Issue
132 July 2001
Inductive Sensors
by
George Novacek
Start
•
LVDT Revisited • The
Works • Electrical
Interfaces • Mechanical
Interfaces • The
Future • Sources &
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LVDT
REVISITED
In this article,
I want to introduce you to another technology, the integrated
inductive sensor developed by the Swiss company CSEM.
What makes this sensor interesting is that in principle
it is similar to the variable differential transformer,
with the coils micro-machined on a chip. Photo 1 shows
the sensor with its driver and decoder electronics encapsulated
for protection. Photo 2 is a microscopic detail of the
business end of the sensor.
 |
|
Photo
1—The
sensor module with its driver and decoder electronics
is merely 0.35² × 1.18² and weighs approximately
0.7 grams.
|
Variable differential transformers and their cousins’
resolvers are robust and, when their output signals are
digitized, can consistently provide 16-bit resolution.
But the coil windings are large and heavy, and the required
precision manufacturing is costly.
 |
| Photo
2—This
is a microscopic detail of the sensor part. You
can see the large octagonal excitation coil, which
is about 0.15² (3.8 mm) across. The four smaller
sensing coils below it are faintly visible. |
The size and
weight are concerns for many reasons. In the transportation
industry, the long-standing maxim is that the cheapest
way to improve efficiency and performance is by reducing
weight. Lower weight and smaller size make it possible
to install sensors in previously impossible locations
and make their mounting less demanding. Their mechanical
characteristics, such as response time and ability to
sustain vibrations are greatly improved. Small size
also improves EMI characteristics, both emission and
susceptibility, resulting in reduced shielding requirements
and further size and weight reduction. [1–5]
On the manufacturing
side, unlike the old-fashioned coil winding, precision,
repeatability, and low cost (with high volume) are inherent
to the micro-machining process, and hardly achievable
by traditional manufacturing methods (just as the miniature
size and weight).
