1 Overview and Benefits
22.05.2017 Mk8 MM End User Guide Page 5
1.3 Micro-Modulation (MM)
To ensure maximum efficiency and reliability of the boiler plant operation, two requirements are of
paramount importance, the air to fuel ratio and the target temperature or pressure:
The air to fuel ratio must be kept to the minimum to ensure complete combustion within the
limitations of the combustion head design. A very high air to fuel ratio will be an indication of
high excess air, which decreases the overall efficiency of the boiler. The fuel valve and air
damper positions set for this minimum air to fuel ratio along the whole commission curve must
be infinitely repeatable to an incredibly high degree of accuracy.
The target temperature or pressure of the boiler should be monitored by the combustion system
and at all times, with exactly the right amount of fuel and air fired to achieve this target value.
Irrespective of load changes, the burner/boiler system should be able to meet the target
temperature or pressure.
The burner’s fuel to air ratio was traditionally governed by mechanical systems which involved multiple
cams, shafts and linkages controlled by one motor. The inherent hysteresis that occurred from the
system design allowing components to be loose, which made the level of accuracy required impossible.
With this poor accuracy, the response of the fuel input to the monitored temperature/ pressure of the
boiler meant that the set target value at most times would overshoot or fall short.
The Micro-Modulation module is the basic building block of the Autoflame System. The Autoflame MM
module provides an easily programmable and flexible means of optimising combustion quality
throughout the load requirement range of the burner/boiler unit whilst ensuring the temperature is
accurate to within 1°C (°F) and pressure to within 1 PSI (0.1Bar). Using direct drive motors to
individually control the air damper and fuel valve(s), gives the optimum combustion of the burner at
every point along the firing range. The allowed error in angular degrees of rotation between the two
servomotors at any position in the load range is 0.1°.
This automated system of burner control can achieve ‘locked on’ near stoichiometric air to fuel mixing
throughout the fuel input range of the boiler while maintaining exact temperature or pressure target
values. The load control incorporates user-variable Proportional Integral Derivative control. The PID
control is infinitely adjustable to match any boiler room requirements.
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