EP0462141A1

EP0462141A1 - Thermometer

Info

Publication number: EP0462141A1
Application number: EP90903900A
Authority: EP
Inventors: Eric Lamont-Gregory
Original assignee: Oxford University Innovation Ltd
Current assignee: Oxford University Innovation Ltd
Priority date: 1989-03-08
Filing date: 1990-03-08
Publication date: 1991-12-27
Also published as: WO1990010854A1; JPH04504000A

Abstract

Thermomètre de contact de surface pour la mesure transcutanée de la température corporelle. Ledit thermomètre comprend un capteur de température supporté par une couche de matière thermo-isolante. On utilise ledit thermomètre en plaçant le capteur contre la peau de sorte que ce dernier soit pris en sandwich entre la couche thermo-isolante et la peau. Ainsi la température du capteur s'élève jusqu'à celle des tissus corporels profonds. On a mis au point un certain nombre de modes de réalisation utilisant des capteurs de température électroniques, des capteurs de température à expansion ainsi que des capteurs de température chimiques. Un exemple de ce dernier, basé sur l'utilisation de cristaux fluides thermochroniques produisant un changement de couleur lorsqu'on les chauffe, est présenté. Dans le cas présent l'affichage comprend un certain nombre de cases (13, 14) affichant la température à l'aide de couleur. Les cases (15, 16) donnent un avertissement de la température corporelle se situant en dehors de la plage normale. Ledit thermomètre est beaucoup plus facile à utiliser qu'un thermomètre au mercure classique.Surface contact thermometer for transcutaneous measurement of body temperature. Said thermometer comprises a temperature sensor supported by a layer of heat-insulating material. Said thermometer is used by placing the sensor against the skin so that the latter is sandwiched between the heat-insulating layer and the skin. Thus the temperature of the sensor rises to that of the deep bodily tissues. A number of embodiments have been developed using electronic temperature sensors, expanding temperature sensors as well as chemical temperature sensors. An example of the latter, based on the use of thermochronic fluid crystals producing a color change when heated, is presented. In the present case, the display comprises a number of boxes (13, 14) displaying the temperature using color. Boxes (15, 16) give a warning of the body temperature being outside the normal range. Said thermometer is much easier to use than a conventional mercury thermometer.

Description

"THERMOMETER"

This invention relates to a thermometer and in particular to a surface contact thermometer for the transcutaneous measurement of the temperature of the human body. The thermometer of the invention is particularly, although not exclusively, suited to neonatal and paediatric use.

A known thermometer of this type is illustrated in Figure 1 of the accompanying drawings. The thermometer comprises a first layer 1 containing a temperature sensor 2, a second layer 3 containing a temperature sensor 4 and backing layer comprising a heater 5. Terminals A, B and C connect to the sensor 2, sensor 4 and heater 5 respectively for connection to external circuitry (not shown). In use the thermometer is positioned so that the layer 1 is directly against the skin surface 6 and the thermometer is left for a period for conditions to stabilise. Heat from the deep body tissues travels outwards through the skin surface and outwardly through the layer 1, then layer 3 and the heater layer. The heater 5 is activated by the external circuitry and controlled in such a way as to equalise the temperature as measured at each of the sensors 2 and 4. In this condition, heat flow from the skin surface to the ambient surroundings is prevented and the skin surface temperature thus rises to the same level as that of the deep body tissues. After the stabilisation period, the deep body temperature can be measured from sensor 2.

The above described thermometer, whilst effective, is complicated and expensive, and requires external circuitry. It is thus not in widespread use in institutions such as hospitals, clinics or in the home. The present invention seeks to provide thermometers which, as well as electronic versions, requiring external circuitry, are also available without any external circuitry for home use, and for use in those parts of the world where a more complicated type of thermometer is inappropriate. In accordance with the invention there is provided a skin surface contact thermometer comprising an insulating holder defining a surface for placement against the skin of a person whose temperature is to be measured, a temperature sensor mounted in or on said holder for measuring the skin temperature, and a thermal insulating layer attached to the insulating holder and positioned so as to sandwich the temperature sensor between itself and the skin. The thermal insulating layer may comprise single or multiple layers of thermal insulating material. Closed or open air layers or vacuum layers may also be employed, either alone or in combination with a layer or layers of thermal insulating material. The thermal insulating material may be a foam plastics material. An example of a material which has been found particularly suitable is known as PLASTAZOTE, a trade mark of BXL.

