Burkert Type 8620 - Manual (Page 112)

mxCONTROL Type 8620
Page 112
Output Override
The output of this module is influenced at certain states (see Figure 51).
Figure 51: Output override (PH_ACID_CAUS)
Acid Stop Limit – Pump Stop (ASL PumpStop)
The pH control module can be connected internally by means of configuration with a corrosion display
for an additional failsafe function. Therefore the ASL-Alarm of the assigned Function (configured as
corrosion display) is evaluated in order to prevent overdosing of acids or bases.
If the corrosion rate of the connected corrosion display exceeds the ASL alarm, this alarm becomes
active. As long as the ASL alarm remains active, both controller outputs - for acids and bases - are
overridden with "0%", i.e. disabled and the two dosing pumps (for acids and bases) are also shut off
for this period.
Maximum Output Timer (MOT)
This function monitors the acid and the caustic controller output of the pH controller in automatic mode
in order to detect whether the outputs have been failed.
If one of the two controller outputs emits the maximum output longer than the defined maximum output
time (MOT), then both controller outputs will be overridden with "0 %".
In this case an alarm “Out fails” is generated and the common alarm output is actuated, too.
The internal timers for counting the time of maximum output will be reset if the control output is smaller
than the maximum control output and the alarm was not yet triggered. The maximum control output is
determined separately for each PI-controller by the parameter "Upper output limit Lim+".
The Maximum Output Timer can be enabled/disabled through the configuration. For a general
description of the MOT refer to chapter 14.1.5.
Both pH controller outputs will be overridden with 0 % until the operator acknowledges the
alarm message with the soft key buttons in the process data menu, even if operation mode
was changed.