Micronor Inc. has introduced what it claims
is the world's first commercially-available absolute Fiber Optic Position
Sensor (FOPS). The new Model MR330 series position sensor offers an all-optical
design which makes it immune to any electro-magnetic interference such as lightning,
radiation, magnetic fields and other harsh environmental conditions. It is also
suited for long distance position sensing over hundreds of meters without being
affected by ground loop problems.
uniqueness of the system is that the sensor is entirely electronically passive
because we avoided implementing any electronics in the unit," says Robert
Rickenbach, chief engineer for Micronor. "That makes the device fundamentally
unique because it can be deployed in areas where lightning might strike, and it
will not get destroyed."
know this to be true from experience with our previous incremental encoder
product which also has zero electronics and uses a fiber optic link to connect
to it. The result is that the unit can be deployed in a wide range of
applications where there are problems using electronic devices," Rickenbach says.
absolute fiber optic sensor uses a novel optical technique embedded in a
passive sensor and active controller connected by a duplex fiber optic link.
The controller transmits a burst of light to the code disk in the sensor which
accurately modulates the spectral components of the light based on angular
position. Position information is imprinted in the optical spectrum of the
light and guided back to the controller for precise position readout. The
sensor requires no electrical power and houses no electronic components
heart of this invention is that we used the light spectrum, the color of the
light, as the information carrier," says Rickenbach. "We're sending a light out
to the sensor that is broadband, on the order of 100 nm wide, in the near
infrared range (850 nm)."
light spectrum is spread over a disk coded almost like a bar code with dashes
of mirrored metal stripes. As the disk turns, each code sequence is different
so there is a unique code at any position as the disk moves.
disk, the bars reflect light only at specific optical wavelengths and only
certain colors of light are returned to the controller over a separate fiber
optic cable. Inside the controller, the light is dissected and analyzed for its
wavelength components and ultimately the result is a position in binary digital
controller keeps the light stable by constantly monitoring the light source and
detecting movements. In addition, the user is presented with a PLC-compatible,
position signal typically used in automation applications such as Modbus or an
analog voltage or current output. The light source used in the sensor pulses
for a very short duration (10 µsec) because when the
disk moves, the system takes a snapshot of actual position and the system
pulses the light at 800 µsec intervals.
MR330's accuracy and EMI immunity make it an ideal sensor for applications that
require precise motion control and position measurement in challenging
environments: oil rigs, satellite antennas, solar panel arrays, actuator
systems, transportation systems, steel mills and medical instrumentation. The
sensor is also classified as a "simple apparatus" and meets ATEX requirements
for use in mines and other hazardous environments. The sensor's immunity to
lightning make it especially suited for outdoor applications such as wind
turbines and antennas.
measures absolute angular position from 0 to 360 degrees with 13-bit (8192
count) resolution at speeds exceeding 2500 rpm. A complete system consists of
the MR332 Passive Sensor, and MR330 Controller which interconnect via a duplex
fiber optic link. The fiber cable used is readily available industry standard
62.5/125µm multimode fiber with Duplex LC connections. The MR330 controller is
powered by 24V dc and features multiple built-in interfaces and protocols for
position read-out making it compatible with most any motion systems.
MR330 controller's powerful embedded processor and firmware offers an extended
set of built-in functions and multiple interface options not available in conventional
encoders or resolvers. The Model MR330-1 SSI Controller offers SSI, USB, RS485
Serial, Modbus RTU, two analog outputs (4-20mA and ±10V) and two digital set