison of controllability

Each result of fuzzy control and PID control is shown

below.

It is understandable that the overshoot due to a change

of set value has been suppressed in fuzzy control.

(4) Auto-tuning

PID parameters are automatically set by controller's

measurement and operation.

(b)

Low PV type

Remarks: (1) Once auto-tuning has been made, PID parameter values

are retained despite power-off operation. Therefore, auto-

tuning need not be repeated for the subsequent operations.

(2) During auto-tuning, control output corresponds to ON/OFF

action. This may cause PV to change widely depending

on process. If such a change is unallowable, auto-tuning

should not be used.

(3) Do not use the auto-tuning function for a process having

a quick response, such as pressure control, flow control,

etc.

(a)

Standard type

(2) Ramp soak function (option)

Function to automatically change the set point value with

elapsing of time, in accordance with the preset pattern,

as shown below. This device allows maximum of 4 ramp

soak programs.

This first ramp starts at the value measured immediately

before the program is executed (PV).

Ramp : Region in which the SP changes toward the

target value.

Soak : Region in which the SP keeps unchanged at

the target value.

Powering on can automatically trigger the program run

(power-on start function), or an external contact signal

can also do that.

(5) Anti-reset Windup (ARW)(*)

Note : *ARW: INTEGRAL action is cut when PV is out range

of AR value.

(3)

Two set points (option)

Change set points digital input.

0.0

Time

20.0

40.0

60.0

80.0

100.0

%

FUZZY

PID

TM1R TM1S

TM2R

TM2S

TM3R

TM3S

TM4R

TM4S

Time

Set point 3

Set point 2

Set point 1

Set point 4

Set point

First

soak

Second

ramp

Third

ramp

Third

soak

Fourth

ramp

Second

soak

Fourth soak

Target point

DI input

Main set point

(SV)

Sub-set point

(

)

AT start

AT operation

ON

ON

OFF

OFF

AT end (PID setup)

PID control

ON-OFF action

PV (Process value)

Set value (SV)

ON 100%

OFF 0%

AT start

AT operation

ON

ON

OFF

OFF

AT end (PID setup)

PID control

ON-OFF action

SV-10%

PV (Process value)

Set value (SV)

ON 100%

OFF 0%

Control output (MV)

100%

50%

MAN

10%

Process value

(PV)

Setting value

(SV)

AR

AR

Proportional

band

PID

action

PD

action

PD

action

I action

cut

I action

cut