Theory and Experiments of Fiber Optic Temperature and Vibration Sensors

Abstract

Fiber optic temperature and vibration sensors were designed and built to take readings in the harsh environment of a steel mill. The sensors are insensitive to electromagnetic noise; making them well suited for the use in such an environment. The temperature sensor uses an optical filter technique. A piece of intrinsic silicon is inserted between two optical fibers and 1064nm wavelength light is transmitted through the silicon. As the temperature increases, the silicon becomes more highly absorbing. The vibration sensor uses an optomechanical technique. Light is transmitted across a short air gap between two optical fibers. One of the fibers acts as cantilever while the other is fixed. As the cantilever vibrates, the transmitted power fluctuates, which enables the detection of the frequency and amplitude of the vibration. Sensors were initially tested under laboratory conditions, and subsequently field tested at ArcelorMittal Dofasco. The temperature sensor has a sensitivity of 0.4°C over the temperature range from 22°C to 120°C. The vibration sensor has a sensitivity of 2.87mV /g peak over a frequency range from 0 to 1250 Hz.