Patent Publication Number: US-2022218936-A1

Title: Humidifier heater base

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/248,663, filed Jan. 15, 2019, which is a continuation of U.S. patent application Ser. No. 14/838,168, filed Aug. 27, 2015, now U.S. Pat. No. 10,252,019, issued on Apr. 9, 2019, which is a continuation of U.S. patent application Ser. No. 13/375,975, filed Jan. 4, 2012, now U.S. Pat. No. 9,174,017, issued on Nov. 3, 2015, which is a national phase of International Application No. PCT/NZ2010/000103, filed Jun. 3, 2010, which claims priority from U.S. Provisional No. 61/184,379, filed Jun. 5, 2009. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to a gas humidification apparatus, particularly but not solely for humidifying a gases supply to a patient or user who require a supply of humidified gas for the treatment of diseases such as Obstructive Sleep Apnea (OSA), snoring, or Chronic Obstructive Pulmonary Disease (COPD) and the like. In particular, this invention relates to the heater base arrangement of a humidification apparatus. 
     Description of the Related Art 
     Devices or systems for providing a humidified gases flow to a patient for therapeutic purposes are well known in the art. Systems for providing therapy of this type, for example CPAP therapy, have a structure where gases at the required pressure are delivered from an assisted breathing unit or blower unit to a humidifier chamber downstream from the blower. As the gases are passed through the heated, humidified air in the humidifier chamber, they become saturated with water vapour. The gases are then delivered to a user or patient downstream from the humidifier, via a gases conduit. Humidified gases can be delivered from a modular system that has been assembled from separate units (that is, a system where the humidifier chamber/heater and the breathing unit/blower are separate items) connected in series via conduits. However, it is becoming more common for integrated blower/humidifier systems to be used, as shown schematically in  FIG. 1 . A typical integrated system consists of a main ‘blower’ or assisted breathing unit which provides a pressurised gases flow, and a humidifier unit that mates with or is otherwise rigidly connected to the blower unit. This mating occurs for example by a slide on or push connection, so that the humidifier is held firmly in place on the main blower unit. An example of a system of this type is the Fisher and Paykel Healthcare ‘slide-on’ water chamber system shown and described in U.S. Pat. No. 7,111,624. 
     Integrated devices are generally more compact and discrete than modular breathing circuit that have been assembled from separate units. A compact and discrete unit is particularly advantageous for home use units, where bedside space is limited, and where a user may also have to transport and set up their own personal unit elsewhere, for example if staying overnight away from home. With compact and integrated units, the set up is generally easier for a user. 
     Generally, home units are used for the relief of sleep apnoea. A mid-use point will usually be during the night, during a users sleep cycle. If refilling or similar is required during use, a user will need to wake up to perform this operation. Having been woken up, the user is required to refill the humidifier chamber. Problems can arise when filling or cleaning these units, as nearly all of the respiratory humidification systems currently available use water as a humidification medium, and cleaning will almost always be carried out with a water based cleaner. Blower and humidifier units are operated and controlled electrically, and problems can occur if the internal electronic parts are not protected. If the internal parts are not protected, any accidental water spillage that takes place can potentially short-circuit the electronics and disrupt the operation of the system. 
     It is an object of the present invention to provide a breathing assistance apparatus which goes some way to overcoming the abovementioned disadvantages or which at least provides the public or industry with a useful choice. 
     SUMMARY OF THE INVENTION 
     In a first aspect, the present invention broadly consists in a heater base assembly for use in a humidifier of the type which is used for heating and humidifying a flow of respiratory gases supplied to a user, comprising: a heater plate having a thermally conductive portion and a perimeter portion around the perimeter of said heater plate, a resilient member having a first portion coupled to said heater plate and a second portion adapted to provide a flange around at least part of said perimeter portion, said resilient member adapted to allow said heater base to be fixed to said humidifier by said flange in such a manner that said heater plate and said first portion can move relative to said humidifier. 
     In a second aspect the present invention broadly consists in a heater base assembly for use in a humidifier of the type which is used for heating and humidifying a flow of respiratory gases supplied to a user, comprising: a heater plate and a resilient member fixed to the heater plate for resiliently mounting the heater plate to the humidifier and providing a fluid barrier between the heater plate and the humidifier. 
     Preferably the resilient member is a flexible gasket or diaphragm for resiliently fixing the heater plate to said humidifier. 
     Preferably said resilient member is moulded to said heater plate. 
     Preferably the first portion is attached to the perimeter portion of the heater plate. 
     Preferably the flange extends around the full perimeter of the heater plate. 
     Preferably the resilient member is adapted to allow said heater base to be fixed to said humidifier by said flange in such a manner that said heater plate and said first portion can move relative to said humidifier in a direction substantially transverse to the general plane of said heater plate. 
     Preferably said thermally conductive portion of said heater plate is substantially planar, and at least part of said perimeter portion is formed out of plane from said thermally conductive portion. 
     Preferably said thermally conductive portion of said heater plate has an upper surface adapted for supporting a humidifier chamber in use, and said perimeter portion is formed so that in use at least part of said perimeter portion is below said upper surface. 
     Preferably the flange is adapted to be clamped between two humidifier components to secure the heater base to the humidifier, at least a portion of the flange being adapted to be at least slightly compressed between the two humidifier components. 
     Preferably the flange is adapted to be clamped between an upper humidifier component and a lower humidifier component, at least a portion of the flange being adapted to be at least slightly compressed between the upper humidifier component and the lower humidifier component. 
     Preferably said resilient member has an upper circumferential groove formed in the upper surface of said flange for accepting a corresponding circumferential projection extending downwards from an upper humidifier component. 
     Preferably said resilient member has a lower circumferential groove formed in the lower surface of said flange for accepting a corresponding circumferential projection extending upwards from a lower humidifier component. 
     Preferably said upper and lower circumferential grooves are vertically aligned. 
     Preferably a portion of the flange is adapted to in use provide a fluid barrier between the heater base and a humidifier component. 
     Preferably a portion of the flange is adapted to in use provide a fluid barrier between the heater base and a humidifier component, the fluid barrier being located between the upper groove and a lower humidifier component. 
     Preferably a portion of the flange is adapted to in use provide a fluid barrier between the heater base and a humidifier component, the fluid barrier being located between the lower groove and an upper humidifier component. 
     Preferably in use a portion of said flange is elastically compressed by substantially between 4% and 20%. 
     Preferably in use a portion of said flange is elastically compressed by substantially 12%. 
     Preferably at least one and preferably both of said upper and lower circumferential grooves taper from a wide mouth to a narrow base. 
     Preferably said resilient member comprises a narrow section formed in said resilient member between said first portion and said flange, said narrow section providing an area in which said resilient member preferentially elastically deflects when said heater plate is displaced relative to said flange of said resilient member in a direction substantially transverse to said general plane of said heater plate in use. 
     Preferably said narrow section comprises a circumferential valley formed in either an upper surface or a lower surface of said resilient member or both. 
     Preferably said resilient member comprises a skirt section formed in said resilient member between said first portion and said flange, in use said skirt section elastically deflecting when said heater plate is displaced relative to said flange of said resilient member in a direction substantially transverse to said general plane of said heater plate. 
     Preferably the first portion is vertically spaced from the flange by the skirt section. 
     Preferably said resilient member is formed as a continuous layer across the upper surface of said heater plate, said continuous layer completely covering said upper surface. 
     Preferably said heater base further has a heating element attached to the underside of said heater plate. 
     Preferably said heater base further has at least one electrical component coupled to the underside of said heater plate, and said resilient member further has a channel formed in the lower surface of said resilient member and running from an inner part or surface of said resilient member to an outer part or surface of said resilient member, said electrical component further having electrical wires that in use extend from said electrical component across said resilient member via said channel. 
