Abstract:
A hot wire anemometer comprising a support member having a data processing system, probe head with a hot wire sensor and an ambient temperature sensor and an extendable portion having conductors therein for transfer of collected data and command data between the data processing system in the handle and the hot wire and ambient sensors in the probe head, thus conveniently allowing the probe head to be extended far from the support member and into a desired test area for accurate data collection to determine the velocity of fluid flow.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a utility patent application based upon earlier filed U.S. Provisional Application Ser. No. 60/257,927 filed Dec. 22, 2000, the disclosure of which earlier filed application is hereby incorporated by reference and the priority of which earlier filed United States Provisional Application is hereby claimed. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     (Not Applicable.) 
     BACKGROUND OF THE INVENTION 
     The present invention relates to processes and apparatus for measuring fluid flow, and more particularly, to a hot wire anemometer. 
     An anemometer is an instrument which measures the velocity of the flow of fluids, such as air or other gases, and in some cases of liquids. While mechanical anemometers, such as cup anemometers are useful for measuring wind speed, hot-wire anemometers are required for more technical applications. 
     Hot-wire anemometers function as thermal transducers which are capable of sensing point flow velocity by means of temperature variations using a heated resistive wire with a nonzero temperature coefficient of resistance. When the electrically heated wire is placed in a flow of fluid, heat is taken away by flow-induced forced convection, i.e., the wire is cooled by the fluid flow. Depending upon the operational mode used, e.g. constant current or constant temperature, either the resistance or the voltage output drop across the wire is then a function of the flow velocity. Thus, in the case of a constant current device, greater flow results in a greater temperature drop over time. 
     Hot wire anemometers are commonly used to measure air velocity in the vicinity of ventilation ducts in occupied buildings. Ventilation ducts are often mounted near the room ceiling or in an otherwise elevated location. Therefore, for applications such as these, the hot wire anemometer must be extended to reach these areas in order to obtain an accurate measurement. There are a number of products on the market that attempt to accomplish this task by using either telescopic heads or extension handles. However, these devices are not ideal. 
     One of the most difficult problems in manufacturing a telescopic probe is that the electronics required to interface with the sensors require several electrical conductors, which are most commonly electrically conductive wires, to pass inside the telescopic section. As the head is rotated, the wires twist, and thus, 360° rotation is not possible. Also, when the telescopic section is collapsed, the wires also have to retract without snagging. Some manufacturers have attempted to overcome this problem by making telescoping anemometers which have a cable that is not fixed at the probe handle end, with the objective of making the cable free to travel up and down the inside of the telescopic section. These devices require a special cable to be used. The cable is typically stiff and not easy to manage, which also, among other things, limits its length and requires an additional electronics module to interface to the measuring instrument. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a solution to the problems and inconveniences associated with prior art anemometers. 
     The present invention is directed to an anemometer comprising a support member with an extendable probe portion having two ends and one or more conductors in the extendable probe portion for electrical flow and transfer of data between a data gathering system located at one end of the extendable probe portion and a data processing and command system located in the support member connected to the other end of the extendable probe portion, or in a remote source such as a personal computer. 
     The preferred embodiment of the inventive anemometer includes a handle and probe. The probe comprises a coaxial telescoping extension having two concentric telescoping sections which are electrically-insulated from each other. Data is gathered by sensors at the probe head end and transferred to a data processor in the handle through the telescoping sections, which comprise the necessary conductors for data and power transfer between the probe head and handle. The probe may be fully rotated and extended to obtain data without being physically obstructed. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     One or more embodiments of the invention and of making and using the invention, as well as the best mode contemplated of carrying out the invention, are described in detail below, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a side view partially in cross section of an embodiment of the inventive device; 
     FIG. 2 is a cross-sectional view of the embodiment of the inventive device shown in FIG. 1 along line  2 — 2  of FIG. 1; 
     FIG. 3 is a cross-sectional view of the embodiment of the inventive device shown in FIG. 1 along line  3 — 3  of FIG. 1; 
     FIG. 4 is a side view partially in cross section of the probe head of the inventive device; 
     FIG. 5 is a functional diagram for the embodiment of the inventive device shown in FIG. 1; 
     FIG. 6 is a second functional diagram of the electronics assemblies for the embodiment of the inventive device shown in FIG. 1; 
     FIG. 7 is a diagram illustrating a sample timing sequence for the embodiment of the inventive device shown in FIG. 1; 
     FIG. 8 is a functional diagram of the electronics assemblies for another embodiment of the inventive device; 
     FIG. 9 is a top view partially in cross section of an alternative embodiment of the inventive device; 
     FIG. 10 is a bottom view partially in cross section of the embodiment illustrated in FIG. 9; 
     FIG. 11 is an enlarged end view of the sensor head of the embodiment illustrated in FIGS. 9 and 10; 
     FIG. 12 is an enlarged top view of the sensor head of the embodiment illustrated in FIGS. 9 and 10; 
     FIG. 13 is an enlarged bottom view of the sensor head of the embodiment illustrated in FIGS.  9  and  10 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following more detailed description of the invention is intended to be read in the light of, or in context with, the preceding summary and background descriptions. Unless otherwise apparent, or stated, directional references, such as “up” , “down”, “left”, “right”, “front” and “rear”, are intended to be relative to the orientation of a particular embodiment of the invention as shown in the first numbered view of that embodiment. Also, a given reference numeral indicates the same or a similar structure when it appears in different figures. 
