Burkert Type 8620 - Manual (Page 132)

mxCONTROL Type 8620
Page 132
Pre-bleed function:
After the 14-day timer has started biocide dosing, it may be desirable to delay the execution until the
corresponding system water conductivity was reduced to a lower level or the parameterizable max.
duration of the pre-bleed function
+TmPB
was reached. The corresponding level of the system water
conductivity before dosing is defined by the PB value (Pre-Bleed Limit) - compare Figure 69 and the
chapters on the conductivity modules (14.3.1 ff).
If a non-ratio conductivity module COND_CONTROL or COND_PI was linked with the biocide
dosing module, then the value of the pre-bleed limit has to be set directly.
If a ratio conductivity module COND_CONTROL_RATIO or COND_PI_RATIO was linked with the
biocide dosing module, then the value of the pre-bleed limit is determined by adding the parameter
"PB ratio" to the current set point at the starting time of the pre-bleed; it will stay constant during the
pre-bleed phase. The calculated pre-bleed is checked concerning its minimum value in order to
prevent a non-reachable pre-bleed limit. If the pre-bleed limit is lower than the control output limiter
(SPLim-), is is set to this value (compare section "Ratio" in chapter 14.3.3).
The pre-bleed function is not active if no conductivity module is linked with the biocide dosing
module.
The purpose of this pre-bleed before biocide dosing is to allow the bleed valve (normally controlled
by a conductivity control) to be held shut for the entire biocide event, thereby maximising contact
time
(kill time) without running the risk of hardness salts precipitating, due to over concentration.
If the pre-bleed was configured by assigning a matching conductivity module, the conductivity module
will be controlled by the biocide dosing regime during the whole dosing process.
Should particular site conditions mean that you cannot take full advantage the above features, it is
possible to disable the functions as follows:
• Pre-bleed If a non-ratio conductivity controller module (COND_CONTROL
or COND_PI) is linked with the Biocide Dosing:
The function is disabled by defining the pre-bleed
limit (PB) to a value above the set
point of the assigned conductivity controller.
If a ratio conductivity controller module
(COND_CONTROL_RATIO or COND_PI_RATIO) is linked with the
Biocide Dosing:
The function is disabled by defining the pre-bleed
pre-bleed ratio (PB ratio) at a value of "0".
• Maximum duration of
the pre-bleed
function.
By defining the configuration setting of the max. pre-bleed timer
MTPB to "Off", the duration of the pre-bleeding is not restricted in
terms of time for both channels.
• Biocide 2/3 – 1/3 split By setting the delay Tm1 = "0", all the biocide of a dosing event will
be added in one process.
• Post dose delay Setting the delay Tm2 = "0", to zero will enable the assigned
conductivity controller to continue controlling immediately after the
dosing process is completed.