13 Draught Control
Mk8 MM Manual Page | 245
13.3.2 Deactivation Window
There is a deactivation window, outside of which no trim occurs, and the air damper remains at the
previously trimmed position until back within the window and trim is required. This deactivation window is
defined by expansion options 85 - delay before compensation and 86 – commissioned angle variation
tolerance. If the draught servomotor has moved more than the set angular degrees “x”, within the time period
set “y”, than no trim functionality will operate, if trim has been performed prior to this deactivation then the
trim is carried forward.
For example, when the burner is first switched on, if the burner comes out of warming in lead-lag control or is
switched from low flame hold to auto mode, there is a high load demand. In these situations the firing rate
may ramp up quickly to meet load demand, at this point if the draught servomotor is required to move greater
than the commissioned angle variation tolerance and quicker than the delay before compensation then no
trim functionality will occur and any trim % will be carried forward.
Figure 13.3.2.i Deactivation Window
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