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Effect of Refractive Index Variation on Two-Wavelength Interferometry for Fluid MeasurementsTwo wavelength interferometry can in principle be used to measure changes in both temperature and concentration in a fluid, but measurement errors may be large if the fluid dispersion is small. This paper quantifies the effects of uncertainties in dn/dT and dn/dC on the measured temperature and concentration when using the simple expression dn = (dn/dT)dT + (dn/dC)dC. For the data analyzed here, ammonium chloride in water from -5 to 10(exp infinity) C over a concentration range of 2-14% and for wavelengths 514.5 and 633 nm, it is shown that the gradients must be known to within 0.015% to produce a modest 10% uncertainty in the measured temperature and concentration. These results show that real care must be taken to ensure the accuracy of refractive index gradients when using two wavelength interferometry for the simultaneous measurement of temperature and concentration.
Document ID
Acquisition Source
Legacy CDMS
Document Type
Technical Memorandum (TM)
Mercer, Carolyn R.
(NASA Lewis Research Center Cleveland, OH United States)
Date Acquired
September 6, 2013
Publication Date
October 1, 1998
Subject Category
Report/Patent Number
NAS 1.15:207925
Funding Number(s)
PROJECT: RTOP 274-00-00
Distribution Limits
Work of the US Gov. Public Use Permitted.
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