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Inductive sensors


Roger Isaksson

Jan 1, 1970
Hi, we are in the process of improving our inductive sensors, or
possibly replace them with other types of sensors. The absolute
precision is not decisive with our differential technology. What is
important is the capability to detect (edge detect) passing cog teeth.
Typically these edges are measured on an underwater submerged spinning
cogwheel. A passing cog induces an electromotive force, due to the
difference in the magnetic field surrounding the coil as the cog
passes, this results in a voltage that is measured. The rate of
passing teeth are below 20/s. The required presicion of the detected
cog edge should be about about 2.5ms and the measuring distance should
be about 8-10mm(preferrably more). The cog height, measured from the
cog wheel axis, is larger than 200mm. The sensor is measuring
submerged in water and the cog wheel are made of metal. The sensor
will be mounted threaded into the cog wheel housing. The housing are
made of magnetic steel, which decreases the sensing distance, using
inductive sensors. The sensor is mounted perpendicular to the cog
wheel axis. The diameter of the sensor housing is 25mm.

Does anyone have any ideas? Right now we can detect up to 8-10mm with
our prototype inductive sensors. The sensor has a 10x60mm cylinder
neodyne magnet, surrounded by a coil(0.15mm wire) with aprox 4000revs.
There are a few parameters that could be altered:

# The diamater ratio between magnet and coil.
# The geometric shape of coil and magnet, edges, konicity, etc.
# Choise of magnet, parameters such as field strength and field
# Number of revs in the coil and wire diameter.


Roger Isaksson