15
3
Operation
3.13
Pre-purge Limit
Normally during pre-purge each control element runs as far as it’s uppermost stop. Now, by
parameters, a limit can be set for each channel that is not exceeded during pre-purge.
3.14
Energy-saving Mode for Scrolling Text Display
The brightness of the display can be adjusted to the ambient light conditions by parameters.
In addition the display can be set to automatically revert to the lowest brightness level if not
operated within a given period of time.
3.15
Separate Ignition Point
In the standard version the ignition point is situated outside the accessible range in order to
set a separate fuel/air ratio. By using parameters, however, the ignition point can be adjusted
so that it lies on the fuel/air ratio control curve.
3.16
Integrated O
2
Trim
–
optimises combustion system
–
saves fuel
–
minimises pollutants
The main purpose of O
2
trim is to compensate for combustion variables that affect combus-
tion. In addition, the O
2
trim system monitors the combustion's fuel/air ratio. A message is out-
put at once if it strays outside the permitted limits.The following are the main perturbing factors
that affect combustion:
The O
2
trim unit is implemented as a free-standing software module. The unit compares the
residual oxygen content in the exhaust gas of a combustion system measured by the LT1/LT2
Lambda transmitter (actual value) with the optimum residual oxygen content (target value).
The target values are stored in the instrument in the form of an
installation-specific curve. The control unit applies a correction until the actual value corre-
sponds to the target.
The calculated output value of the O
2
trim module is transmitted to the fuel/air ratio control
module as a correction input signal.
Air:
Fuel:
System:
Mechanical systems:
Temperature
Calorific value
Burner
Mechanical hysteresis
Pressure
Temperature
Boiler
(free play)
Humidity
Viscosity
Calorific value
Density
Gas pressure fluctu-
ations
Summary of Contents for VMS Series
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Page 129: ...128 10 Appendix Fig 10 9 Ger t 4 Ger t 5 with output regulator...
Page 141: ...140 10 Appendix 10 14 Declaration of Conformity...
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Page 143: ...142 10 Appendix 10 15 Protocol Example...
Page 144: ...143 10 Appendix 10 16 O2 Setpoint Curves...
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