IM-P403-89
EMM Issue 8
17
Valve
open
Closed
Interval
10s
Purge Blowdown Blowdown Blowdown
Conductivity
drops below set
point
Blowdown cycle
20s
20s
Purge Blowdown
Time
Fig. 8 Pulse output with purge time set (>0s)
Water
conductivity
SP
Hysteresis
3.3.4 4 - 20mA retransmit
An isolated 0 - 20 or 4 - 20 mA output is provided as standard, and may be used for remote
display of the TDS level or as an output to a management system. The menu allows both 0
/ 4 mA and 20 mA to be re-ranged.
3.3.5 Bottom blowdown timer
The timer can be used to control the interval and duration of a bottom blowdown cycle.
If a switch box is fitted to the bottom blowdown valve actuator, an alarm can be configured
to indicate if the valve fails to close or to lift off its seat.
3.4 Other features
A test function provides the operator with a diagnostic facility. Inputs can be measured and
outputs can be set from the front panel. The controller also displays the approximate probe
factor directly.
To prevent unwanted or inadvertent changes being made, all commissioning parameters are
protected with a pass code. This can be changed by the user if required.
The BC3250 can communicate via an infrared link between adjacent boiler house controllers
(Spirax Sarco products only). It is designated as a master or a slave unit as required – see
Section 7 – 'Communications'.
3.3.3 Pulsed output
For smaller boilers where the capacity of the blowdown valve is relatively high compared to
the boiler size, the blowdown may be set to pulsed, rather than continuous output, opening
for 10 seconds, and closing for 20 seconds. This slows the rate at which the boiler water is
removed so that the level is not unduly affected, avoiding the risk of triggering a low water
alarm.
Summary of Contents for BC3250
Page 76: ...IM P403 89 EMM Issue 8 76...
