17 Fully Metered Combustion Control
Mk8 MM Manual Page | 296
17.2 Fully Metered Control Expansion Options
The table below shows the Expansion Options used for configuring Direct Modbus.
# Default Range Description
FM: Fuel Flow Meter Offset
FM: Air Flow Meter Offset
FM: Fully Metered Function
The fully metered function maintains the commissioned heat input and
fuel-air ratio based on 4-
20mA signals from the fuel and air mass or
volume flow meters. External water level sensor and 4-
20mA fuel flow
feedback must be disabled.
The fuel-air ratio is derived from the mass flow rates of the fuel and air
going into the burner. The fuel flow meter is wired to terminals EX+ and
EX-, and the 4-20mA signal is scaled by setting expansion option 142. For
setting 0, a volume flow meter is used and a displayed mass flow rate is
calculated using either internal constants or via measured
temperature/pressures. For setting 1, a mass flow meter is used to the
display the mass flow rate, when using a fuel mass flow meter, expansion
options 145 and 147 must be set to 0. Setting 2 is the same as setting 0
but for a volume meter with square root extraction included.
Volume flow meter (with square root extraction)
FM: Fuel Flow Meter Scaling
The fuel flow meter is scaled by setting the flow rate at 20mA feedback
from the flow meter.
0 – 65535 m
3
/hr (ft
3
/hr)
The air flow meter is wired to terminals MF and F-, and the 4-20mA signal
is scaled in expansion option 144. For setting 0, a volume flow meter is
used and a displayed mass flow rate is calculated using either internal
constants or via measured temperature/pressures. For setting 1, a mass
flow meter is used to the display the mass flow rate, when using a fuel
mass flow meter, expansion options 146 and 148 must be set to 0. Setting
2 is the same as setting 0 but for a volume meter with square root
extraction included.
Volume flow meter (with square root extraction)
FM: Air Flow Meter Scaling
The air flow meter is scaled by setting the flow rate at 20mA feedback
from the flow meter.
0 – 65535 m
£
/hr (0ft
3
/hr)