GB2286684A - Skin temperature sensing device - Google Patents

Abstract

A device (2) for monitoring a baby's temperature comprises a thermistor (12) to monitor the baby's skin temperature and a microprocessor to convert the skin temperature to the baby's core temperature and analyse the data. Past temperature readings are stored in memory and a liquid crystal display (8) presents the baby's temperature. Temperature patterns are known which the baby's temperature will follow if the baby is becoming ill. The microprocessor triggers an alarm to alert the baby's carer if such a pattern is detected or if the baby's temperature becomes too high to too low. A switch (10) allows the stored temperatures to be reviewed. The electronics is contained in a housing (4) which attaches to the baby's wrist by straps (6). To calibrate the device a separate temperature sensor for detecting core temperature eg under the arm is connected through a socket (5). <IMAGE>

Description

SKIN TEMPERATURE SENSING DEVICE This invention relates to a skin temperature sensing device, particularly for humans, especially babies.

It is well- known that it is dangerous for a baby (particularly a new-born) to get too cold or to overheat. High temperature is also thought to be a contributing factor in most SIDS cases (Sudden Infant Death Syndrome or cot death). However, it is extremely difficult to estimate a baby's core body temperature from the temperature of its extremities and its colour. While continuous temperature monitoring can be provided in hospital by sensors taped to the baby's skin and connected by wires to display units, this is impractical at home, because it interferes too much with normal life. Most parents therefore rely on estimating the baby's core temperature as often and as best they can. An easy way of providing a continuous temperature reading with an indication of dangerous temperature would therefore be useful.

According to the invention, a skin temperature sensing device comprises a housing adapted for attachment to the human body, the housing being provided with a skin temperature sensing means, a power source, a microprocessor means, a display means and an alarm means, in which the skin temperature sensing means supplies an electronic signal to the microprocessor means, which is operative to convert the signal to a temperature corresponding to the core temperature of the body, periodically to display the core temperature on the display means and to activate the alarm means when the core temperature is outside a predetermined temperature range.

The device can easily be attached to the body for extended periods, and provides a self-contained unit which continuously monitors and displays core temperature, and warns of dangerous temperatures.

The device preferably includes memory means for storing at least one previously displayed core temperature. The memory means may store up to fifty previous readings. These readings are preferably stored every hour or two hours. The housing preferably includes switch means operative to display the stored readings on the display means. The timing of the stored readings may be shown on the display means by numerals and/or indicator lights. The stored readings may be useful for research into temperature patterns in connection with SIDS.

It is known that the temperature of babies and infants who have contracted an illness follows a set pattern before any outward symptoms of the illness become apparent. Detection of this pattern can therefore predict the onset of an illness. Preferably therefore the memory means of the device holds this temperature pattern and the microprocessor means compares the stored core temperature readings with the pattern, and activates the alarm means if the pattern is detected in the stored readings.

The skin temperature sensing means preferably comprises a thermistor, whose resistance varies with temperature. In order to ensure that the thermistor is unaffected by external influences the housing may provide a closed environment for the thermistor. The signal from the thermistor is amplified before reaching the microprocessor means.

The device may be provided with, in addition to the skin temperature sensing means, an environment temperature sensing means. An advantage of an environment temperature sensing means is that temperature fluctuations in the surroundings of the device can be allowed for and so will not influence skin temperature readings taken by the device.

The device may also include means for calibrating the device to the wearer's core temperature. This would allow more accurate readings to be taken. The calibration means comprises an external temperature sensing means which is removably attached to the device. This external temperature sensing means may allow the temperature of the wearer's armpit to be taken.

The microprocessor means conveniently comprises a printed circuit board which includes the memory means.

The display means may comprise a liquid crystal display (LCD) together with one or more indicator lights.

The alarm means preferably comprises an audible tone. The power source is a 3v battery pack.

The housing is preferably attached to the body by straps. The straps may attach the housing to the wrist, or any other suitable place. The housing and straps may be waterproofed.

The device may include transmitting/receiving means. Such transmitting/receiving means would allow the device to communicate with a base station. The base station may contain an alarm means which would be triggered at the same time as the alarm means of the device.

Embodiments of the invention are illustrated by way of example in this accompanying drawings, in which: Figure 1 is a perspective view of a skin temperature sensing device; Figure 2 is a side view, part cut away of the device of Figure 1; Figure 3 shows a schematic of the electronics of the device; and Figure 4 shows a plan view of a display screen of the device of Figure 1.