     Preferably in use the resilient member forms a fluid barrier between the heater plate and the humidifier. 
     In a third aspect the present invention broadly consists in a humidifier of the type which is used for heating and humidifying a flow of respiratory gases supplied to a user, said humidifier adapted to heat the contents of a humidifier chamber which is removably attached in use to said humidifier, said humidifier comprising: a casing or base unit, adapted to hold said humidifier chamber in position relative to said humidifier, a heater base fixed to said casing or base unit, comprising a heater plate and a resilient member, a heating element, said heater plate having a thermally conductive portion and a perimeter portion around the outside of said thermally conductive portion, said resilient member having a first portion coupled to the heater plate, and second portion providing a flange around at least part of said perimeter portion, said heater base fixed to said casing or base unit by said flange in such a manner that said heater plate and said first portion can move relative to said casing or base unit, said heating element adapted to provide heat to said thermally conductive portion of said heater plate in use. 
     In a forth aspect the present invention broadly consists in a humidifier of the type which is used for heating and humidifying a flow of respiratory gases supplied to a user, said humidifier adapted to heat the contents of a humidifier chamber which is removably attached in use to said humidifier, said humidifier comprising: a casing or base unit, adapted to hold said humidifier chamber in position relative to said humidifier, a heater base fixed to said casing or base unit, comprising a heater plate and a resilient member fixed to the heater plate for resiliently mounting the heater plate to the casing or base unit and providing a fluid barrier between the heater plate and the casing or base unit, and a heating element for providing heat to the heater plate. 
     Preferably the resilient member is a flexible gasket or diaphragm for resiliently fixing the heater plate to the humidifier. 
     Preferably said resilient member is moulded to said heater plate. 
     Preferably the first portion is attached to the perimeter portion of the heater plate. 
     Preferably the flange extends around the full perimeter of the heater plate. 
     Preferably the resilient member is fixed to said casing or base unit by said flange in such a manner that said heater plate and said first portion can move relative to said humidifier in a direction substantially transverse to the general plane of said heater plate. 
     Preferably said thermally conductive portion of said heater plate is substantially planar, and said perimeter portion is formed out of plane from said thermally conductive portion. 
     Preferably said thermally conductive portion of said heater plate has an upper surface adapted for supporting a humidifier chamber in use, and said perimeter portion is formed so that in use at least a part of said perimeter portion is below said upper surface. 
     Preferably the casing or base unit further comprises two humidifier components and the flange is clamped between said two humidifier components to secure the heater base to said casing or base unit, at least a portion of the flange being at least slightly compressed between the two humidifier components. 
     Preferably the casing or base unit further comprises an upper humidifier component and a lower humidifier component and the flange is clamped between said upper humidifier component and said lower humidifier component, at least a portion of the flange being at least slightly compressed between the upper humidifier component and the lower humidifier component. 
     Preferably said resilient member has an upper circumferential groove formed in the upper surface of said flange, and said upper humidifier component has a corresponding circumferential projection extending downwards from said upper humidifier component and into said upper circumferential groove. 
     Preferably said resilient member has a lower circumferential groove formed in the lower surface of said flange, and said lower humidifier component has a corresponding circumferential projection extending upwards from said lower humidifier component and into said lower circumferential groove. 
     Preferably said upper and lower circumferential grooves and corresponding said projections are vertically aligned. 
     Preferably a portion of the flange provides a fluid barrier between the heater base and a said humidifier component. 
     Preferably a portion of the flange provides a fluid barrier between the heater base and the humidifier casing or base unit and the fluid barrier is located between the upper groove and the humidifier lower component. 
     Preferably a portion of the flange provides a fluid barrier between the heater base and the humidifier casing or base unit and the fluid barrier is located between the lower groove and the humidifier upper component. 
     Preferably in use a portion of said flange is elastically compressed by substantially between 4% and 20%. 
     Preferably in use a portion of said flange is elastically compressed by substantially 12%. 
     Preferably at least one and preferably both of said upper and lower circumferential grooves taper from a wide mouth to a narrow base, the corresponding projections being correspondingly tapered to match. 
     Preferably said resilient member comprises a narrow section formed in said resilient member between said first portion and said flange, said narrow section providing an area in which said resilient member preferentially elastically deflects when said heater plate is displaced relative to said flange of said resilient member in a direction substantially transverse to said general plane of said heater plate in use. 
     Preferably said narrow section comprises a circumferential valley formed in either an upper surface or a lower surface of said resilient member or both. 
     Preferably said resilient member comprises a skirt section formed in said resilient member between said first portion and said flange, in use said skirt section elastically deflecting when said heater plate is displaced relative to said flange of said resilient member in a direction substantially transverse to said general plane of said heater plate. 
     Preferably the first portion is vertically spaced from the flange by the skirt section. 
     Preferably said resilient member is formed as a continuous layer across the upper surface of said heater plate, said continuous layer completely covering said upper surface. 
     Preferably said heater base further has a heating element attached to the underside of said heater plate. 
     Preferably said heater base further has at least one electrical component coupled to the underside of said heater plate, and said resilient member further has a channel formed in the lower surface of said resilient member and running from an inner part or surface of said resilient member to an outer part or surface of said resilient member, said electrical component further having electrical wires that in use extend from said electrical component across said resilient member via said channel. 
     Preferably in use the resilient member forms a fluid barrier between the heater plate and the humidifier. 
     Preferably said upper component is the wall of a humidifier chamber compartment adapted for containing a humidifier chamber in use. 
     Preferably a lower portion of said wall of said humidifier chamber compartment includes a horizontal wall section, said flange being clamped between said horizontal wall section and said humidifier lower component. 
     Preferably said heater base forms at least part of a base of said humidifier chamber compartment. 
     Preferably said horizontal wall section and said heater base form a base of said humidifier chamber compartment. 
     Preferably an upper surface of the flange is off set downwardly relative to the upper surface of the first portion of the resilient member attached to the plate, so that an upper surface of the compartment wall horizontal section is approximately in plane with said upper surface of the first portion. 
     Preferably said humidifier comprises a locking mechanism for retaining said humidifier chamber in an installed position with the base of said humidifier chamber adjacent to and contacting said heater plate, and when in said installed position said base of said humidifier chamber displaces said heater plate downwards, said resilient member biasing said heater plate upwards against said base of said humidifier chamber. 
     Preferably said locking mechanism is movable from an unlocked position to a locked position and back again, in use movement from said unlocked to said locked position presses said humidifier chamber downwards against said heater plate by a distance, thereby displacing the heater plate downwards by said distance. 
     Preferably said heater base is assembled to said casing or base unit in such a manner that there is a gap below a bottom surface of said resilient member or heater plate or both, said gap sized to allow said heater plate to displace downwardly from a neutral position in use, the gap being greater than said distance. 
     Preferably said heater element is attached to an underside of said heater plate. 
     Preferably said heater element contacts an underside of the heater plate when said heater plate is displaced downwards to at least said installed position, said heater element out of contact with said heater plate when said heater plate is in a raised uninstalled position. 
     The term “comprising” as used in this specification and claims means “consisting at least in part of”. When interpreting each statement in this specification and claims that includes the term “comprising”, features other than that or those prefaced by the term may also be present. Related terms such as “comprise” and “comprises” are to be interpreted in the same manner. 
     To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting. 
     The invention consists in the foregoing and also envisages constructions of which the following gives examples only. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the invention will be described by way of example only and with reference to the following drawings. 
         FIG. 1  shows a schematic view of a user receiving humidified air from an integrated blower/humidifier system of a known, prior art, type. 
         FIG. 2  shows a perspective view of the preferred embodiment of the integrated blower/humidifier (integrated unit) of one aspect of the present invention, the integrated unit having a separate humidifier chamber and blower unit which are both shown, with the humidifier chamber in place within the blower unit ready for use. 
