DIRECTION-SENSITIVE FLOW-RATE INDICATOR

Abstract: Direction-sensitive flow-rate indicator for gaseous or liquid media. It comprises a semi-conductor substrate on which for each dimensional direction at least one thermocouple is arranged, in which the connecting-leads of the ends of each thermocouple extend in the direction-of-flow component of the medium and are, at least about, perpendicular to each other. It also comprises a heating-element for generating a flow-rate dependent temperature-difference in the flowing medium in the longitudinal direction of the said thermocouples, which results in a flow-rate dependent thermo-voltage between the ends of the thermocouples.

Description: The invention relates to a direction-sensitive flow-rate indicator for gaseous or liquid media which comprises a semiconductor substrate on which at least one first thermocouple, in which the connecting-line of the ends of the said one or each thermocouple extends in the direction-of-flow component of the medium, and a heating-element for generating a flow-rate dependent temperature-difference in the flowing medium in the longitudinal direction of the said thermocouple(s) which results in a flow-rate dependent thermo-voltage between the ends of the said one or each thermocouple. Such a direction-sensitive flow-rate indicator is known from the U.S. Patent Specification No. 4.373.386. In this specification, the thermocouple comprises two conducting strips which are connected to one end of two parallel running strips which are insulated from one another and one of which strips is a P-type semiconductor and the other of which strips is an N-type semiconductor and in which both said semiconductor strips are connected at their other end by a metal layer therebetween. Heating-elements are arranged on each side of these strips and radiate the heat generated thereby to the medium flowing, over the thermocouple. Through this there arises a temperature difference between both ends of the semi-conductor strips and therefore the voltage-changes between the semi-conductor strips and the metal layer and metal strips respectively are different so that a thermovoltage arises between the metal strips dependent on the rate-of-flow of the medium. Due to the passive nature of the thermocouple, the voltage is always zero when the temperatures of the ends are the same, that is to say no ′offsetting′ can occur. In order to measure the rate-of-flow in a direction different from the thermocouple's longitudinal direction, two separate substrates are used. According to the invention at least one thermocouple is provided for each dimension in a two-dimensional embodiment of the invention and the lines connecting the ends of the one or each thermocouple are arranged perpendicular alongside each other. The advantage of this arrangement is that only one substrate is needed and thus the design is very simple. In addition hereto, the application of conducting-paths for connecting the thermocouples is made considerably easier since they are now located on a single substrate. The thermocouple between the two ends can be of an arbitrary form, as the thermocouple output-voltage will only be determined by the temperature difference between these ends, provided that the temperature-difference between the ends at a zero rate-of-flow is also equal to zero. It is also possible to arrange each of the thermocouples along one of two perpendicularly lying edges of a preferably square substrate. In a first embodiment of the direction-sensitive flow-rate indicator according to the invention at least one thermocouple is provided in which indicator the one or each the thermocouple comprises two parts which extend in prolongation to one another and which can be connected in series, and in which for both dimensions, like thermo- couples are arranged on the substrate in a cruciform manner. This provides a two-sided symmetrical arrangement with like properties for both rate-of-flow components. In an alternative embodiment of the direction-sensitive flow-rate indicator according to the invention, two preferably alike thermocouples are provided for each dimension and each of which thermocouples extend parallel to one another and can be connected in series such that they form an enclosed rectangle therebetween. The advantage of this arrangement is that a double-sidedly symmetrical arrangement is obtained with like properties for both rate-of-flow components with one large area free for applying the conducting-paths and other components. In a third embodiment of the direction-sensitive flow-rate indicator according to the invention, at least two heating-elements are enclosed in the quadrants formed by cruciformly arranged thermocouples. In a fourth embodiment of the direction-sensitive flow-rate indicator according to the invention, at least one heating-element is arranged within the rectangle. As a result hereof, the symmetry of both rate-of-flow components is still further improved and component connection still even simpler. In a fifth embodiment of the direction-sensitive flow-rate indicator according to the invention each thermocouple is in the form of a thermo-pile each comprising a number of series-connected thermocouples the output-signal from which is an equal number of times higher and thus the sensitivity of the indicator also. The invention will now be further described with reference to the accompanying figures in which: Fig. 1 is a semiconductor substrate with cruciformly arranged thermocouples thereon; Fig.2 is a semiconductor substrate with thermocouples forming the sides of a rectangle thereon and Fig.3 shows the construction of a thermo-pile. Figure 1 shows two parts 42 and 43 of a thermocouple arranged in prolongation with one another on semiconductor substrate 41 and which relate to the rate-of-flow component 44 and two parts 45 and 46 of a thermocouple also arranged in prolongation and which relate to the rate-of-flow component 47. These thermocouples are preferably integrated in the semi-conductor substrates as P and/or N doped strips which are bonded on each side by metal conductors of non-evaporised aluminium. Heating-elements are arranged along the sides of the thermocouples in quadrants 48, 49, 50 and 51 for heating the flowing medium whilst the necessary electronic-circuitry is also located here. Figure 2 shows a semiconductor substrate 61 on which, for each direction component 64 and 67, there are arranged two thermocouples 62, 63 and 65, 66 of thermo-pile form lying parallel with one another whilst the surface 68 between thermocouples 62, 63, 65 and 66 can be used for accommodating one or more heating-elements and electronic-circuitry for the processing of thermocouple output signals and in which the heat generated by the circuitry can partially or completely replace the heat generated by the heating-elements. Finally, figure 3 shows how a number of thermocouples can be arranged to form a thermo-pile. The thermocouples are formed by series-connecting a number of semiconductor strips 71 and 72 which are electrically-insulated from one another in a silicon layer and connected by means of aluminum conductors 73, 74 and 75.

