Abstract:
A probe assembly of a sensor is arranged in an airflow channel. A first probe of the assembly has an inlet. The inlet is at a first point in the airflow channel. A second probe of the assembly has an inlet. The inlet is in fluid communication with the airflow channel. The second probe inlet is closer to a surface defining a perimeter of the channel than is the first probe inlet.

Description:
FIELD 
     The invention relates to a sensor system and apparatus having a probe assembly to measure differential velocity in terms of differential pressure to control air flow in a powered air purifying respirator (PAPR). 
     BACKGROUND 
     Powered air purifying respirators utilize a powered mechanism, such as a blower, to draw ambient air through air purifying elements to remove contaminants from the ambient air. They are designed for use as respiratory protection against atmospheres with solid and liquid contaminants, gases and/or vapors where the concentrations during entry and use are not immediately dangerous to life or health and the atmosphere contains adequate oxygen to support life. 
     U.S. Patent Publication No. 2003/0180149, Volumetric Control For Blower Filtered Devices, refers to a control unit which determines a differential pressure between at least two measuring points. The differential pressure is converted into a control signal to vary a fan&#39;s output. The at least two measuring points can be arranged in the air flow behind a fan impeller and in front of the consumer, in particular, the breathing hood. 
     U.S. Pat. No. 4,899,740, Respiratory System For Use With A Hood Or Face Mask, relates to a system having a blower (battery powered, electric motor operated) connected between inlet and outlet plenums. The motor can be manually switched between high and low speed operation to supply high quantities or air upon demand caused by a high respiration rate and otherwise supply lower quantities of air sufficient for low respiration rates to extend battery life between rechargings. A differential air pressure sensing switch is responsively connected for actuation when the difference between air pressure in the outlet plenum and the pressure of ambient atmosphere is less than a pre-selected value. A battery powered audible alarm sounds upon actuation of the switch to alert the user to the approach of potentially dangerously low air pressure in the outlet plenum and consequently in the mask or hood. 
     U.S. Patent Publication No. 2003/0019494, Method And System Of Calibrating Air Flow In A Respirator, provides for the establishment of control set points in a true calibration protocol through the simple triggering of the microprocessor of a controller. When the trigger is initiated, the microprocessor engages and provides the logic for the calibration cycle. The calibration cycle proceeds until a second trigger terminates the process and establishes the control set point. The calibration sequence of the method relies only on an initiation and termination trigger that is facilitated by components integral to the apparatus. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an isometric view of a powered air purifying respirator, PAPR, embodying the present invention; 
         FIG. 2  is an exploded view of the powered air purifying respirator, PAPR, disclosed in  FIG. 1 ; 
         FIG. 3 . is a sectional view of  FIG. 1  taken along view lines A-A; 
         FIG. 4  is a sectional view of  FIG. 1  taken along view lines B-B; 
         FIG. 5  is a flow diagram embodying the present invention; 
         FIG. 6  is a schematic of a respirator system embodying the present invention. 
         FIG. 7  is a cut away view of a basic representation of a channel of a PAPR having a probe configuration similar to that shown in  FIGS. 3 and 4 . 
         FIG. 8  is a cut away view of a basic representation of a channel of a PAPR showing an alternative probe configuration. 
         FIG. 9  is a cut away view of a basic representation of a channel of a PAPR showing an alternative probe configuration. 
         FIG. 10  is a schematic view of a channel of a PAPR showing an alternative probe configuration. 
         FIG. 11  is a schematic view of a channel of a PAPR showing an alternative probe configuration. 
     
    
    
     DETAILED DESCRIPTION 
     The below discussion and attached drawings disclose examples of embodiments encompassing the invention. Other embodiments of the invention are contemplated and the appended claims are intended to cover such other embodiments as are within the scope and spirit of the invention. 
       FIGS. 1-4  show and describe an example of a partial construction of a powered air purifying respirator  20 , PAPR, embodying the present invention. During operation of the PAPR ambient air is drawn into PAPR housing  22  through filter apparatuses  24  by impeller  26 . The impeller  26  forces air through outlet channel  28  at an air velocity W measured in liters per minute, 1 pm. The air exits channel  28  at air outlet  30  and enters coupling tube  31  and tube or hose (not shown) and into breathing hood or mask (not shown). 
     Any part or all of the pathway the air takes from the time it passes into the filters  24  until it escapes into the breathing hood or mask can be considered an air flow channel. The PAPR can include all components along the air flow channel. 
