Board mounted sensor placement into a furnace duct

A method and apparatus for protecting humidity sensing equipment within an enclosure that can be mounted in the return airflow of a furnace duct. The humidity sensing equipment is mounted on a printed wiring board, which is protected between a mounting base and an operational cover. The mounting base includes a protective shield which allows the humidity sensing equipment to protrude into the furnace duct and prevents damage to the humidity sensing equipment during installation.

CROSS-REFERENCE TO RELATED APPLLCATIONS
 Not Applicable.
 STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
 Not Applicable.
 REFERENCE TO A "MICROFICHE APPENDIX"
 Not Applicable.
 BACKGROUND OF THE INVENTION
 This invention relates generally to the field of humidity control devices,
 and more specifically to humidistat controllers having a humidity sensor
 mounted into a furnace duct.
 In the past, a common approach to humidity control within residential and
 commercial buildings has been to install a humidistat to sense and control
 the ambient humidity within an enclosed space. These humidistats were
 commonly designed to sense the temperature and/or relative humidity within
 the enclosed space and then provide control to a usually remote device,
 which would operate to humidify or dehumidify the room air. Traditionally,
 these humidistats were mounted either on a wall in a common living area,
 or on a furnace duct or plenum.
 Although a conventional wall mounted humidistat is readily accessible to
 the occupants for proper adjustment of the humidity level, it often
 results in significant installation problems due to the type of wall
 construction. Additionally, since the humidistat is commonly configured to
 monitor temperature and relative humidity, there may be instances where
 the sensed humidity may not be an accurate representation of the humidity
 throughout the building. This may then result in an improper adjustment of
 the humidity level.
 Placement of the humidistat on the duct or plenum of a furnace has the
 initial advantage of allowing the humidity-sensing element to be in
 contact with the return air from the building. This allows humidity or
 temperature sensing elements within the humidistat to obtain an average
 relative humidity and temperature of the entire living space. Likewise,
 placement near the furnace typically involves shorter cable runs to any
 associated humidity controlling equipment, saving additional installation
 costs.
 Prior commercial humidistats have generally included at least a relative
 humidity sensing element adapted to be partially enclosed within a
 housing, the housing including a wall or furnace-mountable base and front
 cover attached to the base. The bases of the prior commercial devices were
 generally planar and required a large rectangular cutout in the furnace
 duct to expose the sensing element to the return air. The humidity sensing
 element was often mounted to the front face of the housing, and a cover
 was attachable to the base via forwardly extending spring clips on the
 base ends, which latched over projections formed on the cover ends. One
 example of this type of humidistat may be found in U.S. Pat. No.
 3,523,217.
 Humidistats which are designed to place the humidity-sensing element within
 the return air furnace duct, unfortunately have a significant drawback.
 Due to the size and nature of the humidity control, large rectangular
 holes were required to be cut into the furnace duct or plenum to allow
 exposure of the humidity-sensing element to the duct airflow. These holes
 ranged in size, but were often two inches by four inches, which required
 the cutting to be performed with common sheet metal cutting tools. In a
 typical installation, the installer would create a hole in the ductwork
 (usually by means of a drill), and then further expand the hole to the
 correct size with sheet metal cutting snips. Furthermore, due to the large
 hole placed into the duct or plenum, building inspectors often require
 leaks around these rectangular cutouts to be sealed by caulking.
 The Applicant's invention now described provides an improved humidistat
 mounting method and apparatus which allows sensor placement within a
 furnace duct with minimal damage to the duct.
 BRIEF SUMMARY OF THE INVENTION
 The present invention is a method and apparatus for protecting humidity
 sensing equipment within an enclosure that can be mounted in the return
 airflow of a furnace duct. In the method, a printed wiring board is first
 separated into two sections, which are and electrically connected via a
 flexible jumper. The flexible jumper is then bent so as to position the
 sections in distinct planes, one of the sections being inserted into a
 protective housing. The other of the sections carries a sensor, which is
 operable to sense one or more conditions and relay this information to
 associated controlling equipment located on the second printed wiring
 board.
 Once the flexible jumpers are bent, the printed wiring boards may be
 inserted into a humidistat housing, and the sensing equipment extends
 though an opening in a mounting base. The sensing equipment is protected
 during installation by a protective shield, which is secured to the
 mounting base surrounding the sensing equipment. A cover may then be
 attached to the mounting base and the device may be secured to a furnace
 duct or plenum. Once secured, the sensing equipment extends into an
 opening cut into the furnace duct and is operable to obtain information
 regarding the air within the duct.
 The apparatus of Applicant's invention follows closely the method described
 above.

