Tech Briefs Magazine - October 2021 - ST-21

optimal sensor for their particular
application. For example, active temperature
compensation is necessary if
highly precise measurements are
required. With varying temperatures
there are two factors that can influence
the measurement signal: mechanical
changes, where the geometric dimensions
of the sensor and the target
change in the form of extension or contraction
of the sensor and the target.
And electrical effects have an even
greater impact than mechanical
because of changing electromagnetic
characteristics.
For example, the eddyNCDT 3001
series is specially designed for applications
where conventional inductive displacement
sensors have often reached
their performance limits. They have
compact dimensions and are available
in M12 and M18 housings, covering
measuring ranges from to 2mm to
8mm. They are protected to IP67, and
so are applicable in automation,
machine building, and design.
Furthermore, they are temperaturecompensated
up to 70 °C. They have
high measurement accuracy and linearity
as well as a 5-kHz frequency
response rate and are factory-calibrated
for ferromagnetic and non-ferromagnetic
objects such as aluminum and
steel.
Hydrostatic Bearings
One application for eddy current displacement
sensors is in large machinery
such as stone mills or telescopic installations,
which often work with hydrostatic
bearings. These bearing systems
are continuously supplied with liquid
lubricant via an external pressure supply.
The lubricant is pressed between
the bearing surfaces, which are therefore
continuously separated from one
another by a thin lubricant film. The
bearing surfaces are not exposed to
friction and hence operate wear-free.
This enables sub-micrometer position
control. Any disturbances in the
hydraulics, or drops in pressure, however,
can have disastrous consequences.
This could result in damage to the bearings
and ultimately system failure, causing
high maintenance and repair costs.
The oil gap in hydrostatic bearings,
therefore, requires continuous reliable
inspection. For this application, the
sensor is mounted horizontally to the
bearing shoe, so it is not directly
exposed to the oil pressure. It measures
Sensor Technology, October 2021
Cov
Figure 3. High precision, robustness, linearity, and temperature tolerance allow an eddyNCDT sensor
to track parameters such as the lubrication gap in a combustion engine. (Courtesy of Micro-Epsilon)
through the oil film onto the opposing
bearing surface.
Combustion Engines
The exact position of the piston, the
piston rings, and the existing pressure
conditions are essential information for
manufacturers of combustion engines.
Using simulation tools, this data is primarily
used to make reliable predictions
about wear, friction, and oil consumption.
The eddy current sensor measures
the piston ring and so-called piston secondary
movements, at high accuracies.
Here, the advantages of eddy current
sensors - resistance to the high temperatures
in combustion engines (up to
180°C and even higher for a short period
of time) - are apparent. The prevailing
vibration, pressure, oil, fuel, combustion
gas, and continuous mechanical movement,
do not influence the precision of
the results. In addition, eddyNCDT sensors
offer fast measurement speeds with
small measuring ranges (0 - 0.5 mm)
and extremely high resolution (less than
1μm).
Miniaturization
Micro-Epsilon has developed a sensor
that uses embedded coil technology
(ECT) for miniaturization. This producwww.techbriefs.com
ToC
tion
technique allows almost unlimited
scope in terms of the external design and
geometrical shape of the sensors, while
enabling the evaluation electronics to be
integrated into the sensor. It is constructed
by embedding a two-dimensional
eddy current coil in an inorganic material,
which improves the sensors' stability,
robustness, and thermal resistance.
These sensors are suitable for extremely
harsh applications such as ultra-high vacuums
in semiconductor production.
Eddy Current Displacement Sensors
- Small but Powerful Industrial
Workers
These little sensors are ideal for industrial
environments, where environments
are harshest and most challenging, yet
call for extremely precise measurements.
They can be used in everything
from measuring the gaps in hydrostatic
bearings in large machines, the clearance
between piston and cylinder, to distance
measurements against rollers that
guide plastic films.
This article was written by Martin
Dumberger, Managing Director, MicroEpsilon
USA, (Raleigh, NC). For more information,
contact Mr. Dumberger at
martin.dumberger@micro-epsilon.com or visit
http://info.hotims.com/79418-162.
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Tech Briefs Magazine - October 2021

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