4
IM-P403-47 AB Issue 7
The controller opens the blowdown valve periodically to purge the system and allow a sample
of boiler water to pass the sensor. The electrical conductivity of this sample is compared with
the set point selected on the controller front panel.
If the conductivity is lower than the set point, the controller allows the blowdown valve to close.
If the conductivity is higher than the set point, the valve remains open, allowing the contaminated
boiler water to be replaced by clean make-up water.
The valve closes when the conductivity of the boiler water drops below the set point. Accuracy
for blowdown duties is
±
10%.
Factors reducing the accuracy of control include large variations in boiler pressure and wide
pH swings. Whenever the TDS is measured by taking a manual sample of boiler water, the
result should be compared with the controller set point by pressing the purge button, then
turning the set point (SP) potentiometer until the LEDs change from green to amber. The TDS
can then be read off the set point scale.
If the boiler is operating normally yet the readings differ significantly the controller may simply
be recalibrated to the new TDS reading. If it is found that the calibration has drifted to more than
twice its original setting, then the sensor may need cleaning.
If scale is forming on the sensor tip it is a certain warning that scale will also be forming on the
boiler tubes. Boiler water treatment must be investigated.
2.2 Technical data
Maximum ambient temperature 55°C (131°F)
Minimum ambient temperature 0°C (32°F)
Temperature compensation range 100 - 239°C (212 - 462°F)
Pollution degree 2
Overvoltage catagory II
Indoor use only
Altitude up to 2 000 m (6 561.5 ft)
Humidity
Maximum relative humidity 80% for temperatures up to 31°C (87.8°F)
decreasing linearly to 50% relative humidity at 40°C (104°F).
Protection rating IP40
Maximum cable length (controller to probe) See Table 2 in Section 5
Mains supply voltage
230 V setting 198 V - 264 V
115 V setting 99 V - 132 V
Frequency 50 - 60 Hz
Fuse type
20 mm cartridge, 100 mA anti-surge (T). For the UL version, replacement
fuses must be UL recognised to maintain the integrity of the approval.
Maximum power consumption 6 VA
Maximum 0/4 - 20 mA output load 500 W
Minimum conductivity setting 40 µS/cm or 40 ppm
Terminal torque rating 1 N m (9 lbf ft)
To Next Page
Loading...
