Emerson E2 Manuel D’Utilisation

TE

M

P

E

R

A

T

UR

E

TEMPER

A

T

U

R

E

TIME

TIME

“P” MODE ONLY

“P” + “I” MODES

S

E

T            P

O

I

N

T

S

E

T            P

O

I

N

T

 Once the input value has wandered outside Propor-

tional Mode’s throttling range, the output percentage will 
be at 0% (if below the Throttling Range) or at 100% (if 
above the Throttling Range). At this point, PID is consid-
ered to be in saturation, meaning it is operating at full (or 
zero) capacity and is not able to react any further to 
changes that occur beyond the throttling range. 

Proportional Mode cannot distinguish between a satu-

rated and an unsaturated system; it simply makes propor-
tional adjustments to the output percentage. Therefore, 
once an input value in a saturated system changes direc-
tion, Proportional Mode reacts to correct the movement, 
regardless of how much error exists. As the temperature 
changes direction and again moves in the direction of the 

setpoint, Proportional Mode will reduce the 100% output 
percentage in an attempt to stop the movement and stabi-
lize the temperature.

To put it another way, when a system is saturated, the 

input changes the placement of the Throttling Range. As 
shown in Figure D-2, as the input rises above the Throt-
tling Range, the top end of the Throttling Range rises with 
it. When the input finally changes direction, the Throttling 
Range remains at its new position.

The “I” Mode covers for Proportional Mode’s inability 

to account for saturation. When the input value is outside 
the throttling range, “I” Mode will continue to adjust the 
output percentage to bring the input value towards the set-
point

.

TIME

TIME

“P” MODE ONLY

“P” + “I” MODES

S

E

T            P

O

I

N

T

S

E

T            P

O

I

N

T

THROTTLING

 

RAN

G

E

THROTTLING

 

RAN

G

E

0%

0%

100%

100%

SATURATION

SATURATION

AS INPUT IN SATURATED SYSTEM
CHANGES DIRECTION, THROTTLE RANGE REMAINS

CHANGES DIRECTION, THROTTLE RANGE REMAINS

“I” CORRECTS ERROR AND BRINGS
THROTTLING RANGE BACK TO NORMAL

THROTTLING RANGE 
FOLLOWS INPUT DURING
SATURATION

THROTTLING RANGE 
FOLLOWS INPUT DURING
SATURATION

To determine the “I” Mode adjustment for each update, 

the following calculation occurs:

“I” mode adjustment = K

i

 * (current error)

K

i 

in this equation is called the integral constant. It is 

simply a multiplier that increases or decreases the speed at 
which the “I” Mode will increase or decrease the percent-
age. 

When changing the value of K

i, 

it should be noted that 

small adjustments yield large results. For this reason, it is 
suggested that K

i  

should remain close to 1.0 and certainly 

no less than 0.5 and no greater than 2.0.

The Proportional and Integral Modes provide a good 

method of controlling a closed-loop system. However, in 
special circumstances where the input value is changing 
rapidly, there may be a lag time between when the error is 
noted and the length of time it takes the system to compen-