In use, the temperature sensor, being sandwiched between the skin and the thermal insulating layer, eventually, after a stabilisation period (typically about 5 to 10 minutes), takes up a temperature substantially equal to. that of the deep body tissues. The reason for this is that heat flow from the skin in the area of the thermally insulating material is prevented, or at least substantially reduced by the thermal insulation, so that the skin temperature rises to that of the deep body tissues.

The temperature probe may take various forms depending, amongst other things, upon the anticipated circumstances of use, in particular, whether or not the thermometer is to be. self-contained, or whether it is to be connected to external electronics. Among the self- contained versions, a particularly convenient temperature probe is the thermochromic type, in which a visual, for example colour, change is directly indicative of temperature and can be used to provide a temperature sensor and display all in one. An example is the cholesteric ester type which relies on diffraction of light, or the more recent (and more accurate) chiral nematics type in which fluid crystals are used to detect temperature by means of thermal expansion and resultant variable light diffraction. Also included in the self-contained versions of the thermometer is a mercury or alcohol-in-plastics material thermometer constructed in accordance with the invention. For the "electronic" versions, including the self-contained battery or solar-operated digital type, the temperature sensor may take the form of any of the known electronic temperature sensors - for example resistance, thermocouple or thermistor. Connection means are provided to connect the sensor to associated circuitry which directly records the temperature at the probe on a digital or analogue display.

In order to enhance the level of thermal insulation behind the probe, an embodiment of the invention provides that a thin layer of air, dead air space, or a vacuum is provided between the probe and a reflective film. For maximum effect, this space should take the form of a closed cell or cells of an air or airless cushion - situated between the temperature sensor and the reflective film. Thermal insulation behind the probe is further enhanced by the addition of a reflective film (radiant heat shield) which returns radiant heat from the location of the temperature sensor back to the heat sink (conductive plate) containing the temperature sensor..

In order that the invention may be better understood, several embodiments thereof will now be described by way of example only and with reference to the accompanying drawings in which:-

Figure 1 is a diagrammatic section of a known surface contact thermometer;

Figure 2 is a side sectional view of a self- contained thermometer constructed in accordance with the invention;

Figure 3 is an end sectional view of the thermometer of Figure 2;

Figure 4 is a view of a typical layout of the display of the thermometer of Figures 2 and 3;

Figures 5 and 6 are plan and side views respectively of a fertility thermometer constructed in accordance .with the invention;

Figure 7 is a . diagrammatic exploded perspective view of an electronic version of the thermometer of the invention ;

Figures 8 and 9 are sectional views through two further embodiments of the electronic version of the thermometer of the invention;

Figure 10 is a diagrammatic section of a known self-contained battery powered 'digital' thermometer;

Figure 11 is a diagrammatic view of a self- contained battery powered ' digital ' thermometer constructed in accordance with the invention;

Figure 12 is a side view of the thermometer in Figure 11;

Figure 13 is a view of a self-contained solar powered 'digital' thermometer constructed in accordance with the invention;

Figure 14 is a diagrammatic section of a known mercury-in-glass or an alcohol-in-glass thermometer;

Figure 15 is a diagrammatic view of a self- contained mercury or alcohol-in-plastics material thermometer constructed in accordance with the i nvent i on ;

Figure 16 i s a side view of the thermometer in Figure 15;

Figure 17 is a diagrammatic view of a known self-contained 'digital' tele-thermometer;

Figure 18 is a diagrammatic view of a self- contained 'digital' tele-thermometer constructed in accordance with the invention;

Figure 19 is a diagrammatic view of a self- contained 'digital' multi-sensored tele-thermometer constructed in accordance with the invention;

Figure 20 is a diagrammatic side sectional view of a still further embodiment of the electronic version of the thermometer of the invention; and

Figure 21 is a diagrammatic side sectional view of a thermometer constructed in accordance with the invention for particular use as an adult axilla thermometer. Referring firstly to Figures 2, 3 and 4, there is shown a self-contained version of the thermometer of the present invention. The thermometer is intended for general usage, but finds particular application in neonatal and infant care. As will be clear from the lengthwise section shown in Figure 2, the thermometer comprises a sandwich structure of three basic layers: a bottom layer comprising a film 10 of thermally insulating material, a film 11 of thermochromic material, and a protective film 12 of transparent material. The overall thickness is typically 1.1mm..

