Optical fiber rotation sensor for application in oil refinery and high electromagnetic noise environment Tomasz R. Woliński, Daniel Budaszewski, Andrzej W. Domański, Sławomir Ertman Grzegorz Goleniewski*, and Michał Wydmański * Faculty of Physics, Warsaw Univ. of Technology, Koszykowa 75, 00-662 Warszawa, Poland *ORLEN Refinery, Płock, Poland phone +48 22 234 5689, fax +48 22 234 5743, e-mail: wolinski@if.pw.edu.pl ABSTRACT Preliminary results of the tests performed by using a modular fiber-optic sensor for hydrostatic pressure/temperature and also rotation measurements envisaged for refinery applications are presented. The prototype fiber optic sensor for rotation measurements has been successfully installed and tested in the ORLEN Refinery in Plock, Poland. During the initial tests, we used a rotating machine to measure its rotor velocity whereas the sensor head was connected to a pigtailed laser diode (λ=635 nm) and to a detector by a 100-meters-long loop of multimode optical fibers. The output signals of the optical sensor were transferred into a refinery automatic control system (-2 or -20 V). During tests in the ORLEN Refinery we obtained very good agreement of output signals from standard magnetic sensor and the proposed optical sensor. In addition, the proposed optical fiber rotation sensor was immune to electromagnetic noise that disturbs output signals of the magnetic sensors. Keywords: optical fiber sensors; rotation measurements 1. INTRODUCTION The oil refinery environment is very dangerous and hence must be continuously monitored. The most important parameters to be controlled and continuously monitored in refineries include machine vibration, rotation velocity, temperature, and pressure. Due to high risk of explosion all electric wires and devices must be shielded and kept on save distances. Piezoelectric and magnetic sensors used in refinery industry are sensitive to disturbing electromagnetic fields generated by machines. Additionally, output signals from these sensors are very low what makes the readout uncertain. Emerging optical fibers sensors used instead of electric sensors seem to be excellent replacements absolutely save in the explosive environment such as oil refineries. Moreover, optical fiber sensing technique is preferred in hazardous and dangerous environmental conditions (as oil refineries) due to lack of explosion risk as well as high electromagnetic noise immunity [1-5]. 2. ROTATION VELOCITY SENSING In oil refineries there is a great need for reliable and safe measuring methods for continuous monitoring of different types of vibrations as well as rotation velocity that could be immune to disturbing electromagnetic fields generated by machines. Machine diagnosis methods are based on synchronous analysis that utilizes digital pulses generated by rotating elements: one pulse should correspond to the 360 o rotation. That is why reliable rotation velocity sensors are very important in industrial machines process control. Classical rotation sensors used in vibrations monitoring systems are based on the induced (Foucault) currents and are exactly the same as used for relative vibrations monitoring. The output signals from these current sensors are in the voltage range V ac ~ 80÷100 mV (p-p) for relative vibrations measurements and V ac ~ 2,000 mV (p-p) for rotation measurements. The same measurement systems include also absolute vibration sensors which make use of relatively low voltages: V ac ~ 2÷40 mV (p-p). Hence a combination of 3 different sensors into one measuring system results in the fact that “strong” rotation measurements output signals can badly influence relatively “weak” absolute vibration outputs causing false readouts. That was a main reason to introduce Optical Measurement Systems for Industrial Inspection V, edited by Wolfgang Osten, Christophe Gorecki, Erik L. Novak, Proc. of SPIE Vol. 6616, 66161U, (2007) · 0277-786X/07/$18 · doi: 10.1117/12.729625 Proc. of SPIE Vol. 6616 66161U-1