Compensation Of Hysteresis - Siemens RVW26.000B27 Basic Documentation

Reasons for hysteresis
Effect of hysteresis
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HVAC Products

5.7 Compensation of hysteresis

Mechanical play occurs in the actuator, in the mechanical link to the actuating device
and in the actuating device itself.
After a certain period of time, this mechanical play or hysteresis will increase due to
mechanical wear.
Function «Compensation of hysteresis» provided by the RVW26... is used to offset the
mechanical play within certain limits.
As a result of the hysteresis, one and the same desired position of an actuator has 2
different actual positions:
One actual position when approaching the desired position from below (output ad-
-
justment toward «OPEN»)
One actual position when approaching the desired position from above (output ad-
-
justment toward «CLOSED»)
Fig. 31 illustrates this:
1) The burner's output shall be increased from
will have to travel along the curve from «a» to «b».
2) Then, the burner's output shall be reduced again to
tuator will have to travel from «b» to «a'». For the same output 0, there is thus a
difference «H» in the actuator's position.
Position of actuator
b
a'
H
a
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Fig. 31 Effect of hysteresis
Due to the mechanical play, there is thus a difference between the actuators' real posi-
tion and the position ascertained by potentiometer «P».
M
P
Actuator
Fig. 32 Basic diagram of hysteresis
The hysteresis can have a significant adverse effect on the combustion process.
It can lead to lack of air (formation of CO and soot) or to extreme amounts of excess air
(waste of energy).
Electronic Air / Fuel Ratio Control System
5 Description of functions
 to ‚ , which means that the actuator
 , which means that the ac-
2)
1)
1 2
Transmission of force,
linearization, etc.
Mechanical play
Burner output
(load)
Regulating unit
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CC1P7873.1en
15.10.2002