GB1578015A

GB1578015A - Indusion warmer

Info

Publication number: GB1578015A
Application number: GB1378/76A
Authority: GB
Original assignee: AMSUD INVESTMENTS SA
Current assignee: AMSUD INVESTMENTS SA
Priority date: 1977-01-14
Filing date: 1977-01-14
Publication date: 1980-10-29

Description

(54) INFUSION WARMER (71) We, AMSUD INVESTMENTS S.

A. a Swiss Company, of 6, Rue d'Italie 1211, Geneve 3, Switzerland, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement.

This invention relates to devices for heating a fluid flowing through a flexible tube and one object is to provide a safe and easily operated device suitable for use in hospitals for warming blood plasma from a blood bank as it passes through a giving set to a patient.

According to the present invention a device for heating a fluid flowing through a flexible tube to a required temperature within a predetermined temperature range comprises a block of thermally-conductive material formed with at least one elongate channel having a side which is often along the length of the channel, and into which the tube can be pressed without having access to an end of the tube, electrical heating means for the block, a temperature detector, and an electrical supply circuit connected to control the heating means in response to operation of the detector.

The channel preferably has a cross section which is circular through an angle substantially in excess of 1800 but less than 360" so that the tube can be pressed into it by slight deformation of the tube. However after the tube has been inserted it will then be in good heat conducting relationship with the walls of the channel throughout more than half the peripheral area of the tube so that the heat from the block can be readily transferred to the liquid in the tube.

Preferably there are two temperature detectors, one of which can be set to a desired temperature so that the heating means can be switched on and off in dependence on the temperature being below or above the set value. The second detector is in the nature of a safety device which is arranged to give a warning and/or to cut off the supply or isolate the heating means if the temperature reaches a certain temperature higher than the maximum temperature that can be controlled by the first detector.

The temperature detectors may be in good heat conducting relationship with the block, for example by being fitted into holes bored in the block, or might even be embedded in it preferably close the the place where the tube leads from the block.

Alternatively the detectors could be in a device arranged to clip on or be fastened onto the tube where it leaves the block and then to be in good heat conducting relationship with the tube.

The device preferably has three indicator lamps, one for indicating that the device has been turned on, one for indicating whether or not the set temperature has been reached and one for indicating whether the higher safety temperature has been reached. These are conveniently respectively green, amber and red.

The block or another part of the device preferably has simple instructions printed upon it including a description of the necessary power supply and the diameter of the flexible tube with which the device is designed to operate and preferably also instructions for inserting the tube in the channel.

The invention may be carried into practice in various ways, and one embodiment will now be described by way of example with reference to the accompanying drawings in which; Figure 1 is a underneath view of the base of an infusion warmer; Figure 2 is a top view of the base of Figure 1; Figure 3 is a section on the line 3-3 in Figure 2; Figure 4 is a sectional elevation in the direction of the arrow IV in Figure 2; and Figure 5 is a circuit diagram of the electrical components.

The infusion warmer comprises a cast aluminium base plate 11 having in its lower face four parallel elongate grooves which are very nearly circular in section as shown at 12 in Figure 3, so that an elongate plastic blood-plasma-carrying tube of circular section can be forced through the narrow neck 13 to fit snugly in a groove with good heat-exchange contact between the tube and the groove over almost the complete external surface of the tube. The tube can be curved at the ends of each groove, and wound round to make two complete turns as indicated generally at 14 in Figure 1 with a substantial part of its length in good heatexchange relationship with the wall of one of the grooves Thus a standard plastics tube 10 extending from the bag, of a giving set for the infusion liquid to an infusion needle for insertion into the patient can be forced into the grooves for warming of the liquid without having to have access to the ends of the tube.

In the opposite face of the block 11 are four slots 15 extending parallel with one another through almost the entire length of the block, and each of those contains an electrical resistance heater 20 wound on an insulating former. Each heater is in good heat-exchange relationship with the sides of its slot 15 so that when energised they can heat the block so that the heat can in turn be used to heat the infusion liquid.

