Flowserve URB 2 - Manual (Page 43)

43
Glossary
– continued –
Energizing times (conductivity and capacitance level control):
For each of the four output relays individual time delays for energizing and de-energizing can be set.
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 blowdown
valve will be closed. During stand-by operation the MIN/MAX limits and the monitoring function remain
active.
Once returned to normal operation the continuous blowdown valve is motored into the OPERATING
position or the control position. In addition an intermittent blowdown pulse is triggered 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 α (Tk).
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 25°C set the TK value between 0 and 5.0 %/°C (default
setting 2. %/°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 0 bar, full load 5 bar).
TK (Auto):
For this method a characteristic conductivity-/ temperature curve of the plant (Auto curve) is used
for temperature compensation. However, first a characteristic Auto curve must be recorded. For this
purpose turn the navigation wheel at TK (AUTO) to start and then press the navigation wheel in order to
start recording the curve. Apply the max. service pressure to the steam boiler. During heating up every
0°C above 00°C temperature and conductivity values are recorded and the current temperature is
indicated. After having recorded 25 values or if STOP is selected the equipment stops recording and
saves the Auto curve.
TK (AUTO) is suitable for steam boilers operating with variable pressures.
When the compensation is switched OFF the absolute conductivity will be indicated.