Fault protection system for a respiratory conduit heater element

Abstract

A fault protection circuit for a respiratory conduit heater element in a respirator humidification system is disclosed. The circuit includes a spark detector as well as overcurrent detector. Several variations are included for the spark detector including a two winding transformer, a centre tapped two winding transformer), and a high pass filtered inductor. A semiconductor switching configuration is also disclosed. Once the protection circuit detects a change in current over a certain level, or the average level raises above a threshold, then the current in the heater element is interrupted for a preset period.

1 . A fault protection system for a respiratory conduit heater element comprising: 
 detecting means which include means to detect a rapid change of current in said heater element,    current interruptor means in series with said heater element, and    timer means adapted to control the action of said interrupter means and thereby in use determining the duration of current interruption, said timer means being triggered by said detecting means.    
     
     
         2 . A fault protection system for a respiratory conduit heater element as claimed in  claim 1 , wherein said detecting means also includes a peak current detector for detecting current in the heater element and said timing means is also triggered by said peak current detector when a predetermined threshold current is exceeded.  
     
     
         3 . A fault protection system for a respiratory conduit heater element as claimed in either of claims  1  or  2 , wherein said detecting means comprises: 
 a transformer including a primary and secondary winding, said primary winding adapted to be connected in series with said heater element and a power source,  
 a fill wave rectifier including rectifier input means and rectifier output means, said rectifier input means connected across said secondary winding of said transformer,  
 a low pass filter including filter input means and filter output means, said filter input means connected to said rectifier output means, and  
 a comparator including comparator input means and comparator output means, said comparator input means connected to said filter output means, wherein when the output of said low pass filter reaches the set predetermined threshold, said current interrupter means is controlled to interrupt the current in said heater element.  
 
     
     
         4 . A fault protection system for a respiratory conduit heater element as claimed in either of claims  1  or  2 , wherein said detecting means comprises: 
 a transformer including a centre tapped primary winding and secondary winding, each end of said primary winding adapted to be connected in series with at least one circuit of said heater element and said centre tap adapted to be connected to a power source,  
 a fill wave rectifier including rectifier input means and rectifier output means, said rectifier input means connected across said secondary winding of said transformer,  
 a low pass filter including filter input means and filter output means, said filter input means connected to said rectifier output means, and  
 a comparator including comparator input means and comparator output means, said comparator input means connected to said filter output means, wherein when the output of said low pass filter reaches the first predetermined threshold, said current interrupter means is controlled to interrupt the current in said heater element.  
 
     
     
         5 . A fault protection system for a respiratory conduit heater element as claimed in either of claims  1  or  2 , wherein said detecting means comprises: 
 an inductor adapted to be connected in series with said heater element and a power source,  
 a first high pass filter including first filter input means and first filter output means, said first filter input means connected to a first end of said inductor,  
 a second high pass filter including second filter input means and second filter output means, said second filter input means connected to the other end of said inductor,  
 a full wave rectifier including rectifier input means and rectifier output means, said rectifier input means connected to said first filter output means and said second filter output means respectively,  
 a low pass filter including filter input means and filter, output means, said filter input means connected to said rectifier output means, and  
 a comparator including comparator input means and comparator output means, said comparator input means connected to said filter output means, wherein when the output of said low pass filter reaches the first predetermined threshold, said current interrupter means is controlled to interrupt the current in said heater element.  
 
     
     
         6 . A fault protection system for a respiratory conduit heater element, as claimed in either of claims  1  or  2  wherein said current interruptor means comprises: 
 two same channel MOSFETS connected in series with their source and gate electrodes respectively tied together, said circuit adapted to receive a switching voltage between the commoned gate and source electrodes.  
 
     
     
         7 . A fault protection system for a respiratory conduit heater element, as claimed in either of claims  1  or  2  such that in use when said detecting means determines a fault is present in said heater element said timing means controls said current interrupter means to interrupt the current in said heater element for a predetermined period after said fault is detected, whereby when said predetermined period expires said timing means controls said current interrupter means to allow current to flow through said heater element.  
     
     
         8 . A semiconductor switching circuit for rapidly controlling the AC supply current through a load from a power supply comprising: 
 two same channel MOSFETs connected in series with their source and gate electrodes respectively tied together, said circuit adapted to receive a switching voltage between the commoned gate and source electrodes, their drain electrodes adapted to be connected to a load and a power supply respectively.    
     
     
         9 . A semiconductor switching circuit for rapidly controlling the AC supply current through a load form a power supply comprising: 
 two same channel MOSFETs connected in series with their drain and gate electrodes respectively tied together, said circuit adapted to receive a switching voltage between the commoned gate and drain electrodes, their source electrodes adapted to be connected to a load and a power supply respectively.    
     
