10 Water Level Control
Mk8 MM Manual Page | 173
10.5.2 Operation
Capacitance is a measurement of how much a body can store electrical charge. The capacitance is
measured between the surface area of the probe and the surface area of the boiler shell. As the water level
changes the surface area of the boiler shell covered will change, so a change in the capacitance will be
detected. The measured capacitance will increase as the water level in the boiler rises, as the surface area
covered with water will be bigger with more water in the boiler.
The capacitance readings are constantly checked between both probes, the commissioned value and an
internal hardware reference capacitor (to account for long term drift and temperature variations). Both probes
control typically “high level”, “required level”, “first low” and “second low”. The actual water level readings
taken from both probes are constantly compared and checked against each other, as well the commissioned
water levels. When controlling the required level this data stream is combined with a PI algorithm which
controls either the two-port feed water control valve or the variable speed drive to the feed water pump. Each
probe is self-checked for electrical and mechanical integrity by hardware references and self-checking
software routines. Each probe and its control electronics are compensated for ambient temperature
variations and component drift, guaranteeing absolute safety of operation.
By our method the probes control the required level by learning the wave signature and managing the
turbulence within the boiler shell. This “wave signature management” takes into account the changes in
burner firing rate and any variance in pressure in the boiler shell. Incorporated within the system hardware
are all necessary electronic switching functions to control audible alarms, mute/reset and indication lights
required to meet standard North American and European codes. Safety, accuracy and integrity are
guaranteed.
10.5.3 Specification
Custom length capacitance probes available upon request.
Probe connection– quick connect
Temperature rating of housing
Maximum Allowable Pressure
Maximum Allowable Temperature
Note: The probes must not be cut. If the probes are cut this will act as a short between the positive and
negative plates of the capacitor and will stop the probes from working.
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