Micronor Inc. has introduced what it claimsis the world's first commercially-available absolute Fiber Optic PositionSensor (FOPS). The new Model MR330 series position sensor offers an all-opticaldesign which makes it immune to any electro-magnetic interference such as lightning,radiation, magnetic fields and other harsh environmental conditions. It is alsosuited for long distance position sensing over hundreds of meters without beingaffected by ground loop problems.

"Theuniqueness of the system is that the sensor is entirely electronically passivebecause we avoided implementing any electronics in the unit," says RobertRickenbach, chief engineer for Micronor. "That makes the device fundamentallyunique because it can be deployed in areas where lightning might strike, and itwill not get destroyed."

"Weknow this to be true from experience with our previous incremental encoderproduct which also has zero electronics and uses a fiber optic link to connectto it. The result is that the unit can be deployed in a wide range ofapplications where there are problems using electronic devices," Rickenbach says.

The newabsolute fiber optic sensor uses a novel optical technique embedded in apassive 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 whichaccurately modulates the spectral components of the light based on angularposition. Position information is imprinted in the optical spectrum of thelight and guided back to the controller for precise position readout. Thesensor requires no electrical power and houses no electronic componentswhatsoever.

"Theheart of this invention is that we used the light spectrum, the color of thelight, as the information carrier," says Rickenbach. "We're sending a light outto the sensor that is broadband, on the order of 100 nm wide, in the nearinfrared range (850 nm)."

Thelight spectrum is spread over a disk coded almost like a bar code with dashesof mirrored metal stripes. As the disk turns, each code sequence is differentso there is a unique code at any position as the disk moves.

On thedisk, the bars reflect light only at specific optical wavelengths and onlycertain colors of light are returned to the controller over a separate fiberoptic cable. Inside the controller, the light is dissected and analyzed for itswavelength components and ultimately the result is a position in binary digitalform.

Thecontroller keeps the light stable by constantly monitoring the light source anddetecting movements. In addition, the user is presented with a PLC-compatible,position signal typically used in automation applications such as Modbus or ananalog voltage or current output. The light source used in the sensor pulsesfor a very short duration (10 musec) because when thedisk moves, the system takes a snapshot of actual position and the systempulses the light at 800 musec intervals.

TheMR330's accuracy and EMI immunity make it an ideal sensor for applications thatrequire precise motion control and position measurement in challengingenvironments: oil rigs, satellite antennas, solar panel arrays, actuatorsystems, transportation systems, steel mills and medical instrumentation. Thesensor is also classified as a "simple apparatus" and meets ATEX requirementsfor use in mines and other hazardous environments. The sensor's immunity tolightning make it especially suited for outdoor applications such as windturbines and antennas.

The productmeasures absolute angular position from 0 to 360 degrees with 13-bit (8192count) resolution at speeds exceeding 2500 rpm. A complete system consists ofthe MR332 Passive Sensor, and MR330 Controller which interconnect via a duplexfiber optic link. The fiber cable used is readily available industry standard62.5/125mum multimode fiber with Duplex LC connections. The MR330 controller ispowered by 24V dc and features multiple built-in interfaces and protocols forposition read-out making it compatible with most any motion systems.

TheMR330 controller's powerful embedded processor and firmware offers an extendedset of built-in functions and multiple interface options not available in conventionalencoders or resolvers. The Model MR330-1 SSI Controller offers SSI, USB, RS485Serial, Modbus RTU, two analog outputs (4-20mA and plus or minus 10V) and two digital setpoints.