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Page 112
10.C Shutting Down the Unit
This step must be performed by a qualified service
person.
1.
Turn off the main electrical disconnect switch.
2.
Close all manual gas valves.
3.
If freezing is anticipated, drain the unit and be sure
to also protect the building piping from freezing. All
water must be removed from the heat exchanger or
damage from freezing may occur.
10.D Restarting the Unit
If the system has been drained, see 10.A for instructions
on proper filling and purging.
1.
Turn off the main electrical disconnect switch.
2.
Close all manual gas valves.
3.
Wait five minutes.
4.
Set the aquastat or thermostat to its lowest setting.
5.
Open all manual gas valves.
6.
Reset all safety switches (pressure switch, manual
reset high limit, etc.).
7.
Set the temperature controller to the desired
temperature setting and switch on the electrical
power.
8.
The unit will go through a prepurge period and
ignitor warm-up period, followed by ignition.
BIC Status
Phase
Phase
Standy
Call For Heat
LMV Enable
Pressure Xmitter
Verification
Read (via Modbus) at
ACC State and Display
Touchscreen
Fan Speed Governed by
SIT Demand Signal
End Call for Heat
LMV Disable
Standby
Table 24. BIC Status and LMV Status
LMV States
12
Standby
22
Blower On
24
Component Calibration
30
Prepurge
36
Move to Ignition Position
38
Igniter On
40
Main Fuel On
42
Ignitor Off/Verify Main Burn
60
Run
70
Post Purge
74
Shutdown
Standby
LAARS Heating Systems
10.E Controllers
This unit utilizes three (3) separate controllers to
manage system functions, burner management and air/
fuel ratio control:
- Burner Integrated Control (BIC)
- Linkageless Modulating Valve (LMV)
- Oxygen Controller (O2C)
These controllers communicate with each other
via voltage and current signals, and serial digital
communication using Modbus protocol. The BIC also
communicates with the touch screen display and all
user inputs.
When there is a call for heat the BIC will provide an
enable signal to the LMV which tells the LMV to initiate
burner operation. For this signal to be sent and acted
upon, the safety circuit must be satisfied and both
controllers must be in standby mode.
The system pressure sensors, which measure the
overall system pressure drop must also read zero in
order for the Safety Status to be verified.
The Safety Circuit status can be verified on the
Services/Digital I/O screen. Once the LMV is enabled it
will proceed through the startup states listed in Table 24
until it gets to Run. Once in Run, the LMV will receive
a firing rate demand from the BIC and position the fuel
and air dampers and blower speed accordingly.
After the burner has been on for two (2) minutes
the oxygen trim loop will be enabled and the blower
speed will be adjusted to maintain the preset oxygen
concentration in the boiler exhaust.
The MagnaTherm FT is a direct ignition system and
does not use a separate pilot. A spark ignition is used
to light the main burner at ta pre-set reduced firing rate.
If the main flame is not detected during the "verify main
burner" stage, the LMV will enter a 'Lock-out' mode and
a 'Flame Out' error will appear on the display screen.
If the maximum attempts for ignition has not been
reached, the system will perform an automatic reset and
the ignition sequence will be repeated.
NOTE: Three attempts for ignition is standard before
a 'Hard' lock-out occurs. If a hard lock-out occurs, the
system must be manually reset using the reset button
on the display unit. CSD-1 units have a single attempt
for ignition prior to a hard lock-out.
If the call for heat is satisfied normally, the BIC will
remove the enable signal and the LMV will de-energize
the fuel valves and enter postpurge. Any time there
is an interruption of the BIC safety circuit, both the
LMV enable signal and LMV safety loop signal will be
removed, triggering a burner shutdown. Along with
the circuit components identified in the System Ladder
Logic, the system differential pressure is continuously
monitored while the burner is in operation.
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