         FIG. 3  shows a perspective view of the blower unit of  FIG. 2 , with the humidifier chamber removed (not shown). 
         FIG. 4 a    shows a rear view of the blower unit of  FIG. 2 , with a section line D-D shown. 
         FIG. 4 b    shows a cross-sectional view along section line D-D of the blower unit of  FIG. 2 . 
         FIG. 5  shows an exploded view of the blower unit and the humidifier chamber of  FIG. 2 . 
         FIG. 6  shows a schematic detail view along section line DD of the internal structure of the blower unit. 
         FIG. 7 a    shows a rear view of the humidifier chamber of the present invention, with a humidifier chamber lid and a locking handle shown in exploded view above the humidifier chamber, and a section line A-A shown. 
         FIG. 7 b    shows a cross sectional view along the line A-A of the humidifier chamber, humidifier chamber lid and locking handle of  FIG. 7   a.    
         FIG. 8  shows a cross section of a prior art heater plate mounting arrangement 
         FIG. 9 a    shows a cross-sectional view of a preferred form of a heater base assembly. 
         FIG. 9 b    shows a close-up of one side of the heater base assembly shown in  FIG. 9   a.    
         FIG. 10 a    shows a cross section of an integrated unit that incorporates the heater base assembly of  FIG. 9   a.    
         FIG. 10 b    shows a close up of the lower corner of the integrated unit of  FIG. 10 a   , showing structural detail of the wall and the base of the integrated unit, and the relationship of the heater base assembly to these items. 
         FIG. 11  shows a cross-sectional part view of an integrated unit with an alternative form of a heater base assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A schematic view of the user  3  receiving air from a known, prior art integrated blower/humidifier unit  5  is shown in  FIG. 1 . Pressurised air is provided from an assisted breathing unit or blower  1  to a humidifier chamber  2 . Humidified, heated and pressurised gases exit the humidifier chamber  2  via a conduit  21 , and are provided to the patient or user  3  via a user interface  4 . The user interface  4  shown in  FIG. 1  is a nasal mask, covering the nose of the user  3 . However, it should be noted that in systems of these types, a full face mask, nasal cannula, tracheostomy fitting, or any other suitable user interface could be substituted for the nasal mask shown. 
     The integrated blower/humidifier unit  6  of the present invention can be substituted for the unit  5  of  FIG. 1 . A preferred form of the integrated blower/humidifier unit  6  is shown assembled and ready for use in  FIG. 2 . The integrated blower/humidifier unit  6  has two main parts: A blower unit  7 , having an outer shell  36  which forms part of the blower unit  7  and also encloses the working parts of the blower unit—e.g. the fan, internal ducting and the internal control system; and a humidification unit  31  (described in detail below). 
     Assisted Breathing Unit 
     The preferred form of assisted breathing unit or integrated blower/humidifier unit  6  will now be described with reference to  FIGS. 3-6 . 
     The integrated blower/humidifier unit  6  consists of two main parts: an assisted breathing or blower unit  7  and a humidification unit  31 . The humidification unit  31  is enclosed within the external casing of the integrated blower/humidifier unit  6  in use, except for the top part. The structure of the humidification unit  31  is described in greater detail below. The blower unit  7  has an outer shell  36  which is a generally rectangular block with substantially vertical side and rear walls, and a front face that is angled slightly rearwards. In the preferred embodiment, the walls, base and top surface are all manufactured and connected as far as possible to minimise the occurrence of seams, and any necessary seams are sealed. This outer shell  36  encloses the working parts of the blower unit  7 , and forms part of the blower unit  7 . As shown in  FIG. 3 , a control knob  8  is located on the lower section of the front face of the integrated blower/humidifier unit  6 , with a control display  9  located directly above the knob  8 . A patient outlet  25  is shown passing out of the rear wall of the integrated blower/humidifier unit  6 . In the preferred embodiment, in use the free end of the patient outlet  25  faces upwards for ease of connection. However, the preferred form of patient outlet  25  can be rotated to one side or the other to move or align it in a more convenient position for storage or for a more convenient use position. The patient outlet  25  is adapted to allow both pneumatic and electrical connection to one end of a conduit—e.g. conduit  21 —running between the integrated blower/humidifier unit  6  and a patient interface—e.g. interface  4 . 
     In  FIG. 2 , a locking handle  22  is shown in position on the top surface of the integrated blower/humidifier unit  6 . The locking handle  22  is a separate item that can be unlocked and removed from the remainder of the integrated blower/humidifier unit  6 . The locking handle  22  includes a grip  30 , adapted to act as a handle to allow a user to lift and carry the integrated blower/humidifier unit  6 , and also adapted to enable the locking handle  22  to be rotated from a locked position to an unlocked position. The locking handle  22  can be releasably locked to the remainder of the integrated blower/humidifier unit  6 . The function of the locking handle  22  will be more fully described below in the ‘humidifier unit’ section. 
       FIG. 3  shows the integrated blower/humidifier unit  6  with the locking handle  22  removed and the humidification unit  31  not shown. That is, just the blower unit  7  is shown. The top surface of the blower unit  7  includes a circular humidifier aperture  1000 , leading to an internal humidifier compartment  11 . The opening includes a rim  24  located around the circumference of the opening. In use, a humidifier chamber  12  is located within the internal humidifier compartment  11 . The humidifier chamber  12  will be described in detail below. The humidifier chamber  12  is in use fully enclosed inside the internal humidifier compartment  11 , except for the uppermost part. 
     The internal structure of the blower unit  7  will now be described with reference to  FIGS. 3 to 6 . A heater base assembly  23  is located at the bottom of the internal humidifier compartment  11 . The heater base assembly  23  is mounted to the floor of the internal humidifier compartment  11  in such a way that it has a small amount of elastic or compression resilience. That is, it can be pushed downwards a short distance within the compartment, but will push back against any downwards force that is applied. In the absence of any downwards force it will return to its initial position. 
     A blower inlet port  13  and blower outlet port  14  are located on the wall of the internal humidifier compartment  11 , towards the top of the internal humidifier compartment  11 . In the preferred embodiment, these blower inlet and outlet ports  13 ,  14  are aligned so as to mate with humidifier inlet and outlet ports  15 ,  16  located on the humidifier chamber  12  in use (described in detail below) so as to form a blower-to-humidifier gases route which allows gases to exit the blower unit  7  and enter the humidifier chamber  12 . It should be noted that other forms of blower inlet are possible. For example a conduit running between the blower unit  7  and e.g. the lid of the humidifier chamber  12 . 
     As shown in  FIG. 6 , the integrated blower/humidifier unit  6  includes an inlet vent  101  to draw air in from atmosphere. The integrated blower/humidifier unit  6  also includes a mechanism for providing a pressurised air flow from the inlet vent  101  to the humidifier chamber. This inlet vent  101  can be located wherever is convenient on the external surface of the integrated blower/humidifier unit  6 . In the preferred embodiment it is located on the rear face of the blower unit  7 . In the preferred embodiment, air is drawn in through the inlet vent  101  by a blower fan unit  100  which acts as the preferred form of pressured air flow mechanism. The air is ducted or otherwise directed through the casing to the blower inlet port  13 . In use, air will exit the main body of the blower unit  7  via the blower inlet port  13  and then enter the humidifier chamber  12 , where it is humidified and heated, before passing out of the humidifier chamber  12  through the blower outlet port  14 , which is directly connected to the patient outlet  25 . The heated humidified gas is then passed to the user  3  via e.g. a conduit  21 . The patient outlet  25  is adapted to enable pneumatic attachment of the conduit  21 , and in the preferred embodiment, electrical connection at the patient outlet  25  is also enabled via an electrical connector  19 . A combined electrical and pneumatic connection can be useful for example if the conduit  21  is to be heated. It should also be noted that the outlet connection does not have to be via the housing of the integrated blower/humidifier unit  6 . If required, the connection for the conduit  21  could be located directly on an outlet from humidifier chamber  12 . 
