Temperature sensing apparatus and method of measuring a temperature outside a housing

Abstract

A method for measuring a temperature outside a housing unit includes the steps of measuring a first temperature inside the sealed housing of the housing unit, measuring a second temperature inside the sealed housing of the housing unit, and measuring a airflow speed outside the housing of the housing unit and along the front cover of the housing. A multiple of the difference between the first temperature and the second temperature is added to the first temperature, and a multiple of the product of airflow speed v.sub.A and the difference between the first temperature and the second temperature is further added.

Claims

1. A housing unit, comprising: a housing having a front cover; an electronic assembly disposed inside said housing, said electronic assembly dissipating heat in operation; a first temperature sensor inside said housing; a second temperature sensor inside the housing and disposed at a spacing distance from said first temperature sensor such that said first and second sensors measure mutually different temperatures caused by a flow of heat from said electronic assembly towards said front cover; an anemometer configured to measure airflow speed outside said housing; a processor configured for calculating the temperature outside said housing by further adding or subtracting a multiple of the temperature difference between said first and second sensors, the multiple scaling multiplicatively with the absolute value of the airflow speed |v.sub.A|, an increase in the absolute value of the airflow speed |v.sub.A| by a given percentage yielding an increase in the multiple by the given percentage; and a display; said housing being sealed against an ambient surroundings such that any impact on a reading of said sensors caused by a flow of air into or out of said housing is minimized or eliminated; wherein a temperature outside said housing is calculated based on exactly three measurable quantities, the exactly three measurable quantities being a temperature measured by said first sensor, a temperature measured by said second sensor, and the airflow speed measured by said anemometer.

2. A housing unit, comprising: a housing having a front cover; an electronic assembly disposed inside said housing, said electronic assembly dissipating heat in operation; a first temperature sensor inside said housing; a second temperature sensor inside the housing and disposed at a spacing distance from said first temperature sensor such that said first and second sensors measure mutually different temperatures caused by a flow of heat from said electronic assembly towards said front cover; an anemometer configured to measure airflow speed outside said housing and configured to determine a direction of ambient air flow; a processor configured for calculating the temperature outside said housing by further adding or subtracting a multiple of the temperature difference between said first and second sensors, the multiple scaling multiplicatively with the absolute value of the airflow speed |v.sub.A|, an increase in the absolute value of the airflow speed |v.sub.A| by a given percentage yielding an increase in the multiple by the given percentage; and a display; said housing being sealed against an ambient surroundings such that any impact on a reading of said sensors caused by a flow of air into or out of said housing is minimized or eliminated.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The sole FIGURE of the drawing shows a cutaway view of a housing unit with temperature sensing according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(2) Referring now to the FIGURE of the drawing in detail there is shown a housing unit 1 mounted to the wall 2 of a building. The housing unit 1 shown on the FIGURE is partly installed in-wall. Most parts 4-7 of the unit 1 are, however, mounted on-wall.

(3) The unit comprises a front cover 4. The front cover 4 is preferably made of glass and/or of any other (transparent) polymer. An electronic assembly 5 is arranged behind the front cover 5. The electronic assembly 5 in the preferred, exemplary embodiment comprises elements such as a printed circuit board and/or a microprocessor 15 and/or sensors and/or a (wireless) communication module. A preferred embodiment has a display 6 mounted on top of the electronic assembly 5, such that the display 6 is visible through the front cover 4. Typically, the display 6 is a liquid-crystal display or a display made up of organic light emitting diodes.

(4) The display 6 and the front cover 4 are separated by a gap 7. The gap 7 is typically air-filled. In another embodiment, the gap 7 is (predominantly) filled with helium or with nitrogen.

(5) The housing of the housing unit 1 also comprises side-walls 8. The side-walls 8 of the housing seal the housing unit 1 against any ingress of moisture or of dust. To that end, the side-walls 8 provide no slots or orifices. In other words, the housing unit 1 provides walls that substantially seal the unit from all sides, so no moisture or dust can settle inside the unit. The housing unit 1 does not need to be water-proof or hermetically sealed. It is, however, essential that any temperature measurement inside the unit 1 is not influenced by a flow of air into or out of the unit 1.

