Burkert Type 8620 - Manual (Page 110)

mxCONTROL Type 8620
Page 110
14.5 pH Controller Modules (PH_ACID_CAUS) and
(PH_ACID_OR_CAUS)
The pH control function is designed for P and PI control.
The implemented strategies for pH control include an acid and caustic dosing regime
(PH_ACID_CAUS), whereas each section can be set independently.
Furthermore, the module PH_ACID_OR_CAUS is available, which realises a pH control with only
acid or only caustic substances dosing
.
14.5.1 pH-Control (PH_ACID_CAUS)
This module permits a pH-Control with Acids and Bases and with the optional interface to the
"Corrosion Display" module for additional overdosing failsafe function.
These modules are
explained below.
Figure 48:
(PH_ACID_CAUS)
Set value limiter (SP Limit)
The set point limiter is used to limit the adjustable set point through a minimum and maximum value in
order to prevent the definition of wrong set points, that is, beyond this valid range by the
user/operator.
Ramp for Set point adjustment (SP Ramp)
The Ramp is used to increase or decrease the set point of the controller in a series of small
steps
, thereby avoiding possible instability problems which could occur if large changes to the set
point were made on poorly tuned systems.
If the ramp is activated and the set point is changed to a new value, the controller will not
immediately respond
to the full range. Over a period of time defined by the slope, small changes
will be fed to the controller until the desired new set point has been reached.
If the operator switches from manual to automatic mode and if the ramp is activated, the set point
will be increased/decreased from the last process value in manual mode to the set point in automatic
mode with the defined slope.