     The locking handle  22  and the integrated blower/humidifier unit  6  include a locking mechanism for locking the locking handle  22  to the integrated blower/humidifier unit  6 . In the preferred embodiment the locking mechanism is as follows: the rim  24  includes two mating grooves  26  located just below the rim  24 , spaced opposite each other on the circumference of the rim  24 . More than two of the mating grooves  26  can be used if required. The grooves  26  correspond to an equal number of mating lugs  27  on the locking handle  22 . The mating groove or grooves  26  have an entry point  28  on the rim  24 , with the main part of the groove  26  located slightly below the rim  24 . The lugs  27  are pushed downwards into the entry points  28 , and the handle is rotated so that the lugs enter the main part of the grooves  26  to hold the locking handle  22  in place. Different locking mechanisms can be used if required. 
     Humidifier Chamber with Lid 
     The humidification unit  31  will now be described in more detail with particular reference to  FIGS. 5 and 7 . 
     In the preferred embodiment, the humidification unit  31  is comprised of three main parts: humidifier chamber  12 , lid  32  and locking handle  22  (counted as part of the humidifier unit for the purpose of describing the operation of the integrated blower/humidifier unit  6 ). 
     The preferred embodiment of the humidifier chamber  12  is an open-topped container, with a chamber heat conducting base  17 . The humidifier chamber  12  is sized to fit snugly within the internal humidifier compartment  11  on the integrated blower/humidifier unit  6 . That is, the humidifier chamber  12  is enclosed within the blower unit except for the open top of the humidifier chamber  12 . A fully open topped humidifier chamber is the preferred form of the humidifier chamber  12 . However, an alternative form of the humidifier chamber  12  could have a closed top surface, and would include an opening on the humidifier chamber (not necessarily on the top surface), sized appropriately so that a user can easily fill the humidifier chamber  12 . 
     The humidifier chamber  12  is generally circular, but the lower part of the rear (relative to the integrated blower/humidifier unit  6 ) is flattened as shown in  FIGS. 7 a  and 7 b    to correspond to a ledge  33  on the lower rear side of the internal humidifier compartment  11 . This ensures that the humidifier chamber  12  will always be oriented correctly in use. It should be understood that other methods of achieving the same result could also be used. For example, the humidifier chamber  12  and integrated blower/humidifier unit  6  could include complimentary grooves and slots. The humidifier chamber  12  can also include features such as a fill or level line if required. The humidifier inlet port  15  and a humidifier outlet port  16  are located in the wall of the humidifier chamber  12 , towards the top of the chamber wall. These are positioned so as to align with the blower inlet and outlet ports  13  and  14  when the humidifier chamber  12  is in position, forming the blower-to-humidifier gases route as described above. It is preferred that the corresponding ports on the blower unit  7  and humidifier chamber  12  are shaped so as to minimise air gaps. A good seal is preferred but not required. In the preferred form, the rim or perimeter of the humidifier chamber  12  includes a chamber seal  10 , formed from soft silicone or similar. When the humidifier chamber  12  is placed in position in the internal humidifier compartment  11 , the chamber seal  10  is pressed against the wall or walls of the internal humidifier compartment  11 , and the body of the humidifier chamber  12  and the chamber seal  10  ensure that the humidifier chamber  12  is sealed, so that air exiting the blower through the blower inlet port  13  cannot escape to atmosphere. This helps ensure that a pressurised airstream enters the humidifier chamber  12  in use. If required, a substantially unbroken ring of sealing material such as soft silicone can be added to the wall of the internal humidifier compartment  11  at or close to the upper rim of the humidifier chamber  12 , to form a compartment seal (not shown) instead of or as well as the chamber seal  10 . In alternative embodiments the blower inlet and outlet ports  13 ,  14  are surrounded by resilient sealing gaskets such as silicone gaskets to assist in forming a seal in use. If preferred, the resilient sealing gaskets around the ports can be used as well as the compartment and/or chamber seals. 
     In use, the humidifier chamber  12  is positioned (in the correct orientation) within the internal humidifier compartment  11 . The lid  32  is then placed on top of the humidifier chamber  12 . The lid  32  is sized so that it will pass through the top opening of the integrated blower/humidifier unit  6 , with the lower surface of the lid  32  sealing onto the upper edge of the humidifier chamber  12 . In the preferred embodiment, the lid  32  has an edge perimeter portion that is aligned facing downwards. This has a circumferential recess  34  that is filled with a silicone seal or similar which is pressed onto the upwards facing edge of the humidifier chamber  12  when the lid  32  is in position. This arrangement is shown in  FIG. 7 . In  FIG. 7  the locking handle  22  is also shown vertically above the lid  32  (separate from the lid  32 ). The lid  32  is sized to fit into a recess shown in the locking handle  22  (if the handle shown in  FIG. 7  is pressed vertically downwards onto the lid  32 ). The lid  32  is placed in position on the humidifier chamber  12  once the humidifier chamber  12  has been filled. The locking handle  22  is then positioned above the lid  32 . As has been described above, lugs  27  on the circumference of the locking handle  22  engage with complimentary grooves of grooves  26  on the rim  24 . 
     The compartment and chamber with lid are sized so that the chamber heat conducting base  17  is in contact with at least the plate  44  of the heater base assembly  23  as an upper surface of the lugs  27  contact an upper side of corresponding grooves of grooves  26 . The upper side of grooves  26  is ramped downwards, from the entry point  28  towards the closed end  26   a  of the grooves. Rotation of the locking handle to slide lugs  27  into grooves  26  creates downwards movement of the humidifier chamber  12  against the heater base assembly  23 . Once the lugs have reached the closed end  26   a  of grooves  26 , the humidifier chamber  12  is in a fully installed position. In the fully installed position, the chamber heat conducting base  17  is pressed against at least the plate  44  of heater base assembly  23 . 
     In normal use, a user typically presses or pushes the locking handle downwards, pushing both the lid  32  and the humidifier chamber  12  downwards onto the plate  44  of the heater base assembly  23 . The heater base assembly  23  will give slightly under the downwards pressure, allowing the locking handle  22  to be rotated so that the lugs  27  engage with the grooves  26 . Once the downwards force is removed, the humidifier chamber  12 , lid  32 , and locking handle  22  will be pressed upwards by the reaction force from the resiliently mounted heater base assembly  23 , with the assembly held in place by the lugs  27  and grooves  26 . 
     In the one embodiment shown in  FIG. 3 , the grooves  26  are shaped so that the locking handle  22  cannot be rotated to disengage the lugs  27  without pressing the locking handle  22  downwards slightly first. 
     In the preferred form, the top portion of the lid  32  fits into a central recess in the handle  22 , as can best be seen in  FIG. 7 . The lid  32  and the locking handle  22  are sized so that the lid  32  will snap-fit and be held in place in the locking handle  22  to form an integrated lid unit. The lid  32  can be disengaged from the locking handle  22  by pressing on its top surface or similar. However, it is preferred that the snap-fit will keep them engaged in normal usage. As the handle recess and the lid  32  are circular, they can easily rotate relative to one another when engaged. When the locking handle  22  is rotated to disengage it from the integrated blower/humidifier unit  6 , it will rotate easily relative to the lid  32  (which will not rotate easily due to the seal on the perimeter edge). When the locking handle  22  has been disengaged from the integrated blower/humidifier unit  6 , it can be lifted away from the integrated blower/humidifier unit  6  to remove both the locking handle  22  and the lid  32 . 
