Abstract
Flow measurement and control of cryogens is one of the major requirements of systems such as superconductor magnets for fusion reactors, MRI magnets etc. They can act as an early diagnostic tool for detection of any faults and ensure correct distribution of cooling load while also accessing thermal performance of the devices. Fibre Bragg Grating (FBG) sensors provide compact and accurate measurement systems which have added advantages such as immunity towards electrical and magnetic interference, low attenuation losses and remote sensing. This paper summarizes the initial experimental investigations and calibration of a novel FBG based mass flow meter. This design utilizes the viscous drag due to the flow to induce a bending strain on the fibre. The strain experienced by the fibre will be proportional to the flowrate and can be measured in terms of Bragg wavelength shift. The flowmeter is initially tested at atmospheric conditions using helium. The results are summarized and the performance parameters of the sensor are estimated. The results were also compared to a numerical model and further results for liquid helium is also reported. An overall sensitivity of 29 pm.(g.s-1)-1 was obtained for a helium flow, with a resolution of 0.2 g.s-1. A hysteresis error of 8 pm was also observed during load-unload cycles. The sensor is suitable for further tests using cryogens.
Highlights
This paper summarizes the initial experimental investigations and calibration of a novel Fibre Bragg Grating (FBG) based mass flow meter
The tests were run using helium gas at 298K for calculating different sensor characteristics such as pressure drop across the flow meter, repeatability, linearity etc
The results show that the sensitivity of the meter over the whole range is ~35.5 pm.(g.s-1)-1 for liquid helium, but the initial shift in Bragg wavelength is much more higher, which can result is less environmental errors during measurement
Summary
In case of multiple sensors placed in a single fibre (multiplexing), the reflected wavelength can be selected so that each FBG sensor has a distinct operational range. This property of an FBG sensor to measure very large strains (up to 5000 μm/m) [4] with good accuracy has enabled its use in measurement of various physical parameters such as displacement [5], temperature [6], pressure, strain , vibration, acceleration, torsion[7], fluid flow[8] etc. Some of the initial concepts of FBG based flow measurement used these sensors as a temperature transducer.
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