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Definitions:
LIMIT TYPE
DEV -
Values that deviated from setpoint. The advantage is these values will float with the
setpoint.
SETPOINT -
The target pressure or target temperature the control will maintain.
CUT IN
(Cut In Value) - Determines the point in which the steam pressure (or water temperature)
must reach to start a burner cycle. In DEV option, this a differential value that is subtracted from the
steam pressure or water temperature setpoint.
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. In DEV option, this is a differ-
ential value that is added to the steam pressure or water temperature setpoint.
P-BAND
(Modulating Range) - This determines the proportional band and is the range of steam
pressure (or water temperature) in which the firing rate motor is commanded from its low fire (0%)
to its high fire position (100%). In DEV option, this is a differential value that is
subtracted
from the
steam pressure setpoint or water temperature setpoint.
Whenever the steam pressure (or water temperature) is within the P-BAND, an increase in pressure
(or temperature) value will reduce the control signal to the AIR/FUEL servos, causing the servos to
drive towards its low fire position. Similarly, a decrease in the steam pressure (or water temperature)
will increase the control output signal, causing the valves and dampers to move toward their respec-
tive high fire positions.
The value of the
P-BAND
determines how the PPC4000 responds to changes in the measured vari-
able (steam pressure or water temperature). A small modulating range will cause the control to
respond quickly to small changes in steam pressure or water temperature. A small value of
P-BAND
might result in the SERVOS to move excessively and possibly cause the burner to actually exhibit
short cycle. A large value would reduce the movement of the SERVOS, but may cause the system to
be somewhat sluggish in response to a change in steam pressure or water temperature. Matching the
capacity of the boiler to load system demand are important considerations in setting the
P-BAND
setpoint. Care should be taken when selecting this variable.
HIGH MARGINAL - Provides an indication that the sensor value is approaching the high alarm
limit before the alarm limit is actually reached. For example, a Marginal Stack Alarm may be an
indication of the burner overfiring, fouled heat exchanger, tube leak in heat exchanger, etc. If the
HIGH MARGINAL is exceeded for 4 seconds, the alarm relay will be activated but the system will
not go to lockout.
LOW
FIRE
D
E
STEAM PRESSURE (PSIG)
6
7
8
9
10
11
12
MOD
MAX
C
HIGH
FIRE
100%
20mA
MOD
MAX
(e.g.: 80%)
0%
4mA
P-BAND = 3 PSIG
STM SP = 10
CUT OUT = 2
CUT IN = 0
BOILER
FIRING
RATE MOTOR
OPERATING CONTROL
OPENS AT 12 PSIG AND
CLOSES AT 10 PSIG
FIRING RATE
POSITION
