Background of the Invention Field of the Invention [0001] The subject matter described herein relates generally to sensing devices and, more particularly, to a device and method for increasing the accuracy of temperature measurement.

Related Art

[0002] Sensing devices or probes for measuring temperature such as resistance temperature devices (RTDs) are generally known in the field. Most of these probes have significant thermal capacity and, through their construction, lose heat to their surroundings. This can create problems when a probe comes into contact with a body or surface whose temperature is being measured, referred to herein as the unknown, or body under test. [0003] For example, a probe that attempts to measure the temperature of an unknown is typically at a different temperature, for example room temperature, from the unknown. This creates a heat transfer problem when the probe comes into contact with the body under test. Because the probe is at a different temperature from the unknown, the probe actually changes the temperature of the unknown when the two come into contact. Therefore, the probe may critically interfere with the temperature of the unknown so that an accurate temperature of the unknown cannot be detected.

[0004] When using a known device or probe to measure temperature, it must be in close thermal contact (low thermal resistance) with the body under test. Conversely, the body under test must have a low thermal resistance with the probe. The body under test must have a heat source or sink of some capacity in order to supply or remove heat energy to/from the probe, making the probe temperature the same temperature as the body under test, and sustain the energy losses from the probe at this temperature. If these conditions are not met, the probe will cool or warm the body under test, changing the temperature of the body under test and causing a measurement error.

[0005] To measure the temperature of an unknown with high thermal resistance, a non- contact method is typically used. Commonly, non-contact methods use Infra Red (IR) radiation from the unknown, which is detected by an IR sensor that is usually physically remote from the unknown. However, both noise and surface emissivity limit the system accuracy in the cases where non-contact temperature measuring devices are used.

[0006] Thus, it is desirable to provide a sensing device that more accurately measures the temperature of an unknown with a high thermal resistance. It is further desirable to provide a sensing device that more accurately measures the temperature of an unknown with a low thermal resistance and poor supply of heat. In addition, it is desirable to provide a sensing device that measures temperature more accurately where there is poor thermal contact between an unknown and the sensing device.

Brief Description of the Invention

[0007] In accordance with an embodiment of the present invention, a temperature sensing device for measuring the temperature of a body under test comprises a probe in contact with the body under test and a means for preventing heat transfer to or from the body under test. The means for preventing heat transfer to or from the body under test delivers heat energy to or from the probe. [0008] In another embodiment of the invention, a temperature sensing device for measuring the temperature of a body under test comprises a probe and a heating/cooling source for preventing heat transfer to or from the body under test. The temperature sensing device further comprises a heat flux sensor. A temperature difference between the probe and the heating/cooling source drives a heat flux through the heat flux sensor.

[0009] In yet another embodiment of the invention, a method for determining the temperature of a body under test is provided. The method comprises bringing a probe into contact with the body under test and preventing heat transfer to or from the body under test by delivering heat energy to or from the probe using a thermal energy supply. The method further comprises balancing the temperature of the probe with the temperature of the body under test based upon a heat flux between the probe and the thermal energy supply.

Brief Description of the Drawings

[0010] The following detailed description of an embodiment provided by way of example only is made with reference to the accompanying drawing, in which:

[0011] FIG. 1 is a schematic diagram of a temperature sensing device in contact with a body under test according to an embodiment of the invention.

Detailed Description of the Preferred Embodiment [0012] An embodiment of the present invention concerns a device and method for measuring the temperature of an unknown, or body under test. Energy, namely, heat loss or heat gain, is not supplied to the temperature sensing device by the unknown. Rather, energy is supplied to the temperature sensing device by a thermal energy supply, which serves to balance the temperature of the sensing device with the temperature of the unknown. The thermal energy supply is a means for preventing heat transfer to or from the unknown. In an embodiment of the invention, the thermal energy supply is a heating/cooling source. The device further comprises a heat flux sensor coupled to the heating/cooling source. The heating/cooling source heats or cools the device to the temperature of the unknown, thereby reducing the heat flux sensed by the heat flux sensor to zero.

[0013] Illustrated in FIG. 1, a temperature sensing device 10 according to an embodiment of the invention is shown. Temperature sensing device 10 comprises thermometer element 7, which in turn includes thermometer display 1. Thermometer element 7 may comprise a Resistance Temperature Device (RTD) as known in the art. Thermometer 7 may also be a thermo-couple, thermistor or other temperature sensor which operates over the desired temperature range with the desired accuracy. Thermometer 7 is configured to measure the temperature of the thermal energy supply, shown in FIG. 1 as heating/cooling source 3. Thus any thermal losses and the thermal capacity of thermometer 7 are supplied by heating/cooling source 3 and not by the body of unknown temperature 6, also referred to herein as the unknown or body under test.

[0014] In an embodiment of the invention, heating/cooling source 3 comprises a Peltier Thermoelectric Device, also known as a thermal electric cooler (TEC). When heating/cooling source 3 comprises a TEC, temperature sensing device 10 may be heated or cooled depending on the direction of heat flux. Other systems that have the ability to heat and cool may also comprise heating/cooling source 3.

[0015] In an alternative embodiment, heating/cooling source 3 comprises only a heating source. Heaters suitable for use in temperature sensing device 10 include, for example, resistive elements such as Nichrome wire. In yet another embodiment, heating/cooling source 3 comprises only a cooling source. Coolers suitable for use in temperature sensing device 10 include, for example, evaporative coolers and phase change coolers.

