GB2111753A - Thermally-sensitive controls for electric heaters - Google Patents

Abstract

A thermally-sensitive control of an electric kettle or like container is mountable to the head 2 of an electric heater. A memory metal or snap-acting bimetallic actuator 32 is mounted between the control body 10 and the head 2 so as to be in good thermal contact with part of the heating element, such that in the event of the element overheating, operation of the actuator opens switch means to interrupt the power supply to the heater. The switch means includes two sets of breakable contacts, each set including a movable contact spring 18 adapted for engagement, during normal use of the heater, with a stationary contact 19 mounted directly to a respective cold lead 7 of the heater. <IMAGE>

Description

SPECIFICATION Electric heaters and thermally-sensitive controls therefor This invention relates to electric heaters of containers such as electric kettles, jugs, urns, pans, coffee percolators, laboratory equipment and the like (hereinafter called "containers of the kind referred to") and to thermally-sensitive controls therefor.

The electrical heaters of such containers may either be immersion heaters or similarly constructed heaters mounted externally to the container in good thermal contact with a wall thereof, for example by being brazed to the underside of the container base.

The heating elements of such heaters terminate in so-called cold leads by means of which electrical connections are made to the heater.

Electrical controls for such heaters are well-known which include electrical switch means operable to interrupt the power supply to the heater upon the element thereof overheating after for example having been switched on with insufficient liquid in the container to cover the element. Such an arrangement conventionally includes a set of breakable contacts wired in series with the element and thermally responsive actuating means effective upon the element overheating to break the contacts and thus deenergise the heater.

An example of such a control for use with an immersion heater is described in British Patent Specification No. 1470366 in which the switch means includes a movable contact mounted on a first spring strip connected to a live terminal pin of the control which is adapted to be connected in use to a source of electrical power via a detachable socket connector, and a stationary contact mounted on a second spring strip which is rivetted to the control and a free end of which bears against a cold lead of the element. A neutral terminal pin of the control is electrically connected to the other cold lead of the element via a third spring strip which is connected to the pin and adapted to bear against and make contact with the cold lead.During normal operation the contacts are closed and power can be supplied to the heater; upon overheating of the element a thermally responsive actuator mounted to the control urges the movable contact away from the stationary contact thus opening the heater circuit.

However, the general configuration of the various components of the switch means is somewhat bulky and inconvenient to manufacture. Firstly, for example, the second and third spring clips which contact the bare ends of the respective cold leads need to be firmly mounted within the control and relatively stiff in order to be sufficiently strongly biased againstthe ends of the cold leads so as to make adequate electrical contact therewith. Secondly, the three spring strips which all differ in size and shape must each be carefully dimensioned so that, firstly, the contact precisely align and, secondly, the second and third strips firmly engage the cold leads.

An earilierform of control is described in British Patent Specification No. 1401954 and differs from that described above in that electrical contact to the cold leads of the element is made by means of semi-cylindrical resilient connector tabs which embrace the leads. A first tab is connected to the neutral terminal pin while the second tab forms part of a resilient conductive strip to which the movable contact of the switch means is mounted, the stationary switch contact being connected to the live terminal pin.

A thermally-sensitive control adapted for use with a container of the kind referred to having an externally mounted heater is described in British Patent Specification No. 2042269A and in this arrangement, the electrical connection to the cold leads is achieved by means of spring clips which are in turn respectively connected to a stationary contact of the switch means and to the neutral terminal pin of the control.

However, with these and other similar arrangements, the tabs or clips which make contact with the cold leads complicate the construction of the control and contribute significantly to manufacturing costs.

According to the invention there is provided an electric heater of a container of the kind referred to and a thermally-responsive electrical control for said heater, there being thermally responsive actuating means operable upon the element of said heater overheating and electrical switch means, said switch means comprising two sets of breakable contacts each set including a stationary contact mounted directly to a respective cold lead of the heater element and a movable contact mounted on a resilient conductive strip of said control, wherein, during normal operation, the movable contacts are biased against the respective stationary contacts by said resilient strips and electrical power can be supplied to said heater via said switch means, said movable contacts being displaceable in response to operation of said actuating means upon the element overheating to break said contacts to interrupt the power supply and deenergise the heater.