     Anemometer  10 , as illustrated in FIG. 1, has handle  12  and extendable portion  14 . A battery and its compartment  16  and electronics assembly  18  are located in handle  12 . Probe head  20 , with sensor assembly  22  and a second electronics assembly  24  inside, is secured in anemometer  10  at the end of extendable portion  14 . Extendable portion  14  has outer telescoping section  28  and inner telescoping section  26 . Outer telescoping section  28  is electrically grounded and inner telescoping section  26  is electrically isolated from outer section  28 , thus providing for conduction of electricity through extendable portion  14  and sensor assembly  22 . 
     Both inner telescoping section  26  and outer telescoping section  28  are made up of a plurality of annular pipe-like legs that allow the sections to extend and retract to reach into a flow of fluid. In this embodiment, inner section  26  has annular legs  30 ,  32  and  34 . Outer section  28  has annular legs  36 ,  38 ,  40  and  42 . Annular legs  30 ,  32  and  34  have smaller diameters than legs  36 ,  38 ,  40  and  42 . However, each annular leg  30 ,  32 ,  34 ,  36 ,  38 ,  40  and  42  differs in diameter ranging from the smallest being leg  30  to the largest being leg  42 , thus permitting legs  30 ,  32 ,  34 ,  36 ,  38 ,  40  and  42  to fit within one another. Preferably, the change in diameter between the legs is constant, except for difference in diameter between leg  30 , which is the largest of any leg in inner section  26 , and leg  42 , the smallest of any leg in outer section  28 . Hence, there is a gap  44  between inner section  26  and outer section  28 , as illustrated in FIGS. 2 and 3, which depict cross-sections of extendable portion  14  at the two locations shown in FIG.  1 . 
     Legs  30 ,  32 ,  36 ,  38  and  40  have upper rims that extend inwardly, and legs  32 ,  34 ,  38 ,  40  and  42  have lower rims that extend outwardly, thus interlocking when telescoping sections  26  and  28  are fully extended to prevent legs  30 ,  32 ,  34 ,  36 ,  38 ,  40  and  42  from being pulled apart. Annular leg  34  of inner section  26  and annular leg  42  of outer section  28  are mechanically secured to probe head  20  at one end. Legs  34  and  42  are also electrically connected to a respective one of the two electrical terminals which serve as the output of sensor and electronics assembly  22  and  24 , respectively. 
     Annular leg  30  of inner section  26  and annular leg  36  of outer section  28  are secured to handle  12  at one end. Therefore, when probe head  20  is extended, it pulls annular leg  34 , which extends from inside leg  32 . When the length of leg  34  is fully extended from inside leg  32 , the lower rim on leg  34  contacts the upper rim on leg  32  and pulls leg  32  from inside leg  30 . Legs  36 ,  38 ,  40  and  42  of outer telescoping section  28  extend in the same manner as legs  30 ,  32  and  34  of inner section  26 . 
     Inner section  26  and outer section  28  are electrically connected to the probe head via leads  27  and  29 , respectively, as illustrated in FIG.  4 . 
     In this embodiment, sensor assembly  22  in probe head  20  includes hot wire sensor  46 , comprising the hot wire and a device for measuring its change in temperature, and temperature sensor  48 , such as a thermocouple, for measuring the surrounding air temperature. The temperature reading from temperature sensor  48  is used predominantly for adjusting and calibrating hot wire sensor  46 . 