An electrical circuit shown in detail in Figure 5 is mounted on a printed circuit board 16 which is positioned above the upper face of the base plate as shown in Figure 4. An external insulating cover 17 fits around the side wall of the block enclosing the space containing the printed circuit board 16.

The circuit includes a buzzer 21 and three lamps 22, 23 and 24, and the cover has corresponding openings 25 and 26 through which the sound of the buzzer can be heard, and through which the lamps can be seen.

On the underside of the openings 25 from the buzzer is a diaphragm 27 which is thin enough to enable the sound of the buzzer to be heard, but which seals the interior of the cover 17 from external moisture. The lamps 22, 23, 24 are respectively green, amber and red, and they are illuminated in dependence upon the condition of the circuit as will be described in more detail below.

The buzzer and lamps are mounted on the printed circuit board 16, as are all the electrical components except four transis tors for carrying and controlling the heater current, and thermistors 28 for detecting the temperature of the base plate.

The transistors when energised generate a significant amount of heat, and accordingly they are mounted in good heat conducting relationship with a heat sink 31 comprising an aluminium bridge which is screwed to the upper face of the base plate immediately adjacent a socket for a first thermistor 28 near one end of the base plate. The other thermistor 28 is in a corresponding socket near the other end of the base plate, and they are set to operate at slightly different temperatures, the first thermistor 28 being arranged to operate at 390C and the other thermistor 28 at 41 .50C as will be described below.

The cover 17 carries a clamp comprising a pair of insulating discs 33, each having an axial hole for a bolt 34 and each having a transverse semi-circular groove 35 so that the two discs can be clamped on either side of a stand post by screwing up a handle 36 on the end of the bolt 34 into a nut 37 on the inside of the cover. The opening containing the nut, the openings for the lamps 22-24 and the joint between the cover and the edge of the base plate are all sealed against the entry of moisture.

The electrical circuit is supplied with 12 volts d.c. through a remote lead from a power pack connected to the a.c. mains.

The power pack is in a sealed box with a skirt at least 1 inch tall and an enveloping cover so that the components can be lifted above any moisture that may be on the floor.

When the warmer is to be used, the tube 10 from the giving set bag to the needle is wound into the grooves 12 as shown in Figure 1, and the power supply is switched to the electric circuit so that the green lamp 22 is illuminated.

The heaters 20 are connected across the d.c. supply through a first and second Darlington pair of transistors TR1 and TR2, and a second Darlington pair TR8 and TR9 constituting the four transistors described as mounted on the heat sink 31. The amber lamp 23 is connected across the heaters and is always illuminated when the heaters are energised.

In order to raise the liquid to the desired temperature for delivery to the patient, the circuit is set so that the first thermistor 28 operates at a temperature of 39"C to unbalance an integrated circuit I.C.1. which in turn controls conduction of the Darlington pair TR1 and TR2 by way of a transistor TR3 and a component 1 of an integrated circuit I.C.2. The lamp and heaters are de-energised until the block cools sufficiently for the thermistor 28 to reset the integrated circuit I.C.1. enabling the heaters to be turned on again. The heaters are cycled on and off to maintain the desired temperature of the base plate and hence of the liquid.

If the amber light never goes off, the user can see that the desired temperature is never being achieved.

One danger with this type of equipment, is that the liquid should be heated too much, and accordingly the second thermistor 28 is arranged to respond to a temperature of 41.5"C to switch off the heaters, and also to bring on the red lamp 22 and sound the warning buzzer 21.

If the thermistor 28 reaches 41.5"C, the second Darlington pair TR8 and TR9 is turned off through an integrated circuit I.C.4., a transistor TR6 and a transistor TR7. When that occurs the base drive to a transistor TR5 is removed so that the emitter of the transistor TR6 which was previously held close to earth potential by the transistor TR5 rises to about 4 volts, derived from the stabilised power supply including a zener diode D1 and a resistor R28 by way of a resistor R19. A potential divider in the base circuit to the transistor TR6 including the resistors R34 and R35 prevents the base drive to the transistor TR6 from reaching the 4 volts necessary to turn the transistor TR6 on even after the thermistor 28 has cooled down again, so that the red lamp and the buzzer remain energised until the supply is switched off. The lamp and buzzer are energised in response to the emitter voltage of the transistor TR6 through components 3 and 4 of the integrated circuit I.C.3. and components 2, 4 and 5 of the integrated circuit I.C.2.

