Temperature-sensing Elements Research Articles

Methods for monitoring scour from large-diameter heat probe tests

Scour is the main cause of bridge failures. Monitoring of bridge scour is an essential method to control the damages caused by flood events. In this study, a large-scale tube consisting of heating and temperature-sensing elements was developed, and its application for detecting saturated soil and water was analyzed. Laboratory experiments confirmed the applicability of the thermal sensor for scour-monitoring purposes. Three methods are proposed in this article for analyzing the data obtained from a heat probe. A linear relationship between temperature increase from the initial to the secondary time and heat production in the probe was observed, and a line that can be used to determine scour was introduced. This method is simple and can be used for low-cost, large-diameter heat probes that are easy to fabricate.

A Modular Heat-Sensing Domain Activates K2P2.1 through a Heat-Insensitive Gate

Ion channels often have modular structure with dedicated gating and sensory domains. Ligand binding to a localized site in the sensory domain usually affects channel function through allosteric effects on the gate. It is not clear whether this paradigm is applicable to ion channels regulated by temperature. Indeed, temperature may have an effect on the whole channel structure and thus, bypass the need for a dedicated heat-sensing domain. Heat leads to activation of the ‘leak’ two-pore (K2P) potassium channel K2P2.1 (KCNK2/TREK-1) through opening of a selectivity filter-based outer gate in the extracellular pore domain. We sought to investigate whether the pore plays a role in sensing heat or whether it only functions as a gate that responds to the commands from the temperature-sensing elements located elsewhere in the channel. We found that the incorporation of mutations designed to prevent allosteric communication between the intracellular C-terminal domain and the pore domain of K2P2.1 resulted in channels that remain functional but fail to respond to temperature. These results indicate that the gating mechanism of the pore lacks intrinsic temperature sensitivity and that the heat-sensing elements of K2P2.1 are confined within its C-terminus. Our data provide experimental support for the general notion of the existence of modular temperature sensing domains and highlight functional distinction between gating and sensory elements in heat-sensitive ion channels.

Diode-based microfabricated hot-plate sensor

In recent years, different types of microfabricated silicon ‘hot plates’ have been used as substrates for a variety of gas sensors and in some cases as gas thermal conductivity probes. The temperature-sensing elements in all reported devices have been resistors with varying types of thermal coefficients of resistance. The major difficulty with this approach is the reproducibility of the temperature coefficient of resistance from batch to batch. It is well known that the forward-biased voltage of a constant-current diode is directly proportional to the absolute temperature. While the constant of proportionality depends on the fabrication process, this parameter tends to be reproducible and easily controlled. Utilizing the characteristics of a forward-biased diode also eliminates the need to use materials such as platinum, which is both expensive and catalytic, as the resistive element. In this paper we report on the design and construction of a microfabricated silicon ‘hot plate’ that employs a diode-based temperature-measurement system. The noise level of the measurement corresponds to a temperature difference in the 100 μK range in the vicinity of room temperature. The simplicity and utility of the structure described herein makes it an attractive element for various types of thermal measurements, particularly of the thermal conductivity of pure and mixed gases.

Novel Column Heater for Fast Capillary Gas Chromatography

In this paper, we present two designs for the implementation of extremely fast temperature programming of gas chromatographic columns. Both designs incorporate heating and temperaturesensing elements placed along the column. Resistive heating controls the column temperature via a feedback circuit and a software-selected temperature program. Linear temperature increases up to 10°C/s are obtained. The performance of each design is evaluated for applications to volatile and semi-volatile hydrocarbons. Retention times deviate only slightly in comparison with a standard commercial instrument, and peak widths increase for compounds beyond C 13 . The proposed column heater designs have satisfactory retention time reproducibility. They are lightweight and consume little power, making them promising alternatives for fast portable gas chromatography.

Temperature dependences of fluorescence lifetimes in Cr3+-doped insulating crystals.

The temperature dependences of the fluorescence lifetimes of ${\mathrm{Cr}}^{3+}$ doped insulating crystals, which have been used as temperature-sensing elements or have such potential uses for different temperature regions, are reviewed in terms of the crystal-field strength. Two single configurational coordinate models are proposed to interpret the temperature dependence of ${\mathrm{Cr}}^{3+}$ fluorescence in materials with low and high crystal-field strength. The validities of the two models are demonstrated by their close fit to the lifetime data of the ${\mathrm{Cr}}^{3+}$ fluorescence in appropriate materials. As was shown in thermometric applications, the expressions obtained for the temperature dependence of the fluorescence lifetimes, deduced from the proposed models, are of use as empirical calibration formulae in the assessment of various ${\mathrm{Cr}}^{3+}$ fluorescence lifetime-based thermometers.

Locating method for temperature-sensing elements inserted in solid bodies

Locating method for temperature-sensing elements inserted in solid bodies

Comparative thermal performances of various substrate materials in a simple packaging application: actual versus predicted

A finite element study on the thermal performance of several substrate materials in a simple package application was carried out by D.P Button et al. (Proc. Int. Symp. on Ceramic Substrates and Packages, 1989). Materials examined were aluminium nitride, alumina, epoxy-glass, refractory-glass, and a composite consisting of alumina fibers in a polyimide matrix. Three cooling approaches were addressed: natural convection, forced convection, and a heat sink placed on the substrate face opposite the chip. In the present work, experiments to confirm these model predictions are described. Actual packages were prepared, closely resembling those addressed in the previous study. Thermal Test Chips manufactured by Texas Instruments Inc., were used to make the measurements. These chips are designed for this purpose, containing both resistive heating elements and temperature-sensing elements. The test packages of each material were successively placed in natural convection, forced convection, and heat sink environments, and their respective performances were monitored. The results closely support the conclusions of the earlier model study, although numeric differences are noted. >

Responses of Temperature-Sensing-Element Analogs

Abstract From the standpoint of stability, temperature-sensing elements used in control systems should not contribute much phase lag at the frequency where the open-loop phase lag is 180 deg. For those cases where the temperature-sensing element does not contribute appreciable (less than 30 deg) phase lag around 180 deg, it would be advantageous to have a low-frequency approximation which works for complicated thermal systems. This paper presents such an approximation and establishes its validity for the electrical analogs of many sensing elements. In addition, it shows how the approximation is related to the thermal lag measured during a ramp input and the 63 per cent response time. These results, which are obtained in terms of transfer functions, can be applied to other systems having the same analogs.

Response characteristics of temperature-sensing elements for use in the control of jet engines

The rate at which a temperature-sensing element located in the gas stream of a jet engine responds to sudden changes in temperature is of great practical importance in the control and operation of such an engine. The factors that determine rate of response are discussed, and the significance of the characteristic time is emphasized. It is shown that laboratory determinations of characteristic time must be made under simulated engine conditions in which the rate of heat transfer by forced convection is the controlling factor. Apparatus used at the National Bureau of Standards for measuring characteristic times is described, and typical results are presented. The rate of response of a device in a jet engine varies greatly with engine speed and with the altitude of flight, so that satisfactory performance of a temperature-actuated control system can be expected only if the sensing element responds with sufficient rapidity under starting conditions and at the flight ceiling.