This page presents non-operational arithmetic for a selected low/high firing range, a relative air-fuel tolerance band and an actuator-resolution threshold. It does not establish fuel or air settings, commission a burner, replace flame safeguards or authorize furnace operation.
Combustion-Linkage Setpoint Arithmetic Reference
Explore selected range, tolerance and resolution arithmetic with a deliberately non-operational combustion-linkage schematic.
Equation Used
- Low and high fire are relative selected percentages, not equipment commands.
- The AFR tolerance is normalized around 100% and is not an actual mixture ratio.
- The backlash result is a whole-number resolution threshold, not a fault trip recommendation.
- Purge, ignition, flame supervision, fuel shutoff, interlocks, emissions and equipment limits are excluded.
Actual burner management, safeguards and commissioning must follow the approved equipment documentation and qualified-person procedures.
Illustrative linked-control topology
The animation shows a controller, two separately identified illustrative air/fuel final elements and a combustion chamber. Their motion only sweeps between the selected relative low- and high-fire percentages; it is not a burner sequence or verified ratio curve.
Real burner management must supervise purge, flame, fuel supply and safety interlocks, and commissioning/service must be performed by qualified personnel following the equipment documentation.
What the arithmetic reports
Select relative low fire, relative high fire, a symmetric relative AFR tolerance, servo resolution and a backlash threshold. The calculator reports selected turndown, the lower and upper relative tolerance bounds, and the whole number of resolution increments needed to meet or exceed the selected backlash threshold.
Selected setpoint arithmetic
Turndown = H/L; relative AFR band = 100% ± a; threshold increments = ceiling(b/r).
Selected-input arithmetic
For 10% low fire and 100% high fire, selected turndown is 10:1. A ±2% relative tolerance spans 98% to 102%. A 0.8° threshold at 0.1° resolution requires eight increments.
Not an operating or safety model
No entered value is a recommended burner setting. The reference excludes fuel properties, stoichiometry, oxygen trim, pressure, flow characterization, purge, ignition, flame supervision, trips, interlocks, emissions, furnace geometry and all equipment limits.
Primary and authoritative references
- Siemens LMV5 Burner Management System data sheet — manufacturer documentation for integrated burner, electronic fuel-air ratio, and load control.
- Siemens SQM4 actuator Technical Instructions — manufacturer documentation that the actuator controls load-dependent gas, oil, or combustion-air flow.
Questions
Can these values be applied to a furnace?
No. Use the specific approved burner-control documentation and qualified commissioning personnel.
Is the relative AFR band an actual air-fuel ratio?
No. It is only a percentage band around a normalized 100% reference.
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