GB2405477A

GB2405477A - Temperature measuring apparatus for sensing ambient temperature

Info

Publication number: GB2405477A
Application number: GB0320445A
Authority: GB
Inventors: Brian Back
Original assignee: Radio Tech Ltd
Current assignee: Radio Tech Ltd
Priority date: 2003-09-01
Filing date: 2003-09-01
Publication date: 2005-03-02
Anticipated expiration: 2023-09-01
Also published as: GB2405477B; GB0320445D0

Abstract

Known thermal measuring devices are typically single probes disposed within a simulant material, the simulant material having thermal properties representative of thermal properties of an item to be monitored. However, when an item, for example produce, such as fruit is exposed to thermal stress, the temperature of a core of the item may remain within acceptable temperature parameters whilst the outer surface may not, resulting in spoiling of the item. The present invention addresses this problem by providing a pair of sensors (126, 128) disposed at respective positions within the thermal monitoring device (100) to measure temperatures representative of surface and core temperatures, respectively. The thermal measuring device (100) also calculates heat flow between the pair of sensors. The sensors may be separated by a simulant material acting as a thermal delay mass (131) to change the response of one sensor relative to the other. The thermal delay mass may also be replaced by another.

Description

TEMPERATURE MEASURING APPARATUS

AND METHOD THEREFOR

The present invention relates to a temperature measuring apparatus of the type, for example, used to measure excessive temperature, excessive rate of change of temperature or an integral of temperature over time of items, such as food products. The present invention also relates to a method of measuring temperature.

Temperature measurement is an activity that finds applications in a number of industries for varied purposes, such as food safety, paint storage, chemical manufacture and storage, pharmaceutical manufacture and storage, road transport, storage of artefacts, industrial compositing, and industrial processing and manufacture.

Typically, a so-called single point device, i.e. a single point temperature probe, is employed to measure thermal stress, thermal stress being: excessive temperature, excessive rate of change of temperature, or prolonged exposure to a cumulative temperature profile In order to make any temperature measurement realistic, the temperature probe is sometimes embedded within a stimulant material, such as a ThermoCube_ manufactured by UniCair Limited, or a bottle of glycol so as to provide a fixed thermal delay between the temperature probe and an ambient, the temperature of which is to be measured. In this respect, a number of "formulas" exist as so-called "food simulants". A food simulant is typically a fixed mass of an inert material having an associated specific heat capacity, and into which a single point temperature measuring transducer is inserted. The thermal delay in the form of the simulant serves to simulate the mass, and hence the thermal characteristics, of goods or produce, thereby delaying a response of the transducer. Such - 2 thermal delays are believed to be a way of improving estimation of core temperatures of the goods or produce.

However, the delay imparted by the simulant is fixed. Additionally measurement of core temperature of an item solely is, in some cases, inadequate, because some items, such as produce, can perish on the outside in spite of the core temperature of the produce remaining at a target temperature at all times. For example, the surface of produce stored in a refrigerator located in direct sunlight and having an open door can warm relatively quickly while the core temperature of the produce remains unaffected for a considerable period of time.

According to a first aspect of the present invention, there is provided a thermal measurement apparatus for immersion into an ambient, the apparatus comprising: a first sensor separated from a second sensor by a thermal delay mass, the thermal delay mass having a predetermined thermal conductivity; a processing unit coupled to the first and second sensors for calculating heat flow between the first and second sensors induced by the ambient.

Preferably, the processing unit is arranged to calculate a rate of heat flow between the first and second sensors and/or a direction of the heat flow.

Preferably, the apparatus further comprises: a housing; wherein the first sensor is located at a suitable first position relative to the housing for sensing a first temperature substantially representative of a temperature at a surface of an item to be measured.

Preferably, the housing comprises a peripheral wall and the first sensor is disposed adjacent the peripheral wall.

Preferably, a portion of the peripheral wall comprises a first recess to receive the first sensor.

Preferably, the apparatus further comprises: a housing; wherein the second sensor is located at a second suitable position relative to the housing for sensing a second temperature substantially representative of a temperature of a core of an item to be measured. More preferably, the housing further comprises a second recess to receive the second sensor.

Preferably, the apparatus further comprises: a thermally conductive or thermally resistive mass located adjacent the second sensor. More preferably, the thermal mass is thermally coupled to the second sensor.