If it is desired to resume use of the heater after the supply has been turned off, the action of turning on the supply enables the base drive to the transistor TR5 to appear momentarily through a circuit connected across the d.c. supply consisting of a rectifier D2. in parallel with the resistor R40, that combination being in series with a capacitor C4 and resistors R39 and R38 forming a potential divider to which the base of the transistor TR5 is connected.

Thus the simple cycling of the heaters in response to the first thermistor 28 can be resumed, provided the second thermistor 28 had cooled when the supply ws reconnected, until the second thermistor 28 again detects an excessive temperature.

It is also desirable to provide an indication if the voltage reference used for controlling the thermistors 28 falls below about 10.5 volts.

Component 2 of the integrated circuit I.C.1. compares a fraction of the unstabilised supply voltage through a divider R7 and R8 with the stabilised supply voltage derived from the zener diode D1 through a resistor R9. If the unstabilised supply falls below about 10.5 volts gate 2 of the circuit I. C. 1. and the Transistor TR4 cause the input to I.C.3. to become low. Gates 1 and 2 of the integrated circuit I.C.3, gates 3 and 6 of the integrated circuit I.C.2 and the networks R21, C2 and R22 on the one hand and R23, C1, and R20, on the other hand form a gated astable multivibrator which is then triggered to generate a square wave in response to the input to pin 2 of gate 1 of the integrated circuit I.C.3 becoming low. The square wave is supplied through gates 3 and 4 of I.C.3 and gates 2 and 5 of I.C.2 to operate the buzzer 21 and the red lamp 22 in on/off fashion so that the user will know that the power supply has fallen sufficiently to make the thermistor operation inaccurate.

WHAT WE CLAIM IS: 1. A device for heating a fluid flowing through a flexible tube to a required temperature comprising a block of thermallyconducting material formed with at least one elongate channel having a side which is open along the length of the channel, and into which the tube can be pressed without having access to an end of the tube, electrical heating means for the block, a temperature detector, and an electrical supply circuit connected to control the heating means in response to operation of the detector.

2. A device as claimed in Claim 1 including two temperature detectors one arranged to operate at a temperature related to the required temperature, and the other arranged to operate at a temperature in excess of that.

3. A device as claimed in Claim 2 including two means for removing the supply from the electrical heating means, one operated in response to operation of each of the two detectors.

4. A device as claimed in any of the preceding claims including three lamps for indicating respectively that the circuit has been turned on, that the heater is energised, and that an excessive temperature has been reached.

5. A device as claimed in Claim 4 including means for indicating that the supply volts are lower than a predetermined value.

6. A device as claimed in Claim 5 in which the indication of low supply volts is pulsating energisation of the lamp for indicating an excessive temperature.

7. A device as claimed in any of the preceding claims in which the supply circuit includes one or more transistors for leading the heating current to the heating means, which transistors are mounted in intimate heat contact with a heat sink mounted in close relationship with the detector.

