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Siemens Building Technologies
Electronic Air / Fuel Ratio Control System
CC1P7873.1en
HVAC Products
17 Engineering notes
15.10.2002
17.3 Requirements placed on the actuators and
potentiometers
The electronic control unit RVW26... is designed to provide air / fuel ratio control, or in
other words, to ensures precise positioning of the correcting members for air and fuel.
To accomplish this, the actuating devices and feedback potentiometers, which are used
for signaling the actual position, must satisfy stringent requirements.
For this reason, we have developed suitable actuators and potentiometers for use with
the RVW26...
To ensure reliable operation over long periods of time, we recommend to make use of
this range of products.
Inspections and approvals of RVW2... air / fuel ratio control systems are
only
valid in
connection with our actuators and potentiometers.
If other brands of actuators are used, they must meet the same stringent requirements.
In that case, a separate approval procedure is required.
·
The mechanical link between actuator spindle and feedback potentiometer must be
rigid, with no mechanical play
·
The reproducibility of the end switch position must be better than < ±2 % of the po-
sitioning range
·
The backlash of the actuator’s geartrain must be less than 2 % of the positioning
range (< ±2 % of the positioning range correspond to ±1.8° in the case of a 90°
actuator)
·
The tolerance of the feedback potentiometer’s voltage value in the end switch posi-
tions due to backlash and end switch reproducibility
must be less than 0.2 V
If should be noted that a geartrain’s backlash increases with the number of operating
hours. Also, higher ambient temperatures and vibrations generally have an adverse
effect on the backlash. This should be taken into consideration when doing planning
work.
·
The total resistance must be in the range of 800
W
< R < 1500
W
(nominal value
1000
W
)
·
The characteristic’s tolerance must be no more than ±1 %
0 %
50 %
100 %
0 V
5 V
10 V
U [V]
+
0,1
V
-0
,1
V
78721d05/0501
[%]
)
Fig. 37 Required linearity of the feedback potentiometer
Requirements placed
on the actuators
Requirements placed
on the feedback po-
tentiometers