DETAILED DESCRIPTION OF THE INVENTION
 FIG. 1 shows an exploded view of the humidistat mounting method and
 apparatus of the present invention. The respective parts are shown as may
 be assembled to a furnace duct or plenum 12. The duct mounted humidistat
 10, having sensing elements 14 secured on printed wiring board assembly
 16, a mounting base plate 18, an operational cover 20, and a front cover
 22 may be secured to duct 12 by means of self-tapping screws 23, or the
 like, via mounting holes 68.
 The sensing elements 14 are disposed upon a U-shaped printed wiring board
 assembly 16, having two separate printed wiring boards 24 and 26,
 connected by electrical jumpers 28. The printed wiring board assembly 16
 may initially be assembled in a planar position, as will be explained
 further in FIG. 2, and then bent into a U-shape before assembly onto the
 mounting base plate 18. This approach allows for a cost-effective assembly
 process since all components may be inserted via machine onto a
 single-sided printed wiring board array from the same direction.
 The mounting base plate 18 includes several outwardly projecting bosses 30,
 an aperture 32, mounting holes 34, and a inwardly projecting protective
 shield 36. As shown in FIG. 1, when the device is assembled, printed
 wiring board assembly 16 is adjacent the mounting base plate 18, and
 prevented from further movement toward the mounting base plate 18 by the
 outwardly projecting bosses 30. Mounting holes 34 are provided to receive
 screws 23 that may be used to mount and secure the unit on the furnace
 duct 12. The aperture 32, when the mounting base plate 18 is assembled
 with the printed wiring board assembly 16, aligns with the inwardly
 projection of the sensing elements 14, and allows the sensing elements 14
 to extend beyond the mounting base plate into duct 12 via hole 38.
 Similarly, when the mounting base plate 18 is mounted and secured to duct
 12, the outwardly projecting protective shield 36 extends into hole 38 to
 prevent damage to the sensing elements 14 while the humidistat 10 is being
 handled during installation. Hole 38 may be sized so as to be slightly
 larger than the inwardly projecting protective shield 36. In the preferred
 embodiment, hole 38 is only 3/4 inches in diameter, and may be drilled
 with a mechanical drill or the like. The outwardly projecting protective
 shield 36 extends entirely into hole 38 so that the humidistat 10 may be
 mounted flatly against the level surface of duct 12, minimizing any need
 for the sealing of leaks around the opening in the furnace duct.
 The mounting base plate 18 is connected to the operational cover 20 by
 outwardly extending spring clips 40 on the operational cover ends, which
 latch over projections 42 formed on the mounting base plate ends. The
 operational cover 20 also contains several apertures 44 which allow screws
 66 that are threadably engaged to the printed wiring board assembly 16, to
 project outwardly though the operational cover 20. The heads of the screws
 are received through the operational cover 20 so that wires or jumpers
 necessary for operation may be connected to the components on the printed
 wiring board assembly 16. Mounting holes, generally identified by
 reference numeral 46 on operational cover 20, align with the mounting
 holes 34 on the mounting base plate 18 when the humidistat is fully
 assembled. This allows the insertion of screws (not shown) as previous
 mentioned to secure the humidistat to the duct 12 though mounting holes
 68.
 Front cover 22, containing a large aperture 48 may secured to the
 operational cover 20 so as to protect any wire connections to screw
 terminals 66, and to cover any unsightly mounting screws. When assembled,
 aperture 48 aligns with a knob receptacle 50 to allow an adjustment knob
 (not shown) to extend through the front cover 22. Likewise, a smaller
 aperture 52 aligns with a status indicator 54 on the operational cover 20
 when the front cover 22 is fully assembled. This allows the status
 indicator 54 to be observed even with the front cover 22 fully attached.
 Referring now to FIG. 2A, the printed wiring board assembly 16 is shown in
 an unassembled state. Printed circuit boards 24 and 26 are initially
 secured to temporary rails 56 to be held in a single plane. This allows
 for simple insertion of the humidistat components onto one side of the
 printed wiring board assembly 16, including the sensing elements 14 on
 printed wiring board 26. Flexible jumpers 28 are also electrically secured
 between the printed wiring boards at the same time the boards are
 populated with components. Once the components are fully assembled onto
 the printed wiring board assembly 16, the temporary rails 56 are removed
 and printed wiring board 26 is folded toward printed wiring board 24.
 FIG. 2B depicts the orientation of the printed wiring board assembly 16 as
 it is being assembled into the mounting base plate 18. Flexible jumpers 28
 connect the two separate printed wiring boards 24 and 26, allowing the
 sensing elements 14 to be oriented 180 degrees from the components on the
 front of printed wiring board 24, once the humidistat is fully assembled.
 As explained in FIG. 1, the sensing elements 14 are inserted though the
 mounting base plate 18 and encased by the protective shield 36. Bosses 30
 extend toward the printed wiring board assembly 16 to prevent movement and
 damage to the printed wiring board assembly 16 during operation. This
 allows installers to apply pressure to the screws 66 on the printed wiring
 board 24 through apertures 44 without flexing the printed wiring board 24.
 In the preferred embodiment, the protective shield 36 will operate to
 protect the fragile sensing elements 14 while still allowing adequate
 airflow to the sensing elements 14 to ensure normal humidistat operation.
 Referring now to FIG. 3, the respective parts are shown in an assembled
 state as protected by the front cover 22. Apertures 58 provide opening
 through which electrical cables (not shown) connecting the printed wiring
 board assembly 16 to a humidifier or dehumidifier may conveniently pass
 without interfering with ready assemblage of the humidistat 10. Also shown
 in FIG. 3 are the extending spring clips 60 on the operational cover 20,
 which latch over projections 62 formed on the front cover sides.
 FIG. 4 depicts an alternative embodiment of the mounting base plate
 previously shown and described in FIG. 1. To increase the airflow to the
 sensing elements disposed within protective shield 64, the rear protective
 cover may be excluded. This results in a protective enclosure as formed by
 the remaining four extruding housing shield members.
 In accordance with the foregoing description, the Applicants have provided
 a unique method and apparatus for protecting humidity sensing equipment
 within an enclosure that can be mounted in the return airflow of a furnace
 duct. Although a particular embodiment has been shown and described in
 illustrative purposes, other implementations which do not depart from the
 applicant's teachings will be apparent to those of ordinary skill in the
 relevant arts. It is intended that protection not be limited to a
 disclosed embodiment, but only by the terms of the following claims.