Spirax Sarco BC3250 - 3.3 Outputs

IM-P403-89 EMM Issue 8
16
3.3.2 Purge output
Used only when the probe is mounted in the blowdown line, Purge ensures the sensor
measures the conductivity at boiler temperature. The purge duration time is the time the valve
is open to enable a representative boiler sample to reach the probe. A purge occurs every
PURGE - INTERVAL time either independent of burner firing, or dependent on cumulative
boiler firing time.
Fig. 7 Output with purge time set (>0s)
3.3 Outputs
3.3.1 Continuous output
Used when the probe is mounted in the boiler. The probe is able to constantly monitor the
conductivity from the probe tip to the boiler shell.
Fig. 6 Continuous output (purge time = 0s)
Water
conductivity
SP
Hysteresis
Valve
open
Closed
High conductivity
Time
Blowdown
Keeps valve open until
conductivity drops below
hysteresis
Water
conductivity
SP
Hysteresis
Closed
High conductivity
Time
Purge Purge
Interval
Blowdown
Keeps valve open until
conductivity drops below
hysteresis
Valve
open