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Option 31.0 - Limit Modulation Range (0 to 1) LV3
By default, the control modulates the burner between the set-points P
3
(low fire) and P
h
(high fire), where
P
h
is the last set-point entered in commission ratio mode. If oxygen trim is fitted, it is not possible for any
drive position to be trimmed lower than point P
3
(low fire) or higher than point P
h
(high fire). Basically, you
can’t take fuel or air off at low fire, and you can’t add fuel or air at high fire.
This option parameter allows the engineer to overcome this limitation in one of two ways. First the
modulation range of the burner can be limited so that the burner may only modulate between points P
4
(one set-point above low fire) and P
h-1
(one set-point below high fire). Since oxygen trim is not affected by
this limitation, each drive may be trimmed between the points P
3
and P
h
. This means that it is not possible
to over-fire or under-fire the burner but a degree of trim may still be achieved at high and low fire. Note
that this option may reduce the turn down of the boiler.
Another option, allows the control to adaptively adjust the modulation rate so that the required amount of
trim can be applied. The turn down of the boiler will not normally be limited because the high and low fire
positions of the trimmed drives will still be attained.
Option parameter
31.0 value
Meaning
0
Modulation not limited. Burner modulates from P
3
to P
h
.
Oxygen trim works over full range from P
3
to P
h
, but may not be able to apply
trim at high fire, or low fire – depending on trim direction.
The burner always modulates to the desired modulation rate, which may limit
the system’s ability to maintain the desired oxygen value.
1
Normal modulation range limited to P
4
to P
h-1
always.
Oxygen trim works over full range from P
3
to P
h
, and can apply extra trim at
low and high fire – limited by P
3
and P
h
.
This setting is useful when there is extra capacity (usually air flow) available
for the burner, but otherwise it will reduce the turn-down ratio of the boiler.
Options 31.1 to 31.4 - Trim Type for profiles 1 to 4 (0 to 2) LV3
These option parameters determine which drive will be trimmed (Air or Fuel) in profiles 1 to 4. These
parameters are used together with the parameters entered in option parameters 2.0 to 2.9 to determine
which drives are trimmed, and in which direction.
Parameter
Meaning
31.1
Trim Type for profile 1
31.2
Trim Type for profile 2
31.3
Trim Type for profile 3
31.4
Trim Type for profile 4
Parameter value in
31.X
Meaning
0
No Trim. Do not apply oxygen trim when running on this profile.
1
Air Trim. Trim ‘Air’ drives when running on this profile (see option parameters
2.0 to 2.9.)
2
Fuel Trim. Trim ‘Fuel’ drives when running on this profile (see option
parameters 2.0 to 2.9.)
O 2
Summary of Contents for NEXUS NX6100 series
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