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Siemens Building Technologies
Electronic Air / Fuel Ratio Control System
CC1P7873.1en
HVAC Products
5 Description of functions
15.10.2002
Fig. 14 shows how a correcting variable signal at «X2» produces a change in fan speed
via the «AUX1» curve.
Load
Load signal without the correcting variable
Load´
Load signal for the fan speed
Position
Position of auxiliary actuator with correcting variable «X2 = 0»
D
Pos
Change of actuator position due to correcting variable «X2 > 0»
X2
Correcting variable
DISTURB
Programmable influencing factor (maximum correction)
Setload
Load signal without the correcting variable
Setload´
Load signal for the actuator position
X2
Setload
X2'
Load [%]
Load
Position
AUX1
Set
posit.
78731a02e/1001
Actual
posit.
Position [V]
Load'
Pos
Setload'
DISTURB
D
Fig. 14
Impact of the correcting variable signal on the actuator position
Note:
To ensure the impact of the correcting variable on the volumetric airflow is large
enough, the load displayed by the RVW25...
must
correspond to the real burner output.
Correcting variable signal at
«X2»
Impact on excess air
«X2» not connected
No impact = maximum amount of excess air
«X2» = 0 V
No impact = maximum amount of excess air
«X2» rises
Impact increases, amount of excess air diminishes
«X2» = 9.8 V
Maximum impact = minimum amount of excess air
«X2» = 10 V
Maximum impact, but will be interpreted as a fault after 30
seconds, which automatically sets the impact to 0 (= maxi-
mum amount of excess air)
Note:
If the value of the correcting variable signal «X2»
constantly
exceeds 9.8 V for more
than 30 seconds, the RVW25… and RVW26… interprete this as a fault (e.g. short-
circuit). In that case, the correcting variable is not taken into consideration, which
means that a maximum amount of excess air will be delivered. However, readiness
contact «Q4 - Q5»
does not
open, so that
no
lockout will be initiated. As a warning, the
display of the unit will flash. If steep slopes and / or a large correcting effect is pro-
grammed on the RVW26…, lockout with code «-56» can occur. The correcting variable
becomes active again when the voltage «X2» drops
below 8 V.
When feeding a correcting variable signal to «X2», screened cable should be
used, whereby
one
end of the screen must be connected to terminal «M» of the RVW25...
Legend
Impact of the cor-
recting variable on the
amount of excess air
