1.2 Water Level Features
The Mk7 Expansion Board is used in conjunction with the Mk7 Micro-Modulation (M.M.) burner
controller to report and control levels of water within industrial steam boilers. The intelligent water level
control includes high water alarms, 1
st
low and 2
nd
low alarms. Alarm level reporting deals with the
ability to determine whether the current water level in the boiler is above or below a predetermined
level. These levels vary with each installation, and must therefore be programmed on site by a qualified
commissioning engineer.
Intelligent Water Level Control
The feed water flow is managed by 3-element control, in response to the water level measured by the
capacitance/frequency readings, boiler pressure and the burner’s firing rate. The flow is controlled by
a fully modulating feed water/VSD or by using an on/off signal from a feed water pump. The
Autoflame 3-element level control has been granted a worldwide patent; being the only system that
can combine firing rate, steam pressure and water level within one controller for the purpose of
improving feed water control. Safety, accuracy and integrity are guaranteed.
The two capacitance probes control up to seven operational levels including:
High high level
High level
Pre-high level
Control point or pump on/off levels
Pre-1
st
low level
1
st
low level
2
nd
low level
End of probe level
The capacitance readings are constantly checked between both of the probes, the commissioned value
and an internal hardware reference capacitor (to account for long term drift and temperature
variations).
Both probes have a self-checking feature for mechanical and electrical integrity. The commissioned
levels by the capacitance probes have an accuracy of ± 2mm repeatability.
The patented movement detection of water feature ensures that no static value can be accepted, i.e.
the probes are in turbulent water.
The swell management feature prevents intermittent shutdowns from the 1
st
low being switching due to
increases in steam requirements. The Autoflame Micro-Modulation (M.M.) module knows the firing rate
and boiler pressure, and accommodates for this transient condition by increasing the ‘control point’
level.
The commissioning procedure for water level control, with a Mk7 M.M. unit and Mk7 Expansion
Board, is extremely time-efficient and can be performed at operating pressure.
It is ideal to maintain an amount of water in the boiler appropriate to the amount of steam being
generated. Should the water level drop below this ideal level by an excessive amount, it is necessary
to stop the burner firing. If there is insufficient water in the boiler damage may occur to its structure.
In extreme cases there is the potential for the boiler to explode. The water level control herein is
designed to maintain a satisfactory level of water in the boiler, whilst controlling and reporting low
water level conditions.
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