The 1.7 mm diameter pressure sensor utilizes the principle of light intensity changes, transmitted by two optical fibers, upon reflection from a specially shaped, metal diaphragm deflecting under the effect of pressure. In an ultra low-cost and durable design suitable for automotive applications the sensor compensates for all major temperature effects encountered in combustion engines. The auto-referencing function performed by the sensor’s signal conditioner compensates for the temperature induced LED, photodiode, and fiber-to-opto-electronics coupling errors, sensor thermal drift, as well as fiber bending related light intensity changes. The direct bonding of optical fibers to the photodiode and LED chips results in minimum thermal errors and high part-to-part consistency. Sensor head materials and dimensions are optimized to compensate for the sensitivity changes associated with the diaphragm’s Young’s modulus temperature dependence. The miniature signal conditioner, based on an LED-photodiode transceiver and an ASIC, can be integrated within an automotive connector or a package small enough to fit inside the engine head. Over the signal conditioner temperature range of -40°C to 150°C and the sensor head continuous range of -40°C to 300°C a typical total accuracy of 1-2% is achieved.
In a robust, durable, and low-cost design Optrand pressure sensors utilize the principle of light intensity changes, transmitted by two optical fibers, upon reflection from a specially shaped, metal diaphragm deflecting under the effect of pressure. The non-contact detection principle combined with the diaphragm design optimized for infinite fatigue life translates into a sensor with extraordinary lifetime. The sensor's signal conditioner contains one LED and one photodiode and is permanently attached to the fibers. The electronic circuitry provides the auto- referencing function compensating for the effects of fiber bending, fiber-to-optoelectronics coupling changes, sensor thermal drift, as well as temperature and aging effects of the LED and the photodiode. The results of several along- term test in two key gas machinery applications are reported here: continuous and intermittent monitoring of power and compressor cylinders. In the longest application to date, hundreds of combustion pressure sensors have demonstrated over 12,000 hours or 500-million pressure-cycle lifetime. Dynamic pressure sensors for compressor monitoring have already demonstrated the lifetime of 1 billion cycles and target 5 billions. In compressor applications the sensor demonstrate typical +/- 0.25 percent accuracy while combustion pressure sensor accuracy is typically +/- 1 percent. For almost two years tens of indicator valve- mounted combustion sensor have been monitored for calibration stability demonstrating better than +/- 0.1 percent performance over a 6-month period.
A low-cost fiber-optic pressure sensor is reported designed for use in production automotive engines for combustion monitoring and control. The sensor operates on the principle of changing light intensity due to the reflection oflight from a metal diaphragm moving under the effect of combustion pressure. Two designs are described: one based on the use of a single, multi-mode fiber and the other using two multi-mode fibers. The optoelectronic components used in the sensor include one GaA1As LED operated at 850 am and one or two SI PIN photodiodes. To combat LED intensity and photodiode sensitivity changes over an underhood temperature range of -40°C to 150°C a proprietary auto-referencing technique has been developed that does not require temperature regulation of the optoelectromc package. Telecommunication-grade optical fibers, with core diameters ranging from 50 to 100 microns, are used coated with high temperature coatings. A sensor, as small as 2.8 mm in diameter, can be either directly inserted into an engine head or integrated with a spark plug or a fuel injector. The sensor optoelectromc and electronic components are packaged inside a miniature "smart" connector that connects to an engine controller power supply as well as outputs pressure and sensor health signals. When optimized for high linearity and reduced thermal effects, the spark plug-mounted sensor demonstrates accuracy comparable to that of a laboratory-grade piezoelectric transducer. Under engine operating conditions ranging from idle to full load and maximum RPM, the combined sensor's hysteresis, non-linearity, and thermal shock result in pressure reading accuracy of 1.5% full scale range. With the targeted life-time of 500 Million pressure cycles and price of less than $10, the sensor meets the performance, durability, and cost requirements for production car applications.
A multichannel fiber-optic combustion pressure sensor system is described dedicated to parametric emission monitoring systems (PEMS) for use in natural gas-fueled, stationary, and reciprocating engines. In view of the emerging 1995 emission regulations for large stationary engines, the natural gas pipeline operators have turned their attention to PEMS' for predicting and controlling the amount of polluting emissions such as NOx and HC. We present design considerations and performance data of a 8-channel pressure monitoring system employing fiber-optic combustion pressure sensors. The control/monitoring unit offers capabilities of sensor calibration, health monitoring, and real-time data acquisition. Using an engine position sensor trigger, the monitoring unit can calculate peak pressure, indicative mean pressure, and location of peak pressure. The system allows for 50 kHz, burst mode transfer of multisensor data to a host PC. We demonstrated performance data collected on three large-bore engines and long-term endurance test data. While initially intended for stationary engines, the system can be used in applications requiring portability including moving vehicles.
We report design considerations and performance data of a fiber optic pressure sensor system that is suitable for continouus cobustion pressure measurements. The sensor is designed for 0 to 1000 psi pressure range and sensor housing temperatures ranging from -40 degrees C to 300 degrees C. A durable metal diaphragm design ensures fatigue-resistant long-term sensor operation and linear response. An intelligent autoreferencing technique provides drift- free output and compensates for high temperature and other environmental effects. Performance data is presented from tests performed in passenger cars and large-bore stationary engines. Typical sensor accuracy is +/- 1% at constant temperature and when connected to different interface units. Continuing endurance tests demonstrate excellent sensor durability for over 2000 hours continuous operation or 200 million pressure cycles that the sensors have been exposed to so far. The FiberPSITM pressure sensor system, commercially viable at this time, meets or exceeds the performance of research grade pressure sensors at a fraction of the cost.