With the inventive arrangement, the requirement of spring clips mounted to the control for making electrical connection with the cold leads of the element is avoided. This represents a considerable simplification with regard to manufacture and assembly of the control. Furthermore, the total number of components may be reduced which leads to a reduction in costs and also, if desired, allows the overall size of the control to be reduced.

The stationary contacts could conceivably be mounted to the cold leads in any number of ways.

Preferably cylindrical sleeves secured to the contacts are interference fitted to the cold leads. Alternatively, cylindrical spring clips secured to the contacts may be engaged around the ends of the cold leads.

In a preferred embodiment, the resilient strips to which the movable contacts are mounted are in the form of generally U-shaped leaf springs. The leaf springs are preferably identical and are disposed symmetrically within the control. This represents a further simplification concerning manufacture and assembly.

Furthermore, the use of generally U-shaped leaf springs increases the relative lateral movement between the contacts as they are opened or closed since, during displacement of the free ends of the springs, the springs are caused to both pivot and twist about their mounting. This increases the self cleaning ofthe contact surfaces.

Preferably, the control includes terminal pins adapted for engagement with a separate female socket connector for connecting the heater to a source of electrical power. The resilient strips or leaf springs may conveniently be secured directly to the terminal pins.

In a preferred embodiment, the U-shaped leaf springs includes apertures base portions which surround and are secured to the respective bases of the live and neutral terminal pins. Such an arrangement lends itself to the assembly of the pins and the leaf springs to a body portion of the control in an automated operation whereby costs may be further reduced.

Electrical connection of an earth terminal pin to the heater may conveniently be made by means of a resilient conductive strip which is also provided with an apertured base portion for surrounding the base of the earth pin.

The thermally-responsive actuating means which may take any convenient form such as a memory metal device may be mounted directly either to the heater or to the control. In one advantageous embodiment however, the actuating means in the form of a snap-actuating bimetallic actuator is mounted by means of a stainless steel bridge member which is securablewithin the control. Such a bridge member is the subject of published British Patent Application No. 2097920 application entitled "Thermally sensitive controls for electric heaters".

The thermally responsive actuating means is preferably coupled to the switch contacts by means of a link member which is slidably mounted within a body portion of the control and movable in response to operation of the actuating means so as to engage the free ends of the leaf springs and urge the movable contacts away from the stationary contacts thereby interrupting power supply to the heater.

Preferably, the actuating means is a snap-action device adapted for direct engagement with the link member such as the type described in British Patent Specification No. 1542252 comprising a stressed sheet of bimetal with a generally domed configuration and a central tongue. Such an actuator is adapted to snap between two oppositely dished configurations at a certain critical temperature.

In one advantageous embodiment of the invention, the two sets of contacts are independently breakable in response to operation of the actuating means. The provision of independently breakable contacts is significant from the safety point of view in that should one set become welded together after an extended period of use, for example due to the contact surfaces corroding, then the other set will still open to deenergise the heater in the event of the element overheating. This feature is particularly important where the control forms part of an applicance which in its general use is likely to be left unattended for extended periods of time, for example an early morning tea maker. With such an appliance, failure of the protector switch means due to welded together contacts upon the appliance boiling dry can lead to serious overheating of the element which is extremely dangerous.

In the preferred form of the invention, the link member is pivotable within the control and the arrangement is such that, in the event of one set of contacts becoming welded together, the link member will pivot in response to the acutating means about the welded together set of contacts and open the other set.

In a preferred embodiment, the control further comprises second thermally responsive actuating means coupled to the switch means and exposed, in use of the control, to steam or vapour resulting from liquid within the container boiling and effective to open the switch contacts upon boiling.

In one form of the invention, the control is adapted for use with an immersion heater and has an outer periphery of less radial extentthan a peripheral portion of the immersion heater head so as to be passabie through the opening in the wall of an associated container in or adjacent which the head is adapted to be secured. Such an arrangement is the subject of our copending application claiming priority from British Patent Application No. 8137993 entitled "Thermally-sensitive controls for electric immersion heaters" filed contemporaneously herewith and is advantageous in that the control may be sold fitted to an immersion heater for user fitting as a universal replacement.

The scope of the invention extends not only to the combination of heater and control as aforesaid but also to the heater and control separately.

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is an exploded perspective view of a control taken from the side of the control which in use is secured to the head of an immersion heater.

