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  • 1
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    The constant current loop - A new paradigm for resistance signal conditioning (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A practical single constant current loop circuit for the signal conditioning of variable-resistance transducers has been synthesized, analyzed, and demonstrated. The strain gage and the resistance temperature device are examples of variable-resistance sensors. Lead wires connect variable-resistance sensors to remotely located signal-conditioning hardware. The presence of lead wires in the conventional Wheatstone bridge signal-conditioning circuit introduces undesired effects that reduce the quality of the data from the remote sensors. A practical approach is presented for suppressing essentially all lead wire resistance effects while indicating only the change in resistance value. An adaptation of the current loop circuit is presented that simultaneously provides an output signal voltage directly proportional to transducer resistance change and provides temperature information that is unaffected by transducer and lead wire resistance variations.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: International Instrumentation Symposium, 39th, Albuquerque, NM, May 2-6, 1993, Proceedings (A93-54351 24-35); p. 465-479.
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  • 2
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    Constant current loop impedance measuring system that is immune to the effects of parasitic impedances (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A constant current loop measuring system is provided for measuring a characteristic of an environment. The system comprises a first impedance positionable in the environment, a second impedance coupled in series with said first impedance and a parasitic impedance electrically coupled to the first and second impedances. A current generating device, electrically coupled in series with the first and second impedances, provides a constant current through the first and second impedances to produce first and second voltages across the first and second impedances, respectively, and a parasitic voltage across the parasitic impedance. A high impedance voltage measuring device measures a voltage difference between the first and second voltages independent of the parasitic voltage to produce a characteristic voltage representative of the characteristic of the environment.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Format: application/pdf
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  • 3
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    Current loop signal conditioning: Practical applications (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper describes a variety of practical application circuits based on the current loop signal conditioning paradigm. Equations defining the circuit response are also provided. The constant current loop is a fundamental signal conditioning circuit concept that can be implemented in a variety of configurations for resistance-based transducers, such as strain gages and resistance temperature detectors. The circuit features signal conditioning outputs which are unaffected by extremely large variations in lead wire resistance, direct current frequency response, and inherent linearity with respect to resistance change. Sensitivity of this circuit is double that of a Wheatstone bridge circuit. Electrical output is zero for resistance change equals zero. The same excitation and output sense wires can serve multiple transducers. More application arrangements are possible with constant current loop signal conditioning than with the Wheatstone bridge.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-TM-4636 , H-2026 , NAS 1.15:4636 , 1995 Measurement Science Conference; Jan 26, 1995 - Jan 27, 1995; Anaheim, CA; United States
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  • 4
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    Enthalpy By Energy Balance for Aerodynamic Heating Facility at NASA Ames Research Center Arc Jet Complex (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The NASA Ames Research Center (ARC) Arc Jet Facilities' Aerodynamic Heating Facility (AHF) has been instrumented for the Enthalpy By Energy Balance (EB2) method. Diagnostic EB2 data is routinely taken for all AHF runs. This paper provides an overview of the EB2 method implemented in the AHF. The chief advantage of the AHF implementation over earlier versions is the non-intrusiveness of the instruments used. For example, to measure the change in cooling water temperature, thin film 1000 ohm Resistance Temperature Detectors (RTDs) are used with an Anderson Current Loop (ACL) as the signal conditioner. The ACL with 1000 ohm RTDs allows for very sensitive measurement of the increase in temperature (Delta T) of the cooling water to the arc heater, which is a critical element of the EB2 method. Cooling water flow rates are measured with non-intrusive ultrasonic flow meters.
    Keywords: Meteorology and Climatology
    Type: 48th International Instrumentation Symposium; May 05, 2002 - May 09, 2002; San Diego, CA; United States
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  • 5
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    A Conversion of Wheatstone Bridge to Current-Loop Signal Conditioning for Strain Gages (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Current loop circuitry replaced Wheatstone bridge circuitry to signal-condition strain gage transducers in more than 350 data channels for two different test programs at NASA Dryden Flight Research Center. The uncorrected test data from current loop circuitry had a lower noise level than data from comparable Wheatstone bridge circuitry, were linear with respect to gage-resistance change, and were uninfluenced by varying lead-wire resistance. The current loop channels were easier for the technicians to set up, verify, and operate than equivalent Wheatstone bridge channels. Design choices and circuit details are presented in this paper in addition to operational experience.
