Circuit Integrity Detection System for Detecting The Integrity of A Sensing Wire in Electrically Heated Textiles

Abstract

A circuit integrity detection system for use in detecting the integrity of a sensing wire in a heating pad wherein the integrity of the sensing wire is determined by first driving one end of the sensing wire with a low voltage electrical test signal from a microcontroller, and then checking whether the test signal is present on the other end of the sensing wire, in order to distinguish the test signal from the standard AC line voltage present on the sensing wire, the electrical test signal is preferably of a different frequency than the standard 50-60 Hz AC line voltage. In one embodiment, the test signal frequency is approximately 30 kHz.

What is claimed is: 
     
         1 . An electrically heated textile comprising:
 a heating element in communication with an NTC material, wherein a first signal is generated through the heating element at a first frequency;   a sensing wire for detecting a hotspot created by the heating element;   a test signal generator electrically connected to the sensing wire for generating a second signal on a first end of the sensing wire, wherein the test signal has a second frequency; and   a signal detector for detecting the second signal on a second end of the sensing wire   
     
     
         2 . The electrically heated textile as set forth in  claim 1  further including:
 a layer having a negative temperature coefficient (NTC) positioned between the heating element and the sensing wire. 
 
     
     
         3 . The electrically heated textile as set forth in  claim 2  where the NTC layer is wrapped around the heating element, and the sensing wire is wrapped around the NTC layer. 
     
     
         4 . The electrically heated textile as set forth in  claim 1 , wherein said detecting occurs in the presence of the first signal. 
     
     
         5 . The electrically heated textile as set forth in  claim 4 , wherein the first frequency is different from the second frequency. 
     
     
         6 . The electrically heated textile as set forth in  claim 5 , wherein the first signal is an AC line voltage with the first frequency of approximately 50-60 Hz. 
     
     
         7 . The electrically heated textile as set forth in  claim 6 , wherein the second frequency is at a frequency of approximately 30 kHz. 
     
     
         8 . The electrically heated textile as set forth in  claim 1 , wherein said detecting occurs when the first signal is turned off. 
     
     
         9 . The electrically heated textile as set forth in  claim 8 , wherein the first frequency is different from the second frequency. 
     
     
         10 . The electrically heated textile as set forth in  claim 8 , wherein the first frequency is the same as the second frequency. 
     
     
         11 . A circuit integrity detection system for use in detecting the integrity of a sensing wire in an electrically heated textile, the system comprising:
 a sensing wire for detecting a hotspot created by a heating element of the electrically heated textile, wherein a first signal is generated through the heating element at a first frequency;   a test signal generator electrically connected to the sensing wire for generating a test signal at a second frequency on a first end of the sensing wire;   a signal detector for detecting the second frequency on a second end of the sensing wire.   
     
     
         12 . The electrically heated textile as set forth in  claim 11 , wherein said detecting occurs in the presence of the first signal. 
     
     
         13 . The electrically heated textile as set forth in  claim 11 , wherein said detecting occurs when the first signal is turned off. 
     
     
         14 . A method for detecting the integrity of a sensing wire in an electrically heated textile having a heating element, the method comprising the steps of:
 providing a sensing wire to monitor the electrically heated textile for hot spots;   applying a first signal having a first frequency to the heating element;   applying a second signal having a second frequency to a first end of the sensing wire; and   monitoring a second end of the sensing wire for a return signal corresponding to the second signal.   
     
     
         15 . The method as set forth in  claim 14  wherein the step of monitoring the second end of the sensing wire for a return signal corresponding to the second signal includes the steps of:
 comparing the return signal to a threshold voltage; 
 counting transitions of the return signal above and below the threshold voltage; 
 determining whether the sensing wire is intact based on the number of counted transitions. 
 
     
     
         16 . The method as set forth in  claim 14 , wherein monitoring of the second signal occurs in the presence of the first signal. 
     
     
         17 . A The method as set forth in  claim 14  further comprising the steps of:
 disengaging power to the heating element of the electrically heated textile prior to applying the second signal to the first end of the sensing wire; 
 
     
     
         18 . The method as set forth in  claim 14  wherein the second frequency is different from the first frequency. 
     
     
         19 . The method as set forth in  claim 14  wherein the second frequency is the same as the first frequency.