Burkert Type 8623 - Manual (Page 34)

32 - 8623-2 Standard
english
1
Ti
Characteristic and step response of the P fraction of a PI controller
I fraction:
Function: y =
∫ ∫ ∫ ∫ ∫
x
d
dt
T
i
is the integration or floating time. It is the time that expires until the controller
output has run through the entire correcting range.
Characteristics
A purely I controller completely eliminates the effects of disturbances. It thus has a
favourable static behaviour. Because of its finite correcting speed, it works more
slowly than a P controller and tends to oscillation. It is hence dynamically relatively
unfavourable.
Superimposing the P and I fractions:
With a digital controller with sampling time T
A
and noting that T
i
= K
p
/T
N,
one can
write:
y = K
p
(x
d
+ T
A
/T
N
∑ ∑ ∑ ∑ ∑
x
d
)
y : controller output
K
p
: amplification factor
x
d
: deviation (x
d
= w - x)
T
A
: sampling time
T
N
: reset time
Characteristic Step response
control range
∆
x
c
correcting range
∆
y
floating time T
i
y
max
x
d
y
min
x
d
x