Engineering topics
Publications and source records attributed to Edwards, S. F..
A continuous requirement exists for calibration and environmental testing of instruments in use at multitude of test facilities at Langley Research Center. Brief summarizes several automated systems available for calibration of research instruments to include: six-component balance, multimeter, amplifier, pyrometer, voltage-controlled oscillator, pressure transducer and accelerometer.
A modulated, infrared radiant energy source was developed to calibrate an airborne nadir-viewing pressure modulated radiometer to be used to detect from Earth orbit trace gases in the troposphere. The technique used an 8 cm long, 0.005 cm diameter platinum-iridium wire as an isothermal, thin line radiant energy source maintained at 1200 K. A + or - 20 K signal, oscillating at controllable frequencies from dc to 20 Hz, was superimposed on it. This periodic variation of the line source energy was used to verify the pressure modulated radiometer's capability to distinguish between the signal variations caused by the Earth's background surface and the signal from the atmospheric gases of interest.
Technique measures temperature/voltage drop characteristics of very thin filament. With constant current running through filament, voltage drop is recorded at various temperatures, as measured by calibrated thermocouple.
The design and performance of a calibration device that allows the measurement of a radiometer's field of view are described. The heart of the device is a heated 0.0254-mm (0.001-inch) diameter filament that provides a variable, isothermal line source of radiant energy against a cold background. By moving this discrete line source across the field of view of a radiometer, the radiometer's spatial response can be completely mapped. The use of a platinum filament provides a durable radiation source whose temperature is stable and repeatable to 10 K over the range of 600 to 1200 K. By varying the energy emitted by the filament, the field of view of radiometers with different sensitivities (or multiple channel radiometers) can be totally mapped.
The development of a radiometric technique for determining the spectral and total normal emittance of materials heated to temperatures of 800, 1100, and 1300 K by direct comparison with National Bureau of Standards (NBS) reference specimens is discussed. Emittances are measured over the spectral range of 1 to 15 microns and are statistically compared with NBS reference specimens. Results are included for NBS reference specimens, Rene 41, alundum, zirconia, AISI type 321 stainless steel, nickel 201, and a space-shuttle reusable surface insulation.
Measurements of spectral and total normal emittance have been made on three types of reusable external insulation materials proposed for space shuttles. Emittances were measured in the spectral range 1 to 15 micrometer at temperatures of 800 K and 1100 K using a radiometric measurement technique. Results indicated that the total normal emittance of these materials was less than 0.8 between 800 K and 1300 K. The total normal emittance decreased with increasing temperature. The three ceramic coating candidate materials exhibited a similar spectral emittance distribution.
A technique has been developed to dynamically calibrate fine wire thermocouples of 0.025 mm diam and smaller to 1625 K in less than 10 sec. In this method, the varying physical parameters present under typical dynamic heating conditions are simulated, and therefore, wire deterioration can be related to time, temperature, pressure, and atmosphere. A description of the equipment and procedures is given along with the preliminary results that correlate well with thermoelectric theory.