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Siemens Building Technologies
Electronic Air / Fuel Ratio Control System
CC1P7873.1en
HVAC Products
17 Engineering notes
15.10.2002
Example of a linear gas damper:
40 mV at 20 % output = 2 % accuracy in terms of gas throughput, with appropriate im-
pact on the combustion process and the O
2
value.
78731e03e/1001
D
V
D
[m / h]
3
Throughput V
Fig. 36 Gas damper characteristic
Usually, when close to low-fire operation, the regulating units‘ slope is overproportional.
Also, when the burner’s output is small, a certain change in air volume (
D
V) leads to a
large percentage change in air volume.
This may lead to problems in connection with O
2
trim control.
When installing the actuators according to the wiring diagrams released by this prod-
ucts, the actuators are in their «Fully closed» position when the burner is shut down.
If an actuator shall be in its
«Fully open»
position when the burner is shut down:
·
The control outputs (on / off) must be interchanged
·
The potentiometer connections (U10 / M) must be interchanged
Note:
This changes the assignment of the potentiometer voltage to the damper position.
Position
Feedback voltage from potentiometer
Fully closed
High voltage
Fully open
Low voltage
In this case, the end switch measurement «Fully open» measures the «Fully closed»
position, and vice versa.
