BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

[0001] This invention relates to a solution for measuring a flow speed of an airflow in space.

DESCRIPTION OF PRIOR ART

[0002] Previously there is known a solution for measuring a speed of an airflow in a space by means of a measuring apparatus utilizing an ultrasound elements.

[0003] In the known solution the ultrasound elements are arranged at suitable locations in the space, which may be an air duct section, for instance. When the positions of the ultrasound elements are known, it becomes possible to determine the flow speed by transmitting a signal and comparing a phase difference between the received signals.

[0004] A challenge with the previously known solution is that in order to obtain correct measurements with the apparatus, calibration is needed. One reason which makes calibration necessary is that the mutual positions of the ultrasound elements are not known with a sufficient accuracy.

[0005] Even when attempts are made to arrange the ultrasound elements at specific predetermined positions in the duct section, a sufficient accuracy eliminating the need for calibration can usually not be obtained. Due to this, additional manual operations are needed during installation or flow speed measurements.

SUMMARY OF THE INVENTION

[0006] An object of the present invention is to solve the above-mentioned drawback and to provide a simpler way of obtaining accurate flow speed measurement results. This object is achieved with the apparatus according to independent claim 1 and the method according to independent claim 11.

[0007] When the ultrasound elements are attached to a carrier at predetermined mutual positions, this carrier is arranged at a wall of the space where an airflow is passing, and when the ultrasound elements can be energized via a cable socket to transmit and receive signals between each other via a wall section, a cheap and simple solution is obtained which requires a minimum of manual operations during installation and flow speed measurements.

[0008] Preferred embodiments of the invention are disclosed in the dependent claims.

BRIEF DESCRIPTION OF DRAWINGS

[0009] In the following an apparatus and a method for measuring flow speed will be described in closer detail by way of example and with reference to the attached drawings, in which

[0010] Figure 1 illustrates a first preferred embodiment of an apparatus, [0011] Figures 2 illustrates a second embodiment of an apparatus, [0012] Figure 3 illustrates a third embodiment of an apparatus, and [0013] Figure 4 illustrates a fourth embodiment of an apparatus.

DESCRIPTION OF AT LEAST ONE EMBODIMENT

[0014] Figure 1 illustrates a first preferred embodiment of an apparatus. In Figure 1 an airflow passing through a space 1 is measured by a measuring apparatus including ultrasound elements 15. In this example three ultrasound elements are provided, one ultrasound element 15 with an ultrasound transmitter 2 and two ultrasound elements 15 with an ultrasound receiver 3, 3'. The space may in practice 1 be a part of a ventilation duct or a chamber of a ventilation device in a ventilation system of a building, for instance. The shape or intended purpose of the space is not of importance, as the present invention may be utilized for any type of space 1 passing an airflow. Figure 1 illustrates by way of example a space consisting of a chamber in a plenum box, which may be used to pass an airflow from an air duct into a room space.

[0015] The ultrasound elements 15 and the carrier 4 are preferably during manufacturing permanently attached to each other to form one single sensor which can easily be arranged to a wall 9 of the space 1 . Depending on the implementation, the sensor may be attached to an outer surface of the wall, or alternatively, into one single opening provided in the wall 9. The carrier 4 may be implemented as a circuit board or included in a circuit board, for instance.

[0016] When such a sensor is mass produced, for instance, the ultrasound elements 15 including ultrasound receivers 3, 3' are in each produced sensor always located exactly on predetermined positions, in praxis on a predetermined distance from the ultrasound element 15 including the ultrasound transmitter 2. Preferably the ultrasound elements are arranged on a straight line parallel with the flow direction of an air flow such, that the ultrasound element 15 with the ultrasound transmitter 2 is located in the middle. Consequently, when an interface 7 of a portable measuring unit 5 is connected to the ultrasound elements 15 by conductors of a cable 6 and by a cable socket 8, the predetermined mutual positions of the ultrasound elements 15 are known in advance. This makes calibration of the measuring unit 5 due to variations in the mutual position unnecessary. Additionally, when no battery or other components are needed in the sensor including the ultrasound elements 15 and the carrier 4, the costs of the sensor can be kept very low. In praxis so low, that a high amount of such sensors can during manufacturing or assembly be incorporated in the ventilation ducts of a building, for instance. Energizing and flow speed measurements of these sensors can subsequently be carried out only when needed, by connecting one sensor at a time to a portable measurement unit 5 which contains a battery for energizing the ultrasound elements 15, and possibly also other electric components in the portable measurement unit, if needed, for carrying out flow speed measurements. No battery or other source of energy is therefore needed in the sensor to facilitate flow speed measurements.

