DIXON IAN (GB)
ORME ANDREW (GB)
TAVENER JOHN PETER (GB)
DIXON IAN (GB)
ORME ANDREW (GB)
US4079618A | 1978-03-21 | |||
US3738174A | 1973-06-12 |
1. | Temperature calibration apparatus for calibrating a plurality of different types of temperature sensors, the apparatus comprising: a body having a well constructed and arranged to receive at least one of a plurality of inserts to adapt the body to allow said body to be used in the calibration of a selected one of a plurality of different types of temperature sensors; and, a plurality of inserts each of which is selectively insertable in the well to adapt the body to allow said body to be used in the calibration of a selected one of said plurality of different types of temperature sensors, said plurality of inserts including at least two of the following inserts: (a) a block having at least one recess for receiving a temperature sensor to be calibrated; (b) a substantially solid block; (c) a hollow container containing a liquid; (d) a black body insert to adapt said well to be substantially a black body; and, (e) a fixed point cell. |
2. | Apparatus according to claim 1, wherein said recessed block includes a plurality of recesses of different sizes for respectively receiving different size temperature sensors to be calibrated. |
3. | Apparatus according to claim 1 or claim 2, wherein the body includes means operable to cause rotation of a stirrer provided in said hollow container when said hollow container is inserted in the well. |
4. | Apparatus according to any of claims 1 to 3, wherein the well is defined by walls of the body which are black such that when said black body insert is inserted into said cell, the well is substantially a black body primary source. |
5. | Apparatus according to any of claims 1 to 4, wherein said black body insert is arranged to be insertable into the well to reside at the bottom of the well. |
6. | Apparatus according to claim 6, wherein said black body insert has a matrixed surface which faces outwardly of the well when said black body insert is inserted into the well. |
7. | Apparatus according to any of claims 1 to 6, wherein said well is cylindrical. |
8. | Apparatus according to claim 7, wherein said well has a circular crosssectional shape. |
9. | Temperature calibration apparatus for calibrating a plurality of different types of temperature sensors, the apparatus comprising: a body having a well constructed and arranged to receive at least one of a plurality of inserts to adapt the body to allow said body to be used in the calibration of a selected one of a plurality of different types of temperature sensors, the well being a substantially black body; and, at least one insert which is selectively insertable in the well to adapt the body to allow said body to be used in the calibration of a selected one of said plurality of different types of temperature sensors, said at least one insert including at least one of the following inserts: (a) a block having at least one recess for receiving a temperature sensor to be calibrated; (b) a substantially solid block; (c) a hollow container containing a liquid; and, (d) a fixed point cell. |
10. | Apparatus according to claim 9, wherein said recessed block includes a plurality of recesses of different sizes for respectively receiving different size temperature sensors to be calibrated. |
11. | Apparatus according to claim 9 or claim 10, wherein the body includes means operable to cause rotation of a stirrer provided in said hollow container when said hollow container is inserted in the well. |
12. | Apparatus according to any of claims 9 to 11, wherein said well is cylindrical. |
13. | Apparatus according to claim 12, wherein said well has a circular crosssectional shape. |
14. | Apparatus according to any of claims 1 to 13, comprising a standard calibrated temperature sensor for making a calibrated measurement of the temperature of an insert in the well. |
15. | Temperature calibration apparatus substantially in accordance with the examples as hereinbefore described with reference to and as illustrated by the accompanying drawings. |
A temperature calibration laboratory may be asked to calibrate a number of different temperature sensors which operate according to different measuring principles. Such temperature sensors include contact thermometers, such as thermocouples, industrial platinum resistance thermometers, thermistors, liquid-in-glass thermometers and surface sensors, as well as non-contact thermometers, such as optical thermometers and radiation pyrometers.
To calibrate the different types of sensor, and differing lengths, diameters and shapes of sensor within the different types, a temperature calibration laboratory has previously had to own and maintain a fairly large number of different pieces of apparatus. These include for example metal block baths, stirred liquid baths, black body cavities, surface sensor calibrators, etc. Each of these pieces of apparatus is typically dedicated to one particular type of temperature sensor.
