CleaverBrooks CB120Z, Operation

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SEQUENCE OF OPERATION - OPERATING CONTROL
Note: Refer to Figure 9.
The CB120Z performs the operating control function to cycle the boiler on and off to maintain the
programmed pressure or temperature setpoint. The CB120Z will command the burner on and off
according to the following setpoints located in the CONTROL VAR CONFIG sub-menu:
STM STPT
1
(Steam Pressure Setpoint) - This determines the steam pressure the CB120Z will main-
tain the boiler.
or
WTR STPT
1
(Water Temperature Setpoint) - This determines the water temperature the CB120Z
will maintain the boiler.
CUT IN (Cut In Value) - Determines the point in which the steam pressure (or water temperature)
must reach to start a burner cycle. This is a differential value that is subtracted from the steam pres-
sure setpoint
(STM STPT) or water temperature setpoint (WTR STPT) .
CUT OUT (Cut Out Value) - Determines the point in which the steam pressure (or water tempera-
ture) must reach to end a burner cycle and initiate a normal shutdown. This is a differential value that
is added to the steam pressure setpoint
(STM STPT) or water temperature setpoint (WTR STPT) .
Refer to Figure 8. When the steam pressure (or water temperature) is above the cut out point (Point
“E”), system demand is satisfied and the CB120Z will be in Standby mode. As system demand
increases and the steam pressure (or water temperature) falls below the cut in point (Point “D” - see
note below), the CB120Z will initiate a burner cycle.
Note: The cut in setpoint (CUT IN) is a differential value. Point “D” (steam pressure or water tem-
perature in which the operating control closes) is determined by subtracting the cut in setpoint
(CUT IN) from the steam pressure setpoint (STM STPT) or water temperature setpoint (WTR
STPT).
In Figure 8, the Cut In setpoint ( CUT IN ) is programmed to zero, so the cut in point for the operat-
ing control (Point “D”) is the same as the Steam Pressure Setpoint ( STM STPT ).Burner cut in, cut
out and setpoint are matter of preference and expected boiler performance.
When all other circuits within the Operating Control circuit, L1-3, of the CB120Z are closed, a
burner start-up sequence will be initiated. See Figure 18 for suggested wiring diagram. A burner set-
up sequence consists of Pre-Purge, Pilot Trial For Ignition, and Main Trial For Ignition (MTFI).
Upon completion of the MTFI, the CB120Z moves to AUTO and the firing rate motor is controlled
according to the user programmed setpoint parameters. (see SEQUENCE OF OPERATION - MOD-
ULATING CONTROL section).
Whenever the steam pressure (or water temperature) rises above the cut out point (Point “E” – see
note below), the CB120Z will initiate a normal shutdown sequence (e.g.: de-energize main fuel
valve, drive the firing rate motor to low fire) and proceed through post purge and back to Standby.
Note: The cut out setpoint (CUT OUT) is a differential value. Point “E” (steam pressure or water
temperature in which the operating control opens) is determined by adding the cut out setpoint
(CUT OUT) to the steam pressure setpoint (STM STPT) or water temperature setpoint (WTR
STPT).