I-82

Digital Controller

E5CK

I Fuzzy Self-tuning

Fuzzy self-tuning is a function that enables the E5CK to calculate the

most suitable PID constants for the controlled object.

Features

• The E5CK determines by itself when to perform fuzzy self-tuning.

Fuzzy Self-tuning Function

The fuzzy self-tuning function has three modes.

In SRT (step response tuning) mode, the PID constants are tuned

using a step response method at the time the set point is

changed.

In DT (disturbance tuning) mode, the PID constants are amended

so that the controlled temperature will be within the target range

set in advance when there is external disturbance.

In HT (hunting tuning) mode, when hunting occurs, the PID con-

stants are amended to suppress the hunting.

Note: Be sure to turn on the power supply to the load either before or

simultaneously with the start of Temperature Controller opera-

tion.

Dead time will be measured from the time the Temperature

Controller starts operating. If a load such as a heater is turned

on after the Temperature Controller is turned on, dead time

longer than the actual value will be measured and inappropri-

ate PID constants will be obtained. If an extremely large

amount of dead time is measured, the control amount will be

set to 0% for a short period of time before being returned to

100%, and the constants will then be retuned. Retuning is per-

formed only for large amounts of dead time, so be sure to follow

the precaution given above when starting operation.

Startup Conditions of SRT

SRT will start if the following conditions are satisfied simultaneously

when the E5CK is turned on or the set point is changed.

Note: The last SRT-executed set point is set to 0 before shipping and

when changing from advanced PID control to advanced PID

control with fuzzy self-tuning.

PID Constant Refreshing Conditions

If the step control amount is applied before the maximum tempera-

ture slope (R) is obtained, SRT will not renew any PID constant. If the

proportional band obtained from the R and L values that were mea-

sured before the imposition had been completed is larger than the

present proportional band, the PID constants will be renewed

because the measured value is in the direction towards the suitable

proportional band value, and the set point at that time will be the

SRT-executed set point.

Stable Temperature Status

If the temperature is within the stable range for a certain time, it is

deemed that the temperature is stable. This time is called stability

judgement time. Like PID constants, stability judgement time is

adjusted with fuzzy self-tuning according to the characteristics of the

object to be controlled. Fuzzy self-tuning will not be activated if the

temperature is stable because the Temperature Controller deems

that temperature control is smooth.

Balanced Status

If the process value is within the stable range for 60 s when there is

no output, it is deemed that the temperature is balanced.

Startup Conditions of DT

1. DT will start if the temperature that has been stable varies due to

external disturbance and the deflection of the temperature

exceeds the stable range, and then the temperature becomes

stable, provided that the number of maximum temperature values

is less than four.

2. DT will start if the set point is changed under the condition that

SRT does not start and the temperature becomes stable, pro-

vided that the number of maximum temperature values is less

than four.

If there are four or more maximum temperature values, HT will

start.

At the time the E5CK starts

operating

At the time set point is

changed

1. The set point at the time the

E5CK starts operating is dif-

ferent from the set point used

at the time SRT was last exe-

cuted (see note).

2. The process value at the time

the E5CK starts operating is

smaller than the set point in

reverse operation and larger

than the set point in normal

operation.

1. The new set point is different

from the set point used at the

time SRT was last executed

(see note).

2. The process value is in stable

condition before the set point

is changed.

3. A larger set point value is set

in reverse operation and a

smaller set point is set in nor-

mal operation.

Temperature

Slope (R)

Stable range

Time

SP

Shorter than the stability judgement time

Stability judgement time

Stable

Stable

Set

point

Stable

range

Stable

range

(Set to

15.0

°C

before

shipping)

SP

Temperature

Extreme value 2

Set point change

Time

Extreme value 1