     Heater Base Assembly 
     The heater base assembly  23  has been described above as part of a combined blower/humidifier unit for the purpose of describing the operation of the integrated blower/humidifier unit  6 . However, the heater base assembly  23  forms part of a humidifier sub-unit, with the plate  44  of the heater base assembly  23  in use providing heat to the humidifier chamber  12  for heating the liquid and gaseous contents of the humidifier chamber  12  in order to produce water vapour for humidifying the gases flow through the humidifier chamber  12 . The heater base assembly  23  described below may be incorporated into an integrated blower and humidifier unit such as the integrated blower/humidifier unit  6  described above, or the heater base assembly  23  may be incorporated into a separate humidifier unit that is used as one of several components in a modular respiratory system. Where a humidifier unit is referred to below and in the claims, it is intended for this to mean either a separate humidifier unit (modular system) or a humidifier unit that is a sub-unit forming part of an integrated unit such as integrated blower/humidifier unit  6 . 
     A heater base assembly of a typical humidifier such as those known in the art generally has a small amount of elastic or compression resilience, to in use provide a positive force against the base of a humidifier chamber. A positive force between the chamber base and the heater base ensures good thermal contact between the two. A cross section of a typical prior art heater base assembly is shown in  FIG. 8 . Heater plate  144  is formed from a conductive material such as aluminium, and has an upper surface which is generally planar and which acts as a heating surface in use. A heater element is attached (not shown) to provide heat to the heating surface. In use, the conductive base of a humidifier chamber contacts heater plate  144 , the chamber base heated by the contact with the upper heating surface of the heater plate  144 , the chamber base providing heat to the contents of the chamber. In the prior art arrangement shown, the heater plate  144  is supported by a plurality of posts  140 . Posts  140  are moveably coupled to a base or base assembly  156 . A resilient element or elements, in this example a plurality of helical springs  149  corresponding with support posts  140 , are provided between the heater plate  144  and the base  156 , to bias the plate towards the chamber (not shown) which in use is supported by the heater plate  144 . In use, the chamber is pressed down onto the heater base assembly against the heater plate  144 , and the force of the springs  149 , and is locked in place by a locking mechanism. The springs provide a positive upwards force to bias the plate against the base of the chamber to ensure good thermal contact. 
     The prior art assembly of  FIG. 8  does not provide any fluid barrier between the heater plate  144  and other heater base components. For example, should a user spill water from a chamber onto the heater base  123 , water may flood beneath the heater plate  144 . Such a spill can be inconvenient and difficult to clean and may cause damage to humidifier or integrated blower electrical components. 
     A cross section of an integrated unit that includes an embodiment of the present invention is shown in  FIG. 10 a   . The integrated unit of  FIG. 10  includes a heater base assembly  23 . The heater base assembly  23  is shown separately and in greater detail in cross section in  FIGS. 9 a  and 9 b   . With reference to  FIG. 9 a   , the heater base assembly  23  comprises two main parts: a heater plate  44 , and a resilient member  40  which is attached to the heater plate  44 . 
     The heater base assembly  23  will now be described in more detail with reference to  FIGS. 9 a  and 9 b   . The heater plate  44  is a generally thin flat planar item in the preferred embodiment. In the preferred embodiment, at least a portion of the heater plate is formed from a heat-conductive metal such as aluminium. The heater plate  44  has a thermally conductive portion  44   a , and a perimeter portion  44   b  which runs around the outside of the thermally conductive portion. Preferably the thermally conductive portion  44   a  and the perimeter portion  44   b  are integrally formed. It is preferred that at least part of and preferably the majority of the perimeter portion  44   b  is formed out of plane with the thermally conductive portion  44   a . That is, in use, the perimeter portion  44   b  is below the thermally conductive portion  44   a . Preferably plate  44  is formed to the desired size and shape by stamping and pressing from sheet material. Alternatively heater plate  44  could be machined from a parent material. Preferably plate  44  is round. It should also be noted that although a flat planar plate has been described as the preferred embodiment above, the plate  44  could be otherwise shaped—for example concave or convex if required. 
     In the preferred embodiment, the resilient member  40  is attached to plate  44  by an over moulding process. In the preferred embodiment, at least the perimeter portion  44   b  of plate  44  is located within a mould cavity into which an uncured or unset resilient material is injected. Following cure or setting of this material, the resilient member  40  is formed. An inner portion  40   a  of the resilient member is attached to the perimeter portion  44   b  of plate  44 . 
     Preferably the resilient material is silicon or other suitable resilient or rubber material known in the art. 
     Preferably the perimeter portion  44   b  of the plate  44  is moulded into the resilient member following the overmoulding operation described above. As outlined above, it is most preferred that the perimeter portion  44   b  is formed out of plane with the main portion or thermally conductive portion of plate  44 . For example, the perimeter portion  44   b  of the plate  44  may be bent downwards during a cutting or stamping operation when forming the plate  44  from a sheet material. This provides improved mechanical strength in a direction normal to the plane of the plate  44  (this direction also being a direction in which the plate is deflected in use), and provides improved mechanical bond strength for a given size of heater base assembly  23 . Preferably the out of plane portion of plate  44  is formed so that in use it is below that portion of the plate  44  which in use acts as the thermally conductive portion which is in contact with the base of the humidifier chamber. It should be noted that ‘below’ in this context is used to indicate that the out-of-plane portion is lower than the thermally conductive portion—‘below’ is not used in the sense that the out-of-plane portion has to be underneath the thermally conductive portion (i.e. ‘below’ is used in the sense that the out-of-plane portion is not necessarily obscured from view by the thermally conductive portion if the heater plate is viewed from directly above. However, ‘below’ is used in the sense that this construction (obscured from view) is not excluded, either). 
     Alternatively, the perimeter portion of the plate could be formed upwardly. However this is less preferred as the resilient member, being attached to the perimeter of the plate, would extend upwardly of the upper surface of the thermally conductive portion  44   a  of the plate  44 . With the perimeter portion  44   b  formed downwardly according to the preferred embodiment, the resilient member can be attached to the plate so that an upper surface of the plate  44  is adjacent to or in plane with an upper surface of the resilient member  40 . 
     In the preferred embodiment, a heating element (indicated as item  46  in  FIG. 9 a   ) is attached to the bottom of the plate  44 . Preferably the heating element  46  is attached to the bottom of plate  44  via double sided adhesive tape. Other electrical components such as a thermal protection device may also be attached to the bottom of plate  44 . Electrical wires associated with the heating element  46  and any other electrical components are routed away from the heater plate and associated components via a channel  47  (or channels) which are formed in the lower surface  500  of the resilient member  40 , these channels running from the innermost part or surface of the resilient member  40  to the outermost part or surface of the resilient member  40 . In the preferred form, the heater plate  44  is circular or substantially circular, and the channel or channels such as channel  47  are preferably radially aligned with respect to the plate  44 . 
     The electrical components including the heating element  46  may be encapsulated, for example by a potting resin. A frame  48 , for example a plastic frame for surrounding electrical components, may also be fixed to the bottom of the heater plate  44 . If used, frame  48  provides a cavity into which a potting resin may be poured. Some electrical components, such as a thermal overload protection device, may be encased by a resilient boot  59 , the resilient boot being assembled onto the plate prior to encapsulating other electrical components and wires with, for example, a potting resin. 
     Alternatively, one or more electrical components may be encapsulated by the resilient material which forms resilient member  40 . This resilient material attached to the perimeter of the plate  44  may be continuously formed so that it passes at least partly under the plate  44  to encapsulate one or more electrical components. 
