Infusion fluid warmer comprising printed circuit board heating elements

Abstract

The present invention relates to an infusion fluid warmer comprising a heat exchanger and first and second printed circuit boards comprising respective integrally formed electrically resistive patterns acting as heating elements. The integrally formed electrically resistive patterns are heated by supply of electrical power and thermally coupled to a heat exchanger to warm an infusion fluid flowing through a fluid passage of the heat exchanger.

1 - 18 . (canceled) 
     
     
         19 . An infusion fluid warmer comprising:
 a DC power supply input,   a first printed circuit board comprising a first surface and a second, opposing, surface, wherein the second surface comprises a first integrally formed electrically resistive pattern,   a heat exchanger comprising an upper wall structure and a lower, opposing, wall structure separated by a fluid channel or passage extending between fluid inlets and outlets of the heat exchanger, wherein an outer surface of the upper wall structure is thermally connected to the first resistive pattern; and   a reference resistor connected between the DC power supply input and the first integrally formed electrically resistive pattern; and   a controller configured to:   connect the DC power supply input to the first integrally formed electrically resistive pattern during a first time period to dissipate power in the first integrally formed electrically resistive pattern and connect the DC power supply input to the first integrally formed electrically resistive pattern through the reference resistor during a second time period,   determine, during the second time period, a resistance of the first integrally formed electrically resistive pattern based on a known resistance of the reference resistor;   determine a temperature of the first integrally formed electrically resistive pattern based on the determined resistance of the first integrally formed electrically resistive pattern.   
     
     
         20 . An infusion fluid warmer according to  claim 19 , wherein the infusion fluid warmer comprises an electronic switching circuit comprising a conducting switch state and a non-conducting switch state selectable in accordance with a control signal of the controller,
 where the electronic switching circuit is configured for:   connecting the DC power supply input to the first integrally formed electrically resistive pattern through a controllable semiconductor switch in the conducting switch state; and   connecting the DC power supply input to the first integrally formed electrically resistive pattern through said reference resistor in the non-conducting switch state.   
     
     
         21 . An infusion fluid warmer according to  claim 20 , wherein input and output terminals of the controllable semiconductor switch are coupled in parallel across the reference resistor. 
     
     
         22 . An infusion fluid warmer according to  claim 20 , wherein a resistance of the reference resistor is at least 100 times larger than an on-resistance of the controllable semiconductor switch. 
     
     
         23 . An infusion fluid warmer according to  claim 19 , wherein a resistance tolerance of the reference resistor is less than 1%, and wherein optionally said reference resistor has a small temperature coefficient. 
     
     
         24 . An infusion fluid warmer according to  claim 19 , wherein a resistance of the first integrally formed electrically resistive pattern is less than 11Ω such as between 1 and 7Ω. 
     
     
         25 . An infusion fluid warmer according to  claim 19 , wherein the controller is configured to provide a predetermined delay time, such as between 10 ms and 200 ms, between the first time period and the second time period; wherein power dissipation in the first integrally formed electrically resistive pattern is interrupted during the predetermined delay time. 
     
     
         26 . An infusion fluid warmer according to  claim 25 , wherein the controller is configured to disconnect the DC power supply input to the first integrally formed electrically resistive pattern during the predetermined delay time. 
     
     
         27 . An infusion fluid warmer according to  claim 26 , wherein the controller is configured to disconnect the DC power supply input by opening a second controllable semiconductor switch, connected in-between the reference resistor and the first integrally formed electrically resistive pattern during the predetermined delay time. 
     
     
         28 . An infusion fluid warmer according to  claim 19 , wherein the controller is configured for selectively connecting and disconnecting the DC power supply input to the first integrally formed electrically resistive pattern over time to control a temperature of an infusion fluid flowing through the fluid channel or passage in accordance with a desired or target temperature of the infusion fluid. 
     
     
         29 . An infusion fluid warmer according to  claim 19 , wherein the upper wall structure and the lower wall structure is composed of a material having a thermal conductivity equal to or exceeding 15 W/(m·K) or equal to or exceeding 200 W/(m·K). 
     
     
         30 . An infusion fluid warmer according to  claim 19 , further comprising:
 an outer housing or casing surrounding and enclosing at least the heat exchanger, the first printed circuit board and the second printed circuit board; and   an electrically insulating frame, gasket or ring surrounding and contacting peripheral edges of the upper and lower wall structures of the metallic heat exchanger to prevent physical contact and electrical contact between the heat exchanger and the outer housing.   
     
     
         31 . An infusion fluid warmer according to  claim 19 , wherein the first printed circuit board further comprises:
 at least one additional and separate integrally formed electrically resistive pattern formed on the second surface.   
     
     
         32 . An infusion fluid warmer according to  claim 19 , wherein the controller or switching circuit is bonded or soldered to the first surface of the first printed circuit board. 
     
     
         33 . An infusion fluid warmer according to  claim 19 , further comprising:
 a second printed circuit board comprising a first surface and a second, opposing, surface, wherein the second surface comprises a second integrally formed electrically resistive pattern which is thermally connected to an outer surface of the lower wall structure of the heat exchanger; and   the controller is further configured to connect the DC power supply input to the second integrally formed electrically resistive pattern during the first time period to dissipate power in the second integrally formed electrically resistive pattern.   
     
     
         34 . An infusion fluid warmer according to  claim 19 , further comprising a battery pack comprising a plurality of rechargeable battery cells configured to generate a DC voltage at the DC power supply input.