(6) The temperature measurement as disclosed in this document is based on the heat inside the housing unit 1. In a particular embodiment, heat is predominantly dissipated by the electronic assembly 5. An arrow 9 indicates the direction of the flow of heat from the inside of the housing unit 1 through the front cover 4 to the outside of the unit 1. There is naturally also a flow of heat in the other direction from the electronic assembly 5 to the wall 2.

(7) The housing unit 1 further comprises two temperature sensors 10, 11. A first temperature sensor 10 is ideally arranged underneath or just outside the display 6. The temperature sensor 10 may also installed adjacent to or inside of the electronic assembly 5. The temperature sensor 10 as shown in the FIGURE is close to a side-wall. In another embodiment, the temperature sensors 10, 11 are arranged closer to the center of the housing unit 1. A placement of the sensors 10, 11 closer to the center of the housing unit 1 will mitigate any adverse effect of heat flow through a side-wall.

(8) The temperature sensors 10, 11 are preferably spaced 10 mm apart, more preferably 5 mm apart, and yet more preferably 2 mm apart. The distance between the sensors 10, 11 is large enough, so the temperature drop between the sensors can be measured accurately.

(9) A second temperature sensor 11 is preferably installed underneath the front cover 4. In this position, the sensor 11 is in direct contact with the fluid (air) inside the gap 7. The temperature sensor 11 may also be arranged inside the front cover 4, so there will be no direct contact to any fluid inside the gap 7.

(10) The temperature sensors 10, 11 are preferably thermocouples, or positive thermal resistance elements, or negative thermal resistance elements. The temperature sensors 10, 11 may also be optical sensors rather than electric elements. Optical sensors are typically connected through fiber optics rather than through electric wires. It is also possible to measure the temperature via Raman scattering.

(11) The ambient temperature T.sub.A outside the housing unit 1 also depends on the airflow speed v.sub.A, or wind speed, outside the unit 1. The ambient airflow v.sub.A is indicated in the FIGURE by an arrow 12. By taking into account ambient airflow, the temperature T.sub.A reads
T.sub.A=T.sub.Dc.sub.1.Math.(T.sub.ST.sub.D)+c.sub.2.Math.v.sub.A.Math.(T.sub.ST.sub.D),
where T.sub.D denotes the temperature measured by the sensor 11 and T.sub.S denotes the temperature measured by the sensor 10. The above relationship says the temperature T.sub.A outside the housing unit depends on the difference T.sub.ST.sub.D between the measurements taken from the sensors 10 and 11. The above relation further implies the temperature T.sub.A is a function of the magnitude of ambient airflow. T.sub.A is considered independent of the direction of ambient airflow.

(12) The constants c.sub.1 and c.sub.2 are determined numerically and by experimentation. A series of measurements is carried out in a laboratory with well-defined airflow speeds v.sub.A and with well-defined ambient temperatures T.sub.A. The temperatures T.sub.S and T.sub.D are then measured inside the housing. By fitting the measured values on a computer, the constants c.sub.1 and c.sub.2 are determined. This procedure is preferably carried out separately for each arrangement of temperature sensors 10, 11.

(13) Experimentation shows that one of the advantages of the present temperature measurement is speed. Earlier solutions relied on heat exchange between a temperature probe inside a housing unit 1 and the ambient. Typical time constants were in the range of minutes, with 15 minutes being a typical value. The method and the sensing apparatus proposed herein allow for a temperature measurement that is much faster. A typical time constant is now 2.5 minutes. Time constants below one minute become technically feasible.

(14) To determine the ambient temperature T.sub.A in accordance with the above equation, the magnitude of airflow speed v.sub.A needs to be factored in. A measurement of airflow speed v.sub.A is possible by application of the Bernoulli principle. According to this principle, a flow of air along the surface of the front cover 4 causes a pressure drop in a conduit perpendicular to that surface. The airflow speed is then calculated based on the magnitude of the pressure drop (or pressure rise) in the perpendicular conduit.

