I
TEMPERATURE SENSOR
This invention relates to temperature sensors, and particularly to such sensors in the form of a flexible panel which can conform to the surface of a body whose temperature is being measured. Such sensors have use in a variety of applications, including the measurement of the temperature of human or animal body.
Temperature measurement can be accomplished by a variety of means. Typically, such sensors generate a visible signal in response to a temperature change, as a result of a physical or chemical change in response to the change in temperature. It is also known that electrical characteristics of materials can change with temperature, and the present invention is directed particularly at the exploitation of such characteristics.
The present invention seeks to incorporate a temperature sensing mechanism within a fabric. According to the invention a length of electrically conductive yarn is confined in a section of non-stretch fabric, which yam has an electrical resistance that varies with the temperature in a predetermined manner (ERT yam). The ERT yam follows a tortuous path in the fabric such that there is a substantial length of ERT yarn accumulated in the fabric section relative to the dimensions of the fabric section. Typically, the ratio of the square of the length of the conductive yam in the section to the area of the fabric section is at least one hundred. Preferably, the ratio is at least one thousand and most preferably at least ten thousand.
The length of the ERT yarn can be defined by the resolution requirement of the sensor, the change of its electrical resistance relative to temperature and the gauge of the wire. Care should be taken to prevent contact between different sections of the length of wire as this would effect the performance of the sensor. A change in temperature of the ERT yam will cause a change in its electrical resistance, which could be determined with a suitable circuit such as a Wheatstone bridge.
In sensors according to the invention, the ERT yarn is preferably confined between two layers defining the fabric section. The purpose of this is of course to prevent the ERT yarn from being exposed on either side of the fabric, although this can be permissible if the ERT yam is itself insulated.
Preferred sensors according to the invention comprise two layers each knifted with nonconductive yarns. The ERT yarn can be coupled directly to one or other of the layers, by individual stitches. Additionally or alternatively, the two layers can be interlinked to create a coherent fabric section holding the ERT yarn. Embroidery techniques can also be used.
The ERT yam can comprise a plain metallic wire; for example of copper. A preferred conductive yarn comprises nickel coated copper wire. As noted above, the wire may be covered by an electrically insulating coating.
Metal coated polymeric yarns could also be used. It is also possible to use conductive non-metallic yarns. Such yarns tend to exhibit smaller changes in electrical characteristics, particularly resistance, in response to changes in temperature.
In order to monitor changes in temperature of a sensor according to the invention, the ERT yarn must of course be part of a circuit with means for measuring its electrical resistance. Such a circuit can be completed by making connections to the ERT yarn ends at peripheral points on the fabric section, and this will normally be the case when the fabric section comprising the sensor is produced separately. However, the sensor may be incorporated in the garment fabric, and rather than have separate connections at the penphery of the fabric section, the circuit, or at least conductors connected to the sensor can also be incorporated in the garment fabric. It is also quite possible to have the ERT yarn extending continuously from the fabric section to complete the requisite electrical circuit. It should be noted in this context that while consideration should be given to the electrical characteristics of the yam or conductors in the electrical circuit outside of the fabric section, in most applications of the invention specific consideration thereof will not be necessary as the length of yam within the fabric section will be a sufficient multiple of the length or yam or conductors in other parts of the circuit for any influence thereof to be ignored.
A fabric including a temperature sensor according to the invention can be used in garments to enable monitoring of the wearer's skin temperature on an occasional or continuous basis while the garment is being worn. This can be of value in medical or surgical situations while a patient is undergoing treatment or by an individual in an exercise regime when temperatures and possibly other bodily characteristics are being monitored.
The invention will now be described by way of example, and with reference to the accompanying schematic drawings wherein: Figures 1 and 2 each shown in plan view the location of an ERT yam in a fabric section according to the invention; Figure 3 shows how a sensor according to the invention can be incorporated in a garment fabric; Figure 4 shows a simple circuit for monitoring changes in resistance of the ERT yarn in a sensor of the invention; Figure 5 shows how an ERT yarn may be confined between two knitted layers in a sensor of the invention; and Figure 6 illustrates a technique for knithng a sensor embodying the invention.
The fabric section 2 in Figure 1 comprises non-conductive and non-stretch yams such that the section itself is substantially inextensible in any direction.
