Burkert Type 8620 - Manual (Page 86)

mxCONTROL Type 8620
Page 86
The set point value of the subordinate controller must therefore be configured as "int.casc" and
connected with the control output of the main controller. The control output 0…100%, provided by the
main controller, is then scaled proportionally in the set point Scal- … Scal+ for the subordinate control
loop whereby Scal- and Scal+ represent the scaling limits of the process value of the subordinate
control loop.
Figure 26: Set point adaptation
Tight-closing function (CutOff)
This function causes the valve in automatic mode to close tightly or open all the way outside of a set
value-related control range. This set value-related control range is hereby defined by a lower and
upper set point limit.
If the current set point lies outside of the control range, the module output in automatic mode is
overridden with 0% (tight-closing/zero-point cut-off) or 100% (open completely). The control mode is
resumed again with a hysteresis of 1% in relationship to the scaled process value range.
A possible inversion of the actuator sense of action (see section "Effective direction of the actuator")
causes an inversion of the module output even outside the set point-related control range:
Example:
Normal module sense of action, inverse actuator sense of action.
In automatic operation, the module output is overridden
- with 100% if the set value is smaller than Cut- or
- with 0% if the set value is greater than Cut+ .
The function mode also depends on the selected sense of action of the module (see Figure 27).
The tight-closing function can be run in different modes. In the
Cut- mode,
the set point is checked only
in regard to the lower set point limit
Cut-
, in the
Cut+ mode
only in regard to the upper set point limit
Cut+
. In the modes
Cut- & Cut+,
the set point is checked regarding to lower and upper set point limit.
Cut- Cu
t+
Cut- Cu
t+
Figure 27: Tight-
closing function
(CutOff)
(COMMON_PID)