Preferably, the thermal mass is replaceable with another thermal mass having a different specific heat capacity to a predetermined specific heat capacity of the thermal mass.

Preferably, the thermal mass is adjustable so as to alter, when in use, a thermal response characteristic with respect to the first and second sensors. More preferably, the thermal response characteristic is a thermal conductivity between the first and second sensors.

The thermal mass may be pre-formed and has a predetermined shape.

Preferably, the thermal mass is slug-like.

Preferably, the housing is arranged to define an internal cavity for receiving the thermal mass.

Preferably, the thermal mass is adjustable so as to alter, when in use, an amount of thermal coupling between the thermal mass and the second sensor. More preferably, the amount of thermal coupling between the -4- : thermal mass and the second sensor is an amount of a surface of the thermal mass thermally couplable with the second sensor.

The thermal mass may comprise a tapered external surface.

Preferably, the thermal mass is substantially circular in cross-section. ; Preferably, the thermal mass is hollow.

Preferably, the thermal mass comprises a substantially circumferential wall.

Preferably, the processing unit is arranged to generate a message comprising data corresponding to the calculated heat flow.

Preferably, the apparatus further comprises a transmission unit for transmitting data corresponding to the calculated heat flow.

According to a second aspect of the present invention, there is provided a thermal mass device for altering a thermal response characteristic with respect to a first temperature sensor and a second temperature sensor, the device having a predetermined specific heat capacity.

Preferably, the thermal response characteristic is thermal conductivity.

Preferably, the device further comprises a varying property for adjustment of the thermal response characteristic.

According to a third aspect of the present invention, there is provided a use of a thermal mass for altering a thermal response characteristic with respect to a first temperature sensor and a second temperature sensor. - 5

According to a fourth aspect of the present invention, there is provided a method of monitoring thermal variations experienced by an item in an ambient, the method comprising the steps of: measuring a first temperature at a first point substantially representative of a surface of the item; measuring a second temperature at a substantially representative of a core of the item; and calculating a heat flow between the first and second points.

Preferably, a thermal delay mass is located between the first and second points.

Preferably, the method further comprises the step of: disposing a thermally conductive or thermally resistive mass in thermal contact with the second point. More preferably, the method further comprises the step of: adjusting an amount of thermal coupling of the thermal mass with the second point.

According to a fifth aspect of the present invention, there is provided a 3 thermal measurement apparatus for immersion into an ambient, the apparatus comprising: a sensor thermally coupled to a replaceable thermal I mass device, the thermal mass device providing a predetermined thermal 1 delay with respect to the sensor.

Preferably, the thermal mass device is adjustable.

It is thus possible to provide a temperature measuring apparatus, and method therefore, capable of providing a more realistic representation of temperature of an item within an ambient than known apparatuses and methods, and hence temperature data of improved accuracy. Further, improved accuracy of temperature data can provide an early indication of when an item is about to be spoilt due to a change in the ambient and allow action to be taken to avoid the item becoming spoilt before it is too late to do so. Additionally, the apparatus and method provide realtime transmission of the temperature data. - 6

At least one embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a plan view of an open apparatus constituting an embodiment of the invention; Figure 2 is an isometric view of the apparatus of Figure 1 closed; and Figure 3 is a block diagram of an electronic circuit disposed in the apparatus of Figures 1 and 2.

Throughout the following description, identical reference numerals will be used to identify like parts.

Referring to Figure 1, a thermal monitoring device 100 comprises a puck like cylindrical housing 102 having a first circumferential outer wall 101 and a base (not shown) defining an open cavity 104. The first circumferential wall 101 has a first thin-walled portion 103 disposed in an interior surface thereof. The open cavity 104 is divided into a first open chamber 106, a second open chamber 108 and a third open chamber 110 by a first I partition wall 112 and a second partition wall 114. The first partition wall I 112 is, in this example, orthogonal to the second partition wall 114.

A cylindrical core chamber 116 is disposed, approximately centrally in the housing 102 in a corner between the first and second partition walls 112, 114. The core chamber 116 is defined by a second circumferential wall 118 and merges with the second partition wall 112 at a shared-wall region 121. The shared-wall portion 121 of second partition wall 112 and the second circumferential wall 118 comprises a second thin-walled portion 119. - 7

The first open chamber 106 houses a cell, for example, a battery 120 coupled by wires 122 to an electronic circuit 124 housed in the second open chamber 108.