     As the air passes through channel  28  at velocity W it passes a first point  32  in channel  28 . A first probe  34  of a sensor  36  has an inlet. The inlet  34   a  is at first point  32 . The first probe at its inlet  34   a  measures a stagnation pressure, negative pressure, at first point  32  caused by the air passing through channel  28 . The pressure is negative because the inlet  34   a  faces away from the direction of the air flow in the channel. The velocity of the air at point  32  creates a negative pressure around the inlet  34   a    
     A second probe  40  of the sensor  36  has an inlet  40   a  at second point  42 . The second probe  40  via its inlet  40   a  measures static pressure at second point  42  adjacent said channel  28 . The second point  42  is linearly and radially outward from the first point  32 . Accordingly, the second probe inlet  40   a  is radially outward from said first probe inlet  34   a.    
     The air at point  32  has a particular velocity. The air at point  42  essentially has no velocity. The difference in the velocities of the air between said first point  32  and said second point  42  translates into a differential pressure. In this case the differential pressure is the difference between the negative pressure and the static pressure. Each velocity W correlates to a unique differential pressure 
     In general there is always a difference in velocity between the air velocity measured at points which have differing distances from the center of the channel. The air generally travels faster at points toward the center of the tube versus points at the periphery of the tube. If the flow is laminar the velocity difference will be less pronounced than if it is turbulent. The term pressure includes without limitation negative pressure, stagnation pressure (positive) and static pressure. The term differential pressure includes without limitation a difference in measured pressures at two or more points 
     The sensor  36  transmits signals which embody differential pressures between pressure at said first probe inlet  34   a  and pressure at said second probe inlet  40   a . The signal is transmitted to an electronic apparatus  44 . The electronic apparatus affects a comparison of an average measured differential pressure to a preselected value. If there is a difference between the average measured differential pressure, and the difference is greater than a preselected tolerance value, and the motor is not running at maximum speed, than the electronic apparatus generates signals to adjust motor speed. 
     Referring now in more detail to  FIGS. 3 and 4  the first probe inlet  34   a  of sensor  36  forms an inlet of a channel  34   b  in first probe  34 . The probe channel  34   b  extends from said first inlet  34   a  to first inlet  46  of sensor housing  47  which holds the electronic components of sensor  36 . The second probe inlet  40   a  forms an inlet of a channel  40   b  in second probe  40 . The channel  40   b  leads to a second inlet  48  of sensor housing  47 . The first probe  34  extends through the second probe channel  40   b . The second probe channel  40   b  is concentric to the first probe  34 . 
     The second probe inlet is linearly and radially outward and beyond of a surface  50  forming a perimeter of outlet channel  28 . The first probe inlet  34   a  is located radially and linearly inward from said surface  50  and said second probe inlet  40   a . The second probe inlet  40   a  is closer to surface  50  defining the perimeter of channel  28  than is first probe inlet  34   a . First probe inlet  34   a  is closer to the center of the channel  28  than is second probe inlet  40   a . A single linear axis  56  extends vertically into said first probe inlet  34   a  and said second probe inlet  40   a . The first probe inlet is located around the midpoint of a diameter of outlet channel  28 . The first probe inlet has an angled opening. The angle  54  is preferably 45 degrees relative to a longitudinal axis perpendicular to probe  34 . The angle can range from 0 to 90 degrees. The opening into inlet  34   a  faces away from the direction of air flow  38 . Having the opening  34   a  face away from the direction of air flow  38  better helps control for air turbulence. 
     As best seen in  FIGS. 3-4  the first probe extends into channel  28  through single aperture  58 . The second probe opens into channel  28  through aperture  58 . Single aperture  58  opens into said channel  28  through said surface  50 . The first probe and second probe are formed from a single seamless molded piece of plastic which is coupled to the sensor housing at the sensor housing first  46  and second inlets  48 . 
       FIG. 7  shows a probe construction  60 . Angle  62  of the first probe may vary from 0 to 90 degrees relative to the longitudinal axis perpendicular to first probe  65 . Angle  64  may vary from 0 to 360 degrees. Angle  64  reflects the rotation of the first probe around its axis as measured from axis  61 . The position of the first probe inlet  65   a  may extend a distance from 0 to D. The distance D is the diameter or width or height of the channel  68 . There is a single aperture  69  opening into channel  68 . The aperture opens through channel defining surface  70  of channel  68 . The first probe  65  extends through said aperture. The second probe  67  opens into said aperture  69  and into said channel  68 . The second probe inlet  67   a  forms aperture  69 . The second probe inlet  67   a  and first probe inlet  65   a  are arranged in similar fashion to probe inlets  34   a ,  40   a . The second probe inlet  67   a  is closer to surface  70  than is the first probe inlet  65   a . Both inlets open into channel  68 . 