Confined within the fabric section 2 is a length 4 of ERT yam, which follows a tortuous path within the fabric section between terminals 6 and 8.
The ERT yarn follows multiple sinusoidal paths across one dimension of the fabric section, and the total length of the yam within the section will be such that the ratio of the square of its length to the area of the fabric section will be at least one hundred, preferably at least one thousand, and most preferably at least ten thousand.
Figure 2 shows a similar view to that of Figure 1, but in this embodiment the ERT yarn follows a more straightforward reciprocating path within the fabric section. The ratio of the square of the yarn length to the area of the fabric section will in this embodiment be closer to one hundred.
Figure 3 shows a T-shirt with a temperature sensor 10 embodying the invention forming an integral part of the garment fabric. Conductors 12 and 14 extend respectively from the terminals 6 and 8 on the sensor to circuit terminals 16 and 18 located in this embodiment at the hem of the garment. A monitoring circuit is completed as described below.
A simple temperature monitoring circuit incorporating a sensor of the invention is shown in Figure 4. Connectors 16 and 18 are connected to a source 20 of electrical power and an ammeter 22, through a switch 24. When the switch is closed, the resistance in the circuit, and thereby of the resistance of the ERT yarn 4 in the sensor 10, can be measured as the ratio of the supply voltage to the ammeter reading. While the conductors 12 and 14 are shown in both of Figures 3 and 4 as separate components, they will normally be extended lengths of the ERT yarn 4. It will be appreciated from Figure 3 that their lengths will be significant in that they extend a substantial part of the entire length of the garment, but relative to the length of ERT yarn 4 within the sensor 10, this length will be small. Depending on the nature of the path followed by the ERT yam 4 within the sensor 10, this additional length of ERT yam may either be ignored, or accounted for in calculating changes in the resistance of the ERT yarn in the sensor from the ammeter reading (22).
In sensors according to the invention, the ERT yam 4 will be confined in the fabric section such that the ERT yarn 4 is not electrically exposed. This is preferably accomplished in sensors according to the invention by confining the ERT yam between two layers 26 and 28 of fabric as shown in Figure 5. In this embodiment each layer is itself knitted with non-conductive yams, with interlinking by cross-over yarns 30. This structure confines, secures and protects the yam 4 from exposure.
The fabric section defining a temperature sensor according to the invention should be substantially non-extensible in any direction in order to avoid any extension of the ERT yarn confined therein. Any stretching of the ERT yam will have an additional effect on its resistance, and risk generating an inaccurate temperature reading. Minor flexure of the ERT yarn will not have a significant effect. Thus, when incorporated in a garment, the sensor should be located close to the point at which the temperature is to be monitored, but not in a location where there is likely to be substantial flexure.
The position shown in Figure 3, substantially centrally at the upper front or rear of a T-shirt, is appropriate.
A technique of creating such a sensor via the route of computerised flat-bed knitting machine is illustrated in Figure 6. However, the same technique can be used to knit the sensor on non-computerised flat-bed and circular knitting machines as well as on warp knitting machines.
The ERT yarn 32 is accumulated between the courses of an interlock knitted structure. The interlock structure is the most stable basic knitted structure and thus would provide an excellent platform for creating temperature sensors. The main structure 34 for the sensor is a knitted course of alternating odd needles on the front bed and at the same time knitting the alternating even needles on the rear bed, following with a course of alternating even needles on the front bed and at the same time knitting the alternating odd needles on the rear bed both of these courses are knitted as tight as possible. In between each of the courses that make up the interlock structure a nickel plated copper wire 32 (ERT yam) is laid-in without forming a loop. This is followed by another course of ERT laid-in yam 36 which is made up of numerous ends of the main yam 34; the reason for this is to fill out any space between the main courses of the base interlock structure. This method of knitting would lock the interlock course in the course direction, especially when this laid-in ERT yarn changes its direction; i.e. when it is laid-in in the opposite direction during the next courses of knitting. The wale or vertical column of stitches direction is also helped to be locked by this laid-in ERT yam.
Using this method of knitting a combination of the basic interlock structure and laid-in ERT yarn, provides a more stable knitted structure with very little stretch in either the course or the wale direction. This technique gives a good stable structure for holding the nickel plated copper wire in place.