Thermal Transducers Research Articles

Metrological support to computerized tests on aircraft gas-turbine engines under transient conditions

Metrological support to data-acquisition systems (DAS) is improtant in providing comparability in the measured characteristics of gas-turbine engines (GTE) during development, routine production, and operation. A basic problem in the dynamic calibration of a means of measurement is to reproduce the test signal. This can be illustrated for laser systems designed for the dynamic calibration of temperature and pressure-measurement channels, which are the most widely used in testing GTE. A laser system is described that enables one to determine the amplitude, phase, transient, and pulse characteristics of thermoanemometers, resistance thermometers, and thermoelectric thermometers, including thin-wire and thin-film components, with various gas flow speeds and temperatures. This apparatus can be used in calibrating thermal transducers at frequencies up to 200 kHz with a basic error of 0.5 dB. The gas speed range is 0-200 m/sec with a maximum gas temperature of 600 degrees K. Laser methods provide dynamic calibration for pressure channels in DAS. Dynamic calibration has been applied to pressure transducers by means of a pulsed laser. The light pulse is supplied to the sensing element and produces the dynamic equivalent of a pressure pulse.

Use of thermal transducers for measuring the molecular velocity distribution function

Use of thermal transducers for measuring the molecular velocity distribution function

An experimental test of acoustical reciprocity calibration applied to thermal transducers in superfluid helium

An experiment will be described which has verified an extension of the reciprocity calibration technique to reversible thermal transducers in superfluid helium. A plane‐wave resonator of circular cross section was capped at both ends by reversible teflon electret diaphrams which contained many razor slits to generate or detect thermal waves (second sound). The resonator also incorporated a thermophone and a dc biased carbon resistance thermometer to set independent upper and lower limits on the amplitude of the temperature oscillations within the resonator. The acoustical resonance data was acquired and analyzed by a computer controlled system described previously [D. V. Conte and S. L. Garrett, J. Acoust. Soc. Am. Suppl. 1 72, S82 (1982)]. The temperature excursions measured by the reciprocity method fell between the upper and lower limits which, for lower modes, were separated by only a few percent. At higher modes the lower limit departed from the upper limit due to the thermal inertia of the resistance thermometer. Temperature excursions smaller than 10−8 °K/[(Hz)1/2] were detectable using the electret transducers and a pre‐amplifier with a noise floor of 10−8 V/[(Hz)1/2]. [Work supported by the NPS Foundation Research Program.]

The use of a heat flux transducer for measuring non-evaporative heat exchange in man

Ten healthy males, 20-45 years of age, were subjected to measure the non-evaporative heat exchange by using thermal flux transducers at different ambient temperatures, atmospheric pressures, air velosities and body postures. Fifteen thermal flux transducers were mounted on each subject at the same points as Winslow's method (1936) proposed for calculating mean skin temperature. Non-evaporative heat exchange (Q) was computed from 15 heat flux measurements using the same weighting formula of Winslow. Evaporative heat loss (E) was estimated from body weight changes measured on a Potter bed scale. Metabolic heat production (M) was estimated indirectly from the oxygen consumption and carbon dioxide production. Mean body temperature was estimated from mean skin temperature calculated from 15 points and the esophageal temperature. In a wide variation of environmental conditions the summation of body heat storage during the experiment equaled that of the heat that reduced E and Q from M. However, the transducer seemed to overestimate the non-evaporative heat exchange of the body at high ambient temperatures where sweat rate was very high. The above results suggest that thermal flux transducer is a reliable tool in estimating non-evaporative heat exchange under a wide variation of environmental and physical conditions when used with great caution.

Measurement of the efficiency coefficient of a coaxial thermal transducer in a microcalorimeter at 18 GHz

Measurement of the efficiency coefficient of a coaxial thermal transducer in a microcalorimeter at 18 GHz

Evaluation of Large Carbon Composite Cones Using Thermal Transducer

A series of nondestructive tests utilizing a new thermal detector, known as a thermal transducer, has been conducted on a group of large carbon-carbon test cones. A description of the operating principles and special fixtures required to use the thermal transducer is provided. Results of thermal and other standard NDT methods are compared and recommendations regarding the capabilities of the thermal transducer are made.

