Showing papers on "Junction temperature published in 1977"

Thermocouple temperature measurement circuit having cold junction compensation

Abstract: A thermocouple temperature measuring circuit has input terminals connectable to the thermocouple to form the cold junctions of the thermocouple. An input amplifier amplifies the thermocouple signal. A cold junction temperature compensation circuit includes means for sensing the temperature of the cold junctions and for providing an output signal which exhibits a predetermined coefficient between cold junction temperature and output signal magnitude. The output signals of the amplifier and compensation circuit are summed at a summing junction and provided to an output amplifier for supply to a temperature indicating meter. A bias means is also coupled to the summing junction for providing a bias suitable for adjusting the magnitude of the output signal in accordance with the low temperature to be indicated on the meter. The gain of the output amplifier may be adjusted so that the variation in output signal responsive to hot junction temperatures is sufficient to drive the meter through the temperature range displayed on the meter.

Filamentary thermal instabilities in IMPATT diodes

Abstract: The unstable growth of thermal filaments in a diode with a fixed bias current is calculated on the basis of a model which includes thermal conduction in the plane of the junction, as well as perpendicular to it. The growth time of the instability is shown to be longer than the thermal relaxation time by the ratio of the space-charge resistance to the differential negative resistance. Analytic results are obtained for small temperature disturbances which are initially Guassian functions of the transverse coordinate. If A is the area of the junction, the negative differential resistance must be of the order of the space-charge resistance multiplied by 16W2/π2A (where W is the thickness of the active region) or the filament can dissipate itself by diffusing outward and spreading over the entire junction area before the temperature rise becomes very large. The voltage fluctuation relaxes to its equilibrium value in the thermal relaxation time, which is independent of the differential resistance. Pulsing a diode will tend to prevent an instability from becoming destructive, provided the off-time is long enough to cool the heated filaments which develop during the pulse transmission.

Temperature change detector

Abstract: A temperature change detector comprising a heat sensitive semiconductor switching device (heat sensitive thyristor) and which switches when a temperature of an element whose temperature is to be detected is changed by a specific value with respect to the ambient temperature. A variable impedance element such as a thermistor or a diode whose resistance is varied depending upon the ambient temperature is connected between the P gate terminal and the cathode terminal of the heat sensitive thyristor which is thermally coupled to the element whose temperature is to be detected, whereby the effect of the ambient temperature on the switching temperature characteristic of the heat sensitive thyristor is compensated.

High Temperature Thermal Characteristics of Microelectronic Packages

Abstract: This paper describes results of the computer-analysis pottion of a research program which was conducted to study the thermal characteristics of microcircuits in high temperature environments. A special IC chip, bonded to an alumina chip carrier, was modeled for these simulations. It was found that thermal resistance values and thermal time constants nearly double when the chip carrier temperature is increased from 70 to 257°C. For a chip power dissipation of 1.5 W, the peak junction temperature increased from 138 to 385°C, an increase of 247°C, while the chip carrier only increased by 187°C. The thermal time constant of the junction peak temperature rise, measured relative to the chip carrier, increased from 15 to 26 µs over the same temperature range.

Experimental Investigation of Multilayer Insulation With Room Temperature Outside and Liquid Helium Temperature Inside

Abstract: Experiments on multilayer insulation were conducted with the conditions of room temperature outside and liquid helium temperature (4.2K) inside. By varying the total number of radiation shields, heat trans fer rate and transverse layer-by-layer temperature distribution were measured. Experimental data with liquid nitrogen (77K) were also ob tained and the difference in heat transfer rate between from room tempera ture to liquid helium temperature and from room temperature to liquid nitrogen temperature was demonstrated.Prior to the experiment, preliminary consideration was made as to the determination of each radiation shield temperature in multi-shield system. A single parameter A, which represents the conductive to radiative heat transfer ratio, was introduced, and it is shown that in the case of constant emissivity, the temperature distribution may be computed with the simple method introduced in this investigation. From the temperature distribution thus obtained, it is possible to calculate the total ...

Thermal Resistance of Microelectronic Packages

Abstract: : Computer simulation, IR and electrical temperature measurements were compared and evaluated for special thermal test packages. The junction size was varied and elevated chip-carrier temperatures were studied to determine their effects on the thermal characteristics. In addition a comparison of the film- carrier chip interconnection technique versus wire-bonding techniques was made. In general, the data showed that thermal resistnace increased significantly with elevated temperatures and with decreasing junction size. Thermal time constants increased with elevated temperature and increasing junction size. Little difference was found between the film carrier and wire-bond interconnection techniques when the chip is bonded to a chip-carrier, but the film carrier is significantly better if the chip is heat sunk only through its leads.

Minimization of temperature distortion in thermocouple cavities

Abstract: Introduction A DIRECT measurement of transient surface temperature and heat flux is often difficult. For example, a surface involves two modes of heat transfer, say radiative and convective heat transfer. In this case, if the measuring probe has a different radiative property from that of the surface, erroneous measurements will result. Therefore, indirect estimation by inverting the temperature history inside the heat conducting solid as measured by a thermocouple is often used for prediction of the surface temperature and heat flux. Beck, Herring and Parker, Frank, Imber and Khan, Stolz, and Chen and Thomsen have developed inversion solutions for this purpose. Since all of these solutions assumed that the cavity drilled into the solid does not distort the true temperature distribution, it is, therefore, important that the temperature measurement by an interior probe be accurate and involve little distortion or error. From studies made by Chen and Li and Beck, it was found that with a proper combination of the thermocouple cavity diameter, cavity depth, and the thermocouple material, the magnitude of the distortion of the temperature field with respect to space or time can be minimized. In this Note we study the optimum combination of geometrical parameters and material properties to eliminate the temperature distortion.