53
Safety functions on the Slave boards
When the Outlet Temperature > 90°C for 5s, the Slave board shuts down (no. 46).
When the Return Temperature > 80°C for 5s, the Slave board shuts down (no. 47).
When the Flue Gas Temperature > 80°C for 5s, the Slave board shuts down (no. 48) and the fan operates for 10 minutes
at maximum speed.
The Slave board can protect the primary heat exchanger against insufficient water circulation by means of a flow switch
and by monitoring the difference between the flow and return temperatures.
The control on the ΔT uses a parameter, ΔT_max (pre-set to 35°C) and limits the output of the burner as follows:
seguente:
if ΔT_max -5°C > ΔT > ΔT max – 10°C burner modulation
if ΔT_max > ΔT > ΔT_max –5°C burner at minimum
if Δ_T > Δ_T_max burner off.
A sensor is also provided to shut down the heat exchanger if pressure in the combustion unit drops below 0.5 bar.
MANAGEMENT OF THE MIXING VALVE
The mixing valve is controlled by the following parameters:
Mix_valve_step_open_time: Par.28 pre-set to 5s
Mix_valve_step_close_time: Par.29 pre-set to 7s
Mix_valve_interval_time: Par.30 pre-set to 5s
Mix_valve_p_hyst: Par.31 pre-set to 2°C
Mix_valve_still_hyst: Par.32 pre-set to 2°C
Before opening or closing, the valve waits the time set
for Par.30.
It opens if:
T_low inlet temperature < Setpoint_low – Par32
It closes if:
T_ low inlet temperature > Setpoint_low + Par32
Within the interval, the valve remains in the current posi-
tion.
If:
T_ low inlet temperature < Setpoint_low – Par31 it opens
for a time equal to half of the value set for Par. 28
If:
T_ low inlet temperature > Setpoint_low + Par31 it closes
for a time equal to half of the value set for Par. 29.
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