[0016] Connected to heating/cooling source 3 is heat flux sensor 4. Heating/cooling source 3 and heat flux sensor 4 are connected so as to minimize thermal resistance at their junction and distribute energy across the surface area of heat flux sensor 4. Heat flux sensor 4 may comprise any device that gives an electrical output proportional to the heat energy or 'flux' which flows through it. [0017] Heat flux sensor 4 is also connected to sensor probe 5. Heat flux sensor 4 and sensor probe 5 are also connected so as to minimize thermal resistance at their junction and distribute energy across the surface area of heat flux sensor 4. In an embodiment of the invention, heat flux sensor 4 is disposed in between heating/cooling source 3 and probe 5. Probe 5 provides a means of thermally connecting heat flux sensor 4 to the unknown 6. Thus, probe 5 may be constructed of a material of high conductivity and low thermal mass, including, but not limited to diamond or ceramic material. Typically, probe 5 is made as small as possible to minimize its thermal resistance and thermal mass while allowing a practical mechanical construction and providing adequate convenience to the user.

[0018] Referring back to heat flux sensor 4, heat flux sensor 4 outputs electrical signals to feedback control circuit 2, which comprises an amplifier. The electrical signals are proportional to the magnitude and direction of the heat flux through heat flux sensor 4. Based on those signals, control circuit 2 adjusts the power to heating/cooling source 3 so as to bring the heat flux to zero or approximately zero. Indicator 8 indicates when this condition is achieved, and control circuit 2 enters a neutral state. At this point, the unknown temperature can be read from the display 1.

[0019] Indicator 8 receives output signals from control circuit 2 and comprises a light source (not shown) that turns on when the reading on display 1 is valid. Indicator 8 may also comprise an alarm that sounds when the reading is valid. Regarding display 1 , the displayed temperature value itself may be blank until valid, flashed until valid, or replaced by a word such as "wait" until valid. Indicator 8 is any form of indication to the user that the temperature balance has settled and hence the displayed reading on display 1 is valid. [0020] Referring to the use of temperature sensing device 10 described above to determine the temperature of the unknown 6, probe 5 is first brought into contact with the body under test or unknown 6. When there is a thermal resistance between temperature sensing device 10 and the unknown 6, there is a heat flux either into or out of probe 5. In either case, the temperature of probe 5 becomes different from that of heating/cooling source 3. The temperature difference between sensor probe 5 and heating/cooling source 3 drives a heat flux through heat flux sensor 4.

[0021] Heat flux sensor 4 outputs signals to control circuit 2, and control circuit 2 passes a corresponding current to heating/cooling source 3. The current passed from control circuit 2 adjusts the power to heating/cooling source 3 such that the heat flux sensed by heat flux sensor 4 is brought to zero. The current passed may be proportional to the magnitude and direction of the sensed heat flux. The output of control circuit 2 is also connected to indicator 8. Based on the type of indicator comprising indicator 8, indicator 8 is configured to indicate or show when the heat flux is zero, or approximately zero. [0022] Initially, when probe 5 is brought into contact with the unknown 6, temperature sensing device 10 and the unknown 6 are usually at different temperatures. When device 10 is cold compared to the unknown 6, there is a heat flux into probe 5. Alternatively, when device 10 is hot compared to the unknown 6, there is a heat flux out of probe 5. The discussion to follow refers to the temperature balance between the device 10 and the unknown 6 in the case where device 10 is cold compared to the unknown 6. The method of the alternative case mentioned above can also be appreciated.

[0023] As described above, when device 10 is cold compared to the unknown 6, there is a heat flux into probe 5. In response to that heat flux, the temperature of probe 5 becomes greater than that of heating/cooling source 3. The temperature difference between sensor probe 5 and heating/cooling source 3 drives a heat flux through heat flux sensor 4. Heat flux sensor 4 outputs electrical signals to control circuit 2, which passes electrical signals to the power source of heating/cooling source 3. In this case, a thermal electric cooler and conventional heater, as described above, are both appropriate heat sources comprising heating/cooling source 3.

[0024] As sensor probe 5 heats toward the temperature of the unknown 6, the heat flux reduces, and in a classical control system manner, the temperature of sensor probe 5 becomes equal to the temperature of the unknown 6. With a large gain value in the control circuit 2, there is no temperature difference across heat flux sensor 4. Thus, there is no thermal load presented to the unknown 6, which allows for more accurate temperature measurement. [0025] Temperature sensing device 10 serves to balance the temperatures of the elements mentioned below so that the heat flux equals zero. The heat flux equals zero when sensor probe 5, heating/cooling source 3, and thermometer element 7 are the same temperature, and the heat flux into or out of the unknown 6 via probe 5 is also zero. Therefore, when the heat flux equals zero, sensor probe 5 is at the same temperature as the unknown 6. At this point, display 1 of thermometer element 7 should accurately reflect the temperature of the unknown 6. [0026] The displayed temperature value on display 1 , the measurement valid indication from indicator 8, and any other data may instead or additionally be transferred from the sensing system 10 to a remote display computer or other instrument using a data interface such as an analogue signal or a digital interface. [0027] The construction and arrangement of the system and method for a temperature sensor, as described herein and shown in the appended figures, is illustrative only. Although only a few embodiments of the invention have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g. variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the appended claims. Accordingly, all such modifications are intended to be included within the scope of the present invention as defined in the appended claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. In the claims, any means-plus-function clause is intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the preferred and other exemplary embodiments without departing from the spirit of the embodiments of the invention as expressed in the appended claims. Therefore, the technical scope of the present invention encompasses not only those embodiments described above, but also those that fall within the scope of the appended claims.