       FIGS. 10 a  and 10 b    show how the heater base assembly  23  of  FIG. 9 a    may be incorporated into a humidifier assembly. In the embodiment shown, the humidifier assembly is part of an integrated blower/humidifier unit  6 . However, the humidifier assembly could be part of a stand-alone humidifier. The resilient member  40  has an outer part which extends outwards from the perimeter or perimeter portion of the heater plate  44  around the perimeter or perimeter portion of the heater plate  44 . As described above and as shown in  FIG. 9 b   , the inner portion  40   a  of the resilient member is attached to the perimeter portion  44   b  of the heater plate  44 . The outer part provides a resilient perimeter flange  40   b  around at least a part and preferably the whole of the perimeter portion of the plate. The resilient perimeter flange  40   b  is clamped in a sandwiched arrangement between two humidifier components. It is preferred that the resilient perimeter flange is clamped between an upper humidifier component and a lower humidifier component. 
     The open-topped internal humidifier compartment  11  is defined by a vertical compartment wall  54  extending substantially vertically from the base of the compartment. In the preferred embodiment as shown, the vertical compartment wall  54  is curved around on itself so that the internal humidifier compartment  11  is generally circular in plan view. In the preferred form shown, the flat portion  510  and ledge  33  interrupt the otherwise uniform circular nature of the internal humidifier compartment  11 . These items (flat portion  510  and ledge  33 ) ensure correct orientation of the humidifier chamber  12  within the internal humidifier compartment  11  in use—the humidifier chamber  12  can only be positioned in the internal humidifier compartment  11  in one orientation. A lower portion of the vertical compartment wall is preferably formed as an approximately annular horizontal section  55 . Horizontal section  55  forms part of the compartment base. 
     A humidifier compartment inner base  56  is located below the humidifier compartment base. In the preferred form, the resilient perimeter flange  40   b  of the resilient member  40  is clamped between the vertical compartment wall  54  and the compartment inner base  56 . Preferably the resilient perimeter flange is clamped between the horizontal section  55  and the compartment inner base  56 . 
     The horizontal section  55  and vertical compartment wall  54  may be integrally formed, or may be separate parts that are assembled together. Once assembled, the heater base assembly  23  and the horizontal section  55  form the base of the humidifier compartment. 
     Alternatively, the compartment wall may not include a lower horizontal section. In this alternative embodiment, a lower perimeter edge of the vertical wall interfaces directly with the heater base assembly  23 . In this embodiment, the resilient perimeter flange is clamped between a perimeter edge of the vertical compartment wall  54  and the compartment inner base, with the heater base assembly  23  forming the base of the internal humidifier compartment  11 . 
     The compartment inner base may form a wall of a sub housing. For example, as shown in  FIG. 10 a   , the compartment inner base  56  is a top wall of a fan sub housing  400 . The fan sub housing houses the blower fan unit  100 . 
     The compartment inner base  56  may not extend across the full surface of the compartment base. For example, the compartment inner base  56  may be formed as an annular flange. For example, an annular flange may be attached to the compartment wall section with fasteners extending through holes passing through the resilient member  40 , the resilient member  40  being clamped between the annular flange and the horizontal section  55 . 
     The vertical compartment wall  54  and the horizontal section  55  are fixedly coupled or attached to the compartment inner base by any suitable attachment method known in the art. For example, the vertical compartment wall  54  and horizontal section  55  may be attached to the compartment inner base by screw fasteners. Alternatively the compartment wall may be clipped to the compartment inner base, the vertical compartment wall  54  p.m. a the horizontal section  55  and the compartment inner base  56  sharing mating halves of a clipping arrangement. Alternatively, the vertical compartment wall  54  and the horizontal section  55  may be attached to the outer shell  36  or other component, the compartment inner base also being attached to the outer shell  36  or same other component, fixedly coupling the vertical compartment wall  54  the horizontal section  55  and the compartment inner base  56  together. 
     The compartment wall and the compartment inner base  56  are formed and then assembled within the humidifier unit so that there is a fixed vertical distance between, for example, horizontal section  55  and compartment inner base  56 . The wall and base items are in the preferred embodiment formed from a rigid plastic or similar so when the humidifier unit is assembled there will always be a known, fixed distance between these items or e.g. the edges and walls thereof. The fixed vertical distance between the vertical compartment wall  54  the horizontal section  55  and the compartment inner base  56 , at least a portion of the resilient perimeter flange  40   b  is compressed slightly. Compression of the resilient member  40  assists with maintaining the position of the heater base assembly  23  within the humidifier unit assembly. 
     The resilient member provides a water or fluid barrier between the outside or user accessible surfaces of the humidifier and internal components of the humidifier. Compression of the resilient perimeter flange  40   b  between the vertical compartment wall  54  the horizontal section  55  and the compartment inner base  56  creates a fluid or water barrier between the heater base assembly  23  and the vertical compartment wall  54  and the horizontal section  55 . A compressed portion of the resilient perimeter flange  40   b  provides a fluid barrier between the heater base assembly  23  and the upper humidifier component. The compressed portion of the resilient perimeter flange  40   b  provides a fluid barrier between the heater base assembly  23  and the humidifier compartment wall. In the assembled humidifier unit, the heater base assembly  23  forms at least a part of the base of the internal humidifier compartment  11 . A fluid or water barrier between the heater base assembly  23  and the compartment wall ensures that at least some liquid spilt inside the humidifier compartment cannot reach the internal components of the humidifier unit. Liquid spills are preferably contained within the internal humidifier compartment  11 . 
     Preferably the water barrier provided by the resilient member  40  is a seal that provides a water tight barrier between the heater base assembly and the mating humidifier components such as the humidifier compartment wall. Alternatively, the water barrier may provide a partial seal between the heater base assembly and the humidifier; even a partially water tight barrier that prevents some spilt fluid from passing from the humidifier compartment to the internal components of the humidifier unit can provide a useful benefit. 
     Preferably an upward surface  400   a  of the resilient perimeter flange is off set downwardly relative to the upper surface  400   b  of the inner portion  40   a  of the resilient member attached to the plate  44 , so that, when assembled together, an upper surface of the compartment wall horizontal section is approximately in plane with the upper surface  400   b  of the resilient member  40  attached to plate  44 . 
     As shown in  FIGS. 9 a  and 9 b   , the fluid barrier portion  45  in the preferred embodiment of resilient member  40  is formed as follows: an upper groove  43  is formed in an upper surface of the resilient member. The compartment wall horizontal section has a corresponding upper projection  53  extending downwards, which locates into the upper groove  43  when the humidifier unit is assembled. Preferably the upper groove  43  extends continuously around the resilient member, the upper groove  43  being located intermediate between an outer perimeter  40   c  of the resilient member and an outer perimeter of the plate  44 . Preferably the upper projection  53  extends continuously around an inner perimeter portion of the horizontal section  55 , as shown in  FIGS. 10 a  and 10 b   . Alternatively, the upper projection  53  may extend continuously around the compartment wall horizontal section at a position intermediate between an inside perimeter of the horizontal section  55  and the vertical compartment wall  54 . 
     Preferably the upper projection  53  is tapered to assist with alignment of the compartment wall with the heater base assembly  23  during assembly of the humidifier unit. Preferably the upper groove  43  is correspondingly tapered, tapering from a wide mouth to a narrow base. 
     The upper projection  53  provides a reduced cross sectional area for easier compression of the resilient member  40 , when compared to no projection. This allows for easier assembly of the humidifier unit as a reduced force is required to compress the resilient member to a desired state of compression. Compression of the resilient member  40  between the upper projection  53  and the compartment inner base creates the fluid barrier for containing fluid spills within the internal humidifier compartment  11 . 
     In the most preferred form, the fluid barrier portion  45  in the resilient member  40  is further formed by the inclusion of a second groove  42  formed in the lower surface  500  of the resilient member  40 . In the preferred form, the compartment inner base also has a corresponding lower projection  52  which in use extends upwards and locates within the second groove  42  when the humidifier unit is assembled. Preferably the second groove  42  extends continuously around the resilient perimeter flange  40   b , the second groove  42  being located intermediate between the outer perimeter  40   c  of the resilient member and the outer perimeter of the plate  44 . In the preferred embodiment, the lower projection  52  extends continuously around the compartment inner base  56  and corresponds to the continuous second groove  42 . 
