Cleaver-Brooks ClearFire CFLC Series, Operation And Maintenance Manual, Page: 255 / 290

Appendix E Falcon Lead Lag
E-47
• Sequencer - the sequencer determines which unit will be the next one to turn on or turn off.
Overall Control
LL MASTER ENABLE: DISABLE, ENABLE,
LL MASTER MODBUS PORT: MB1, MB2
If Disable is selected then all LL master functions are inactive. If Enable is selected then it acts as the active bus
master on the ModBus port it is assigned.
LL OPERATION SWITCH: OFF, ON
This controls the LL master in the same way that the Burner switch controls a stand-alone unit. If "On" then the LL
master is enabled to operate. If this parameter is "Off" then the LL master turns off all slaves and enters an idle or
standby condition.
Periodic Data Polling messages
The LL master uses polling to discover new slave devices and to periodically refresh the information it has about
known slave Falcon devices.
Thereafter it polls the known devices to make sure they are still present and to obtain updated status information. It
also periodically polls the entire slave address range to discover any new slave devices.
A polled device is read to determine the values of the following data items:
a. The slave's type (compatibility) as indicated by the Slave type
b. The slave enable status Slave enable
c. The slave mode as set in Slave mode
d. The slave sequence order as set in Slave sequence order
e. Demand-to-firing delay: mm:ss or None
This delay time is needed by the LL master to determine the length of time to wait between requesting a
slave to fire and detecting that it has failed to start. It should be set to the total time normally needed for the
burner to transition from Standby to Run, including such things as transition to purge rate, prepurge time,
transition to lightoff rate, all ignition timings, and some extra margin.
f. CT - Burner run time
This parameter will be needed if measured run-time equalization is being used.
Slave Control
The LL master sends each active slave a command and also performs a slave status read for each known slave
device. It also sends a Master status broadcast that is heard by all slaves.
There are 5 commands that might be sent:
•
All slaves are commanded to turn off and remain off.
• The LL master sends message to slaves that are off, to turn their fans on.
• The LL master suspends operation which request a burner to recycle and remain in Standby if it has not yet opened
its main valve (e.g. it is in Prepurge or PFEP) but to keep firing if it has reached MFEP or Run. This suspend may be
for the fan to be on or off in standby.
This message is used to abort the startup of a slave that is not yet firing (because demand went away just before it
was firing), but to keep it on if it actually is firing (the LL master will discover what happened in a subsequent status
response).
The LL master also sends this message to a slave that is OnLeave. (This ensures that if the slave is firing when it
returns to LL master control, it will stay that way until the master has decided whether to use it; or conversely, if the
slave stops firing for some reason that it will not start up again until the LL master has requested this.
In either case, the command will be to turn on the off cycle fan if any other slave burners are firing, or to turn the fan
off if the slave is the only slave that might (or might not) be firing.
• The LL master sends message to turn the burner on and to assign the burner’s firing rate.
If the commanded modulation rate is less than the burner’s minimum modulation rate, then the burner should
always operate at its minimum rate.