Design and development of an economical temperature compensated bidirectional fiber Bragg grating flow sensor

Abstract

A target-type cantilever based temperature compensated fiber Bragg grating (FBG) flow sensor is designed and developed with economical demodulation and data acquisition schemes. FBG is glued on the surface of a thin elastic stainless steel cantilever in pre-strained condition. The cantilever is mounted inside a flow channel by a special purpose brass holder with a height and direction adjustable threaded stem. The sensor is interrogated by an optical spectrum analyzer (OSA) and indigenously developed twin FBGs and chirped FBG—FBG intensity demodulation schemes. Response of the sensor is investigated in the flow rate range of 0–10 l min−1 in both forward and reverse flow directions. In spectral demodulation, the flow sensor offered a linear response in the full investigated range with a sensitivity of 19.2 pm/(L/min). However, the twin FBGs demodulation scheme presented a linear behaviour in the range of 4–10 l min−1 with sensitivities of 1.22 ± 0.03 μW/(L/min) and 29.89 ± 0.55 mV/(L/min) detected by the high speed power meter and photodetector, respectively. The novel CFBG-FBG intensity demodulator offered a linear response throughout its tested range and can offer a flow rate detection up to 265 l min−1 at the present sensitivity of the sensor with the condition that the cantilever-FBG system must be strong enough to withstand the higher flow rates. The temperature of the fluid is monitored by an FBG temperature sensing probe connected to the flow channel using intensity demodulation scheme by another pair of twin FBGs. Temperature compensation of the flow sensor is performed by arithmetic operations over the reflection intensities due to temperature probe to the results of the flow rates using a cost-effective data acquisition scheme.