8. A device as claimed in any of the preceding claims in which the/or each channel is open at both ends of the block.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. on and off to maintain the desired temperature of the base plate and hence of the liquid. If the amber light never goes off, the user can see that the desired temperature is never being achieved. One danger with this type of equipment, is that the liquid should be heated too much, and accordingly the second thermistor 28 is arranged to respond to a temperature of 41.5"C to switch off the heaters, and also to bring on the red lamp 22 and sound the warning buzzer 21. If the thermistor 28 reaches 41.5"C, the second Darlington pair TR8 and TR9 is turned off through an integrated circuit I.C.4., a transistor TR6 and a transistor TR7. When that occurs the base drive to a transistor TR5 is removed so that the emitter of the transistor TR6 which was previously held close to earth potential by the transistor TR5 rises to about 4 volts, derived from the stabilised power supply including a zener diode D1 and a resistor R28 by way of a resistor R19. A potential divider in the base circuit to the transistor TR6 including the resistors R34 and R35 prevents the base drive to the transistor TR6 from reaching the 4 volts necessary to turn the transistor TR6 on even after the thermistor 28 has cooled down again, so that the red lamp and the buzzer remain energised until the supply is switched off. The lamp and buzzer are energised in response to the emitter voltage of the transistor TR6 through components 3 and 4 of the integrated circuit I.C.3. and components 2, 4 and 5 of the integrated circuit I.C.2. If it is desired to resume use of the heater after the supply has been turned off, the action of turning on the supply enables the base drive to the transistor TR5 to appear momentarily through a circuit connected across the d.c. supply consisting of a rectifier D2. in parallel with the resistor R40, that combination being in series with a capacitor C4 and resistors R39 and R38 forming a potential divider to which the base of the transistor TR5 is connected. Thus the simple cycling of the heaters in response to the first thermistor 28 can be resumed, provided the second thermistor 28 had cooled when the supply ws reconnected, until the second thermistor 28 again detects an excessive temperature. It is also desirable to provide an indication if the voltage reference used for controlling the thermistors 28 falls below about 10.5 volts. Component 2 of the integrated circuit I.C.1. compares a fraction of the unstabilised supply voltage through a divider R7 and R8 with the stabilised supply voltage derived from the zener diode D1 through a resistor R9. If the unstabilised supply falls below about 10.5 volts gate 2 of the circuit I. C. 1. and the Transistor TR4 cause the input to I.C.3. to become low. Gates 1 and 2 of the integrated circuit I.C.3, gates 3 and 6 of the integrated circuit I.C.2 and the networks R21, C2 and R22 on the one hand and R23, C1, and R20, on the other hand form a gated astable multivibrator which is then triggered to generate a square wave in response to the input to pin 2 of gate 1 of the integrated circuit I.C.3 becoming low. The square wave is supplied through gates 3 and 4 of I.C.3 and gates 2 and 5 of I.C.2 to operate the buzzer 21 and the red lamp 22 in on/off fashion so that the user will know that the power supply has fallen sufficiently to make the thermistor operation inaccurate. WHAT WE CLAIM IS:

1. A device for heating a fluid flowing through a flexible tube to a required temperature comprising a block of thermallyconducting material formed with at least one elongate channel having a side which is open along the length of the channel, and into which the tube can be pressed without having access to an end of the tube, electrical heating means for the block, a temperature detector, and an electrical supply circuit connected to control the heating means in response to operation of the detector.

9. A device as claimed in any preced

ing claims in which the/or each channel has a cross section which is circular through an angle substantially in excess of 1800 but less than 360" by virtue of the open side into which the tube can be pressed.

10. A device as claimed in any of the preceding claims in which the/or each chan nel is cut in one face of the block and grooves for the heating means are cut in the opposite face of the block.

11. A device as claimed in any of the preceding claims in which the components of the electrical supply circuit are mounted on a printed circuit board.

12. A device as claimed in any of the preceding claims including an audible warn ing device responsive to indication of an excessive temperature.

13. A device as claimed in Claim 12 in which the device has a cover with an opening for sound from the audible device which opening is covered by a sealing diaphragm.

14. A device as claimed in any of the preceding claims energised by a d.c. line connected to a remote power pack sealed against the entry of moisture.

15. A device as claimed in any of the preceding claims having a cover on the block carrying a clamp enabling the cover and block to be mounted on a stand.

16. A device for heating a fluid flowing through a flexible tube to a required tem perature constructed and arranged substan tially as herein specifically described with reference to the accompanying drawings.

Reference has been directed in pursuance of seefion 8 of the Patents Act 1949, to specification No. 1446412