Measuring and testing – Volume or rate of flow – Proportional
Patent
1998-04-27
2000-03-14
Williams, Hezron
Measuring and testing
Volume or rate of flow
Proportional
7320423, G01F 168
Patent
active
060357118
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a device for determining direction and speed of an air flow, comprising a chip which is provided with two mutually perpendicularly positioned pairs of measuring circuits placed at a distance opposite each other, four heating elements in positions coinciding with the measuring circuits and a control circuit, which chip is fixed onto a substrate.
Such a chip is known for instance from the European patent 0 313 120 in which is described a direction-sensitive flow speed indicator for gaseous or liquid media which contains a semiconductor substrate on which two thermocouples are arranged for each direction component. The thermocouples take the form of a thermopile and lie parallel to each other while the surface between the thermocouples can be used to arrange one or more heating elements and an electronic circuiting for processing the output signals of the thermocouples. The chip is mounted on a substrate along which the air flow is guided. The substrate is heated by means of the heating elements, preferably so-called heating rheostats. Due to the air flowing over the substrate a temperature gradient builds up over the substrate, wherein the lowest temperature occurs where the air flow first makes contact with the substrate while the highest temperature occurs where the air flow leaves the substrate. The gradient is measured by means of the thermocouples and the progress of the gradient is a measure for the flow speed. Because the chip preferably contains four thermocouples placed in a square, the direction of the air flow can also be determined with the same arrangement.
Such a chip is preferably accommodated in a housing, as described for instance in the European patent 0 402 977. This patent describes a device for measuring a speed and direction of a flowing medium which consists of a axis which supports a construction of an upper and a lower, substantially identical circular discs, which discs are fixed at a determined mutual distance perpendicularly of a collective axis. A directionsensitive thermal velocity meter (for instance the chip as described above) is placed on a third disc with a diameter smaller than that of both the other discs, between which the third disc is arranged. The chip faces toward the upper of the two discs.
A number of problems occur with the known device. It is for instance not always possible to obtain an homogeneous temperature distribution in the substrate. Variations can result in disturbances of the gradient and thereby measurement errors. In addition, the temperature fluctuations in the substrate can cause hysteresis in the material surrounding the substrate. Furthermore, ambient factors such as a high outside temperature can affect the measurement values.
The present invention has for its object to provide a device for determining the direction and speed of an air flow which is improved relative to the known devices.
To this end the invention provides a device for determining the direction and speed of an air flow, comprising a chip which is provided with two mutually perpendicularly positioned pairs of measuring circuits placed at a distance opposite each other, one or more preferably four heating elements in positions coinciding with the measuring circuits and a control circuit, which chip is fixed onto a substrate, wherein the mounting between chip and substrate is substantially homogeneous. The homogeneous mounting ensures that the heat which is generated onto the chip by the heating elements is transferred uniformly and homogeneously to the substrate. The substrate is hereby also heated homogeneously and uniformly and a reliable measurement can be performed.
The mounting between the chip and the substrate is preferably effected by gluing. Gluing takes place in a manner such that no air bubbles and other unevenness which could disturb an homogeneous mounting are enclosed. An air bubble does not permit good heat transfer. An air bubble could occur round an unevenness.
The substrate with the chip thereon is preferably accommodated in a hous
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Patent Abstracts of Japan, vol. 12, No. 319 JP, A 63 085364 (Sharp Corp.) Apr. 15, 1988.
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Hagedoorn Arend
Huijsing Johan Hendrik
Van Oudheusden Bastiaan Willem
Verhoeven Huibert Jan
Kwok Helen C.
Mierij Meteo B.V.
Williams Hezron
Zovko Mark
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