Electric heating – Heating devices – With heater-unit housing – casing – or support means
Patent
1987-01-07
1988-11-29
Goldberg, E. A.
Electric heating
Heating devices
With heater-unit housing, casing, or support means
219212, 219529, H05B 334
Patent
active
047884177
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an electrical heating pad, in particular a mattress, comprising a number of partially overlapping resistor foil elements.
BACKGROUND OF THE INVENTION
An electrically heated mat with partially overlapping resistor foil elements is known from U.S. Pat. No. 2,745,942. In this known mat, the resistor foil elements are disposed in three layers, one on top of the other, and the outline or outer contour of each element basically coincides with the contour of the mat. However, the individual resistor foil paths are displaced or staggered relative to the foil paths of the other foil elements, so that the various foil paths supplement each other and together cover substantially the whole surface area of the mat. In this way, a uniform and intensive heating of the mat can be achieved.
SUMMARY OF THE INVENTION
The main object of the present invention, on the other hand, is to provide an electrical heating pad which can be monitored in use so that local heat variations, in particular hot spots, can be detected. A further object is to control the heating in such a manner that local heat variations, e.g., those caused by a non-uniform load, are eliminated. Thus, it is desirable to achieve a uniform temperature distribution over the pad even when the load or heat transfer is concentrated to certain portions of the pad.
A special application, where such monitoring and control of the heat is important or even critical, is the use of the pad as a mattress for a patient during surgery. Of course, the normal physiological temperature control of the human body is then partially non-effective, and there is consequently a need for a mattress which can monitor and preferably control the temperature at all portions thereof.
According to the invention, the above-mentioned main object is met by an electrical heating pad, in which the various foil elements cover different regions of the pad and are positioned in such an overlapping configuration that in substantially all portions of the pad there are at least two overlapping foil element parts, wherein each foil element in such a pair of partially overlapping foil elements has a separate pair of feed terminals for electrically feeding the foil elements separately so as to permit individual sensing of the respective temperature-dependent resistance thereof. Thus, the foil elements have a dual function, i.e., they serve as heating elements as well as temperature measuring elements, and no separate temperature sensing means, such as thermistors, are needed. If a hot spot occurs, the temperature increase will be sensed by at least two foil elements, or at least one if the other does not operate properly. Upon detection, this information can be used to provide an alarm signal or to control the electrical power supplied to the particular foil element or elements so as to maintain a uniform temperature distribution.
The invention also concerns electrical circuitry for electrically feeding and monitoring such a heating pad, the circuitry including a number of circuit units connectable between a power source and each one of the terminal pairs of the pad, each such circuit unit being adapted to sense the temperature-dependent resistance of the corresponding foil element, whereby the temperatures of the various foil elements are monitored individually. Preferably, these circuit units are also adapted to control the feeding voltage to the terminal pairs so as to keep all parts of the heating pad at a predetermined temperature value.
The partially overlapping arrangement of the foil elements in the pad, especially in combination with the electrical circuitry for feeding, monitoring and control thereof, provides excellent security. Thus, if a particular foil element or the control thereof fails, this will be taken care of by the other, partially overlapping foil elements. In case the remaining operative foil elements cannot provide adequate compensation, the respective foil elements are preferably inactivated by means of a security swit
REFERENCES:
patent: 2745942 (1956-05-01), Cohen
patent: 3739142 (1973-06-01), Johns
patent: 4149066 (1979-04-01), Niibe
patent: 4322604 (1982-03-01), Kawamura et al.
patent: 4507546 (1985-03-01), Fortune et al.
patent: 4514619 (1985-04-01), Kugelman
Goldberg E. A.
Kanthal Medical Heating AB
Lateef M.
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