Endress+Hauser Liquiline CA80SI - Page 92

Operation Liquiline System CA80SI
92 Endress+Hauser
Menu/Setup/Additional functions/Limit switches/Limit switch 1 ... 8
Function Options Info
Delta value Settings depend on the
measured value
Operating mode = Change rate
The slope of the measured value (MV) is
monitored in this mode.
An event is generated if, in the given timeframe
(Delta time), the measured value increases or
decreases by more than the specified value
(Delta value). No further event is generated if
the value continues to experience such a steep
increase or decrease. If the slope is back below
the limit value, the alarm status is reset after a
preset time (Auto Confirm).
Events are triggered by the following conditions
in the example given:
t
2
- t
1
< Delta time and ∆MV1 > Delta value
t
4
- t
3
>Auto Confirm and ∆MV2 < Delta value
t
6
- t
5
< Delta time and ∆MV3 > Delta value
Delta time 00:01 to 23:59
Factory setting
01:00
Auto Confirm 00:01 to 23:59
Factory setting
00:01
t
MV
t
1
t
2
t
3
t
4
t
5
t
6
MV
1
MV
2
MV
3
A0028526
 70 Rate of change
11.6.2 Controller
Controller structure in Laplace representation
A B
A0015007
 71 Block diagram of the controller structure
A Neutral zone I Integral value
B Output limiting D Derivative value
K
p
Gain (P ‐ value) αT
V
Damping time constant with α = 0 to 1
T
n
Integral action time (I ‐ value) e Control deviation
T
v
Derivative action time (D ‐ value) w Set point
T
w
Time constant for set point damping x Controlled variable
T
wu
Time constant for anti ‐ windup feedback y Manipulated variable
P Proportional value
The controller structure of the device comprises set point damping at the input to prevent
erratic changes in the manipulated variable if the set point changes. The difference
between the set point w and the controlled variable (measured value) X results in the
control deviation which is filtered by a neutral zone.
The neutral zone is used to suppress control deviations (e) that are too small. The control
deviation thus filtered is now fed to the actual PID controller which divides into 3 parts
based on the P (proportional), I (integral) and D (derivative) values (top-down). The