Burkert Type 8620 - Manual (Page 103)

mxCONTROL Type 8620
Page 103
14.3.3 On-/Off-Ratio Control (COND_CONTROL_RATIO)
This module allows a simple On-/Off ratio control of the conductivity with an optional interface to the
"Biocide-Dosing" module.
These modules
are explained
below.
Figure 42: COND_CONTROL_RATIO
Ratio
Since the quality of the incoming water (make-up water) is varying, the conductivity of the incoming
water is measured and used for determining the current set point of the conductivity control of the
system water.
The internal calculation of the set point SP takes place as described below:
PV2
*
k
x
ratio
PV2 SP
SP = kx * PV2 SP-Limitation, so that SP
is within alarm limits
(Alarm-, Alarm+) of PV1 SP > SPLim
(SP has to be
greater than offset)
Alarm-
Alarm- Alarm+
Alarm+
Output
In-
put
SP
Lim
SPLim
Output
In-
put
Figure 43: Set point calculation (COND_CONTROL_RATIO)
First the process value is multiplied with the ratio factor Kx. Afterwards the result is limited to the
input alarm limits
of the System Channel conductivity input, in order to avoid providing a set point,
which causes later on an input alarm. Then the result is checked, whether it is smaller than the
required set point minimum SPLim ("Set Point minimum", internal value). If not, it will be set to SPLim.
The set point minimum SPLim is calculated internally in the following way:
SPLim = PV2 (of Make-Up Channel) + Offset + Switching Hysteresis [µS/cm]
If a sensor/input error occurs on Make-Up-Channel, the last valid calculated set point will be
used!