Figure 2 is an exploded perspective view of the control illustrated in Figure 1 taken from the opposite side of the control and showing the immersion heater head.

Figure 3 is a perspective view similar to Figure 2 with certain parts of the control removed.

Figure 4 is a cross-sectional view taken from one side of the control of Figures 1 to 3 mounted to the head of an immersion heater showing the overcentre spring mechanism in the deactivated position.

FigureS is a view similar to Figure 4 but showing the overcentre mechanism in the operational position.

Figure 6 is an elevational view, partly broken away, of the end of the control adapted to be secured to the immersion heater head.

Figure 7 is a cross-sectional view taken along line 7-7 in Figure 6 showing the switch contacts open.

Figure 8 is a view similar to Figure 7 but showing the switch contacts closed.

Figure 9 is a view similar to Figures 7 and 8 but showing one contact open and one closed.

Figure 10 is a plan view of the over centre spring for the control illustrated in Figures 1 to 9.

Referring firstly to Figures 1 to 5, a thermallysensitive control 1 is mounted on the head 2 of an electric immersion heater. The cup-like head 2 is retained in a water-tight manner in an opening formed in the wall 4 of an associated container by means of an externallaythreaded retaining ring 3 which urges a peripheral flange 9 of the had 2 against the inside of the wall 4 compressing a resilient O-ring seal 5 therebetween as shown in Figure 4. The immersion heater head 2 carries a tube 6 for the egress of steam from the interior of the container which tube is brazed to the head and extends, in use, above water level within the container. The immersion heater comprises two cold leads 7 and a hot return 8 which passes underneath the cold leads 7 and is brazed to the head 2 so as to be in good thermal contact therewith.The low position of the hot return 8 enables the container to boil small quantities of liquid if desired.

The control 1 comprises a body portion 10 of thermo-plastic material, mounted snugly within the head 2 by means of three bolts 11 which engage threaded female studs 12 brazed to the inside of the head, and a cover member 13 which is secured to the body portion 10 by means of a single central fixing bolt 14. The body portion 10 includes a horizontal shelf member 15 which lies close to the central longitudinal axial plane of the control 1 and defines at the side of the body portion remote from the head, upper and lower segmental voumes of the control lying respectively above and below the central horizontal axial plane of the control. Three terminal pins 16 are secured to and extend through the body portion 10 and include a live pin, a neutral pin and an earth pin for connection to a female socket connector to supply mains electrical power to the heating element.The end portions of the pins 16, which extend parallel to and are disposed below the shelf member 15, are arranged in a triangular relationship with the central or earth pin lying below the live and neutral pins. The cover member 15 defines a shroud 17 which surrounds the pins 16 and is shaped so as to snugly receive a standard socket connector.

The live and neutral pins are each connected to a respective cold lead 7 via a pair of breakable contacts, each pair including a movable contact 18 and a stationary contact 19 mounted directly to a respective cold lead 7. The stationary contacts 19 may be mounted to the cold leads 7 by means of cylindrical spring clips to which the contacts 19 are secured and which are simply pushed over the ends of the cold leads. Alternatively, the stationary contacts 19 might be mounted to the cold leads 7 by means of interference-fitted sleeves. The movable contacts 18 are mounted towards the free ends 22 of respective generally 'U'-shaped leaf springs 20 formed from resilient metallic strip material.The leaf springs 20 extend upwardly adjacent the side of the body portion 10 facing the head from the bases of the respective live and neutral terminal pins and are secured thereto by means of apertured base portions 21 of the leaf springs 20 which surround the base portions of the pins. During normal operation of the heater, the leaf springs 20 urge the movable contacts 18 against the respective stationary contacts 19 and electrical power may be supplied from the live and neutral terminal pins to the element. The earth pin, by virtue of its disposition towards the outer periphery of the control, is conveniently electrically connected with the head 2 by means of a metallic spring clip 29 which is secured to the base of the pin and directly engages the inside of the head 2.

A generally 'U' shaped link member 23 of moulded plastics material lies in a horizontal plane of the control slightly below the switch contacts 18, 19 and includes a transverse arm 24 disposed between the body portion 10 and the head 2, beneath the contacts, and two spaced longitudinal arms 25. The longitudinal arms 25 extend through the body portion 10 and are slidably mounted in axially directed channels 26 formed on either side of the body portion 10 close to the outer periphery thereof.

