Blood warming apparatus with digital display and monitoring circuit

Claim 2

Fluid warming apparatus for heating a refrigerated fluid such as blood to a predetermined nominal temperature, comprising: a housing defining a heating chamber for the fluid means including at least one electric heater element operable from an applied electric current in thermal communication with the fluid in said heating chamber for heating the fluid as it passes through the chamber; control circuit means responsive to the output temperature of the fluid for generating a heater control signal; switch circuit means electrically connected between said heating element and a source of electrical current, and responsive to said heater control signal, for controlling the application of current to said heating element to maintain the fluid at said predetermined nominal temperature; temperature sensing means for generating an analog output signal indicative of the output temperature of said fluid, said temperature sensing means including an output terminal, a constant current source, a thermistor in thermal communication with said fluid at the output of said heating chamber, and first and second resistances; said constant current source being connected to one terminal of said thermistor and being connected to a plane of reference potential through said first resistance; said output terminal being coupled to said other terminal of said thermistor and being connected to said plane of reference potential through said second resistance, the sum of said first and second resistances being selected to substantially linearize the temperature-voltage characteristic of said analog output signal at said output terminal over a predetermined temperature range, the ratio of said resistances being selected to provide a desired voltage level on said output terminal at a selected temperature within said operating range; and temperature display means coupled to said output terminal and linearly responsive to said analog output signal for producing an output display indicative of the output temperature of the fluid.

Claim 3

Fluid warming apparatus as defined in claim 1 wherein said first and second resistances comprise a potentiometer, the arm of said potentiometer being connected to said plane of reference potential and being adjustable to obtain said desired voltage level on said output terminal at said selected temperature.

Claim 4

Fluid warming apparatus as defined in claim 1 wherein said fluid is blood, and said predetermined operating range extends from approximately 30° C. to 40° C.

Claim 5

Fluid warming apparatus as defined in claim 1 wherein the sum (R 1 +R 2 ) of said first and second resistances is given by ##EQU6## where said temperature range extends from a temperature T1 to a temperature T2, and V 1 equals the desired output voltage at T1, V 2 equals the desired output voltage at T2, R T1 equals the resistance of said thermistor at T1, and R T2 equals the resistance of said thermistor at T2.

Claim 6

In a fluid warming apparatus for heating a refrigerated fluid such as blood to a predetermined nominal temperature, and of the type including a housing defining a heating chamber for the fluid, means including at least one electric heater element operable from an applied electric current in thermal communication with the fluid in said heating chamber for heating the fluid as it passes through the chamber. control circuit means responsive to the output temperature of the fluid for generating a heater control signal, and switch circuit means electrically connected between said heating element and a source of electrical current, and responsive to said heater control signal, for controlling the application of current to said heating element to maintain the fluid at said predetermined nominal temperature, a temperature monitoring system comprising, in combination: temperature sensing means for generating an analog output signal indicative of the output temperature of said fluid, said temperature sensing means including an output terminal, a constant-current source, a thermistor in thermal communication with said fluid at the output of said heating chamber, and first and second resistances; said constant current source being coupled to one terminal of said thermistor and being connected to a plane of reference potential through said first resistance; said output terminal being coupled to said other terminal of said thermistor and being connected to said plane of reference potential through said second resistance, the sum of said first and second resistances being selected to substantially linearize the temperature-voltage characteristic of said analog output signal at said output terminal over a predetermined temperature range, the ratio of said resistances being selected to provide a desired voltage level on said output terminal at a selected temperature within said operating range; and alarm generator means responsive to said output signal for generating an alarm upon the output temperature of said fluid exceeding said predetermined operating range.

Claim 7

In a fluid warming apparatus for heating a refrigerated fluid such as blood to a predetermined nominal temperature, and of the type including a housing defining a heating chamber for the fluid, means including at least one electric heater element operable from an applied electric current in thermal communication with the fluid in said heating chamber for heating the fluid as it passes through the chamber. control circuit means responsive to the output temperature of the fluid for generating a heater control signal, and switch circuit means electrically connected between said heating element and a source of electrical current, and responsive to said heater control signal, for controlling the application of current to said heating element to maintain the fluid at said predetermined nominal temperature, a temperature monitoring system comprising, in combination: temperature sensing means for generating an analog output signal indicative of the output temperature of said fluid, said temperature sensing means including an output terminal, a constant-current source, a thermistor in thermal communication with said fluid at the output of said heating chamber, and first and second resistances; said constant current source being coupled to one terminal of said thermistor and being connected to a plane of reference potential through said first resistance; said output terminal being coupled to said other terminal of said thermistor and being connected to said plane of reference potential through said second resistance, the sum of said first and second resistances being selected to substantially linearize the temperature-voltage characteristic of said analog output signal at said output terminal over a predetermined temperature range, the ratio of said resistances being selected to provide a desired voltage level on said output terminal at a selected temperature within said operating range; and alarm generator means responsive to said output signal for generating an alarm upon the output temperature of said fluid exceeding said predetermined operating range.

Claim 8

A temperature monitoring system as defined in claim 5 wherein said first and second resistances comprise a potentiometer, the arm of said potentiometer being connected to said plane of reference potential and being adjustable to obtain said desired voltage level on said output terminal at said selected temperature.

Claim 9

A temperature monitoring system as defined in claim 5 wherein said fluid is blood, and said predetermined operating range extends from approximately 30° C. to 40° C.

Claim 10

A temperature monitoring system as defined in claim 5 wherein the sum (R 1 +R 2 ) of said first and second resistances is given by ##EQU7## where said temperature range extends from a temperature T1 to a temperature T2, and V 1 equals the desired output voltage at T1, V 2 equals the desired output voltage at T2, R T1 equals the resistance of said thermistor at T1, and R T2 equals the resistance of said thermistor at T2.