Figures 1 and 2 shows a device for attachment to a baby's wrist, for monitoring the baby's temperature to detect when undesired temperature or temperature patterns occur. It consists of a plastics housing 4 to which straps 6 attach allowing the device to be securely fastened to the baby's wrist. The housing 4 contains a skin temperature sensing means, a thermistor 12, which senses the temperature of the baby's wrist under the device. It also contains a 3v battery (not shown), and a microprocessor means (not shown) for calculating the core temperatures. On top of the device is a display means, a liquid crystal display (LCD) 8, for displaying relevant information.

Also on top of the device is a switch 10 which is used for operating the device and an environment temperature sensing means 3 for monitoring the environment. An audible alarm means, not shown, is provided for attracting the attention of the baby's carer. There is also a means for calibrating the device to the wearer's core temperature. A socket 5 is adapted for connection of an external temperature sensing means (not shown).

A radio transmitter/receiver (not shown) is also provided.

The straps 6 are of similar construction to plastics name tags currently used in hospitals. They attach to the base of the housing and pass around the baby's wrist, thus securing the device in place. The housing 4 is coated in silicon rubber, applied to seal and waterproof the device.

The thermistor 12 has a negative temperature coefficient and is mounted at the top of a recess 14, formed in the housing 4 of the device. The lowermost surface 16 of the device is a flexible sealing lip resting against the baby's skin and sealing the recess. The sealed recess 14 provides a closed environment for the thermistor 12 to operate in and allows for more accurate temperature readings.

A schematic of the electronics of the skin temperature sensing device is shown in Figure 3. The temperature sensor is the thermistor 12 which is capable of reading the temperature to 0.050C accuracy.

The output signal of the thermistor is initially amplified and then input to the analogue to digital converter (ADC) input of the microprocessor. This is the PIC16C71 device, which is particularly suitable for this application, having small dimensions, low power consumption, 3.0 volt operating voltage and the necessary ADC input. The microprocessor is run at the lowest practical speed, which is possible as high speed calculations are not necessary, and has the advantage that less battery power is consumed and the likelihood of interfering with other electrical devices in the vicinity is reduced.

The microprocessor means includes a memory means for storing the calculated core temperatures. The memory may however be provided separately from the microprocessor as is well known in the art although this requires more physical space.

The microprocessor connects to a display driver which drives the LCD. Figure 4 shows a schematic of the display. There is provided a battery low indicator light 22, two separate temperature displays 20, 30, capable of displaying to a tenth of a degree accuracy, and two separate means 26, 28 for displaying which reading of the day has been taken. The means 26 comprises three indicator lights, while the means 28 is a digital display on the LCD.

Other devices connected to the microprocessor are the non-latching switch 10, which is an input, an audible warning device (not shown), and a transmitting/receiving (not shown) means for communicating with a base station.

To ensure the accuracy of the readings in particular to take account of battery voltage drop, a reference resistor has been incorporated. This allows the signal produced by the thermistor to be compared to that produced by the resistor and thus fluctuations in the battery voltage can be eliminated.

In operation the microprocessor reads the thermistor 12 and reference resistor once a minute.

The true temperature that the thermistor is recording is calculated, allowing for battery fluctuations. The temperature recorded corresponds to the baby's skin temperature.

Such a skin temperature is not a stable parameter and so cannot be relied upon to indicate the health of the baby. The baby's core temperature is a much more reliable indication. The skin temperature is converted to a core temperature by the microprocessor. When the device is first placed on the baby's wrist it may be calibrated using the socket 5. An external temperature sensor, which is provided with the device, connects to this socket. The core temperature of the baby, e.g.

the temperature under the armpit, is taken with the external sensor which is then removed from the socket 5. The external sensor gives the microprocessor a known value from which it can calculate conversion factors to convert the skin temperate to the core temperature.

Once the device is running a weighted average of recently taken temperatures is displayed on the LCD.

This average is given by the formula (0.5 x current reading) + (0.25 last reading) + (0.125 last but one reading) + (...). Such an average will remove rapid fluctuations due perhaps to movement, electronic noise, etc.

The environment temperature sensing means 3 is also provided to make the temperature reading more stable. Any sudden variations in the temperature of the environment may affect the reading of the skin temperature. The provision of the environment temperature sensing means will allow such variations in the skin temperature reading to be account for.

Every hour the current temperature of the baby is written to memory; a temperature history is therefore maintained. Data within the memory is retained until it needs to be overwritten, that is until all the available free memory has been used. No time marking is held as there is a fixed period between readings.

Temperature patterns are known which the baby's temperature follows if the baby is incubating an illness. Such a pattern is stored in the memory.

Hourly, after the new temperature is stored, the microprocessor interrogates the stored temperatures to determined if they fit the stored temperature pattern.

