Burkert Type 8620 - Manual (Page 94)

mxCONTROL Type 8620
Page 94
14.3 Conductivity Control Modules
Several control strategies are implemented for a closed loop control of system water conductivity by
means of a bleed valve. Depending on the fluctuation of the incoming water (make-up water) quality,
either a simple or a ratio control should be used.
Simple Control
If the incoming water quality is relatively constant, traditional volumetric dosing of Scale &
Corrosion inhibitors combined with a single fixed conductivity control strategy (On-/Off- or PI-Control)
is the standard approach (Simple control).
Ratio Control
If the incoming water quality is varying, ratio control of the conductivity (e.g. within a cooling system)
will be an extremely useful way to control system water concentration.
If the incoming water varies too much in its composition, it will be possible for the scale and corrosion
inhibitors to be under or overdosed because the controller makes no allowance for the change in
cycles of concentration (ratio of concentration of dissolved salts in incoming water and in the system
or circulation water ).
The ratio control uses a dual strategy for conductivity control: on the one hand, in the incoming
water and on the other hand, in the system water. Ratio control maintains the cycles of concentration
within the cooling system by maintaining a fixed ratio between the incoming water and system water,
thereby optimising the inhibitor concentrations level.
For ratio control either the On-/Off-Ratio-Control or the PI-Ratio-Control can be used.