A first temperature sensor 126 and a second temperature sensor 128 form part of the electronic circuit 124 and respectively abut the first thinwalled portion 103, and in the second thin-walled portion 119 via the aperture 121. An antenna 130, also forming part of the electronic circuit 124, extends through a small aperture (not shown) in the second partition wall 114 into the third open chamber 110. A thermal delay mass 131, sometimes known as a "potting compound" or simulant, fills the second open chamber 108 and hence a space between the first and second sensors 126, 128. It should be appreciated that, in addition to the thermal delay mass 131, the electronic circuit 124, and the proximity of adjacent walls and chambers of the thermal monitoring device 100 contribute to an overall thermal mass of the second open chamber 108; the overall thermal mass influences the responses of the first and second sensors 126,128.

When in a closed state (Figure 2), a lid 200 having an approximately I central aperture 202 is placed over and fixed to the housing 102. The I approximately central aperture 202 is located so as to be in registry with the second circumferential wall 118 when the lid 200 is in place, thereby permitting access to the core chamber 116 when the thermal monitoring device 100 is in the closed state. The lid 200 also comprises a shallow tamper-evident recess 214 that abuts the central aperture 202.

In this example, a periphery of the approximately central aperture 202 can be marked, for example, by providing enumeration 204 around the periphery so as to indicate setting positions.

A tapered slug 206 fits into the core chamber 116 and is rotatable within the core chamber 116. The tapered slug 206 is a thermally conductive or 8 resistive mass that can be formed from any suitable material depending upon the application for the thermal monitoring device 100, for example plastic or metal. For an accelerated reaction to temperature changes, a high thermal conductivity material can be employed, such as brass. When an extended thermal delay is needed, a low thermal conductivity material, such as low density plastic foam can be employed.

The slug 206, in this example, comprises a sloping circumferential wall 208 extending from an end plate 210. The height of the sloping circumferential wall 208 relative to the end plate 210 varies as a function of a position along the circumference of the wall 208. In this example, the wall 208 tapers linearly, but it should be appreciated that other profiles can be used to alter an amount of thermal contact between the slug 206 and the second sensor 128.

When the slug 206 is located in the core chamber 116, a tamper-evident I adhesive strip 212 is disposed in the complimentary shallow recess 214 on the lid 200. The strip 212 is sufficiently long so that the strip 212 overlies and adheres to an external surface of the end plate 210.

Referring to Figure 3, the electronic circuit 124 comprises a Printed Circuit Board 300 (PCB) to which the first and second sensors 126, 128 are coupled. When the PCB 300 is located in the second open chamber 108, the remaining space in the second open chamber 108 is substantially filled with a so-called "potting" material. The "potting" material is a mass that provides a thermal delay between the first and second sensors 126, 128.

The first and second sensors 126, 128 can be any known transducer suitable for measuring temperature, for example, so-called PT100 or PT1000 transducers, thermocouples, integrated semiconductor transducers, thermistors, or quartz crystals. - 9 -

The first sensor 126 is coupled to an input terminal of a first signal conditioner 302, for example, a first transimpedance amplifier or a first Analogue to Digital Converter (ADC). An output terminal of the first conditioner 302 is coupled to a first input terminal of a microcontroller 304.

Similarly, the second sensor 128 is coupled to an input terminal of a second signal conditional 306, for example, a second transimpedance amplifier or a second ADC. An output terminal of the second conditioner 306 is coupled to a second input terminal of the microcontroller 304. In an alternative example, the functionality of the first and second conditioners can be incorporated into the microcontroller 304.

An output terminal of the microcontroller 304 is coupled to a radio data module 308 by a data bus 309 and a "wake-up" line 311. The radio data module 308 comprises a data modulator 310 coupled to an RF transmitter circuit 312. The antenna 130 is coupled to the RF transmitter circuit 312.

In this example, an Application Specific Integrated Circuit (ASIC) is I programmed to perform the functions of the radio data module 308. The ASIC can, if required, combine the functionality of the data modulator 310 and the RF transmitter circuit 312 into a single function.

Power to components forming the electronic circuit 124 is supplied by the battery 120 via voltage supply rails (not shown).

The first and second sensor 126, 128 are sited on the PCB 300 so as to be located in the respective positions mentioned above with respect to the first thin-walled portion 103 and the second thin-walled portion 121.

