6
Important notes
Terms and definitions
Stand-by mode (conductivity control)
To avoid loss of water, the continuous blowdown control and the programme-controlled intermittent
boiler blowdown (if activated) can be de-activated during stand-by operation or when the burner is
switched off. An external control command will be triggered and, as a result, the continuous blow-
down valve will be closed. During stand-by operation the MIN/MAX limits and the monitoring function
remain active.
After the equipment switches back to normal operation the continuous blowdown valve is motored
into the OPERATING potion or the control position. In addition an intermittent blowdown pulse is trig-
gered off (provided that automatic intermittent boiler blowdown has been activated and an interval
period and pulse duration has been set).
Temperature compensation (conductivity control)
The electrical conductivity changes as the temperature falls or rises. To obtain meaningful readings it
is therefore necessary that the measurements are based on the reference temperature of 25°C and
that the measured conductivity values are corrected by the temperature coefficient factor.
For automatic temperature compensation the following three settings are available: TK Linear, TK
Norm or TK Auto.
TK (Linear)
To ensure that the readings are based on 2 5°C set the TK value between 0 and 3.0 %/°C (default
setting 2.1 %/°C. This setting permits the linear temperature compensation of the measured value
over the whole measuring range. This method is usually applied for steam boilers operating at
constant service pressure. After the TK is set and the service pressure is reached use a calibrated
conductivity meter to measure the conductivity of the boiler water and compare the reading with
the indicated conductivity value. If the reading differs from the indicated conductivity change the TK
setting until they tally.
TK (Norm)
Since conductivity is not a linear function of temperature over a larger temperature range, various
conditioning agents and different basic conductivities were used in order to ascertain empirical
conductivity/temperature curves. These curves are stored as standard curves and can be used for
temperature compensation. TK (NORM) is suitable for boilers operating with variable pressure, which
means that the boiler does not have a fixed working pressure (e. g. low load 10 bar, full load 15 bar).
TK (Auto)
For this method a characteristic conductivity/ temperature curve of the plant is used for temperature
compensation. The installation specific readings are recorded during the heat-up phase and stored
as Auto curve. TK (AUTO) is particularly suitable for steam boilers operating with variable pressures.
Cell constant and correction factor (conductivity control)
The cell constant is a geometric quantity characteristic of the conductivity electrode and is taken into
account when calculating the conductivity. However, in the course of time this constant may chance,
e. g. due to dirt deposits accumulated on the measuring electrode. Deviations can be compensated
by changing the correction factor.
Purging of the continuous blowdown valve
To prevent the continuous blowdown valve from getting stuck the valve can be rinsed automatically.
At regular intervals the continuous blowdown valve is motored into the open position. When the
purging time is over, the valve is motored into the OPERATING position or into the required control
position.
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