The length of the thermometer ^"is typically 110mm.. The film 10 is typically made of a foam plastics material, or similar. A suitable product is known as PLASTAZOTE, a trade mark of BXL. The film 10 may alternatively be fabricated in a multi-layer of different density foams to give an enhanced thermal effect in the smallest - 5 -

I

thickness. The film 11 is such as to change colour, or give the appearance (usually by diffraction effects) of changing colour, with temperature change. Such films are well known in domestic thermometers and utilise cholesteric esters for the temperature indication, arrange in a display to illuminate numbers representative of the indicated temperature. However, much improved accuracy can be obtained by the use of the more recently developed chiral nematic crystals (see above) which give an indication of variable colour according to the temperature being measured.

There are clearly various ways in which the temperature information can be presented to the user. One example is illustrated in Figure 4, in which the normal range of body temperature (36.0-37.7°C) is highlighted in the central part, and the upper and lower ranges displayed to the right and left respectively. In the "hot" and "cold" ranges, the display is arranged as a series of boxes 13,14 respectively to provide a precise measure of temperature to the nearest degree centigrade. In addition, if the temperature is in the range 30 to 35°C, a "cold" box 15 illuminates, and if the temperature is in the range 38 to 41°C, a "hot" box 16 illuminates. Thus the user can obtain a rapid indication as to whether the patient is cold, hot or normal without necessarily having to know the particular temperature. Such more general indications may also prove useful in under-developed countries where the level of numeracy is poor.

In order to protect the edges of the thermochromic structure and also to make the thermometer more comfortable to use, it is preferred that the thermally insulating film 10 extends widthwise beyond the edges of the films 11 and 12 and is thickened to provide foam edges 17. This construction defines a protective and heat insulating cradle for the films 11 and 12 and thus eliminates a possible fall off in temperature at the long edges of the films 11 and 12 which might degrade the display. In use, the thermometer is placed so that the film 12 lies against the skin surface. If necessary the thermometer may be attached by means of surgical adhesive tape. For example, in neonatal use, the thermometer may be placed against an infant's skin in an area midway between the shoulders and waist and the infant placed to lie on its front, thus trapping the thermometer between the infant's body and the mattress. Because of the thermally insulating backing, heat loss from the skin in the area of the thermometer is greatly reduced so that the skin temperature rises to that of the deep body tissues. The thermochromatic layer 11 thus likewise rises to the same temperature which latter is displayed in the manner described above. In order to take a temperature reading, the thermometer, is removed from the patient, after a period for stabilisation, and viewed directly. The temperature indication lasts for a sufficient time for a reasonably leisurely reading to be taken. Because the contact thermometer is not inserted into a body orifice, the risk of injury and cross infection is reduced to a minimum. In children and adults, the same effect can also be achieved by placing the contact thermometer, in its insulating holder, in the closed axilla with the arm held firmly against the side for a period of ten minutes. A thermometer specifically designed for this application is described below.

There will now be described a "fertility" version of the thermometer of Figures 2 to 4, for use with the symptothermic method of family planning. The symptothermic method for determining the optimum time of fertility is currently being used by family planning services world-wide. This method uses daily measurements of oral temperature which if plotted out in chart form reflects a step-wise rise of temperature during ovulation. This temperature rise is seen consistently at mid-cycle and will eventually return to the previous temperature level by the beginning of the next cycle. Oral temperatures taken by a mercury thermometer is the standard technique of choice and usually the temperature change range is between 0.1 - 0.3°C. Frequently these mercury thermometers are confusing to read, difficult to see, and require special handling such as shaking down the mercury which may result in breaking the thermometer itself. Referring to Figures 5 and 6, the fertility thermometer consists of a thermochromic disc 50 approximately 50 millimetres in diameter comprising eight equal segments 51, each of 45° angular extent. Successive segments are arranged so as to be in one degree steps of temperature. The disc has a raised 5mm clear plastic cover 52 shaped to form a 5mm air gap. The reverse aspect of the thermometer, which comes into direct contact with the skin surface, is made of a highly thermally conductive material.