The transverse arm 24 of the link member 23 includes two stepped abutments 27 at either end thereof adjacent the longitudinal arms 25 which abutments 27 are adapted to engage respective free ends 22 of the leaf springs 20 whereby movement of the link member 23 in a direction away from the head 2 causes the fre ends 22 of the springs 20 and the respective movable contacts 18to be displaced in a direction away from the head 2 thereby opening the contacts and interrupting the power supply to the heater.

During displacement of the free ends of the U-shaped leaf springs, the springs are caused to both pivot and twist about their mountings. This causes an increased relative lateral movement between the contacts as they are opened or closed which results in the surfaces of the contacts being self cleaning.

In addition, two vertical abutment arms 90 extend upwardly from the link member transverse arm 24 which are provided with abutment surfaces 91 adapted for engagement with the uppermost portions of the respecive leaf springs 20. Upon displacement of the link member 24 away from the head, the abutment surfaces 91 engage the leaf springs slightly after engagement thereof by the abutments 27 and urge the contacts further apart.

A first thermally responsive actuating means comprises a snap-action bimetalic actuator 28 of the sort described in British Patent Specification No.

1,542,252. The bimetallic actuator 28 is mounted on a stainless steel bridge member 30 as described in more detail below and overlies the bases of the terminal pins 16. A lower peripheral portion 31 of the actuator 28 is held in good thermal contact with wedge-shaped protrusion 43 formed on the inside of the head 2 towards the bottom thereof adjacent to the point where the hot return 8 of the element is welded thereto, and an upper bridge portion 32 of the actuator 28 is adapted for engagement with a central abutment surface 33 formed on the 'U'shaped link member 23. The actuator 28 is calibrated with a nominal operating temperature of 140"C so as to undergo snap action when the element overheats.

Thus, when the element overheats after for example having been switched on dry, the actuator 28 reverses its curvature by snap-action whereupon the bridge portion 32 engages and moves rightwardly, i.e. away from the head, the link member 23 which in turn pushes the movable contacts 18 away from the stationary contacts 19 as shown in Figure 7 so as to cut off the power supply to the heating element.

An important safety feature of the preferred control arises from the fact that the 'U'-shaped link member 23 in addition to being slidable in a substantially axial direction is pivotable to a limited extent in its horizontal plane about a vertical axis.

Such pivotal movement is accomodated by the outer edges of the longitudinal arms 25 of the link member 23 being contoured within the channels 26 so as to define curved surfaces 34 which abut the outer wall of respective channels 26 there being a lateral clearance between the major part of the edges of the arms 25 and the channels 26. Thus, in the event of either pair of contacts 18, 19 becoming welded together after an extended period of use, upon operation of the actuator 28 engagement of the bridge portion 32 thereof with the abutment surface 33 of the link member 23 will cause the link member 23 to pivot about the welded-together pair of contacts and open the remaining pair as shown in Figure 9 thereby de-energising the heater.This additional safety feature is particularly significant where the container forms part of an appliance which in general use is likely to be left unattended for extended periods of time such as, for example, an early morning automatic tea maker.

The stainless steel resilient bridge member 30 includes a pair of spaced lateral flanges 35 projecting from each side thereof which fit snugly within respective generally rectangular apertures 36 formed at either side of the body portion 10 and through which the lowermost two of the body portion mounting bolts 11 extend. As the bolts 11 are tightened, the flanges 36 bear directly against the respective female studs 12 of the head and are firmly clamped between the heads of the respective bolts 11 and the studs 12 within the apertures 36. In this way, the stainless steel flanges 35 act as spacers between the heads of the mounting bolts 11 and the ends of the studs 12 and prevent undue stresses being imparted to the plastic body portion as is bolted to the head.Thus, the body portion may be tightly clamped to the head without the possibility of inadvertently damaging the plastic by overtightening the lowermost bolts.

The bimetallic actuator 28 is mounted to the bridge member 30 by means of its tongue 37 which passes between two folded-over ears 38 of the bridge member 30 and over a folded-up ramp 39 thereof which enters an aperture in the tongue 37.