[0017] An advantage with such a solution is that ventilation ducts and other components of the ventilation system of a building, for instance, may be provided with a great number of such relatively cheap sensors, which in praxis can be connected to any compatible measuring unit 5, as the compatible measuring units 5 have been configured during manufacturing to work with these sensors having the predetermined positions for the ultrasound elements 15.

[0018] The measuring unit 5 may be implemented by a portable computer with a battery, for instance, where a software run by a processor controls the operation of the measuring unit 5 and the ultrasound elements 15.

[0019] Figure 2 illustrates a second embodiment of an apparatus. The embodiment of Figure 2 is very similar to the one explained in connection with Figure 1 . Therefore, in the following the embodiment of Figure 2 will be explained mainly by pointing out the differences between these embodiments.

[0020] In Figure 2 it is assumed that the apparatus comprising the space T is of a different type, such as a straight tube having a circular or rectangular cross-section, and that this tube with the space T may be used for air flows in two different directions. The first possible flow direction from left to right is illustrated by arrow 10', while the second possible flow direction is opposite, in other words from right to left. [0021] Two ultrasound elements 15 each with an ultrasound receiver 3 and 3' only are attached to the carrier 4' in Figure 2. The ultrasound receivers 3 and 3' of the ultrasound receiver pair are attached to the carrier 4' at the same predetermined distance X from a third ultrasound element 15 including an ultrasound transmitter 2 only. The transmitter and the receivers are on a straight line which is parallel with the flow direction of the airflow 10'. Consequently, the ultrasound element 15 with the ultrasound transmitter 2 is arranged in a center position between the ultrasound elements 15 with the ultrasound receivers 3, 3 such that the distance X from the ultrasound transmitter to each ultrasound receiver of the ultrasound receiver 3, 3' pair is the same.

[0022] If the example of Figure 2 the wall 9' delimiting the space T is provided with an opening 1 T and the carrier 4' is attached to the opening 1 T to provide the ultrasound elements 15 with direct access to the space T, in praxis with access to an interior of the duct section. As illustrated in Figure 2, the ultrasound element 15 with the ultrasound transmitter 2 is attached to the carrier 4 to transmit ultrasound signals across the space T towards an opposite wall section 12'. From this wall section 12' the ultrasound signals are reflected back to the ultrasound elements 15 with the ultrasound receivers 3, 3'.

[0023] As in Figure 1 , an interface 7 of a portable measuring unit 5 is connected to the ultrasound elements 15 via conductors 13' and a cable socket 8. In a large building, maintenance personnel may be provided with their personal portable measuring unit 5, which can be connected to the socket 8 of any apparatus only for a period of time needed to measure the speed of the air flow in the space T of this apparatus.

[0024] During flow speed measurements, the portable measuring unit 5 energizes the ultrasound elements 15 to transmit and receive signals. When the measuring unit 5 transmits a signal by means of the ultrasound transmitter 2, this signal is reflected from the wall section 12' for reception by the measuring unit 5 via the ultrasound receivers 3, 3' of the receiver pair. Based on a phase difference between signals received via the ultrasound receivers 3, 3' the measuring unit is able to calculate a flow speed of the airflow 10' through the space T.

