MULTI POLYMER POSITIVE TEMPERATURE COEFFICIENT HEATER
FIG3 is a simplified view of an alternative PTC heating element  FIG4 is a simplified view of a second alternative PTC heating element
FIG3 is a simplified view of alternative heating element 110, which is similar to heating element 10 in that it employs bus bars 12 and power source 18 in generally the same manner. As shown, heating element 110 includes polymer inks 114 and 116, which are similar to polymer inks 14 and 16, as discussed above, except that they are arranged as layers in a parallel relationship. In this sense, the total resistance (RT) of element 110 is calculated based on the sum of each polymer ink layer, such that 1/RT = 1/R1 + 1/R2. Due to this relationship, the total resistance RT will always be less than that of any individual resistor, and RT will decrease with each additional polymer ink layer added in this manner to element 110. Such an embodiment can be useful, for example, in certain heating applications for which one of the commercially available PTC inks has a resistance that is too high for such applications.  FIG4 is a simplified view of second alternative heating element 210, which is similar to element 10, except that it includes three polymer inks-214, 216, 224-arranged as layers in series. Third polymer ink 224 can be any of the commercially available inks discussed above with respect to element 10, and has different properties than either polymer ink 214 or 216. The addition of polymer ink 224 can help further customize the operating range of element 210. Alternative embodiments can further include a parallel arrangement and/or more than three polymer inks arranged in series or parallel.
simplified view
210
element
214
than either polymer ink
12
bus bars bus bar
116
includes polymer inks
18
power source
110
element
224
polymer ink
114
includes polymer inks
['1. A heating element comprising: a first bus bar (12) disposed to receive current from a power source; a second bus bar (12) non-adjacent to the first bus bar; and a polymer ink section extending between the first and second bus bars, the section comprising a plurality of PTC polymer inks (14,16) each different from one another; wherein the second bus bar is electrically connected to the first bus bar via the polymer ink section.']