     In the preferred embodiment, the lower projection  52  is tapered to assist with alignment of the heater base assembly  23  onto the compartment inner base during assembly of the humidifier unit. In the most preferred form, the second groove  42  is tapered from a wide mouth to a narrow base. 
     The lower projection  52  provides a reduced cross sectional area for easier compression of the resilient member  40 . This allows for easier assembly of the humidifier unit as a reduced force is required to compress the resilient member to a desired compression. Compression of the resilient member between the lower projection  52  and the compartment horizontal section assists in forming a fluid barrier which contains fluid spills within the internal humidifier compartment  11 . 
     As outlined above, in the preferred form, the heater base assembly  23  has the upper groove  43  and second groove  42 . Preferably the second and upper grooves  42 ,  43  are aligned in a vertical direction—that is, when assembled into the humidifier unit and in use, the upper groove  43  is directly above the second groove  42 . The part of the resilient member  40  that is sandwiched between the vertically aligned lower and upper projections  52 ,  53  acts as the fluid barrier for containing spills within the internal humidifier compartment  11 . Preferably the dimensions of the projections, the set distance between the projections, and the corresponding thickness of resilient material located between the second and upper grooves  42 ,  43  are calculated so that a vertical compression of the resilient member of approximately 12% is achieved when the humidifier unit is assembled. However, any range of compression between 4% and 20% has been found to be acceptable. A wider range could also be considered, although this is not preferred. 
     The resilient material either side of the fluid barrier portion  45  may be slightly compressed. Alternatively, the resilient material either side of the fluid barrier portion  45  can remain uncompressed in the assembled humidifier unit. It is most preferred that the resilient material outside of the fluid barrier portion  45  (e.g. the material between the outer perimeter  40   c  and the seal portion  45 ) is compressed slightly in the assembled humidifier unit. This compression of the resilient material outside of the fluid barrier portion  45  is less than the compression of the fluid barrier portion  45 . Alternatively, the resilient material outside of the fluid barrier portion  45  can remain uncompressed in the assembled humidifier unit. 
     The material within the fluid barrier portion  45  (e.g. the material between the fluid barrier portion  45  and the plate  44 ) is compressed slightly in the assembled humidifier unit. This compression of the resilient material within the fluid barrier portion  45  is less than the compression of the fluid barrier portion  45 . Alternatively, the resilient material within the fluid barrier portion  45  can remain uncompressed in the assembled humidifier unit. 
     As can be seen from the above description, the fluid barrier portion of the resilient member is clamped between or sandwiched between the vertically aligned lower and upper projections  52 ,  53 . The inner portion  40   a  of the resilient member  40  is overmoulded and permanently connected to the heater plate  44 . Therefore, the resilient member  40  provides a fluid barrier between the heater base assembly  23  and the humidifier compartment wall. Additionally the resilient member  40  acts as a suspension member as will now be described. 
     As shown in  FIGS. 10 a  and 10 b   , in the preferred embodiment, a gap  50  is provided between the heater base assembly  23  and the compartment inner base. The gap  50  is between the lower surface  500  of the resilient member  40  and an upper surface of the compartment inner base  56 . In use, the heater plate and a portion of the resilient member are displaced downwardly (with the clamped portion or resilient perimeter flange of the resilient member  40  remaining in place). Alternatively, the compartment inner base  56  may be absent except for the portion of the compartment inner base  56  clamping the resilient perimeter flange  40   b.    
     The gap  50  allows vertical downward movement of that part of the heater base assembly  23  which is not clamped. The gap  50  is present when the resilient member  40  is un-deflected. The resilient member  40  is un-deflected when the humidifier chamber  12  is not installed within the internal humidifier compartment  11  with the plate  44  in a raised or uninstalled position. As described previously, to install the humidifier chamber  12  within the internal humidifier compartment  11 , the humidifier chamber  12  is positioned within the internal humidifier compartment  11  and the lid  32  is then placed on top of humidifier chamber  12 . The lid  32  and locking handle  22  is pressed down slightly, allowing the locking handle to rotate so that the lugs  27  engage with grooves  26 . Pressing the lid and locking handle downwards presses the chamber heat conducting base  17  of humidifier chamber  12  onto the heater base assembly  23 . The resilient member  40  of heater base assembly  23  and the gap  50  beneath the heater base assembly  23  allows the heater plate  44  to move downwards with respect to the vertical compartment wall  54  and the horizontal section  55 . With the humidifier chamber  12  in the installed position, the resilient member  40  remains in a deflected state. In the deflected state, the resilient member  40  provides an upwards force, pressing or biasing the thermally conductive portion  44   a  of heater plate  44  against the base of e.g. humidifier chamber  12  to ensure good thermal contact. 
     It should be noted that the way in which the humidifier chamber  12  locks to or is held by the humidifier unit in an installed position is not important. For example, a humidifier assembly according to the present invention may not enclose the humidifier chamber within a chamber compartment as in the preferred embodiment described above. Other retaining or locking mechanisms other than the grooves  26  and lugs  27  described above may be used to retain the chamber in an installed position where the heater plate is displaced downwardly against the action of the deflected resilient member  40 . 
     As shown in  FIG. 7 a    or  FIG. 7 b   , the chamber heat conducting base  17  preferably extends slightly proud of the periphery portion  18  of the base. As best shown in  FIG. 9 a   , in the preferred embodiment, the resilient member  40  does not extend all the way across the top surface of the heater plate  44 , but forms a circumferential ridge above and around the outside perimeter of the heater plate  44 . The chamber heat conducting base  17  and the resilient member  40  are dimensioned so that the chamber heat conducting base  17  will fit within the saucer section formed by the ridge of resilient member  40  attached to the heater plate  44 , and the chamber heat conducting base  17  directly contacts the heater plate  44  over substantially the whole of the surface of the chamber heat conducting base  17 . In the preferred embodiment, the amount which the chamber heat conducting base  17  extends downwardly proud of the periphery portion  18  is slightly greater than the thickness or height of the ridge of resilient material above the surface of the heater plate  44 , to ensure there is no interference between the resilient member  40  and the humidifier chamber, so that good contact between plate  44  and chamber heat conducting base  17  occurs. Alternatively the whole base of the humidifier chamber may fit within the inner dimension of the resilient member. 
     Preferably the gap  50  allows enough vertical movement of the heater plate  44  to allow the locking handle lugs  27  to lock fully into grooves  26  without the gap  50  completely closing. This ensures the humidifier chamber may be installed by downwards deflection of the resilient member only—that is, without further significant compression of the resilient member. This helps ensure that the force required to press the chamber into position does not become excessive. For example, in the preferred embodiment, the gap provides approximately 1.1 mm of vertical travel, and the amount of vertical travel required to slide locking lugs  27  from the entry point  28  into grooves  26  is approximately 0.7 mm. 
     When deflected downwards, the resilient member  40  provides an upwards force to the heater plate so that the heater plate  44  is pressed against the chamber heat conducting base  17 . 
     The inventors have found that a force of approximately 29N is desirable for pressing the chamber onto heater plate  44  (and vice versa) to fully install the humidifier chamber  12  within the internal humidifier compartment  11 . A force of this magnitude is not overly difficult for a user to over come by rotation of the locking handle lugs  27  into grooves  26 , and this amount of force provides good contact pressure between the chamber heat conducting base  17  and the heater plate  44  for good thermal connection. 
     To achieve a desirable deflection force required to install the humidifier chamber  12  into the internal humidifier compartment  11 , the resilient member further has a necked or narrow section  49  located between the inner portion  40   a  and the clamped portion of the resilient member  40 . Narrow section  49  is formed by forming or including a valley  41  in either the lower or the upper side or surface of the resilient member  40 . It is preferred that the valley  41  is formed in the bottom surface of the resilient member as shown in  FIGS. 9 a  and 9 b   . Alternatively, the valley may be formed in the upper surface of the resilient member  40 , or both surfaces of the resilient member. 