[0025] As the ultrasound receivers 3, 3' are arranged on the carrier 4' at predetermined positions in relation to the transmitter 2, in this case at a predetermined distance X from the ultrasound transmitter, no calibration is needed for the measuring unit regarding the mutual positions of the receiver and transmitters. Instead this calibration may have been carried out for the measuring unit already during manufacturing of the measuring unit, such that the measuring unit directly can carry out measurements for this sensor type. [0026] However, the same measuring unit 5 may be utilized for flow speed measurements in spaces having different sizes, such as ducts having different duct diameters. In order to correctly determine the flow speed, the measuring unit needs to know the measurement parameters which are dependent on the size of the space 1 ' in question. To obtain measurement parameters for the size in question, the measuring unit 5 is at an initial stage of the measuring configured to control the ultrasound element 15 with the ultrasound transmitter 2 to transmit an ultrasound pulse. The reflected pulse is received by the measuring unit with at least one ultrasound element 15 with an ultrasound receiver 3, 3'. After reception of the reflected pulse, the measuring unit 5 determines a progress time between transmission and reception, and obtains from a memory 14 measurement parameters corresponding to the determined progress time. Consequently, as the speed of ultrasound in air is known, by knowing the progress time, it is possible to determine the size of the space and the suitable measurement parameters. A table for different progress times and related measurement parameters can therefore in advance be stored in the memory 14 of the measuring unit 5.

[0027] An advantage with such a solution is that no calibration of the portable measuring unit 5 is needed once it is connected to a new sensor of an apparatus, as the predetermined mutual positions of the ultrasound elements 15 are previously known (standardized) by the measuring unit, and as the measuring unit is capable of automatically identifying the size of the space T and obtain the needed measurement parameters.

[0028] Figure 3 illustrates a third embodiment of an apparatus. The apparatus of Figure 3 is very similar to the embodiments explained in connection with Figures 1 and 2. In the following the embodiment of Figure 3 will be explained mainly by pointing out the differences between these embodiments. [0029] In Figure 3 the carrier 4" is provided with ultrasound elements 15 including a plurality of ultrasound receiver pairs, each ultrasound receiver pair having ultrasound receivers 3 - 3', 31 - 3T and 32 - 32' at different predetermined distances from each other than the other ultrasound receiver pairs. The ultrasound elements 15 also include an ultrasound element 15 with an ultrasound transmitter 2. The transmitter 2 is arranged in a center position between the ultrasound receivers such that the distance to each ultrasound receiver 3, 3' 31 , 31', 32 and 32' of an ultrasound receiver pair is the same. Each of the illustrated three ultrasound receiver pairs with receivers 3 - 3', 31 - 31 ' and 32 - 32' is assigned for use within a predefined flow speed range.

[0030] By utilizing several ultrasound receiver pairs with a different mutual distance between each other, such that each ultrasound receiver pair has ultrasound receivers at a different distances from each other than any of the other ultrasound receiver pairs, the flow speed measurement accuracy can be improved, consequently each ultrasound receiver pair is assigned for use within a predefined flow speed range. In the following, it will by way of example bee assumed, that in the memory 14 of the measuring unit 5 a table is maintained according to which:

[0031] - ultrasound receiver 3, 3' pair: assigned for flow range 8-16 m/s, [0032] - ultrasound receiver 31 , 31 ' pair: assigned for flow range 4-7 m/s, and [0033] - ultrasound receiver 32, 32' pair: assigned for flow range 0,5 - 3 m/s. [0034] After each obtained flow measurement result, the measuring unit 5 makes a selection of which ultrasound elements 15 to use for the following measurement. In this selection the measuring unit 5 compares the last obtained flow speed measurement result with the flow speed ranged assigned for the ultrasound receiver pair of the ultrasound elements 15 used to obtain the previous flow speed measurement result. If the last flow speed measurement result has reached a lower limit of the flow speed range assigned for the previously used ultrasound receiver pair, the measuring unit selects for use ultrasound elements with an ultrasound receiver pair having ultrasound receivers located further away from each other than the previously used pair, as this improves the accuracy of measurements. Consequently, if the last flow speed measurement result of 4 m/s has been obtained with the ultrasound receiver 31 , 31 ' pair, ultrasound receiver 32, 32' pair will be selected for the next flow speed measurement.