    Keywords: Electronics and Electrical Engineering
    Type: NASA-TM-104309 , H-2049 , NAS 1.15:104309 , Strain Gage; Feb 07, 1995 - Feb 08, 1995; El Segundo, CA; United States
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  • 6
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    Thermal-structural test facilities at NASA Dryden (1992)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The National Aero-Space Plane (NASP) has renewed interest in hypersonic flight and hot-structures technology development for both the airframe and engine. The NASA Dryden Thermostructures Research Facility is a unique national facility that was designed to conduct thermal-mechanical tests on aircraft and aircraft components by simulating the flight thermal environment in the laboratory. The layout of the facility is presented, which includes descriptions of the high-bay test area, the instrumentation laboratories, the mechanical loading systems, and the state-of-the-art closed-loop thermal control system. The hot-structures test capability of the facility is emphasized by the Mach-3 thermal simulation conducted on the YF-12 airplane. The Liquid-Hydrogen Structural Test Facility, which is presently in the design phase, will provide the capability of thermally testing structures containing hydrogen.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-TM-104249 , H-1818 , NAS 1.15:104249 , Annual Society for Flight Test Engineers Symposium; Aug 03, 1992 - Aug 06, 1992; Hauppauge, NY; United States
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  • 7
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    DACS II - A distributed thermal/mechanical loads data acquisition and control system (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A distributed data acquisition and control system has been developed for the NASA Flight Loads Research Facility. The DACS II system is composed of seven computer systems and four array processors configured as a main computer system, three satellite computer systems, and 13 analog input/output systems interconnected through three independent data networks. Up to three independent heating and loading tests can be run concurrently on different test articles or the entire system can be used on a single large test such as a full scale hypersonic aircraft. Thermal tests can include up to 512 independent adaptive closed loop control channels. The control system can apply up to 20 MW of heating to a test specimen while simultaneously applying independent mechanical loads. Each thermal control loop is capable of heating a structure at rates of up to 150 F per second over a temperature range of -300 to +2500 F. Up to 64 independent mechanical load profiles can be commanded along with thermal control. Up to 1280 analog inputs monitor temperature, load, displacement and strain on the test specimens with real time data displayed on up to 15 terminals as color plots and tabular data displays. System setup and operation is accomplished with interactive menu-driver displays with extensive facilities to assist the users in all phases of system operation.
    Keywords: RESEARCH AND SUPPORT FACILITIES (AIR)
    Type: ITC/USA/''87; Oct 26, 1987 - Oct 29, 1987; San Diego, CA; United States
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  • 8
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    The constant current loop: A new paradigm for resistance signal conditioning (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A practical, single, constant-current loop circuit for the signal conditioning of variable-resistance transducers was synthesized, analyzed, and demonstrated. The strain gage and the resistance temperature device are examples of variable-resistance sensors. Lead wires connect variable-resistance sensors to remotely located signal-conditioning hardware. The presence of lead wires in the conventional Wheatstone bridge signal-conditioning circuit introduces undesired effects that reduce the quality of the data from the remote sensors. A practical approach is presented for suppressing essentially all lead wire resistance effects while indicating only the change in resistance value. Theoretical predictions supported by laboratory testing confirm the following features of the approach: (1) the dc response; (2) the electrical output is unaffected by extremely large variations in the resistance of any or all lead wires; (3) the electrical output remains zero for no change in gage resistance; (4) the electrical output is inherently linear with respect to gage resistance change; (5) the sensitivity is double that of a Wheatstone bridge circuit; and (6) the same excitation and sense wires can serve multiple independent gages. An adaptation of the current loop circuit is presented that simultaneously provides an output signal voltage directly proportional to transducer resistance change and provides temperature information that is unaffected by transducer and lead wire resistance variations. These innovations are the subject of NASA patent applications.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TM-108744 , NAS 1.15:108744 , Instrument Society of America 39th International Instrumentation Symposium; May 03, 1993 - May 06, 1993; Albuquerque, NM; United States
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  • 9
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    Radar-Data-Processing System (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Report describes radar data system at NASA Western Aeronautical Test Range. System provides real-time and recorded data about flightpaths of research aircraft and Space Shuttle. Called RADATS, processes data from three radars simultaneously; interacts with system operator; enhances data by introducing corrections and smoothing; controls range, azimuth, and elevation of radars; and automatically calibrates itself before and after missions. Software classified into three kinds of programs: utility, real-time, and calibration. Equipment exhibited exceptional reliability. Software matured to become virtually trouble-free.
    Keywords: ELECTRONIC SYSTEMS
    Type: ARC-11782 , NASA Tech Briefs (ISSN 0145-319X); 12; 11; P. 39
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  • 10
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    The Anderson Current Loop (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Four-wire-probe concept applied to electrical-resistance transducers. Anderson current loop is excitation-and-signal-conditioning circuit suitable for use with strain gauges, resistance thermometers, and other electrical-resistance transducers mounted in harsh environments. Used as alternative to Wheatstone bridge. Simplifies signal-conditioning problem, enabling precise measurement of small changes in resistance of transducer. Eliminates some uncertainties in Wheatstone-bridge resistance-change measurements in flight research. Current loop configuration makes effects of lead-wire and contact resistances insignificantly small. Also provides output voltage that varies linearly with change in gauge resistance, and does so at double sensitivity of Wheatstone bridge.
    Keywords: ELECTRONIC COMPONENTS AND CIRCUITS
    Type: DRC-00001 , NASA Tech Briefs (ISSN 0145-319X); 18; 12; P. 30
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