Instrumentation & Measurement Magazine 25-8 - 11

Ice
Spacer material
CX
Electrodes
Fig. 4. Photo of an ice sensor during a field experiment.
Fig. 2. Illustration of the principle of capacitive ice sensing, based on [18]. Ice
accretion influences the capacitance between electrodes. From measurements
of Cx
information about the state of ice accretion has to be determined.
Capacitive Ice Sensing on Overhead Power Lines
In cold climate regions, atmospheric ice accretion is considered
a severe safety issue for infrastructure such as power lines [12],
blades of wind turbines [13], antennas, etc. [14]-[17]. Sensing
systems to detect early ice accretion and to provide reliable
measurements for the thickness of ice are therefore of high interest
[18]. Among different sensing modalities, such as radar
[14], vision based or optical systems [19], capacitive sensing
was identified as potential sensing technology. Fig. 2 illustrates
the principle of capacitive ice sensing. It is based on the
distinct dielectric material properties of ice with respect to water
and air [20]-[22].
For the development of a capacitive sensor it is important
to understand all influences on the measuring capacitances.
Fig. 3 summarizes key elements for the research on a capacitive
ice sensor. The first column illustrates research for the front
end of the capacitive sensor, i.e., how the measurement capacitances
depend on water or an ice cover.
The second column of Fig. 3 represents a special feature of
the measurement problem. Natural ice accretion is a random
process. It depends on the temperature, the wind, the humidity,
etc., leading to a unique ice layer for each icing event.
However, ice layers of the same average thickness can lead to
different measurement capacitances. Knowledge about these
phenomena is essential with respect to the understanding
about the sensor. Both columns are characterized by an experimental
character in order to derive models for these effects.
Based on understanding about these aspects, dedicated electrode
designs [24], measurement circuits and signal processing
techniques can be developed for the successful application of
capacitive sensing technology for ice sensing.
Fig. 4 shows a photo of a field test with ice sensors for overhead
power line applications, which were designed according
to the described approach [25]. The test was conducted in a
glacier area in Austria. Prior to these tests the probes were extensively
tested in lab test beds to verify their correct behavior.
The photo in Fig. 4 was taken during an icing event. The inset
in the figure on the left shows the measured ice thickness.
Based on these tests, the successful application of capacitive ice
Fig. 3. Design process and steps for the development of a capacitive ice sensor, based on [18], [23].
November 2022
IEEE Instrumentation & Measurement Magazine
11

Instrumentation & Measurement Magazine 25-8

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