Application Of A Correcting Variable - Siemens RVW26.000B27 Basic Documentation

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5.8 Application of a correcting variable

Application of a correcting variable represents a possibility to interfere in the operation
of the RVW26..., aimed at optimizing the combustion process.
For instance, using the correcting variable input of the RVW26..., an O
system RPO25... can be employed in conjunction with the air / fuel ratio control sys-
tem.
Using the oxygen value as a reference, practically all disturbance factors that affect the
combustion process will be taken into account.
An analog DC 0...10 V signal can be fed to the correcting variable input «X2».
This correcting variable signal acts either only on the auxiliary actuator (AUX1)
or, optionally, on both auxiliary actuators (AUX1 and AUX2) (refer to «Program-
ming»).
A correcting variable signal reduces the position of the auxiliary actuators that deter-
mine the amount of air, and thus always the amount of excess air for the combustion
process.
When using operation with an impact from both auxiliary actuators, the readjustment of
the O valve is made in parallel.
2
This readjustment of the O
and to the influencing factor «DISTURB»:
Correcting variable X2 (V) x DISTURB (%)
Setload´ (%) = Setload (%) -
Setload Load signal without the correcting variable
Setload´ Load signal with influence of the correcting variable
X2 Correcting variable
DISTURB Programmable influencing factor (maximum correction)
The relative effect on the amount of air ensures that a certain correcting signal has
nearly the same impact on the amount of excess air, irrespective of burner output. This
is true only if the load / position curves are programmed such that the LOAD graduation
is proportional to the actual output of the burner (refer to «Commissioning notes for
burners»).
When used in connection with the RPO25... and RVW25..., the impact of the correcting
variable must be set to the maximum value, since the RPO25... provides O
in this application.
If, for some reason, the impact of the correcting variable must be restricted, the follow-
ing table can be used:
DO
DISTURB
2
» 1 %
5 %
» 2 % 10 %
» 4 %
20 %
» 5 % 30 %
» 8 % 50 %
Electronic Air / Fuel Ratio Control System
5 Description of functions
value is made proportionally to the current burner otuput
2
x Setload (%)
10 (V) x 100 (%)
trim control
2
trim control
2
CC1P7873.1en
15.10.2002