The portion 41 of the bridge member 30 which carries the bimetallic actuator 28 is longitudinally offset from the side arms 42 of the bridge member so as to provide necessary clearance between the periphery of the actuator and the bridge member for the actuator to reverse its curvature by snap-action and to permit the necessary movement of the bridge portion 32 of the actuator. In addition, as seen most clearly in Figure 4, the portion 41 which carries the ears 38 and the ramp 39 is at an acute angle to the vertical wall of the head 2 so as to ensure that lower peripheral portion 31 of the actuator 28 is in intimate contact with the protrusion 43. The actuator 28 is mounted on the bridge member 30 by lifting the bridge portion 32 over the ears 38 while sliding the tongue 37 between the ears 38 and over the ramp 39.

Once the ramp 39 enters the tongue apertue 40, the actuator is retained in place. However, should an actuator malfunction during testing of the control, it may conveniently be replaced simply by deforming the free end of the tongue clear of the end of the ramp and there is no need to replace any of the other parts of the control.

The stainless steel bridge member 30, having a relatively low thermal conductivity and heat capacity, minimises heat-loss from the actuator 28 and as such the actuator reacts quickly to overheating of the element.

In the illustrated embodiment an overcentre spring mechanism 44 is disposed above the shelf member 15 on the side of the body portion remote from the element head i.e. above the axial horizontal plane of the control. The mechanism 44 includes a lever member 45 having a generally semi-cylindrical profile so as to fit snugly within the upper segmental space of the control. The lever member 45 is pivotably mounted to the body portion by means of two knife edges 46 formed integrally with the member 45 which engage in respective pivot notches 51 formed respectively in spaced arms 47 extending from the body portion 10 in a direction parallel to the shelf member 15.An overcentre spring 48 extends between notches 49 formed at the free ends of the arms 47 and notches 50 formed in the lever member 45 in the end thereof remote from the knife edges 46 and biases the knife edges 46 into engagement with the pivot notches 51. As illustrated in Figure 10, the wire spring 48 is a combined double spring and includes two U-shaped portions 80,81 disposed in back-to-back relation. Each U-shaped portion interconnects a pair of generally parallel arms 82,83 one of which arm 83 is common to both U-shaped portions. The spring imparts a symmetrical biasing force on the lever member 45 and is sufficiently low rate to adequately accommodate the pivotal movement of the member 45.The lever member 45 is pivotable between a first stable position as shown in Figure 5 wherein a lower surface of the lever member 45 engages stops 53 formed on the free ends of the arms 47 and a second stable position shown in Figure 4. In moving from the first stable position to the second, the lever member 45 passes through an unstable dead centre position in which the spring notches 49, 50 and the knife edges 46 all lie in a common horizontal plane.

A bimetallic actuator 56 similar to the actuator 28, but having a nominal operating temperature of 80"C is located below the lever member 45 and lies at an acute angle to the shelf member 15 between the arms 47 which engage the outer periphery of the actuator 56 and serve to locate the actuator laterally.

The base of the actuator 56 rests on support members 57 of the body portion and is retained longitudinally by a projection 58 at the end of the shelf member which abuts the bridge portion of the actuator 56. A small cut-out 100 is provided on the outer periphery of the actuator and is engaged by a small projection on the control to prevent rotation of the actuator. During assembly, the actuator is simply dropped into position and is later secured in place when the cover member 13 is mounted by means of flanges 59 thereof which extend over the bridge portion of the actuator 56 thereby clamping it to the shelf member 15.

Steam or vapour resulting from liquid within the container boiling is transmitted to the actuator 56 via an aperture 60 formed in the body portion 10. The steam tube 6 is sealed to the aperture 60 by means of a silicone rubber sleeve 61 one end of which is stretched over the end of the tube 6 and the other end of which is pushed into the aperture 60. The upper wall of the aperture 60 is upwardly tapered at the side adjacent the head.

Upon liquid within the container boiling, steam or vapour impinges on the steam sensitive bimetallic actuator 56 which then reverses its curvature by snap-action so that its tongue 62 engages and bears upwardly against a post 63 extending downwardly from the lever member 45 thus tripping the lever member 45 from its first stable position to its second stable position. The lever member 45 includes two downwardly projecting legs 65 which extend either side of the shelf member 15 and terminate within notches 65 formed in the longitudinal arms 25 of the 'U'-shaped link member 23. A strengthening bridge 66 extends between the legs 64 and passes between the body portion arms 47 and shelf member 15.