If such a pattern is detected the microprocessor alerts the baby's carer.

The audible warning device is used to alert the baby's carer to a distressed condition of the baby. A warning is triggered if the baby's temperature is too high, too low or if a temperature pattern is detected.

The warning sound is different for each of the three triggers. This ensures that the baby's carer is not overly concerned by an alarm, that is being made to think the baby has an abnormal temperature when only a temperature pattern has been detected. The transmitting/receiving means is also activated when an alarm is triggered. The transmitting/receiving means is in communication with a base station which also contains an alarm. The base station can be carried by the baby's carer. The carer is this immediately alerted to a distressed condition of the baby even if they cannot hear the alarm on the device itself.

The switch 10 allows the temperature history to be viewed. Once the switch has been depressed the stored temperatures are displayed sequentially, on the temperature display 30 with the current reading being displayed first, progressively older readings are then displayed. On the temperature display 20, the baby's current temperature is constantly in view. In between the readings the number of the reading is displayed, 1, 2, 3 etc. The number is held for F a second, and the corresponding stored temperature is displayed for 1 second. This pattern cycles until all the data has been viewed. If the button is pressed for a second time, during the display cycle, the display reverts to the current temperature of the baby.Cycling the data like this has the advantage that only one button press is required, meaning that the user does not have to keep moving the baby's arm.

Once the batteries of the device have been depleted the silicon rubber casing can be removed.

This is achieved by paring the rubber away with an instrument such as a scalpel. The batteries can be replaced, the electronics checked, and the device then resealed for re-use.

An alternative to storing each individual temperature in the memory would be to store the difference between the previous and current temperatures. If temperature fluctuation is small between the readings this will reduce the amount of memory required.

In a modification, not shown, the display means may consist simply of a three or four digit LCD. A battery low indicator would also be provided in addition to the LCD. In such an embodiment if the temperature history were being reviewed, there would be no indication of the baby's current temperature.

The plastics housing 4 may be of ABS plastics, which is non-toxic. Alternatively the device may be encapsulated in an epoxy resin, or the housing may be made entirely of silicon rubber.

The skin temperature monitoring device may have applications outside baby temperature monitoring. For instance an adult version may be desirable. This may be useful in aids research, for instance. The socket 5 could be permanently connected to an external temperature sensor recording the user's core temperature.

More than one battery may be required to provide the necessary power.

Claims (17)

1. A skin temperature sensing device comprising a housing adapted for attachment to the human body, the housing being provided with a skin temperature sensing means, a power source, a microprocessor means, a display means and an alarm means, in which the skin temperature sensing means supplies an electronic signal to the microprocessor, which is operative to convert the signal to a temperature corresponding to the core temperature of the body, periodically display the core temperature on the display means and to activate the alarm means when the core temperature is outside the predetermined temperature range.

2. A skin temperature sensing device according to claim 1 which is provided with memory means for storing at least one previously displayed core temperature.

3. A skin temperature sensing device according to claim 2 in which up to 50 previous core temperatures can be stored in the memory means.

4. A skin temperature sensing device according to any preceding claim in which readings of the core temperature are taken 2 hourly.

5. A skin temperature sensing device according to any of claims 1 to 3 in which readings of the core temperature are taken hourly.

6. A skin temperature sensing device according to any of claims 2 to 5 in which switch means is provided to cause the display of the stored core temperature readings.

7. A skin temperature sensing device according to any of claims 2 to 6 in which the memory means holds a temperature pattern, and the microprocessor means compares the stored core temperature readings with the pattern and activates the alarm means if the pattern is detected.

8. A skin temperature sensing device according to any preceding claim in which the temperature sensing means is a thermistor.

9. A skin temperature sensing device according to any preceding claim in which the temperature sensing means is provided within a closed environment.

10. A skin temperature sensing device according to any preceding claim in which an environment temperature sensing means is provided.

11. A skin temperature sensing device according to any preceding claim which includes means for calibrating the device to the wearer's core temperature.

12. A skin temperature sensing device according to claim 11 in which the calibrating means is an external temperature sensing means which is removably attached to the device.

13. A skin temperature sensing device according to any preceding claim in which the display means is a liquid crystal display.

14. A skin temperature sensing device according to claim 13 in which indicator lights are provided in addition to the liquid crystal display.

15. A skin temperature sensing device according to any preceding claim which includes transmitting/receiving means.

16. A skin temperature sensing device according to any preceding claim in which the skin temperature sensing device is worn 6n the wrist.

17. A skin temperature sensing device as described herein, with reference to the accompanying drawings.