Camus Hydronics MFH060 Installation, Operation And Service Manual page 31

Mode 8: External Direct Drive Operation
This mode is designed only for hydronic heating operation. This mode allows for an external control to
operate the boiler through an analog direct drive input signal provided by a boiler sequencing control, such
as, the S12 Sequencer. When operating in this mode the external heat demand and DHW demand are
disabled.
An external boiler sequencer provides a positive 0-10 VDC input signal to the control at +V(in), and the
negative signal is applied to the Com/- input.
The boiler remains off while the direct drive input signal range is between 0 to 0.5VDC. Once the direct
drive input signal reaches 0.5VDC the control turns on the appliance pump and changes the modulating
output to Start Modulation level until the flame is proved and then the modulating output is adjusted to
track the direct drive input signal up to the maximum of 10VDC which is equivalent to maximum input
rate. When the direct drive signal modulates down to 0.5VDC, the boiler operates at minimum fire. When
the signal drops below 0.5VDC the burner is shut off and the pump continues to circulate until the PUMP
DELAY timer expires, whereupon the pump shuts off.
The external boiler sequencer can specify the boiler inlet temperature. However, the BOIL MAX setting
o
limits the highest temperature at the outlet sensor. If the outlet temperature exceeds 210 F, the
modulating output immediately changes to 0% and the burner is shut off. The burner is to remain off until
o o
the minimum off timer is satisfied and the boiler outlet temperature falls by 2 F (1 C) below the BOIL MAX
setting.
Figure 21: Mode 8 Piping & Electrical Layout
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