     The hot wire is stretched to be self-supporting between a pair of supports within hot wire sensor  46  for exposure of the hot wire to the gas stream. The material of which the hot wire is formed has a temperature coefficient sufficiently large so that the cooling effects of flowing gas may be readily detected by the temperature measuring device included in hot wire sensor  46 . For fast temperature response, the hot wire is very thin, typically between about 2 and about 20 microns to provide a sensing area large relative to its mass. The material is chosen to be stable throughout the operating temperature range of the hot wire and chemically non-reactive with the gases in the fluid stream to which it is exposed. Preferably, the heat capacity is low and the thermal conductivity is high, factors which contribute to rapid response. Suitable materials for hot wires that are typically used include certain metals and metal alloys, in particular tungsten and platinum alloys. 
     As illustrated in FIG. 5, electronics assemblies  18  and  24 , located in handle  12  and probe head  20 , respectively, comprise the electronics and/or software needed for data acquisition, conversion, processing and transfer from the sensors (i.e., hot wire sensor  46  and temperature sensor  48 ) to a computer. 
     As illustrated in FIG. 6, electronics assembly  18  comprises communications interface  50 , typically a pair of multi-conductor electrical connectors which serve as a port. Interface  50  allows data captured by microprocessor  56  to be transferred to a remote source, such as a hand-held or personal computer  54 , via cable, infrared or wireless transmission. Microprocessor  56  controls all the basic functions of anemometer  10 . Anemometer  10  may also be directly controlled by computer  54  through interface  50  or other connection with electronics assembly  18 . 
     Microprocessor  56  operates timing sequencer  58  which generates the necessary timing pulses for the various anemometer functions which includes setting the timing and reading sequence required to take readings from sensors  46  and  48 . 
     FIG. 7 is a diagram illustrating a sample timing sequence for this embodiment. Trigger pulse driver  172  provides pulse to sensor electronics  24 . Power is transferred to sensor electronics  24  and is stored in power supply  174 . To gather data from  24 , the microprocessor  156  causes pulse driver  172  to remove power (t 1 ) and apply a low resistance across the circuit for a short duration to discharge the line (t 2 ). This event is detected by the trigger pulse detector  176  which begins timer  158 . At t 2 , the Multiplexor switch  164  will connect the voltage from Hotwire sensor conditioning  168  to the line  114 . The line voltage stabilizes during period t 3 . Between t 4  and t 5 , the microprocessor  156  causes sample and hold  178  to capture the voltage and present it to Analog to digital convertor  162 . These events occur while timer  158  is still running. At t 6 , timer  158  completes its timing interval and switches multiplexor switch  164  over to the thermocouple signal conditioner  170  to connect its voltage to the line  114 . The line voltage changes and staibilizes at t 7 . At t 8  to t 9 , the microprocessor  156  retriggers sample and hold  178  to acquire the thermocouple voltage. This voltage is stored and will be transferred to the analog to digital convertor  162  when it completes the previous conversion. At t 10 , the microprocessor  156  causes pulse driver  172  to re-apply power to the line to begin the next cycle. The power supply  174  maintains power for the sensor electronics  24  from t 1  to t 10  and will be recharged after t 10 . 
     Timing sequencer  58  can also be programmed directly from computer  54 . When initiated, timing sequencer  58  energizes sensor assembly  22  for a predetermined amount of time to allow the hot wire to reach its correct operating temperature. The hotwire in hot wire sensor  46  is heated to approximately 130 Degrees Celsius. This heating occurs when the anemometer  10  is turned on. Once the operating temperature is reached, data acquisition routine  60  is then prompted to receive and process signals from electronics assembly  24  in probe head  20 . Airflow is calculated by measuring the voltage required to maintain the hot wire at 130 degrees Celsius. The greater the airflow across the sensor  46 , the more power (and thus more voltage) required. Temperature sensor  38  is used to compensate the air speed calculation for errors introduced when the usage temperature varies from the temperature the anemometer is initially calibrated at. Sensor  48  is also used to directly display the measurement temperature. 
     Data acquisition routine  60  decodes the signals sent by electronics assembly  24  into separate analog signals which are then converted by analog-to-digital converter  62  and read by microprocessor  56 . This process is repeated until probe head  20  is switched off. Microprocessor  56  synchronizes the analog-to digital convertor  62 , timing sequencer  58  and data acquisition routine  60  to capture readings at the correct time. 
     Signals received by data acquisition routine  60  are generated from data retrieved by sensor assembly  22  and conditioned by electronics assembly  24  before being transferred through extendable portion  14 . In this embodiment, electronics assembly  24  comprises time dependant multiplexor  64  and sensor signal conditioner  66 . Multiplexor  64  encodes signals from hot wire sensor  46  and temperature sensor  48  in sensor assembly  22 . The combined signal is then sent via inner and outer sections  26  and  28  to electronics assembly  18  in handle  12  using a form of time domain multiplexing. Sensor signal conditioner  66  provides an interface to sensors  46  and  48  and also amplifies and conditions the signals before they are passed to multiplexor  42  for encoding and subsequent transmission to electronics assembly  18  in handle  12 . 
