issue: May 2009 APPLIANCE Magazine
Appliance Engineer - Electronics Report
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An ultrathin inductive position sensor that requires no magnet to operate offers robustness, EMI immunity, and a small footprint.
(www.posic.com), a manufacturer of position sensing products based in
Neuchâtel, Switzerland, introduced a new type of inductive position
sensor for measuring the speed and position of gears, disks, and linear
bands. With an ultrathin profile and requiring no magnet to operate,
the sensor offers a robust and compact alternative to optical or
magnetic sensors typically used in home appliance and consumer
electronics, says Sietse Wouters, marketing and sales manager.
performance of optical sensors is affected by contaminations like dust,
particles, fluids, or condensation. The magnetic sensors do not have
this problem, but they are sensitive to magnetic fields in the
environment,” Wouters explains. “POSIC’s integrated microcoil inductive
sensor has high tolerance for adverse environmental conditions such as
water, oils, and metal filings, and is insensitive to magnetic fields.”
This suits the sensor to applications in which harsh environments,
electromagnetic pollution, and size are major concerns.
small form factor comes from a technology that integrates a
differential microcoil transformer onto a silicon chip with the
associated electronics. “Typical inductive sensors have coils that are
wire-wound or integrated on a multilayer PCB. To our knowledge, POSIC
is the only company that has pushed the miniaturization down to the
chip level,” says Wouters. “As you can imagine, all kinds of coupling
and crosstalk may occur if this cointegration is not perfectly
controlled. It required a lot of time and good engineering skills to
get to the performance that we achieve today,” he tells APPLIANCE. With
the silicon chip containing the sensor elements and the electronics
thinner than 0.5 mm, the total profile of the sensor and target is
generally between 2 and 3 mm or less.
says two sensing techniques are instrumental in enhancing the sensor’s
robustness. “The differential measurement principle is applied, so any
perturbation that acts on both sides of the differential coil-pair is
eliminated from the differential signal,” he explains. “The principle
of frequency modulation is also applied. The primary coil of the
transformer structure generates an ac magnetic field with a frequency
of 1 MHz. This field is coupled into the secondary coils and the
coupling is amplitude-modulated by the target, for example, steel gear.
The 1-MHz am-signal is synchronously demodulated, which means that any
interference, such as a 5–10-kHz PWM signal to drive an electric motor,
is filtered out.” Those factors make the sensor especially robust
against the magnetic fields and electromagnetic interference, Wouters
Another advantage of the sensor is its
ease of adoption. “Many semiconductor position sensors are supplied in
the form of an integrated circuit. The engineer has to design a PCB
that holds the sensor into a mechanical environment,” Wouters says.
“The POSIC sensor is ready for cable soldering and can be glued,
screwed, or clipped directly into a mechanical application.” The firm
also offers evaluation kits with its sensors, allowing an engineer to
start off within a few minutes.
comes in standard as well as custom versions. “The sensor must be
positioned with a certain accuracy into a 3-D mechanical system to
accurately measure the position and speed of an object,” Wouters says.
“Our experience is that no two mechanical systems are the same, and
therefore it is impossible to define a ‘standard’ mechanical form that
fits in all systems.” In order to overcome this problem, the firm
offers a limited number of standard sensors and the possibility to
adapt the mechanical interface.
used in appliances and CE become smaller while delivering increased
torque, Wouters says, the electromagnetic pollution will increase.
Those applications will benefit from sensors that are insensitive to
the magnetic fields created by their magnets and windings and the EMI
created by brushes and PWM drive signals.
sensors have an operating temperature range of –40° to 125°C and work
with gears and disks made of ferromagnetic materials such as iron and
nickel, as well as electrically conducting materials such as aluminum,
copper, and brass.
integrates a differential microcoil transformer onto a silicon chip
together with the associated electronics, making the sensor both
compact and robust.
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