[0035] Similarly, if the previous flow speed measurement result has reached an upper limit of the of the flow speed range assigned for the previously used ultrasound receiver pair, the measuring unit selects for use ultrasound elements with an ultrasound receiver pair with ultrasound receivers located closer to each other than the previously used pair, which will improve the accuracy. Consequently, if the last flow speed measurement result of 7 m/s has been obtained with the ultrasound receiver 31 , 31 ' pair, ultrasound receiver 3, 3' pair will be selected for the next flow speed measurement.

[0036] Only in case the last flow speed measurement result has not reached a lower limit or an upper limit of the flow speed range assigned for the previously used ultrasound receiver pair, the previously used ultrasound receiver pair is maintained in use. Consequently, if the previous flow speed measurement result of 5 m/s has been obtained with the ultrasound receiver 31 , 31 ' pair, ultrasound receiver 31 , 3T pair of the previously selected ultrasound elements will be maintained in use for next flow speed measurement.

[0037] The above explained solution makes it possible to obtain a very accurate flow speed measurement solution with the same measurement apparatus over a very wide flow speed range.

[0038] Figure 4 illustrates a fourth embodiment of an apparatus. The apparatus of Figure 4 is very similar to the embodiments explained in connection with Figure 3. In the following the embodiment of Figure 4 will be explained mainly by pointing out the differences between these embodiments.

[0039] A main difference with the embodiment in Figure 4 is that each ultrasound element 15' attached to the carrier 4' includes both an ultrasound transmitter 2 and an ultrasound receiver 3, 3', 31 , 3T. Consequently, both ultrasound receivers and ultrasound transmitters are provided at the predetermined positions of the receiver 3 - 3', 31 - 3T pairs.

[0040] Due to use of ultrasound elements 15' including both transmitters and receivers, the measurement may be carried out slightly differently. Instead of receiving signals from one transmitter with two receivers, each ultrasound element 15' of a pair may first transmit to the other one of the same pair, and after this the roles are reversed, such that the ultrasound element 15' of the pair which previously received, will transmit while the other ultrasound element of this par will receive the signal. Similarly as in the previous embodiments the measuring unit 5 will energize the ultrasound elements 15' to transmit and receive signals to each other via a wall section 12' of the space which is opposite to the wall 9' of the space T to which the carrier 4" with the ultrasound elements is arranged.

[0041] In the situation illustrated in Figure 4 arrows have been provided to indicate that the centermost ultrasound elements 15' with the receiver 3-3' pair in turns use their respective transmitter 2 to transmit an ultrasound signal to each other via the wall section 12' and their respective receiver 3, 3' to receive the signal transmitted by the other ultrasound element 15'. In praxis it may in many implementations be sufficient to provide only this one pair of ultrasound elements to the carrier 4". In that case the measurements are carried out by utilizing only one ultrasound receiver 3 - 3' pair, as is the case also in the embodiment Figure 1.

[0042] However, in Figure 4 it is by way of example assumed that also a second pair of ultrasound receivers 31 - 3T is in use, which makes it possible to improve the accuracy of the measurements by selecting for use ultrasound elements assigned for the flow speed range which best matches the previous obtained flow speed measurement in a similar way as has been explained in connection with the embodiment of Figure 3. In that case a difference to the embodiment of Figure 3 is that each time another pair of ultrasound receivers is selected for use, also the used transmitters changes. In other words, the transmitters 2 of the centermost ultrasound elements 15' are used only as long as the centermost pair of receivers 3-3' is in use. Once the outermost ultrasound elements 15' with the receiver 31 -31 ' pair are selected for use, also the transmitters 2 of these outermost ultrasound elements 15' are taken into use.

[0043] It is to be understood that the above description and the accompanying figures are only intended to illustrate the present invention. It will be obvious to a person skilled in the art that the invention can be varied and modified without departing from the scope of the invention.