DUAL HEATER WITH CTP AND FIXED RESISTANCE ELEMENTS BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION The present invention relates to a heating panel that includes a heating element with CTP (positive temperature coefficient) and a heating element of fixed resistance. DESCRIPTION OF THE PREVIOUS TECHNIQUE In the prior art, fixed resistance heaters are basic elements. However, in environments with higher ambient temperatures or lower heat transfer, these heaters may overheat. An example of a dual attache heater that uses fixed resistance elements is KANTHAL 4010 NR 410-1100. Heaters with CTP (positive temperature coefficient), such as those disclosed in U.S. Pat. No. 4,857,711 granted to Watts, have a resistance that increases in response to increasing temperatures. Fundamentally, this increased resistance reduces the power output versus a constant input voltage. However, in several applications, users prefer a heater with multiple positions (such as "high" and "low") that are typically not available in a CTP heater. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a self-regulating heater, particularly at higher operating temperatures. It is therefore an object of the present invention to provide a heater that can operate with high power at low operating temperatures, for maximum heat transfer. It is therefore a further object of the present invention to provide a heater having multiple power positions. These and other objects are achieved by providing a heater panel with a CTP heater (positive temperature coefficient) printed on a first side of the heater panel, and a secondary heater screen with a fixed resistor printed on the second side of the heater panel. Terminal connections are made through a gap that acts as a perforation, to create an interchangeable three-point connection that is used for high and low power positions. Alternatively, a heater printed on a single-sided screen with multiple layers with a dielectric layer can be used to separate the two individual heating elements. BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of the present invention will be apparent from the following description and claims, and from the accompanying drawings, wherein: Figure 1 is a plan view of the heater of the present invention. Figure 2 is a plan view of the CTP conductive layer of the present invention. Figure 3 is a plan view of the CTP thermistor layer of the present invention. Figure 4 is a plan view of the fixed resistance layer of the present invention. Figure 2 is a plan view of the dielectric layer used in the alternative embodiment of the present invention to separate the CTP layer from the fixed resistance layer. DETAILED DESCRIPTION OF THE PREFERRED MODALITY Now making detailed reference to the drawings, in which similar numbers refer to similar elements in the different views, it can be seen that the Figure
1 is a plan view of the dual heater 10. The dual heater 10 includes a heater panel 12 which acts as a substrate on which subsequent layers comprising the heating elements and possibly a dielectric layer are superposed, as will be explained below. Typically, the fixed resistance heater element is printed on coil 14 (see also Figure 4) on a first side of the heater panel 12, and is in electrical communication through the positive high-power terminal 18 and the common ground terminal. , thus forming an electrical circuit. Figure 2 is a plan view of a conductive layer CTP 22 which is in electrical communication with the low power positive terminal 16 and the common ground terminal., and which further includes parallel rows of conductive elements 23. The conductive layer CTP 22 provides an electrical connection for the thermistor layer CTP 24, as shown in Figure 3. The conductive layer CTP 22 is immediately adjacent to the thermistor layer CTP 24. to provide this electrical connection. The variable resistance as a function of temperature is provided by the inherent characteristics of the thermistor layer CTP 24, in which the thermistor heating elements 25 are provided in parallel rows of conductive elements 23. Typically, the conductive elements 23 are perpendicular to the elements thermistor heaters 25. The fixed resistance heater element in coil 14 is - separated from the combination of the conductive layer CTP 22 and the thermistor layer CTP 24 by the heater panel 12 (i.e., the fixed resistance heater element in coil 14 is printed on the first side of the heater panel 12, and the conductive and thermistor layers CTP of variable resistance 22 and 24 are formed on a second side of the heater panel 12) or by a dielectric layer 26 as illustrated in Figure 5 ( that is, the fixed resistance heater element in coil 14 is printed on the first side of the heater panel 12, and the conductive and thermistor layers CTP of variable resistance 22 and 24 are formed on only one side of the heater panel 12, where the dielectric layer 26 separates the heating element 14 from the combination of the conductive and thermistor layers CTP 22 and 24). Typically, a three-way interchangeable connection (not shown) is used with terminals 16, 18 and 20 to provide high and low power positions. In the low power configuration, an electrical circuit is formed between the low power positive terminal 16 and the ground terminal 20, thereby providing an electrical circuit through the conductive layer CTP 22 and the thermistor layer CTP 24. This provides a self-regulating and low-power heat source to be used at high ambient temperatures, or low heat transfer situations. In the high power configuration, an electrical circuit is formed between the high-power positive terminal 18 and the ground terminal 20, thereby providing an electrical circuit through the fixed resistance heating element in coil 14. This provides a source of relatively non-self-regulating and high-power heat for low ambient temperatures (as in the case of being below 0 ° C), or situations of high heat transfer. In this way, the aforementioned objects and advantages are effectively obtained. Although preferred embodiments of the present invention were disclosed and described herein, it should be understood that the present invention is by no means limited by the preferred embodiments, and that its scope should be determined by that of the appended claims.