     Movement of the heater plate  44  downwards from a resting position is achieved by deflection of the resilient member  40 . The clamped portion of the resilient perimeter flange  40   b  is clamped in position and remains stationary relative to the humidifier assembly as outlined above. The inner part or inner portion  40   a  is attached to the heater plate  44  and moves downwards with the heater plate  44  when the humidifier chamber is placed in position. Elastic deflection of the resilient member  40  between the inner portion  40   a  and the clamped portion generally occurs through the narrow section  49 . The resilient member  40  deforms (generally through the narrow section  49 ) as it is deflected during downwards movement of the heater plate  44 , and an inner side  51  of the upper groove  43  may deflect away from the upper projection  53 , creating a crevice between the inner side  51  and a side of the upper projection  53 . Liquid from a spill inside the compartment may enter the crevice. However, once the humidifier chamber  12  is removed from the internal humidifier compartment  11 , the resilient member deflects back to a resting shape, closing the inner side  51  of the upper groove  43  against the corresponding side of the upper projection  53 . This closing of the crevice squeezes liquid from the area between the upper groove  43  and upper projection  53 . Due to the compression of the fluid barrier portion  45 , no liquid passes beyond the fluid barrier provided by the resilient member, even with maximum deflection of resilient member  40 . 
     In an alternative embodiment, the resilient member is formed continuously across the upper surface of the heater plate, completely covering the upper surface of the heater plate. During the over moulding process, the uncured or unset resilient material is allowed to flash across the upper surface of the heater plate  44 , creating a heater base assembly with a continuous resilient material upper surface. The resilient material covering electrically isolates the heater plate from user contact, and provides corrosion protection. 
     In a further alternative embodiment, the heater element may be attached to the compartment inner base or other humidifier component. In this alternative embodiment, the heater element does not contact the heater plate  44  when the heater plate  44  is in a raised position with the resilient member  40  in an un-deflected state. When the humidifier chamber is installed within the humidifier compartment, the heater plate  44  is moved downwards against the action of the deflected resilient member  40  to a lowered position. In the lowered position, the bottom of the heater plate  44  makes thermal contact with the heating element attached to the inner compartment base or other humidifier component to heat the heater plate and the conductive base of the chamber above. This embodiment has the advantage that the heater plate  44  cools more quickly when the chamber is removed from the internal humidifier compartment  11 , as contact between the heater plate  44  and the heater element is lost when the humidifier chamber  12  is removed from the heater plate  44 . The heater element is preferably elastically mounted to the inner compartment base or other humidifier component to allow some vertical movement of the element once in contact with an underside of the heater plate. The spring constant of the elastic mounting of the heating element may be different to the spring constant of the elastic mounting of the heater plate. For example, the spring constant of the elastic mounting of the heating element could be higher than the spring constant of the elastic mounting of the heater plate. 
     An alternative heater base assembly is illustrated in  FIG. 11 . The same item numbering used to describe the previous embodiment of  FIGS. 9 a  and 9 b    have been used to describe like parts of the alternative embodiment of  FIG. 11 . 
     A difference between the embodiments of  FIGS. 9 and 11  is the cross sectional shape of the resilient member  40 . The resilient member in the heater base assembly  23  of  FIG. 11  is preferably attached to the plate  44  and assembled to a humidifier assembly as previously described with reference to the embodiment of  FIGS. 9 a  and 9 b   . With reference to  FIG. 11 , an inner portion  40   a  of the resilient member  40  is attached to a perimeter portion  44   b  of plate  44 . Preferably the resilient member is moulded to the plate. As shown in  FIG. 11 , the resilient member is moulded or attached to a lower surface of the plate. An outer part of the resilient member forms a resilient perimeter flange  40   b  around at least a part and preferably the whole of the perimeter portion of the plate. The resilient perimeter flange  40   b  is claimed in a sandwiched arrangement between two humidifier components, the horizontal section  55  and compartment inner base  56  in  FIG. 11 . A fluid barrier is formed between the heater base assembly and a humidifier compartment as previously described with reference to the embodiment of  FIG. 9 . 
     Bridging between the inner portion  40   a  and the resilient perimeter flange  40   b  of the resilient member is a skirt portion  40   d . The skirt portion  40   d  allows vertical movement of the heater plate  44  with respect to the resilient perimeter flange of the resilient member. 
     In the illustrated embodiment, the skirt portion  40   d  spaces the inner portion  40   a  of the resilient member from the resilient perimeter flange  40   b  of the resilient member. A vertical gap  50 ′ between the inner and outer parts of the resilient member allow vertical movement of the heater plate  44  relative to the outer part of the resilient member fixed to the humidifier assembly. The gap  50 ′ is present when the resilient member is un-deflected, when the humidifier chamber  12  is not installed within the humidifier compartment with the plate  44  in a neutral or non-displaced position. Once the chamber is installed into the humidifier and on the heater base, the resilient member is deflected. In the deflected state, the resilient member provides an upwards force to bias the plate  44  against the base of humidifier chamber  12 . 
     Preferably the gap  50 ′ provides enough vertical movement to allow a chamber to be installed onto the heater base without the gap  50 ′ fully closing, as previously described with reference to the embodiment of  FIG. 9 . 
     The amount of force required to displace the heater plate downwards may be determined by the thickness of the skirt portion  40   d  of the resilient member  40  or the length of the skirt section or both. 
     The resilient member provides a gasket or diaphragm between the heater plate  44  and the humidifier structure to resiliently mount the heater plate  44  within the humidifier assembly. The intermediate portion of the resilient member bridging between the clamped portion of the resilient member and the inner portion of the resilient member coupled to the plate  44  allows vertical movement of the heater plate. 
     Further alternative embodiments may present themselves to a person skilled in the art without departing from the present invention. For example, the resilient member may form a bellows shape or other shape designed to achieve a desired amount of resistance to displacement of the heater plate relative to the humidifier base or casing. 
     Furthermore, the resilient member may be alternatively attached to a component fixed to the heater plate. For example, the resilient member may be moulded or otherwise attached to the frame  48  attached to the bottom of the heater plate  44 . Attachment of the frame to the heater plate couples the resilient member to the heater plate without direct bonding between the heater plate and the resilient member. 
     The heater base assembly according to the present invention is a vertically compact assembly. When assembled into a casing as part of a humidifier assembly, the compact nature of the heater base assembly helps to reduce the humidifier assembly or integrated unit assembly height to assist in achieving a desirable compact unit for home use. The heater base assembly according to the present invention when assembled as part of a humidifier assembly or integrated unit provides a fluid barrier that prevents or at least reduces spills contacting internal blower or humidifier components and contains spills within the humidifier compartment. The heater base assembly according to the present invention has a resilient element that in use acts to provide a desirable amount of force between the heater plate  44  and the conductive base of the humidifier chamber, to bias the heater plate against the base of the chamber. In the context of this specification, a desirable amount of force is an amount of force which can be easily overcome by a user when installing a humidification chamber into the humidifier, yet provides sufficient contact force to achieve good thermal contact between the chamber base and heater plate. 
     The foregoing description of the invention includes preferred forms thereof. Modifications may be made thereto without departing from the scope of the invention as claimed. 
     It should also be noted that when terms such as for example ‘top’, ‘bottom’, ‘above’, ‘below’, ‘upper surface’, ‘lower surface’ and ‘underside’ are used, these refer to the orientation of the device described or claimed when it is in use. These terms are used to describe the orientation or location of features relative to one another when the device is in use, and when these terms are used, should be read in this manner. Use of these terms is not intended to limit the device as described or claimed in any other fashion.