Claims: 1. A direction-sensitive flow-rate indicator for gaseous or liquid media comprising a semiconductor substrate (41, 61) on which at least one thermocouple (42, 43, 45, 46, 62, 63, 65, 66) is arranged, said at least one thermocouple (42, 43, 45, 46, 62, 63, 65, 66) having two temperature-sensitive ends (602, 603, 605, 606, 612, 613, 615, 616), said ends (602, 603, 605, 606, 612, 613, 615, 616) being arranged on a connecting line extending in the direction of one flow component (44, 47, 64, 67) of the medium, and further comprising a heating-element for generating a flow-rate temperature-difference in the flowing medium in the direction of the said connecting line(s) which results in a flow-rate dependent thermo voltage between the ends (602, 603, 605, 606, 612, 613, 615, 616) of the said at least one or each thermocouple (42, 43, 45, 46, 62, 63, 65, 66), characterized in that at least one thermocouple (42, 43, 45, 46) is provided for each dimension in a two-dimensional embodiment of the invention and in which the connecting lines for the respective dimensions are arranged perpendicular to one another, and in which the one or each thermocouple comprises two parts (42, 43, 45, 46) which extend in prolongation to one another and which can be connected in series and in which for both dimensions alike thermocouples (42, 43, 45, 46) are arranged on the substrate (41) in a cruciform manner. 2. A direction-sensitive flow-rate indicator for gaseous or liquid media comprising a semiconductor substrate (41, 61) on which at least one thermocouple (42, 43, 45, 46, 62, 63, 65, 66) is arranged, said at least one thermocouple (42, 43, 45, 46, 62, 63, 65, 66) having two temperature-sensitive ends (602, 603, 605, 606, 612, 613, 615, 616), said ends (602, 603, 605, 606, 612, 613, 615, 616) being arranged on a connecting line extending in the direction of one flow component (44, 47, 64, 67) of the medium, and further comprising a heating-element for generating a flow-rate temperature-difference in the flowing medium in the direction of the said connecting line(s) which results in a flow-rate dependent termo voltage between the ends (602, 603, 605, 606, 612, 613, 615, 616) of the said at least one or each thermocouple (42, 43, 45, 46, 62, 63, 65, 66), characterized in that at least one thermocouple (62, 63, 65, 66) is provided for each dimension in a two-dimensional embodiment of the invention and in which the connecting lines for the respective dimensions are arranged perpendicular to one another, and two preferably alike thermocouples (62, 63, 65, 66) are provided for each dimension and each of which thermocouples (62, 63, 66, 65) extend parallel to one another such that the thermocouples (62, 63, 66, 65) enclose a rectangle (68) there between and that the thermocouples (62, 63, 65, 66) are connected in series. 3. A direction-sensitive flow-rate indicator as claimed in claim 1, characterized in that at least two heating-elements are enclosed in the quadrants (48, 49, 50, 51) formed by cruciformly arranged thermocouples (42, 43, 45, 46). 4. A direction-sensitive flow-rate indicator as claimed in claim 2, characterized in that at least one heating-element is arranged within the rectangle (68). 5. A direction-sensitive flow-rate indicator as claimed in any one of the foregoing claims, characterized in that the said thermocouple (42, 43, 45, 46, 62, 63, 65, 66) is in the form of a thermo-pile.

Inventors: HUIJSING, JOHAN HENDRIK, VAN OUDSHEUSDEN, BASTIAAN WILLEM
Applicants: BRONKHORST HIGH-TECH B.V.
Application year: 1988
Main classification: G01F1
IPC codes: G01F1, G01P13, H01L35, G01P5