Siemens SIPART DR21 - 3.5 Control algorithm; Control algorithm; Controller direction of effect

3 Functional description of the structure switches
3.5 Control algorithm
Manual
SIPART DR21
C73000-B7476-C143-08
91
3.5 Control algorithm
D Control algorithm
The PID-control algorithm is implemented as an interaction-free parallel structure and follows
the ideal controller equations whilst neglecting the filter constants and the cycle time.
- P-controller
ya = Kp ⋅ xd + yo or
ya
xd
=  Kp
- PI-controller
ya = Kp (xd + xd dt) +yo(t) or = Kp (1 + )
1
Tn

t
0
y
a
xd
1
j
 ⋅ Tn
- D-element connection (zD-part)
The D-element connection can be added optionally.
ya
E
Tv
vv
= Kp
j
 ⋅ Tv
1+j
 ⋅
The input variable E for the D element is xd, x, x1,-z, or +z depending on the setting of
S47.
- z-connection
The z-part can be added optionally to the controller output ya.
ya = c6 ⋅ zor
ya
z
=  c6
D Controller direction of effect
The controller direction of effect is set with S46. It must always have the opposite behavior
(negative follow-up) to the controlled system (including final control element and transmitter).
S46= 0, normally acting controller (+Kp, rising x causes falling y) for normally acting systems
(rising y causes rising x)
S46=1, reversing controller (-Kp, rising x causes rising y) for reversing systems (rising y
causes falling x).