Thermal measuring and testing – Heat flux measurement
Reexamination Certificate
2000-02-18
2002-10-29
Gutierrez, Diego (Department: 2859)
Thermal measuring and testing
Heat flux measurement
C374S142000, C073S204220
Reexamination Certificate
active
06471395
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a heat transfer monitoring and/or measuring device, especially a flow indicator or a flow meter for media flowing through a pipe, a tank or a fitting, with a sensor housing and with at least one sensor element, the sensor element having a metallic sensor surface which comes into contact with the flowing medium. In particular, the invention relates to a heat transfer monitoring and/or measuring device of the type known from U.S. Pat. No. 5,848,094.
2. Field of the Invention
As has been stated above, the heat transfer monitoring and/or measuring device under consideration is intended for media flowing through a pipe, a tank or a fitting, but this is only a sample enumeration. It is simply a matter of a flowing medium being present. The medium under consideration can flow also, for example, through an open trough instead of a tube and in particular, a valve or slide can be used as the fitting.
It is important to the heat transfer monitoring and/or measuring device that, in any case, the sensor surface of the sensor element comes into contact with the flowing medium. This is of course accomplished when the heat transfer monitoring and/or measuring device is located entirely within the pipe, the tank or the fitting. Generally, a heat transfer monitoring and/or measuring device of the type under consideration is, however, installed in a pipe, tank or fitting such that it projects only partially into the pipe, tank or fitting. Often this is done by the heat transfer monitoring and/or measuring device having an outside thread and being screwed with its outside thread onto a corresponding inner thread of the pipe, tank, or fitting. However, there are also installation situations which are characterized by only the sensor element, only a part of the sensor element or only the metallic sensor surface of the sensor element projecting into the pipe, tank or fitting. In the extreme case, it can be sufficient for the metallic sensor surface of the sensor element within the pipe, tank or fitting to end flush with the pipe, tank or fitting.
It was stated at the start that the invention relates to a heat transfer monitoring and/or heat transfer measuring device. The heat transfer monitoring device stands for an embodiment in which heat transfer is simply monitored, in which therefore only the presence or absence of a certain heat transfer is ascertained. Conversely, the heat transfer measuring device stands for an embodiment in which heat transfer is measured; therefore an analog measured value which corresponds to the heat transfer is obtained which can also be converted into a digitized measured value. In other words, a heat transfer monitoring device yields a qualitative statement “heat transfer present above a given threshold” or “heat transfer absent above a given threshold,” while a heat transfer measuring device delivers a quantitative statement with respect to heat transfer.
Heat transfer monitoring or measuring devices of the type which are under consideration here and which were addressed differently above are used especially for acquiring heat transport by flowing media. They are then flow indicators or flow meters, in the sense of the aforementioned differentiation, the flow indicator corresponding to the heat transfer monitoring device and the flow meter corresponding to the heat transfer measuring device.
Generic heat transfer monitoring or measuring devices and flow indicators or flow meters often work according to the calorimetric principle. Generally, temperature difference measurement is used. A first temperature measurement element measures the actual measurement temperature, the measurement temperature resulting from the heat output of a heating element, the temperature of the flowing medium and the flow-dependent heat transport capacity of the flowing medium. Furthermore, generally a second temperature measurement element measures a reference temperature. For the teaching of the invention, the measurement of the reference temperature is not absolutely necessary; it can be omitted, for example, when the temperature of the flowing medium is known.
A heat transfer monitoring or measuring device or a flow indicator or flow meter can include a heating element and at least one temperature measuring element, as explained above. Here, the heating element can also assume the function of the temperature measurement element or the function of the above explained second temperature measurement element; it is then a heating and temperature measurement element.
For the purposes of the present invention, it is irrelevant whether one heating element or one temperature measurement element or whether one heating element and two temperature measurement elements or whether one heating and temperature measurement element is or are utilized. All that is important is, as stated initially, that there is at least one sensor element which can be a heating element, a temperature measurement element or a heating and temperature measurement element; in addition there can also be a second sensor element, under certain circumstances even a third sensor element.
In the prior art, heat transfer monitoring and/or measuring devices, especially flow indicators and/or flow meters of the initially desired type are extensively known, especially those which work using the calorimetric principle. In particular, heat transfer monitoring and/or measuring devices of the initially mentioned type are known in which sensor elements are built in a special manner. Thus, an embodiment is known (U.S. Pat. No. 5,848,094) in which two sensor elements, specifically a heating element and a temperature measurement element, are integrated into a sensor part of the sensor housing which comes into contact with the flowing medium without projecting significantly into the flowing medium, and the parts which are integrated into the sensor part of the sensor housing are made pin-shaped. An embodiment is also known (published German Patent Application 197 19 010) in which the sensor elements—a heating element and a temperature measurement element -are made pin-shaped and project out of the sensor housing.
In the heat transfer monitoring and/or measuring devices under consideration, the sensor housing is normally made heat-insulating, for example, from plastic, while the sensor element or sensor elements are made to have good thermal conductivity, specifically, are made of material with good thermal conductivity, for example, copper or silver. Coating the sensor elements is also known, for example, coating sensor elements made of copper with nickel, silver or gold, or coating sensor elements made of silver with gold. These coatings are exceedingly thin, for cost reasons, and thus, generally are not free of pores. Thus, a material is often chosen for the coating which is chemically more inert than the material of the sensor element otherwise is.
One problem is common to the known heat transfer monitoring and/or measuring devices, with respect to the sensor element, i.e., that disruptive layers are deposited or form on the often very small sensor surfaces which come into contact with the flowing medium and lead to the properties of these heat transfer monitoring and/or measuring devices, especially sensitivity, changing over time, generally degrading.
In the prior art, attempts have been made to meet the problem of deposition or formation of fault layers on the metallic sensor surfaces of the sensor elements which come into contact with the flowing medium, by mechanical or chemical cleaning. However, on the one hand, this is complex, and on the other hand, it cannot lead to the properties, especially sensitivity, remaining stable over time.
SUMMARY OF THE INVENTION
In view of the foregoing, a primary object of the present invention is to effect a solution of the problem of the “deposition or formation of disruptive layers” which is superior to that of the prior art.
The heat transfer monitoring and/or measuring device (hereafter, the shortened term “monitoring
Buhl Peter
Reichart Walter
De Jesús Lydia M.
ifm electronic GmbH
Nixon & Peabody LLP
Safran David S.
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