In use, the thermometer would be held in the hand, and would thus be easy to read, convenient, and require no special handling prior to taking the temperature measurement. Operation is based on the use of thermochromic fluid crystals which produce a colour change when heated due to crystal expansion and the refraction of light. Temperature readings will remain stable as long as the thermometer stays in contact with the surface of the hand due to the presence of the air cushion formed by cover 52 which insulates and prevents loss of heat from the thermometer into the ambient air.

One advantage of the use of peripheral over central body temperatures is that the degree of rise in skin temperature is much greater than seen in the use of oral temperature measurement. Thus the 1- 2.0°C change seen following ovulation makes this method more reliable in detecting the time of maximum fertility. The actual method of using this thermometer would consist of holding it with both hands for three minutes in a standard position. This would be done each day early in the morning before rising out of bed. This would be done to prevent the effects of peripheral vasoconstriction secondary to postural changes. Temperatures will then be plotted daily and the recorded temperature curve used for the purposes of family planning or birth control.

Referring now to Figure 7, there is shown a first electronic 'resistance' version of the thermometer of the invention. It will be understood that the drawing is highly diagrammatic and is not to scale. As before, the thermometer comprises a sandwich structure of three layers; a layer 20 of thermal insulating material, a layer 21 which comprises a temperature sensor, and a protective layer 22 of transparent material. The layer 21 comprises a resistive microcircuit whose electrical resistance changes sensitively with temperature. A cable 23 connected to the microcircuit leads to a jack plug 24 or similar for connection to external circuitry (not shown). The nature of this circuitry depends upon the particular type of sensor used - all are well known and will not be described further. Alternative temperature sensors include thermocouple or thermistor types.

Advantageously, the thermal insulating layer 20 is formed with a c ircu ferential ly upstanding rim (not shown) which, as with the previous embodiment, defines a protective and heat insulating holder in which the temperature sensor layer is situated. Such an insulating holder could be supplied for use with existing temperature probes of any type, for example rectal, skin or oesophageal. Thus the user can utilise any temperature probe which happens to be handy for the measurement of deep body temperature. The thermometer is used in a similar manner to the self-contained version, and functions in the same manner. Temperature readings are taken directly with the thermometer in place, the temperature indication being provided by means of an analogue or digital display forming part of the associated circuitry.

Unlike the thermochromatic insulated contact thermometers described above and shown in Figures 2 to 6, the other versions of the thermometer constructed in accordance with the invention are ideal for continuous body temperature measurement, particularly, but not exclusively, in neonatal and paediatric use, since there is no need to remove the thermometer from between the body and mattress of the patient, in order to take a temperature reading. Reference is now made to Figure 8 of the accompanying drawings which shows a second embodiment of the electronic version of the thermometer. In this embodiment, the electronic temperature sensor is embedded in a thermally conductive plate (heat sink) 30 which is supported by a film 31 of impermeable material such as plastics material on the rim of the insulating holder 32 of thermal insulating material, for example, foam plastics material, as above. Between the insulating material and the plate 30 is a closed cell 33 of dead air space. In addition, between the closed cell 33 and any further insulating cells or material 34 is. located a reflective film 29. This film 29, which may take the form of a parabolic mirror, but not exclusively so, which may or may not be flexible reflects radiant heat back towards the conductive plate (heat sink) 30 containing the temperature sensor. The sensor itself (not shown) may be as above - i.e. thermistor, thermocouple or temperature resistive. The closed air cell assists .in providing a thermally • insulating backing for the sensor. The plate 30 is preferably of metal, for example aluminium, silver, platinum, palladium or stainless steel. The film 31 is of impermeable plastics material such as vinyl sheet or rubberised plastics material.

In use, the thermometer is placed with the top surface, containing the plate 30, in contact with the patient's skin. In a typical application the thermometer is placed between the skin and mattress of a body lying supine or prone on a mattress, thus exploiting the naturally occurring area of zero or negligible heat flow from skin to mattress. The thermally insulating layers 32,33 ensure that zero or near-zero temperature gradient is achieved whether the infant is lying on the thermometer or not. Some versions of the thermometer may contain pressure sensing means (not shown) such as a pressure sensitive microswitches to provide an alarm if the probe becomes dislodged from contact with the skin.

The zero or low temperature gradient ensures that the skin temperature, and hence that of the plate 30, rises to that of the deep body tissues for accurate measurement of the deep body temperature.

