Instruction Manual

18-0650-02 Revsion A
Page 2 of 13
I. INTRODUCTION
The RJC Model 650 Fiber Optic Measurement System (FOMS) is a microcontroller based Instrument
designed to support measurements made using RJC pressure sensor assemblies. The Model 650 is
NOT designed or certified for making measurements in humans.
The Fiber Optic Measurement System and related sensor assemblies are manufactured by RJC
Enterprises, L.L.C., 11711 N Creek Parkway South, Suite D-103, Bothell WA 98011, USA.
II. THEORY OF OPERATION
The pressure sensor design is based on the Fabry-Perot interferometer, in which two parallel,
minimally separated, partially reflecting surfaces form an optical reflecting cavity. If one of these
parallel surfaces is a pressure sensitive diaphragm, changes in external pressure cause a change in
depth of the optical reflecting cavity, which in turn alters optical cavity reflectance spectra.
The Instrument contains an 850nm LED whose emissions reach the sensor via an optical fiber. In the
sensor’s optical reflecting cavity, the spectral distribution of LED light is modified as a function of
cavity depth, and this spectrally altered light is reflected back down the fiber to the Instrument. Light
returning to the Instrument is optically split into two spectral components; the photocurrents from
these two components form a ratiometric signal which in turn correlates with changes in the measured
parameter
Pressure sensors based on this technology have been manufactured and sold for industrial applications
since 1988 (MetriCor/Photonetics), and for selected medical applications since 1993 (Integra
NeuroSciences). The combination of small size, high performance, and immunity to electromagnetic
noise make this pressure sensor an obvious choice for modern medical product applications.
For additional information, see Wolthuis et al. “Development of Medical Pressure and Temperature
Sensors Employing Optical Spectrum Modulation” in IEEE Transactions on Biomedical Engineering,
vol. 38, no. 10, pp 974-981, October 1991, and Reesink et. al. “Feasibility Study of a Fiber Optic
System for Invasive Blood Pressure Measurements” in Catheterization and Cardiovascular
Interventions, vol. 57, pp 272-276, 2002.