Description Of Oper Controls - Siemens LFL Series Technical Instructions

Description of operating controls and their functions
Power
Reset and Alarm
Operating limit
OLS
Limit switches
LGP
HGP
LWS
High Limit
Fuel proof of closure
POC
Combustion air blower
CAB
Combustion air switch
CAS
Ignition
High fire purge inter-
lock
OPEN
Low fire start interlock
MINIMUM
Fully closed
ECONOMY
Release to modulate
Flame sensor input
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Siemens Building Technologies
LFL input (1) HOT and LFL input (2) NEUTRAL are used for control power,
LFL output (3) ALARM, for alarm indication
LFL input (21) RESET, as show for reset and/or remote shutdown
Pressure or temperature activated, the operating limit switch (OLS),
Closes, for burner start-up sequence to begin, and Opens, for a burner controlled shutdown
Pressure, temperature, or level activated, limit switches examples include:
Low gas pressure (LGP) opens on low gas pressure
High gas pressure (HGP) opens on high gas pressure
Low water switch (LWS) opens on low water
These limit and are considered either to be recycle or non-recycle, (manual reset),
and are connected between; LFL output (5) RECYCLE and LFL input (4) RECYCLE
Recycle limit switches are used when it is desireable to stop the burner when the switch opens,
and restart it again, automatically, when the switch closes again.
Non-recycle limit switches are used when it is desireable to lockout the burner when the switch
opens and prevent if from automatically restarting again. These switches must be manually reset,
on the switch itself, as well as require you to push the reset button on the LFL to allow a new start-
up sequence.
The High Limit switch is almost always a non-recycle limit switch, and is usually connected to;
LFL input (1) HOT
NFPA 85, CSD-1 and UL795 require the HGP, LGP to cause a shutdown and be manually reset.
Most burner / boiler insurance codes also require a LWS.
The fuel proof of closure (POC) switch is integral to the fuel valve and activated by the valve
mechanics. The POC prevents a burner start-up if the fuel valve is not in the proved close posi-
tion.
LFL input (12) POC, is provided for this purpose. Note -This is a 'Precondition for Startup' and
must be powered to start a sequence.
The combustion air blower (CAB) provides combustion air to the burner. Not all installations re-
quire the LFL to control the CAB. The LFL provides terminals for two options:
LFL output (7) M2, powered after a 2 sec delay, and continues through postpurge.
LFL output (6) M1, powered immediately, and stops prior to postpurge.
The combustion air switch (CAS) is used to prove that combustion air is being provided. Most
burner / boiler insurance codes require a CAS.
LFL input (14) COMBUSTION AIR PROVE, is connected to the normally open (NO) terminal
of the CAS, and closes when air pressure is present.
LFL input (13) COMBUSTION AIR TEST SW, is connected to the normally closed (NC) termi-
nal of the CAS, to make sure the contacts have not welded.
The LFL provides options for; interrupted pilot, intermittent pilot, and direct ignition as follows;
LFL output (16) IGNITION, for the ignition transformer
LFL output (17) PILOT, for interrupted (pilot on only during ignition), or
LFL output (18) MAIN DIR IGN, for the main fuel valve on direct ignition
LFL output (19) MAIN PILOT, for the main fuel valve on piloted ignition
Generally, an actuator position switch, or a differential pressure switch, that is used to prove the
actuator is at the high fire position. Some codes require the high fire position (open) be proved
during prepurge.
LFL output (9) OPEN, is provided to drive the actuator to this position. *See Note below
This switch is also, generally, an actuator position switch, that is used to prove the actuator is at
the low position. Some codes require the low fire (minimum) position be proved during ignition.
LFL output (10) MINIMUM, is provided to drive the actuator to this position. *See Note below
This switch is as well, generally another actuator position switch that proves it is at the fully
closed (economy) position. This position is desired following post purge to minimize heat losses.
LFL output (11) ECONOMY, is provided to drive the actuator to this position. *See Note below
*Note LFL input (8) FEEDBACK, is provided to confirm each of these positions.
LFL output (20) RELEASE, enables an external load controlled and/or to indicate "Burner On"
LFL inputs (22) (23) (24) FLAME can be used for a UV sensor or flame rod
for intermittent (pilot on when burner is on)
HVAC Products
11.15.2004