(15) Windmill anemometers also allow for a determination of ambient airflow. A propeller could, for instance, be installed on the surface of the front cover 4. The angular speed of the propeller and/or the torque applied to the propeller then become a measures of airflow speed v.sub.A.

(16) Sonic anemometers can also deliver accurate airflow speed measurements. Sonic anemometers rely on the time of flight of a sonic pulse. In order for a sonic anemometer to be included in the present housing unit, a pair of transducers is arranged on the front cover. Typically, this pair of transducers is spaced 10 cm to 20 cm apart.

(17) A hot-wire anemometer 13 is yet another technical means to determine airflow speeds. In order to implement a hot-wire anemometer 13 in a housing unit 1, an electric conductor is arranged on the surface 14 of the front cover 4. In a preferred embodiment, the conductor is a film of TiO.sub.2 or of ZnO. The conductor is preferably covered by a thin non-conductive coating. The non-conductive coating reduces measurement errors due to moisture, dust, grease etc. At the same time, the coating is thin enough, so the conductor is cooled effectively through any ambient airflow along the surface of the front cover.

(18) The conductor of the hot-wire anemometer 13 is arranged at a distance from the temperature sensors 10, 11. This particular arrangement reduces heating of the temperature sensors 10, 11 and thus reduces false readings due to the influence of the conductor.

(19) A ZnO or TiO.sub.2 conductor on the surface may also be employed for a direct measurement of ambient temperature. The resistance of the conductor is also a function of temperature. Consequently, ambient temperature may be calculated from the resistance of the conductor.

(20) In yet another embodiment, airflow speed is not measured by the housing unit 1 itself but by a component of a room automation system. The latter component is separate from the housing unit 1. The latter component may be the room automation system itself.

(21) It seems worth stressing that the above procedure for determining the constants c.sub.1 and c.sub.2 may also have to be carried out separately for different anemometers.

(22) It is yet another advantage of the present disclosure that a housing unit 1 now also measures airflow speed v.sub.A. In certain embodiments, an anemometer will even determine the direction of ambient airflow. A measurement of airflow speed (and possibly of wind direction) is yet another measurement value to be sent from a housing unit 1 to a room automation system. The airflow speed value may then support the decision making process inside the room automation system. In other words, the control of blinds, of lighting, of heating, of ventilation etc will become more accurate and more reliable.

(23) The calculations, the data sampling of temperature and airflow speed, the methods, and the processing steps described in the present application may be performed by a software executed by a general purpose processor or by a digital signal processor (DSP), by an application specific integrated circuit (ASIC), by a field programmable gate array (FPGA), by discrete components or any combination thereof. Different hardware and/or software components may be used for performing the functions of the different blocks, and even with a single block.

(24) Steps of a method according to the present application may thus be embodied in hardware, in a software module executed by a processor, or in a combination of the two. The software may include a firmware, a hardware driver run in the operating system, or an application program. Thus, the invention also relates to a computer program product for performing the operations presented herein. If implemented in software, the functions described may be stored as one or more instructions on a computer-readable medium. Some examples of storage media that may be used include random access memory (RAM), read only memory (ROM), flash memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, other optical disks, or any available media that can be accessed by a computer or any other IT equipment and appliance.

(25) The processor can be configured for calculating the temperature outside said housing by further adding or subtracting a multiple of the temperature difference between said first and second sensors, the multiple scaling multiplicatively with the absolute value of the airflow speed |v.sub.A|, an increase in the absolute value of the airflow speed |v.sub.A| by a given percentage yielding an increase in the multiple by the given percentage.

(26) It should be understood that the foregoing relates only to certain embodiments of the invention and that numerous changes may be made therein without departing from the spirit and the scope of the invention as defined by the following claims. It should also be understood that the invention is not restricted to the illustrated embodiments and that various modifications can be made within the scope of the following claims.

(27) The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: 1 housing unit 2 wall 3 part of the housing unit installed in-wall 4 front cover 5 electronic assembly 6 display 7 gap 8 side-wall of the housing 9 direction of heat flow 10 temperature sensor 11 temperature sensor 12 airflow speed on the surface of the housing unit