     
         10 . A fault protection system for a respiratory conduit heater element comprising: 
 detecting means which includes a peak current detector for detecting current in the heater element    current interruptor means in series with said heater element, and    timer means adapted to control the action of said interruptor means and thereby in use determining the duration of current interruption, said timer means being triggered by said detecting means, when a predetermined threshold current is exceeded.    
     
     
         11 . In a respiratory humidification system wherein a conduit connects a patient to a humidifier, said conduit being heated by a respiratory conduit heater element controlled by said humidifier, the improvement comprising that said humidifier includes a fault protection system for said heater element comprising: 
 detecting means which include means to detect a rapid change of current in said heater element,    current interruptor means in series with said heater element, and    timer means adapted to control the action of said interruptor means and thereby in use determining the duration of current interruption, said timer means being triggered by said detecting means.    
     
     
         12 . In a respiratory humidification system as claimed in  claim 11 , the improvements further comprising that said detecting means also includes a peak current detector for detecting current in the heater element and said timing means is also triggered by said peak current detector when a predetermined threshold current is exceeded.  
     
     
         13 . In a respiratory humidification system as claimed in either of claims  11  or  12 , the improvements further comprising that said detecting means comprises: 
 a transformer including a primary and secondary winding, said primary winding adapted to be connected in series with said heater element and a power source,  
 a full wave rectifier including rectifier input means and rectifier output means, said rectifier input means connected across said secondary winding of said transformer,  
 a low pass filter including filter input means and filter output means, said filter input means connected to said rectifier output means, and  
 a comparator including comparator input means and comparator output means, said comparator input means connected to said filter output means, wherein when the output of said low pass filter reaches the first predetermined threshold, said current interrupter means is controlled to interrupt the current in said heater element.  
 
     
     
         14 . In a respiratory humidification system as claimed in either of claims  11  or  12 , the improvements further comprising that said detecting means comprises: 
 a transformer including a centre tapped primary winding and secondary winding, each end of said primary winding adapted to be connected in series with at least one circuit of said heater element and said centre tap adapted to be connected to a power source,  
 a full wave rectifier including rectifier input means and rectifier output means, said rectifier input means connected across said secondary winding of said transformer,  
 a low pass filter including filter input means and filter output means, said filter input means connected to said rectifier output means, and  
 a comparator including comparator input means and comparator output means, said comparator input means connected to said filter output means, wherein when the output of said low pass filter reaches the first predetermined threshold, said current interrupter means is controlled to interrupt the current in said heater element.  
 
     
     
         15 . In a respiratory humidification system as claimed in either of claims  11  or  12 , the improvements further comprising hat said detecting means comprises: 
 an inductor adapted to be connected in series with said heater element and a power source,  
 a first high pass filter including first filter input means and first filter output means, said first filter input means connected to a first end of said inductor,  
 a second high pass filter including second filter input means and second filter output means, said second filter input means connected to the other end of said inductor,  
 a full wave rectifier including rectifier input means and rectifier output means, said rectifier input means connected to said first filter output means and said second filter output means respectively,  
 a low pass filter including filter input means and filter output means, said filter input means connected to said rectifier output means, and  
 a comparator including comparator input means and comparator output means, said comparator input means connected to said filter output means, wherein when the output of said low pass filter reaches the first predetermined threshold, said current interrupter means is controlled to interrupt the current in said heater element.  
 
     
     
         16 . In a respiratory humidification system as claimed in either of claims  11  or  12  the improvements further comprising that said current interruptor means comprises: 
 two same channel MOSFETS connected in series with their source and gate electrodes respectively tied together, said circuit adapted to receive a switching voltage between the commoned gate and source electrodes.  
 
     
     
         17 . In a respiratory humidification system as claimed in either of claims  11  or  12  the improvements further comprising that in use when said detecting means determines a fault is present in said heater element said timing means controls said current interruptor means to interrupt the current in said heater element for a predetermined period after said fault is detected, whereby when said predetermined period expires said timing means controls said current interrupter means to allow current to flow through said heater element.  
     
     
         18 . In a respiratory humidification system wherein a conduit connects a patient to a humidifier, said conduit being heated by a respiratory conduit heater element controlled by said humidifier, the improvement comprising that said humidifier includes a fault protection system for said heater element comprising: 
 detecting means which includes a peak current detector for detecting current in the heater element    current interruptor means in series with said heater element, and    timer means adapted to control the action of said interruptor means and thereby in use determining the duration of current interruption, said timer means being triggered by said detecting means, when a predetermined threshold current is exceeded.