Siemens LMV 5 Series, Technical Instructions, Page: 195 / 374

LMV Series Technical Instructions
Document No. LV5 ‐ 1000
SCC Inc. Page 23 Section 6
NumberTauSuspend ‐ The length of time after main flame light ‐ off that is required until an accurate,
representative O
2
value is read by the O
2
sensor. Basically, the time it takes to replace all of the air in
the boiler with products of combustion. This parameter is a multiplier that is taken times the delay time
at low fire ( Tau Low ‐ Fire ) to determine the length of waiting time before a representative O
2
value is
measured and the O
2
trim can engage.
If Tau Low ‐ Fire was read to be 5 seconds during O
2
Control Curve commissioning, and
NumberTauSuspend is set to 10, then the O
2
trim would engage 50 seconds after main flame light ‐ off.
A setting of 10 will work for almost all applications, and will be conservative for most. Higher numbers
(more waiting time) are more conservative and lower numbers are less conservative.
Menu path: Params & Display > O2Contr/Alarm > Gas Settings > Startmode
Startmode ‐ This determines how the burner transitions from light ‐ off to engaging the O
2
trim. Two of
the modes, “Ign Load TC” and “IgnPtWithTC”, require a combustion air temperature sensor.
Immediately after main flame light ‐ off, the O
2
sensor does not have a valid reading since the gas path of
the boiler is full of air. Some burner designs, most notably ultra ‐ low NOx mesh burners, require some
type of compensation at light ‐ off to ensure flame stability before the O
2
sensor has a valid reading. Four
options are available:
1. Standard ‐ Burner will modulate right after light ‐ off, not waiting for the O
2
trim to engage. O
2
trim
will engage after the time defined by NumberTauSuspend expires at the burner’s current load.
2. Ign Load TC ‐ This will vary the ignition positions (special positions) of the actuators based on the
combustion air temperature and also based on a defined load number (parameter Load of Ignition ).
This also will drive the "temperature compensated" actuators to Point 2 (or whichever point is
defined by parameter StartPointOp ). The burner will be held in Phase 60 at Point 2 (or whichever
point is defined by parameter StartPointOp ) until the time defined by NumberTauSuspend expires.
The burner will then be released to modulate with the O
2
trim active.
3. IgnPtWithTC ‐ This will not vary the ignition positions (special positions) of the actuators based on
the combustion air temperature. It will drive the actuators from the temperature ‐ compensated set
ignition positions to Point 2 (or whichever point is defined by parameter StartPointOp ). The burner
will be held in Phase 60 at Point 2 (or whichever point is defined by parameter StartPointOp ) until
the time defined by NumberTauSuspend expires. The burner will then be released to modulate with
the O
2
trim active.
4. IgnPtWoutTC ‐ Similar to “IgnPtWithTC”, but less accuracy due to the lack of a combustion air
sensor.
On burners with a wide flame stability band, such as traditional nozzle mixing burners with little or no
FGR, a StartMode setting of “standard” typically works well. On burners with a more narrow flame
stability band (low and ultra ‐ low NOx mesh burners), “IgnPtWithTC” typically works well.
Menu path: Params & Display > O2Contr/Alarm > Gas Settings > Startmode
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