AERCO BMS 168 - Manual (Page 37)

If SWITCH IN PUTS is selected, the BMS will
automatically switch to Constant Setpoint
mode if a sensor or remote input error
occurs. Once the sensor or remote input
error has been cleared, the BMS will
automatically switch to the previous mode.
When selecting SWITCH INPUTS, the
reference temperature for the Constant
Setpoint mode must be preset. See Section
5 for programming steps.
Regardless of whether SHUTDOWN or
SWITCH INPUTS is selected, the BMS will
shut down and close the fault relay contacts
if the header sensor circuit fails.
4.4.2 SYS ENABLE
Pressing and releasing this key allows you
to select the INTERLOCK 1 enable setting
of
START ENABLED or ALWAYS
ENABLED.
The START ENABLED feature will not
enable the boiler plant until the outside air
temperature falls below the system start
temperature. If the boiler plant begins to
operate and Interlock 1 is open, the BMS
will wait 30 seconds before stopping the
boilers and displaying a fault message.
This feature is intended for use with
auxiliary equipment having limit switches.
For instance, dampers with proving end
switches, can be triggered by the BMS
system start relay as the boilers start. If the
dampers do not open, the end switch wired
to Interlock 1 will not make (close) and the
BMS will shut down the boilers.
The ALWAYS ENABLED feature allows the
boilers to run, regardless of the system start
and outside air temperature settings. This
feature is used when there is a loss of an
outside air sensor or one is not installed. It
will also function if an outside air
temperature sensor is present. It should be
noted that if either Interlock 1 or 2 opens,
the BMS will shut down the boilers.
The system start relay will close only after
the outside air temperature falls below the
system start temperature, whether START
ENABLED or ALWAYS ENABLED is
selected. AERCO recommends that the
system be equipped with a flow switch that
is interlocked to the BMS. This is especially
important if ALWAYS ENABLED is selected
and the BMS is controlling the pumps based
on outside air temperature, or the BMS is
interfaced with an energy management
system that is controlling the pumps.
4.4.3 MAX PWR INPUT
This key provides two distinct functions.
First, it is used to establish the maximum
firing rate percentage for the boilers being
controlled by the BMS. Second, it permits
adjustment of the pulse width modulation
(PWM) signal supplied to the boilers.
• Pressing and releasing the MAX PWR
INPUT key once displays the maximum
allowable firing rate percentage for the
boilers (MAX POWER INPUT 100%). If
desired, the maximum firing rate of the
boilers can be limited to values below
100%. This is useful if there is a problem
with gas supply pressure.
For example, if gas pressure is too low,
the boilers can be run at a lower firing
rate temporarily until proper gas pressure
can be restored. If necessary, adjust the
firing rate using the ▲ or ▼ arrow key.
• Pressing and releasing the MAX PWR
INPUT key a second time displays a
PWM TIMEBASE CAL message. If
necessary, the PWM pulse width ON
time can be adjusted using the ▲ and ▼
arrow keys. Pressing the ▲ arrow key
increases the pulse width ON time and
pressing the ▼ key reduces the ON time.
The PWM TIMEBASE CAL is adjustable
from -30 to 30 (Default = 0).
The PWM TIMEBASE CAL should only
be adjusted when all boilers are
indicating a firing rate above or below the
firing rate being supplied by the BMS
PWM signal. If necessary, individual
boilers can be adjusted via their
respective C-More Control Systems.
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