Elimination of potentially harmful electrical and magnetic fields from electric blankets and other electrical appliances

• US 5,218,185 A
• Filed: 10/11/1989
• Issued: 06/08/1993
• Est. Priority Date: 08/15/1989
• Status: Expired due to Fees

• Current Assignee: Trustees of The Thomas A D Gross 1988 Revocable Trust
• Original Assignee: Trustees of The Thomas A D Gross 1988 Revocable Trust
• Inventors: Gross, Thomas A. O.
• Primary Examiner(s): Walberg, Teresa J.
• Application Number:
  US07/419,892
• Time in Patent Office: 1,336 Days
• Field of Search: 219/528, 219/529, 219/549, 219/212, 219/501, 219/505
• US Class Current: 219/528
• CPC Class Codes: H05B 6/34 Arrangements for circulation of melts

Abstract

Diverse methods for eliminating potentially harmful periodically varying electrical and magnetic fields which emanate from electric blankets, heating pads, and other electrical appliances intended for use proximate to the human body. One approach entails the use of a self-shielding coaxial cable as the heating element with core and sheath connected electrically in flux-cancelling fashion to minimize emanated magnetic and electrical fields. Another approach involves the use of heating elements, may otherwise be of currently conventional construction, powered with filtered dc to avoid potentially harmful alternating fields and produce harmless stationary fields instead. Ground integrity assurance means are also provided to avoid the emanation from the blanket or appliance of alternating electric fields which might otherwise result from connection to an improperly polarized alternating current source.

Claims

1. An electrically heated blanket or pad comprising:

electrical conductors adapted for connection to a source of alternating electrical current;

an electrically energizeable heating element for utilization proximate to the human body; and

a control device interconnecting said heating element with said electrical conductors, said control device comprising a high-frequency oscillator energized from said electrical conductors, and rectifying and filtering means for providing rectified and filtered electrical currents, the output of said oscillator supplying said electrical heating element through said rectifying and filtering means to substantially eliminate low frequency currents through said heating element, thereby to minimize the emanation of low frequency periodically varying magnetic fields from said heating element.

2. The combination of claim 1 wherein the frequency of said oscillator is above 20 kHz and below 3 MHz.

3. The combination of claim 1 wherein said rectifying and filtering means comprise a pair of center-tapped rectifiers across the output of said oscillator and at least one shunt capacitor.

4. An electrically heated blanket or pad comprising:

electrical conductors adapted for connection to a source of alternating electrical current;

an electrically energizable heating element for utilization proximate to the human body; and

a control device interconnecting said heating element with said electrical conductors, said control device comprising a high-frequency oscillator for energization by said source of alternating current, a rectifier connected to the output of said oscillator for providing rectified electrical currents to said heating element, and filtering means for smoothing the rectified electrical currents, thereby to minimize the emanation of periodically varying magnetic fields from said heating element.

5. The combination of claim 4 wherein the frequency of said oscillator is above 20 kHz and below 3 MHz.