Preferred FlexFit 110 User Manual

1-8 Description – Burner Management System
FlexFit – Linkageless Control – Revision 1.0
PREFERRED
UTILITIES MFG CORPORATION
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Description of BMS Sates
Boot
When power is initially applied to the FlexFit, it will perform initial self-checks on itself and boot into either the standby state or
the lockout state, depending on its state prior to losing power.
Standby
During the standby state, the BMS will command all fuel/air devices to their standby positions and ensure fuel bus power and
safety relays are deenergized. During the standby state, a technician or engineer can change restricted and non-restricted parameters,
and the current fuel selection may be changed.
Standby is the state from which the BMS starts an operating sequence following a call for heat with the operating limits (L1-13)
input energized
Safe Start Checks
During safe start checks, the fuel/air ratio curve data are veried, parameter values are checked for conicts, and minimum/
maximum limits are checked. If all fans are off, the non-recycling limits (3-P) and high re switch (purge interlock) (L1- 8) switches
are veried to be open.
The BMS initiates a lockout if the fuel valve Proof of Closure Switches (POCS) (if installed) are detected as open or if a false
ame is detected. If no lockout or other error has occurred, the start sequence is continued.
Prestart
During prestart, all combustion servo calibration data, parameters, and feedback potentiometer alignments are checked by
forcing the servos rst to their fully closed and then to their fully open positions. The servo for the unselected fuel is not checked.
When the above items have been proven, the combustion servos are sent to the purge position. The start sequence is now on
hold until non-recycling limits are made. Then, the BMS will test the safety relay by deenergizing the K1 coil and ensuring there is
no power detected on the safety bus.
Purge
Once the purge interlock is satised, the purge timer is started. During the purge cycle, the purge interlock can open intermittently
but for no more than 30 seconds (cumulative). The purge timer stops counting when a purge interlock is open. If the purge interlocks
are open for more than 30 seconds, the FlexFit will lockout. After the purge time is complete, the FlexFit will drive the servos to their
ignition positions.
Pilot Trial for Ignition (PTFI)
After the servos are proven in their ignition positions, the ignition transformer and pilot valve outputs are energized. A pilot ame
must be proven present before the PTFI times out (10 seconds), or a lockout will result (does not apply to direct spark ignition mode).
The pilot test hold function (see "Pilot Test Hold" on page 3-51) can be turned on before the ame has been proven so a pilot
turndown test can be performed, and the servos can be positioned to allow air or fuel adjustments for proper light-off.
Main Trial for Ignition (MTFI)
When the pilot ame is proven, the FlexFit energizes the main fuel valve. The pilot valve and ignition transformer deenergize
10 seconds after the main fuel valve is energized. From this point forward, the main ame must be proven continuously, or a lockout
will occur.
Release to Modulate
The FlexFit releases control of the combustion servos (fuel/air ratio control) to the FlexFit-CC. The fuel remains at the ignition
position while all other air and FGR devices must move to their corresponding curve positions within 20 seconds, or a lockout will
occur. Servo pacing is now enabled. Any servos that are not being used are commanded to the standby position. Based on the
process variable (steam PSI or water temperature) to setpoint comparison, a ring rate demand signal is generated that positions
the appropriate servos to their proper positions.
Assured Low Fire Cutout (ALFCO) Option
When the FlexFit detects that there is no longer a call for heat and parameter "P1.2.6 Assured Low Fire Cutoff" on page 4-62 is
enabled, all combustion servos are commanded to the low re position before the SSOVs are deenergized. If the ALFCO is disabled,
the SSOVs close immediately when there is no longer a call for heat.
Post Purge
After the fuel valves have deenergized, the fans continue to operate until the post purge time has elapsed. All combustion
devices remain in their last position. All fans and auxiliary outputs are deenergized.
Note
The descriptions of each
state to follow assumes
default parameter values
are set; the descrip-
tions can change
depending on how the
FlexFit is congured.
Note
From this point, restricted
parameters may not be
changed until the BMS has
returned to the standby
or lockout state. The
programming of non-re-
stricted parameters is
not allowed during safe
start check and prestart.
Note
In the commission mode,
the FlexFit holds at the
light-off position so the
technician can adjust
the fuel and air servos.
Note
A lockout closes
the SSOVs immedi-
ately, regardless of
ALFCO setting.

Preferred FlexFit 110 Specifications

General

Brand	Preferred
Model	FlexFit 110
Category	Controller
Language	English