Analysis of the thermal flowmeter operating from a pulsed-heat injection source

An analytical relation for the thermal flowmeter, operated in a closed- loop form, is derived in terms of increase in heat injection rate and mass flow rate over the laminar as well as turbulent flow ranges. It is pointed out in the analysis that a thermal flow transducer may be characterized by two easily measurable parameters. A description is given of the 1/4 in thermal flowmeter, operated from a small pulsed-heat source, which can measure water flow rates from 50 lb to h-1 to 1500 lb h-1. The analytical relation is verified against the output of this flowmeter and it is shown that the pulsed-heat source improves the flowmeter output characteristics compared with the DC heat source and provides a signal whose frequency depends upon the flow rate.

Light Scattering from Density Variations Excited inHe4by a Thermal Transducer

We have observed light scattering from the density variations in the first- and second-sound modes generated simultaneously by a thermal transducer in superfluid ${\mathrm{He}}^{4}$. Measurements of the temperature dependence of the density variations in both sound waves agree with the theoretical treatment by Lifshitz of the density-temperature coupling.

Use of contactless vacuum thermal transducers in pressure measurements

Investigations showed that the TVB-6 transducer can be used with standard measuring equipment (EPP-09, numerical voltmeters, etc.) in measuring absolute pressures of 1.33–1330 Pa. The relative mean square error of the transducer is 5%. Its service life is 100 h. The transducer, which is made commercially, is compact and cheap. However, it requires a highly stable feed current and its characteristic is nonlinear.

The technique of thermal measurements in excitable tissues.

The first recorded measurements of temperature changes in a muscle during contraction were made more than 120 years ago by means of a series of thermocouples connected to a galvanometer. The technique is the same today. In principle it is that of the adiabatic isoperibol calorimeter (Wadsö, 1970); heat generated by the system under study is shared with a thermal transducer, the electrical output of which is a measure of the consequent change of temperature and may be displayed by one of several devices. Most exponents in this field have to rely on home-produced assemblies and it is the intention of this article to consider the practical details of the separate components and, where possible, to discuss some of the various innovations which different workers have brought to the technique.

High speed thermal imaging transducer for practical ndt applications

High speed thermal imaging transducer for practical ndt applications

Investigation Into Manufacturing Errors On APlaner Machine

This paper presents an investigation into machining errors found on a CNC planer machine. Difficulty in achieving specified tolerances had been experienced on components requiring cutting of both sides. Out of tolerance components are either scrapped or reworked, increasing costs and reducing production efficiency and quality. Initially, thermal expansion was suspected as being the main cause of the errors. Tests were carried out using thermal imaging, temperature sensors and displacement transducers to provide a better understanding of the machines behaviour. The production process was also studied to identify areas for improvement. Based on the test results an improved set up and machining procedure was devised that would overcome the machine deficiencies, with probing and knowledge about the time variant errors being identified as key areas. These procedures have been implemented resulting in significant improvements in production efficiency and quality.

A thermal transducer for examining the field distribution in the cavity of an IR laser

A thermal transducer for examining the field distribution in the cavity of an IR laser

Thermal Surface Impedance for Plane Heat Waves in Layered Materials

Thermal surface impedance is defined as the ratio of temperature to heat flow for plane steady-state sinusoidal heat waves at the surface of a sample. The general analytical expression relating thermal surface impedance of a two-layer material to the thermal properties of the layers and the conductance of the joint between them is given. Computed values for the special cases of two layers in perfect contact and of a single layer are graphically presented. Experimental data supporting the graphic presentation were obtained with a novel thermal transducer method. The close theoretical relationship between the sinusoidal steady-state impedance and transient behavior is also briefly discussed.

Thermal transducer of the speed of flow

Thermal transducer of the speed of flow

Construction and Evaluation of a Miniature Net Radiometer

The miniature net radiometer was constructed by enclosing a blackened thermal transducer within four polystyrene radiation windows. The outer two radiation windows were hemispherically shaped (one-inch radius) so that the response to varying angles of incidence would follow the cosine law and precipitation runoff would be facilitated. The miniature net radiometer was calibrated in the laboratory in a chamber capable of simulating both solar and terrestrial radiation, and was found to be equally sensitive to both. The response to varying angles of incidence follows the cosine law. The output is not affected by wind or ambient temperature, and the size of the instrument enables its use to measure net radiation close to a surface or within a, plant canopy without appreciably altering the net radiation by shading.

Use of an Economical Thermal Transducer as a Net Radiometer 1

An instrument used to measure net radiation is described. A number of these instruments, because of their size and inexpensiveness, can be used within an experiment when connected to a single recorder by a switching mechanism.