       FIGS. 8 ,  9 ,  10  and  11  show further alternative probe constructions  72 ,  74 ,  76  and  78 .  FIG. 8  is similar to  FIG. 7  except second probe inlet  82  extends into the channel  268  by approximately ½ the radius of the channel  268 . Both the second probe inlet  82  and the first probe inlet  80  face away from the air flow direction  38  and thus measure negative pressure caused by the air traveling at a particular velocity around inlets  80 ,  82 . The second probe inlet  82  and the first probe inlet  80  measure a stagnation pressure (negative). The stagnation (negative) pressures are however different because the inlets are at different linear and radial distances from the surface  269  defining the perimeter of the channel  268 . 
       FIG. 9  shows an arrangement similar to  FIG. 8  except the first probe inlet  80  is facing towards the flow of air  38 . The inlet thus measures stagnation pressure (positive) or impact pressure caused by the velocity of the air at the point where the first probe inlet is in the tube.  FIGS. 7 ,  8  and  9  show first and second probes extending into the PAPR&#39;s outlet channel through a single aperture  58 ,  69  and  270 . 
       FIG. 10  shows the use of a first probe  94  and a second probe  96  wherein each of the probes enter outlet channel  98  through two different apertures  99   a  and  99   b . The first probe is located so its inlet  94   a  is at a point in the channel equal to the length of the channels radius measured from the surface  100  defining the perimeter of channel  98 . The second probe inlet  96   a  is about a length ½ the radius from the perimeter  100 . The first and second probes are laterally oriented along a single axis  102  as opposed to vertically oriented along a single axis. The second probe inlet  96   a  is closer to the perimeter than said first probe inlet  94   a .  FIGS. 7 ,  8  and  9  are considered vertically oriented along a single axis  104 .  FIG. 11  shows the use of three probes  106 ,  108  and  110 . Each probe extends through a different aperture of the surface  100  defining the channel  98 . Each of the probes inlets are linearly aligned, and laterally oriented along a same radius. Probes  106  and  110  are fluidly coupled to provide a single outlet to the electronic guts of the sensor. 
     The probe inlets shown in all figures are all within two inches of each other. 
     Referring now to  FIGS. 5 and 6 , the electronic apparatus has a memory component  150  having stored data from which a desired flow rate or differential pressure Y maybe preselected. Also preselectable from the stored data is a tolerance value θ. Further, preselectable from the data, is a lower threshold flow rate or differential pressure value Z. The desired values Y, θ and Z are preselected prior to operation of the PAPR. The values are stored by the PAPR as the operating values for the PAPR. The apparatus also includes a reader, filter and data averager  152 . The reader reads signals from the sensor as measured differential pressure values based on measurements from first probe inlet  34   a  and second probe inlet  40   a . The reader reads measurements from the sensor 50 times every 0.5 seconds. The data averager averages and filters the 50 readings to provide an average pressure X. Of course different frequencies and intervals for measurements can be used to create an X value. 
     The electronic apparatus further has a comparator  154  and a motor speed sensor  156 . If the motor speed is not a maximum, the comparator compares the average value X to the preselected value Y. If the difference between the X value and the preselected Y value is not greater than the preselected tolerance, θ than the electronic apparatus after a 10 millisecond time delay again reads, filters and averages data from the sensor to provide another X value for further comparison to the preselected Y value. 
     If the difference between the X and Y value is greater than the preselected tolerance value than the comparator  152  sends a signal to a controller  156  which sends a signal to switched mode power supply, SMPS  158 , which adjusts motor speed. The motor speed is increased if the difference between the average value X and the preselected value Y is greater than 0. The motor speed is decreased if the difference is not greater than 0. The motor speed is adjusted to try and produce and maintain an X value within the selected tolerance θ of the selected Y value. Once the motor speed is adjusted and after a 10 millisecond delay, the reader, filter and averager calculate a further average X for comparison. 
     If the electronic apparatus&#39; motor speed sensor detects the motor speed is running at maximum the X value is compared to the preselected lower threshold Z value as opposed to the preselected Y value. If the X value is less than the lower threshold Z value than an alarm sounds. If the X value is not less than the Z value, after a 0.5 second delay the reading and averaging cycles again.