Referring now to Figure 9 there is shown a third embodiment of the electronic version of the thermometer. This embodiment is very similar to that shown in Figure 8 and will not be described in detail. The main difference is that an extra thermally I insulating layer 34 is provided between the air cell 33 and the cradle 32. The layer 34 may also be made of foam plastics material, but of a lesser density than that of the insulating holder. The thermometer is used and operates in the same manner as that shown in Figure 8, save for an enhanced heat loss characteristic due to improved thermal insulation.

In both the thermometers of Figures 8 and 9, wire means (not shown) are used to connect the temperature sensor embedded in the plate 30 to adjacent circuitry (also not shown) for analysing and displaying the temperature readings taken from the thermometer.

Reference is now made to Figure 11 of the accompanying drawings which shows a fourth embodiment of the electronic version of the thermometer. This '^' version is of the self-contained battery powered 'digital' type. A known thermometer of this type is illustrated in Figure 10 of the accompanying- drawings . The thermometer comprises battery powered electronic circuitry (not shown) contained within the plastic casing 35 and a digital display panel 36. A battery compartment is typically contained within the plastic casing 37. A temperature sensor is embedded in plastic surrounded by a metal cap 38 and an on/off switch 39. The shaft of this thermometer 40 is usually inserted into the mouth or rectum or is placed in the axilla to obtain a body temperature reading. The use of this thermometer has limited applicability in neonatal and infant care because many parents are unable to insert a thermometer into the rectum and oral temperature-taking in neonates and infants is not advisable. Because an infant must be undressed to insert a fluid-in-glass thermometer they are not suited for long-term or frequent measurements of body temperature. . Referring again to Figure 11, the shaft 41 of the thermometer is made of a pliable and durable plastics material. The temperature sensor 42 is connected to the battery powered electronic circuitry (not shown) by means of wires (only partially shown). The positioning of the temperature sensor 42 in the insulating holder is as described in Figures 8 and 9 above, and illustrated in Figure 12.

Reference is now made to Figure 13 of the accompanying drawings which shows a solar cell 43 powered version of the 'digital ' thermometer of Figures 11 and 12.

The thermometers described in Figures 11, 12 and 13 are used in a similar manner to the other self- contained versions of the thermometer described above, and function in the same manner.

Reference is now made to Figures 15 and 16 which show a self-contained mercury or alcohol-in- plastics material thermometer, constructed in accordance with the invention. A known thermometer of this type is illustrated in Figure 14 of the accompanying drawings. A material that expands a predictable distance in a column with changes in temperature is contained in a well 44 located at one end of the thermometer. When heated, the thermally expansive material rises along the length of the column 45 and is visible. Gradation markings 46 located along the length of the shaft of the thermometer 47 are located at known distances from the well and correspond to the temperature from heating the well.

Thermometers of the mercury or alcohol-in-glass type have been known to cause injury in neonates, infants and children. Being glass and therefore easily broken, fluid-in-glass thermometers are not ideally suited for use in the home or by health-care workers in developing countries who would have to carry the glass thermometer from place to place. Because an infant must be undressed to insert a fluid-in-glass thermometer into a body orifice, they are not suited for long-term or frequent measurements of body temperature.

In the Figure 15 version, the well 44 and the column 45 containing thermally expansive material, is constructed of a thin layer of impact- resistant plastics material. The construction of the insulating holder surrounding the well is as shown in Figures 8 and 9 above. The entire length of and both sides of the shaft 47 are insulated with varying densities of thermal insulating materials 32 and 34. In addition, the thermometer may be placed in an insulating holder 17 (not shown) as illustrated in Figure 3.

The thermometer described in Figures 15 and 16 is used in a similar manner to the other self-contained versions of the thermometer, constructed in accordance with the invention described above, and functions in the same manner.

Reference is now made to Figure 18, which shows a first self-contained battery, or alternatively solar-powered, digital thermometer constructed in accordance with the invention. Figure 17 of the accompanying drawings is of a known "digital" tele- thermometer of this type. With reference to Figure 19 of the accompanying drawings which shows a first multi- sensored version of the 'digital' tele-thermometer constructed in accordance with the invention. The version of the invention and the electronic versions of the thermometer described in Figures 7, 8 and 9 may also contain more than one temperature sensor. Multi-site 'differential body temperature assessment' i.e., the temperature difference between deep-body and a peripheral body temperature site, allows the user to distinguish raised body temperatures which are the result of environmental-overheating (hyperthermia) from raised body temperatures that are associated with illness (fever).