     Sensor signal conditioner  66  may include two conditioners, as shown in the embodiment in FIG. 8, a hot wire conditioner  168  and a thermocouple conditioner  170  for data from hot wire sensor  146  and thermocouple  148 . 
     Turning on anemometer  110  initiates battery  116  which supplies the power supply  117  in handle  112 . The cable to the computer has several conductors. Three conductors are used for communications (in, out and ground). Two other conductors can be used to provide power to the probe. The power supply  117  will automatically disconnect the internal battery and switch over to external power if available. 
     Trigger pulse generator  172  initiates a pulse and transfer of power to probe head  120  through extendable portion  114 . Power supply  174  maintains and provides power to electronics and sensors  122  and  124  in probe head  114 . Trigger pulse detector  176  detects the initial pulse from generator  172  and initiates timer  158 , which sets the timing sequence for two-channel multiplexor switch  164  to collect data from sensor conditioners  168  and  170 . Sensor conditioners  168  and  170  retrieve raw data from sensors  146  and  148 , respectively. Data is transferred from multiplexor  164  through extendable portion  114  into electronics assembly  118  in handle  112 , where it is temporarily held in memory  178  before being converted from analog to digital by converter  162  and processed by microcontroller  156 . Initial readings are typically used for calibration purposes and stored in memory  180 . Readings may also be transferred through an interface with personal computer  154  via a driver such as RS 232  driver  150  as illustrated in this embodiment. 
     In an alternative embodiment, as illustrated in FIG. 9, Anemometer  210  has a handle  212  and an extendable portion  214 . A battery and its compartment, and electronics assembly are located in handle  212  as in the previous embodiment. Probe  220 , with sensor assembly  222  and a second electronic assembly  224  inside, is secured in anemometer  210  at the end of extendable portion  214 . Extendable portion  214  has an outer telescoping section  226  and inner telescoping section  228 . As in the previous embodiment, outer telescoping section  226  is electrically grounded and inner telescoping section  228  is electrically isolated from outer telescoping section  226 , thus providing for conduction of electricity through extendable portion  214  and sensor assembly  222 . As described in the previous embodiment, both inner telescoping section  226  and outer telescoping section  228  are made up of a plurality of annular pipe-like legs that allow the sections to extend and retract to reach into a flow of fluid. Sensors  245  and  247  are soldered on the top  252  and  254  and bottom  256  and  258  to a pads on a printed circuit boards  260 . Board  260  having  2  pads on the top surface and  2  pads on the bottom surface. 
     In this embodiment, sensor assembly  222  in probe head  220  includes a hot wire sensor bead  245  and two connecting wires  246 . 
     Sensor assembly  222  also includes a temperature sensor  248  with a welded thermocoupler sensor junction  247  for measuring the surrounding air temperature. The temperature reading from temperature sensor  248  is used predominantly for adjusting and calibrating hot wire sensor  245 . 
     Hot wire bead  245 , and thermocoupler  247  are masses of material, preferable substantially spheroid, with a size of 0.5 mm diameter, made of glass encapsulated platinum wire with a 10m W/K dissipation factor. The spheroid shape allows the gases or liquids to flow over the surface in a more even manner and with less turbulence than an irregularly shaped mass or wire. Additionally, by knowing the mass of bead  245  and the physical characteristics of its materials, more accurate calculations can be obtained than with an irregularly shaped wire or wire. Temperature sensor 248 is of a conventional K type thermocoupler design, typically having a diameter of 0.2 mm, and made of Nickel Chromium/Nickel Aluminum, and having a bead of diameter of 0.5 mm, made by welding the two wires together to give approximately 40 μV/°C characteristics of the material. 
     In use, ambient and flow air are measured simultaneously. Typically, the technician first connects the probe to the HPC and extends the probe to allow the probe head to be paced in the air flow to be measured. 
     Next the technician switches on and waits a few seconds for the probe to stabilize. The probe is then placed in the air flow and rotated so that the air flows across the sensor without being obscured by the protective cover, then the technician reads the corresponding air flow and temperature. The built in averaging, min/max and logging functions of the HPC can be used in desired. 
     While illustrative embodiments of the invention have been described above, it is, of course, understood that various modifications will be apparent to those of ordinary skill in the art. Many such modifications are contemplated as being within the spirit and scope of the invention.