while the heating pad may be susceptible to embodiment in different forms herein will be described in detail an exemplification of the principles of the heating pad which is not intended to limit the spirit and scope of the appended claims . fig1 shows an electrically heated pad generally designated 10 , as well as a cord set 12 , 14 , and 16 , and a controller 18 . the overall dimensions of the heating pad 10 may be 24 ″ by 36 ″, a size sufficient to lend therapeutic heat treatment to an entire body region , but not so large as to thermally affect the entire body of a user . the heating pad 10 comprises a pair of opposed multi - layer constructions 20 housed in an outer supplemental cover of shell 24 . each multi - layer construction 20 includes a water - resistant outer shell 24 and a scrim 26 separated by a layer of a non - woven batting material 28 . the batting material 28 is included to both enhance the comfort of the pad 10 during its use , as well as to provide an air - insulation layer within the construction 20 . the opposed constructions 20 are sandwiched around a resistive heating wire 30 . without some mechanism for retaining the heating wire 30 in its designated pattern between the scrims 26 , any physical manipulation of the heating pad 10 could result in its displacement . in order to secure the heating wire 30 in place , the two opposed scrims 26 are welded in such a manner as to produce retaining channels 32 between the looped heating wire 30 . additionally , the outer periphery of the pad 10 is welded together to secure together the two opposed constructions 20 . alternatively , the opposed scrims 26 of the heating pad 10 may be physically secured in any of the other well - known methods of securing component materials in a textile , including , but not limited to , sewing , gluing , or melting . as mentioned above , the outer shells 24 are preferably a water - resistant material . further , both the outer shells 24 and the scrims 26 comprise an electrically non - conductive heat - resistive material . the outer shells 24 and the scrims 26 may be comprised of a polymer . such polymer may be one of a polyester , polyvinyl chloride , or polypropylene . as the heating pad is a therapeutic heat source and it is contemplated for long duration use , the pad 10 can be thermally limited to reduce the potential for harm to a user . as such , the heating pad 10 operates at 45 watts or less than a standard electric blanket . further , the resistive heating wire 30 may comprise a positive or negative temperature coefficient ( ptc or ntc ) wire . such wires can operate along their length as discrete localized sensors suited for detecting localized hot spots and in the case of the ptc wire , increasing their resistance in response to an increase in the applied electrical current . operation of such wires , as well as an exemplary safety circuit used in association therewith is discussed in greater detail in co - owned u . s . pat . no . 6 , 355 , 912 , issued to allard on mar . 12 , 2002 , and which is fully incorporated herein by reference . as best seen in fig2 , the heating wire 30 may be provided in an exemplary pattern sufficient to extend its generated heat to all parts of the heating pad 10 . in an effort to avoid undesired localized hot spots and to prevent shorting out the wire 30 itself , care must be taken to maintain a minimum distance between loops of the heating wire 30 as it is wrapped throughout the heating pad 10 . in operation and as best seen in fig3 , the heating pad 10 is a heat generator . cord set 12 , 14 , and 16 draw power from a source 34 , generally a common household outlet , through plug 12 and delivers it to controller 18 via cord 14 . controller 18 houses all of the electronics , including the microprocessor 36 , required for varying the electrical draw needed for increasing or decreasing the thermal output of the resistive heating wire 30 in accordance with a selected user - demanded setting . the electricity is delivered to the resistive heating wire 30 via cord 16 which is connected to the heating wire 30 using detachable connectors ( see fig1 and 2 ). controller 18 may comprise any of the many known rotary or switch type devices suitable for operating a multi - setting electrical appliance . the collection of switches , buttons , and other user - operable mechanisms designed to allow the user to select , set or otherwise operate the heating pad 10 in the various modes available , collectively form the user interface 37 . the user interface 37 may include a plurality of individual heat settings , including a “ high ”, a “ low ”, and multiple intermediate settings , as well as a setting specifically designated to initiate the cyclic heating operation of the pad 10 . the user interface 37 may further include a joint or individual “ on ” and “ off ” buttons or switches . alternatively , the user interface 37 can include an individual “ off ” setting and the activation of the heating pad 10 may be achieved by default when the heating pad 10 is set to “ low .” finally , the controller 18 may include an at least two digit display 38 associated with the microprocessor 36 for indicating the currently selected setting of the heating pad 10 . during the cyclic heating mode , the microprocessor 36 in cooperation with an internal clock 39 operates to control both the time and temperature settings of the heating pad 10 based on a pre - programmed pattern . similarly , driven by signals from the microprocessor 36 , regulator 41 may serve to alter the current flow into resistive heating wire 30 to appropriately adjust the temperature as set by the user through user interface 37 whether the heating pad 10 is operating in the constant temperature mode , the timed mode , or as pre - programmed in the cyclic heating mode . while any cyclic heating pattern can be used , an exemplary cycle pattern may raise the heating pad &# 39 ; s temperature to between 120 ° and 125 ° f . over the first thirty minutes of the cycle . after maintaining such temperature for a predetermined period of time , the pad 10 may cycle its temperature back down to between 105 ° and 110 ° f . and remain at that level for a period of approximately thirty minutes . the pad 10 can continue to cycle between the higher and lower temperature ranges for any period of time . the heating pad 10 may include an auto - off feature that terminates the operation of the pad 10 regardless of the mode in which it is operating after a maximum of ten hours . those skilled in the art can now appreciate from the foregoing description that the broad teachings of the disclosure can be implemented in a variety of forms . therefore , while this disclosure includes particular examples , the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the disclosure .
a therapeutic low wattage heating pad safe for use in a bed and to sleep with while in operation includes a pair of opposed multi - layer constructions housing a resistive heating wire . the heating pad is operable in a plurality of consistent heating modes at various temperature levels , as well as a cycling mode that offers a varying range of temperatures over a period of time .