The thermometers described in Figures 18 and 19 are used in a similar manner to the other self- contained versions of the thermometer constructed in accordance with the invention described above, and function in a similar manner. Certain features such as a clock and the ability to convert between various temperature scales (as seen in Figures 18 and 19) are included in several versions of the thermometer constructed in accordance with the invention.

There will now be described, with reference to Figure 20, an alternative construction of probe to those illustrated in Figures 8 and 9. The design consists of a heat sink 60, for example 0.25mm thick and 15mm in diameter. The heat sink may be composed of any one of a number of materials of high thermal conductivity. One such material is high purity aluminium. The heat sink comes into direct contact with the skin. The thermistor, thermocouple or thermal resistive sensor 61 is attached to the inner surface of-the heat sink. As shown, the temperature sensor 61 extends from the inner surface of the heat sink through an appropriately sized aperture 62 in the centre of the heat sink so_.that part of the sensor is level with the outside surface of the heat sink. The attachment technique is therefore such that the temperature sensor and the heat sink become one unit, for all practical purposes. The rear of the temperature sensor is contained within a dead air space 63. In the neonatal version of the device the dead air space is approximately 8mm in diameter. The dead air space is defined by an aperture formed in a thin layer 64 of soft foam-like plastic material which is a good thermal insulator. One of the insulating materials from which this layer may be constructed is a low density polyethylene foam "Plastazote" , a product of BXL Plastics Limited. The layer 64 in the neonatal version of the invention is approximately 3mm thick and 25mm in diameter. Immediately adjacent, to the plastic insulating layer 64 is a thin layer 65 of metallised plastic approximately 3 microns thick and 15mm in diameter. This layer 65 is located in the centre of the thermometer probe and does not extend to the sides. One of the metallised plastic materials that may be used for this layer is alu iniumised mylar, a product of Metalising Products, with the metallisation facing the air space 63. Behind layer 65 is an additional insulating layer 66 of glass fibre paper, also 15mm diameter in the neonatal version. There are a number of insulating materials from which the layer 66 may be constructed. One such material is Atlas glass fibre paper, a product of Ash Fibre Processors Limited, of approximately 0.6mm thickness. The next layer, 67, is a further layer of metallised plastic 3 microns thick and 15mm in diameter, also with its metallisation facing upwards. The layer 67 is also located in the centre of the probe and does not extend to the sides. The sixth layer 68 is a second layer of soft foam-like insulating material that is approximately 1 to 1.5mm thick and 25mm in diameter. In some versions of the invention the layer 68 also contains a dead air space (not shown). The final layer consists of a thin layer 69 of metallised plastic approximately 3 microns thick and 25mm in diameter.

The overall thickness of this versioo of the invention is typically between 3.25 and 3.75mm. In some cases, a specially designed probe will be used to ascertain the deep tissue temperature of a limb tissue, for example, the calf. Some alterations of the above mentioned design would be made.

Each of the layers of the invention described above perform the same functions as those materials described in other parts- of the description of this invention. Referring now to Figure 21 there is shown an embodiment of the invention for adult axilla deep body temperature measurement. The design consists of a heat sink 70, for example 0.25mm thick and 15mm in diameter. The heat sink may be composed of any one of a number of materials of high thermal conductivity. One such material is high purity aluminium. The heat sink 70 comes into direct contact with the adult's skin. The thermistor, thermocouple or thermal resistive sensor 71 is attached to the inner surface of the heat sink. As shown, the temperature sensor 71 is positioned behind an aperture 72 in the centre of the heat sink so that part of the sensor is exposed through the aperture. The attachment technique is therefore such that the temperature sensor and the heat sink become one unit, for all practical purposes. The rear of the temperature sensor is contained within a dead air space 73. In the adult version the dead air space is approximately 8mm in diameter. The dead air space is defined by an aperture formed in a layer 74 of soft foam-like plastic material which is a good thermal insulator. One of the insulating materials from which this layer of the invention may be constructed is a low density polyethylene foam "Plastazote", a product of BXL Plastics Limited, but not exclusively so. The layer 74 in the adult version is approximately 1.5mm thick and 25mm in I diameter. Immediately adjacent to the plastic insulating layer 74 is a thin layer 75 of metallised plastic approximately 3 microns thick and 15mm in diameter. The layer 75 is located in the centre of the thermometer and does not extend to the sides. One of the metallised plastic materials that may. be used in the layer 75 is aluminiumised mylar, a product of Metalising Products, with the metallisation facing the air space 73. Behind layer 75 is an additional insulating layer 76 of glass fibre paper also 15mm diameter in the adult version. There are a number of insulating materials from which this layer may be constructed. One such material is Atlas glass fibre paper, a product of Ash Fibre Processors Limited, of approximately 0.6mm thickness. The next layer, 77, is a further layer of metallised plastic, for example 3 microns thick and 15mm in diameter, also with its metallisation facing upwards. The layer 77 is also located in the centre of the device and does not extend to the sides. The sixth layer 78 is a second layer of soft foam-like insulating material that is approximately 1 to 1.5mm thick and 25mm in diameter. In some versions of the invention this layer also contains a dead air space (not shown). The next layer consists of a thin layer 79 of metallised plastic approximately 3 microns thick and 25mm in diameter. The whole of this construction is contained in a soft foam rubber ovoid 80 with the heat sink level and conforming to the shape of the outside surface of the ovoid, as shown in Figure 21. The principal advantage of this construction of the thermometer is that the thermal insulation of the temperature probe is not affected when the axilla is open because the foam ball expands as the arm moves away from the chest.