We present a theoretical and experimental study of a tapered optical fiber-based sensor design that significantly increases optical detection sensitivities for measurement of small mechanical deflections in diaphragm-type fiber optic pressure sensors. By using tapered fibers, we experimentally observed up to eight-fold increases in optical signal modulation levels. We also discuss taper design considerations that maintain system optical power throughput and provide consistent increases in numerical apertures.
We describe a theoretical and experimental study of an intensity-based, dual-wavelength referenced fiber optic temperature sensor utilizing temperature-induced spectral shifts of optical thin-film interference coatings, deposited on a sensor fiber end. We present coating design considerations that lead to significant increase in transition region spectral shifts and coating-reflected signal modulations, for sensitive temperature measurement. Experimental results demonstrate that high density coating-based sensors provide consistent and repeatable temperature sensing, while low density coating-based sensors experience significant and inconsistent spectral variations and degradation under temperature cycling.
We present a novel dual-diaphragm-based, integrated pressure and temperature sensor design for aerospace applications that require accurate, durable, and temperature-compensated pressure sensors. We discuss potential improvement in the sensor's high-temperature capabilities, and demonstrate significant increases in signal-to-noise performance and accuracy, resulting from the dual-diaphragm design. We also describe an integrated optoelectronic transceiver design, employing a dual-wavelength error compensation approach, for pressure and temperature sensing. Other issues leading to practical sensor systems are also discussed.
We present design considerations of a diaphragm-type fiber optic combustion pressure sensor employing a low-cost optoelectronic transceiver. The key transceiver element is a tapered optical fiber bundle-based coupler design that relaxes critical alignment requirements, and allows the use of low-cost components. Sensor system evaluation data are presented for high-engine-load and high-combustion-temperature conditions, and for known detection. The test results closely resemble outputs of a heat-sunk flame-shielded, instrumentation-grade piezoelectric reference transducer, and demonstrate better temperature stability.
We present experimental results from fiberoptic spectroscopy apparatus measuring whole blood's optical attenuation over a continuous wavelength range of 0.6 - 1.0 micrometers . Relative optical density (OD) spectra at a number of hematocrit values and oxygenation levels is obtained. The role of hematocrit in affecting spectral shape is discussed based upon relatively simple relationships derived from experimental data. A specific partial differential equation emerges from the analysis. This equation relates scatter-dependent experimental OD to oxygen saturation, hematocrit and purely absorbing, nonscattering constituents--and is obeyed over an extended wavelength range. A three-wavelength algorithm using experimental absorbances at LED-compatible wavelengths accurately provides both hematocrit and oxygen saturation values, for hematocrit levels between 0.2 and 0.6 in the presence of oxygenated and reduced Hb species. Optical system comparison between spectroscopic data and modeled LED behavior indicates the algorithm can be mapped to the design and implementation of discrete components for clinical use.
A theoretical approach is developed to evaluate pressure detection sensitivity and its temperature dependence for diaphragm-type fiber optic combustion pressure sensors. Temperature-induced mechanical response variations and diaphragm optical reflectivity degradation, particularly at high temperatures, are identified as the two major factors that produce errors in sensitivity, and hence in pressure measurement. Experimental results using hermetically sealed sensor construction prove the feasibility of maintaining diaphragm optical reflectivity under high temperatures. This analysis predicts that simple temperature compensation could reduce temperature-induced errors in sensor output, and obtain desired pressure measurement accuracies. Engine tests performed with the present fiber optic sensors demonstrate good signal-to-noise performance and temperature stability.
This paper presents preliminary sensor designs and reports initial test results for the implementation of real-time simultaneous oxygen saturation and blood pressure measurement. Closed-lumen catheter-type in-vivo sensing schemes incorporate a proven, well-established distal-tipped fiberoptic pressure sensor. Spectroscopic oxygen saturation determination is multiplexed with pressure sensing in a shared transceiver approach, and oxygen saturation sensitivity may be enhanced via synchronous pressure detection. Operating principles for pressure and oxygen saturation measurement are described, and various catheter side-port oxygen saturation sensor designs are explored. Experimental methods and results are presented, and sensor sensitivity is examined.
KEYWORDS: Sensors, Fiber optics sensors, Combustion, Temperature metrology, Digital signal processing, Fiber optics, Environmental sensing, Head, Chemical elements, Optoelectronics
This paper describes a diaphragm-based, multi-wavelength fiber optic pressure sensor that is suitable for combustion monitoring and control applications. Through the simultaneous optical detection of sensor temperature and diaphragm deflection, temperature induced inaccuracies are significantly reduced. Design criteria for high temperature sensors are outlined and initial experimental results are presented.
Fiber optic sensors typically suffer from environmental effects that result in drift temperature sensitivity and bending induced inaccuracies. This paper describes a rugged fiber optic pressure sensor free of these inaccuracies and suitable for environmental and process control applications. A high degree of stability and accuracy is achieved through the use of wavelength referencing and in-situ calibration techniques. The critical issues for performance described in the paper are related to the opto-electronic interface the fiber link and the sensing element. Commercialization issues are also addressed.
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