Whilst, in this example, specific sensor locations have been described, it should be appreciated that the first sensor 126 can be located at any i suitable first position for sensing a first temperature representative of a temperature of a surface of an item to be measured. Similarly, the second sensor 126 can be located at any suitable second position for sensing a - 10 second temperature representative of a temperature of a core of the item to be measured.

In preparation for operation, a suitable slug, having an appropriate specific heat capacity for simulating the item to be measured, is selected and inserted into the core cavity 116 and rotated to an appropriate position. By rotation of the slug 206 to the appropriate position, a more accurate simulation of the thermal characteristics of the item to be measured is achieved. For example, a slug formed from an appropriate thermally conductive or resistive material is selected to be representative of an item to be measured, such as cheese. By rotating the slug 206 so as to alter the amount of the sloping circumferential wall 208 that is thermally coupled to the second sensor 128, fine calibration of the thermal conductivity between the first and second sensors 126, 128 can be achieved so as to simulate the thermal characteristics of a particular type of the item. In the example of cheese, fine calibration can be employed to simulate Camembert cheese. Consequently, a choice of an appropriate slug can be used to impose a suitable heat flow protection envelope characteristic of permitted surface and core temperature limits for an item to be monitored.

The taper-evident strip 212 is then applied over the shallow recess 214 and the end plate 210.

In operation, the temperature monitoring device 100 is immersed amongst the items to be monitored, for example packets of cheese or peaches, and hence is exposed to a same ambient as the items to be monitored. The temperature at the first sensor 126 and the temperature at the second sensor 128 are measured at regular intervals by the microcontroller 304 and the microcontroller 304 then calculates a rate of heat flow between the first and second sensors 126,128. - 11

The microcontroller 304 also calculates a direction of the heat flow. One or more of a surface temperature, a core temperature, the calculated heat flow data, or the direction of the heat flow are then encoded and incorporated into a message comprising a unique address code to identify the temperature monitoring device 100. The message also comprises, in this example an error check sum. The radio data module 308 is then awaken from a "sleep mode" using a "wake-up" signal issued by the microcontroller 304 via the "wake-up" line 311, and the message generated by the microcontroller 304 is communicated to the radio data module 308 by the microcontroller 304. Thereafter, the message is transmitted by the radio data module 308 to a remote receiving station (not shown). Optionally, the microcontroller 304 can be provided with a data and time stamp function to add date and time data to the message.

Assuming thermal equilibrium, the thermal delaying mass stores heat energy. Provided the ambient remains constant, the first and second sensors 126, 128 sense a same temperature and hence make heat flow between the first and second sensors 126, 128 occur. In such circumstances, the temperature of produce is assumed to be the temperature measured at the first and second sensors 126, 128.

Upon change in the ambient, heat flows in or out of the thermal delay mass 131, resulting in the first and second sensors 126, 128 responding differently with respect to each other, depending upon a net thermal resistance in a thermal path passing through the first and second sensors 126, 128. By providing the slug 210, the thermal delay with respect to the second sensor 128, in particular, is altered in order to bring about either a fast or slow response by the second sensor 128. The existence, at each of the first and second sensors 126, 128, of different temperature permits determination of the direction of heat flow and the rate of heat flow through measurement of the respective temperatures at the first and second sensors 126,128. - 12

Although the above example has been described in the context of the thermal monitoring device comprising two sensors, the principle of employing the thermal delay mass, in the above example the slug 206, is equally applicable to a single sensor device. - 13

Claims

1. A thermal measurement apparatus for immersion into an ambient, the apparatus comprising: a first sensor separated from a second sensor by a thermal delay mass, the thermal delay mass having a predetermined thermal conductivity; a processing unit coupled to the first and second sensors for calculating heat flow between the first and second sensors induced by the 1 0 ambient.

2. An apparatus as claimed in Claim 1, wherein the processing unit is arranged to calculate a rate of heat flow between the first and second sensors and/or a direction of the heat flow.

3. An apparatus as claimed in Claim 1 or Claim 2, further comprising: a housing; wherein the first sensor is located at a suitable first position relative to the housing for sensing a first temperature substantially representative of a temperature at a surface of an item to be measured.

4. An apparatus as claimed in Claim 3, wherein the housing comprises a peripheral wall and the first sensor is disposed adjacent the peripheral wall.

5. An apparatus as claimed in Claim 3 or Claim 4, wherein a portion of the peripheral wall comprises a first recess to receive the first sensor.