Each of the layers of the invention described above perform the same functions as those materials described in other parts of the description of this invention .

One version of this thermometer (not shown) is also constructed in the shape of a flat disc, as shown in the neonatal version of the invention, except that the heat sink is located towards the outside surface of the thermometer, whereas in the neonatal version, the heat sink is located in the middle of the thermometer.

Claims

C LA I MS

1. A skin surface contact thermometer comprising an insulating holder defining a surface for placement against the skin of a person whose temperature is to be measured, a temperature sensor mounted in or on said holder for measuring the skin temperature, and a thermal insulating layer attached to the insulating holder and positioned so as to sandwich the temperature sensor between itself and the skin.

2. A thermometer as claimed in claim 1 wherein said thermal insulating layer comprises a layer of foam or expanded material.

3. A thermometer as claimed in claim 1 wherein said holder is shaped so as to define a closed layer of air, or vacuum, to form said thermal insulating layer.

4. A thermometer as claimed in claims 2 and 3 wherein said thermal insulating layer comprises at least one said layer of air or vacuum laminated with at least one layer of foam or expanded material.

5. A thermometer as claimed in either one of claims 3 or 4, further including a reflective film on that surface of the layer of air or vacuum remote from the temperature sensor.

6. A thermometer as claimed in any one of claims 2, 4 or 5 wherein said thermal insulating layer comprises a layer of foam plastics material.

7. A thermometer as claimed in any one of the preceding claims wherein the temperature sensor is mounted in or on a plate of thermally conductive material, and wherein the holder is adapted so that, in use, said plate lies against the skin surface to thereby provide a substantial area of thermal contact between the skin surface and the temperature sensor.

8. A thermometer as claimed in any one of the preceding claims wherein the temperature sensor is of the thermochromic type.

9. A thermometer as claimed in any one of claims 1 to 7 wherein the temperature sensor is of the closed-cell expansive material type.

10. A thermometer as claimed in any one of claims 1 to 7 wherein the temperature sensor comprises an electronic temperature sensor having leads for connection to electronic circuitry by means of which the temperature at the sensor can be read.

11. A thermometer as claimed in claim 8 wherein the thermometer comprises a sandwich structure of three layers: a bottom layer of thermally insulating material, an intermediate layer of thermochromic material and a top layer of transparent material and wherein, onto the top layer, is printed boxes and indicia to assist the user in the interpretation of the temperature reading presented by the appearance of the layer of thermochromic material.

12. A thermometer as claimed in claim 10 further comprising a handle, and a stem for attaching said handle to the housing, and wherein said electronic circuitry is contained within the handle and powers a display located in a wall of the handle.

13. A thermometer as claimed in either one of claims 10 or 12 further including solar cells for powering the electronic circuitry.

14. A thermometer as claimed in^'claim 10 wherein the housing takes the form of a block of resilient material having a shape suitable to enable it to be easily retained in a body crevice, such as the axilla.

15. A thermometer as claimed in claim 14 wherein said block is substantially ovoid in shape.