Thus, upon the lever member 45 being tripped from its first stable position to its second stable position the legs 64 thereof engage the ends of the notches 65 and pull the link member 23 rightwardly away from the element head and open the switch contacts as described above. The effect is that when the liquid within the container boils the actuator 56 trips the lever member 45 from its first to its second position thereby opening the switch contacts and deenergising the heating element.

As described above, the steam or vapour is shielded from the electrical components on the side of the body portion facing the head by means of the resilient sleeve 61. On the lower side of the body portion, the terminal pins 16 are shielded from steam and from condensed liquid by the shelf member 15 and by the cover member shroud 17.

Liquid condensing on the shelf member 15 runs off the member at each side into a peripheral passage defined between the shroud 17 and the outer wall of the cover member 13. An aperture 67 is provided at the base of the cover member to allow condensed liquid within the peripheral passage to drain out of the control. The shroud forming portion of the cover member cooperates with the body portion to form a capillary seal 101 therebetween to prevent liquid seeping into contact with the terminal pins.

A knob 68 is pivotably mounted above the lever member 45 for manually resetting the control after the overcentre mechanism has been tripped as a result of liquid within the container boiling. The knob 68 is mounted by means of a flange 70 thereof which is held between a shoulder 69 projecting from the body portion and part of the cover member. When the knob 68 is pressed downwardly, the lever member 45 is returned to its first position thus allowing the movable contacts 18 to move into contact with the respective stationary contacts 19 and the electrical power supply to the element can be resumed.

Upon movement of the link member in response to operation of the switch-onçdry actuator 28, the lever member is tripped slightly after the contacts are opened. Thus, if an attempt is made to energise the heater with no liquid in the container by manually holding the knob in the closed position, the actuator 28 will cycle causing the contacts to repe atedly open and close thus preventing serious overheating of the element.

The embodiment of the control illustrated herein is particularly suitable for sale ready-mounted to the immersion heater a replacement element for userfitting. However, the illustrated control may serve solely as a switch-on-dry protector unit simply by omitting the over-centre mechanism and associated actuator.

Claims (10)

1. An electric heater of a container of the kind referred to and a thermally-responsive electrical control for said heater, there being thermally responsive actuating means operable upon the element of said heater overheating and electrical switch means, said switch means comprising two sets of breakable contacts each set including a stationary contact mounted directly to a respective cold lead of the heater element and a movable contact mounted on a resilient conductive strip of said control, wherein, during normal operation, the movable contacts are biased against the respective stationary contacts by said resilient strips and electrical power can be supplied to said heater via said switch means, said movable contacts being displaceable in response to operation of said actuating means upon the element overheating to break said contacts to interrupt the power supply and deenergise the heater.

2. A heater and control as claimed in claim 1 wherein the stationary switch contacts are secured to the cold leads by means of cylindrical sleeves secured to the contacts which are interference fitted to the ends of the cold leads.

3. A heater and control as claimed in claim 1 or 2 wherein the control includes terminal pins adapted for engagement with a separate female socket connector for connecting the heater to a source of electrical power, said resilient strips being secured directly to the terminal pins.

4. A heater and control as claimed in any preceding claim wherein the resilient strips are in the form of generally U-shaped leaf springs.

5. A heater and control as claimed in claims 3 and 4 wherein the leaf springs include apertured base portions which surround and are secured to respective bases of line and neutral terminal pins of the control.

6. A heater and control as claimed in claim 4 or 5 wherein the actuator means is coupled to the movable contacts by means of a link member which is slidably mounted to a body portion of the control and is movable in response to operation of the actuating means so as to engage the free ends of the leaf springs and urge the movable contacts away from the stationary contacts.

7. A heater and control as claimed in claim 6 wherein the actuating means comprises a snapacting bimetallic actuator adapted for direct engagement with the link member.

8. A heater and control as claimed in any preceding claim wherein the two contact sets are independently breakable in response to operation of the actuating means.

9. A heater and control as claimed in any preceding claim wherein the control further comprises second thermally responsive actuating means coupled to the switch means and exposed, in use, to steam or vapour resulting from liquid within the container boiling and effective to open the switch contacts upon boiling.

10. An electric heater and a thermally-sensitive control therefor substantially as herein described with reference to the accompanying drawings.