6. An apparatus as claimed in Claim 1, further comprising: a housing; wherein r - 14 the second sensor is located at a second suitable position relative to the housing for sensing a second temperature substantially representative of a temperature of a core of an item to be measured.

7. An apparatus as claimed in Claim 6, wherein the housing further comprises a second recess to receive the second sensor.

8. An apparatus as claimed in any one of the preceding claims, further comprising: ; a thermally conductive or thermally resistive mass located adjacent the second sensor.

9. An apparatus as claimed in Claim 8, wherein the thermal mass is thermally coupled to the second sensor.

10. An apparatus as claimed in Claim 8 or Claim 9, wherein the thermal mass is replaceable with another thermal mass having a different specific heat capacity to a predetermined specific heat capacity of the thermal mass.

11. An apparatus as claimed in any one of Claims 8 to 11, wherein the thermal mass is adjustable so as to alter, when in use, a thermal response characteristic with respect to the first and second sensors.

12. An apparatus as claimed in Claim 11, wherein the thermal response characteristic is a thermal conductivity between the first and second; sensors.

13. An apparatus as claimed in any one of Claims 8 to 12, wherein the thermal mass is pre-formed and has a predetermined shape.

F - 15

14. An apparatus as claimed in Claim 13, wherein the thermal mass is sluglike.

15. An apparatus as claimed in any one of Claims 8 to 14, wherein the housing is arranged to define an internal cavity for receiving the thermal mass.

16. An apparatus as claimed in any one of Claims 9 to 15, wherein the thermal mass is adjustable so as to alter, when in use, an amount of thermal coupling between the thermal mass and the second sensor.

17. An apparatus as claimed in Claim 15, wherein the amount of thermal coupling between the thermal mass and the second sensor is an amount of a surface of the thermal mass thermally couplable with the second sensor.

18. An apparatus as claimed in any one of Claims 9 to 17, wherein the thermal mass comprises a tapered external surface.

19. An apparatus as claimed in any one of Claims 9 to 18, wherein the thermal mass is substantially circular in cross-section.

20. An apparatus as claimed in any one of Claims 9 to 19, wherein the thermal mass is hollow.

21. An apparatus as claimed in any one of Claims 9 to 20, wherein the thermal mass comprises a substantially circumferential wall.

22. An apparatus as claimed in any one of the preceding claims, wherein the processing unit is arranged to generate a message comprising data corresponding to the calculated heat flow.

J - 16

23. An apparatus as claimed in any one of claims 1 to 22, further I comprising a transmission unit for transmitting data corresponding to the calculated heat flow and/or temperatures.

24. A thermal mass device for altering a thermal response characteristic of a first temperature sensor with respect to a second temperature sensor, the device having a predetermined specific heat capacity.

25. A device as claimed in claim 24, wherein the thermal response characteristic is thermal conductivity.

26. A device as claimed in Claim 24 or Claim 25, further comprising a varying property for adjustment of the thermal response characteristic. I

27. A use of a thermal mass for altering a thermal response characteristic of a first temperature sensor with respect to a second temperature sensor.

28. A method of monitoring thermal variations experienced by an item in an ambient, the method comprising the steps of: measuring a first temperature at a first point substantially representative of a surface of the item; measuring a second temperature at a substantially representative of a core of the item; and calculating a heat flow between the first and second points.

29. A method as claimed in Claim 28, wherein a thermal delay mass is located between the first and second points.

30. A method as claimed in Claim 28 or Claim 29, further comprising I the step of: - 17 disposing a thermally conductive or thermally resistive mass in I thermal contact with the second point.

31. A method as claimed in Claim 30, further comprising the step of: adjusting an amount of thermal coupling of the thermal mass with the second point.

32. A thermal measurement apparatus for immersion into an ambient, the apparatus comprising: a sensor thermally coupled to a replaceable thermal mass device, the thermal mass device providing a predetermined thermal delay with respect to the sensor.

33. An apparatus as claimed in Claim 32, wherein the thermal mass I device is adjustable.

34. A thermal measurement device substantially as hereinbefore described with reference to the accompanying drawings.

35. A thermal mass device for altering a thermal response characteristic substantially as hereinbefore described with reference to the accompanying drawings.

36. A method of monitoring thermal variations experienced by an item in an ambient substantially as hereinbefore described with reference to the accompanying drawings.