Furthermore, a temperature calibration laboratory must also have standard thermometers to which the sensors submitted for calibration can be referred. These standard thermometers themselves must be regularly checked to ensure that they still meet their specifications. Where necessary, the standard thermometers have had to be sent away to a higher authority for recalibration.
A temperature calibration laboratory is therefore a complicated and expensive facility. It will need to have and maintain a variety of pieces of apparatus, standard thermometers, indicators and the like. The laboratory will have to temporarily close down its calibration function when its standard thermometers are being recalibrated externally.
According to a first aspect of the present invention, there is provided temperature calibration apparatus for calibrating a plurality of different types of temperature sensors, the apparatus comprising: a body having a well constructed and arranged to receive at least one of a plurality of inserts to adapt the body to allow said body to be used in the calibration of a selected one of a plurality of different types of temperature sensors; and, a plurality of inserts each of which is selectively insertable in the well to adapt the body to allow said body to be used in the calibration of a selected one of said plurality of different types of temperature sensors, said plurality of inserts including at least two of the following inserts: (a) a block having at least one recess for receiving a temperature sensor to be calibrated; (b) a substantially solid block; (c) a hollow container containing a liquid; (d) a black body insert to adapt said well to be substantially a black body; and, (e) a fixed point cell.
The present invention provides a temperature calibration apparatus which can be easily adapted by using different inserts to allow the same basic apparatus to be used for calibrating a very wide range of temperature
sensors. It is only necessary for the user to purchase and/or store one basic set of the apparatus and a range of inserts which will be needed by the user. The apparatus can perform all of the functions traditionally performed by a temperature calibration laboratory, and can, in its preferred embodiment, even recalibrate its own standard thermometer. The user can purchase the basic apparatus and only those inserts which will actually be used for calibration by the user. The user can obtain other inserts for calibrating other types of temperature sensors as and when the need arises. In an example, the same basic apparatus, with appropriate inserts, can be used to calibrate different types of temperature sensors covering the temperature range of-50°C to 1200°C. Such temperatures can be maintained for sustained periods and typically within 1 milliKelvin or less of the set or desired temperature.
Storage space is saved as the inserts themselves can typically be relatively small. It is not necessary to store bulky calibration apparatus dedicated to each type of temperature sensor to be calibrated as is the case in the prior art.
The recessed block will typically be used to provide a dry block bath. The substantially solid block will typically be used in the calibration of surface sensors.
The hollow container containing a liquid will typically be used to achieve higher calibration accuracy and-can be used for example to provide an ice/water (0°C) or a steam/water (100°C) mixture; other liquids which can be used include alcohols or acetone for lower temperatures and oils of different types for higher temperatures. The black body insert will typically be used when the apparatus is to be
used to calibrate optical or radiation pyrometers. The fixed point cell will typically be used to provide a well defined fixed temperature, such as the triple point of water, or the melt point of indium or gallium.
Said recessed block may include a plurality of recesses of different sizes for respectively receiving different size temperature sensors to be calibrated.
The body preferably includes means operable to cause rotation of a stirrer provided in said hollow container when said hollow container is inserted in the well. This ensures that the liquid is well mixed and therefore at a substantially uniform temperature throughout the liquid.
Such rotation means may be a rotating magnet positioned under the hollow container, the stirrer being caused to rotate by the rotation of the rotating magnet.
The well may be defined by walls of the body which are black such that when said black body insert is inserted into said cell, the well is substantially a black body primary source. The walls may be coated with a suitable black paint or may be black anodised aluminium for example.
Said black body insert may be arranged to be insertable into the well to reside at the bottom of the well.
Said black body insert preferably has a matrixed surface which faces outwardly of the well when said black body insert is inserted into the well.
Said well is conveniently cylindrical. Said well preferably has a circular cross-sectional shape.
According to a second aspect of the present invention, there is provided temperature calibration apparatus for calibrating a plurality of different types of temperature sensors, the apparatus comprising: a body having a well constructed and arranged to receive at least one of a plurality of inserts to adapt the body to allow said body to be used in the calibration of a selected one of a plurality of different types of temperature sensors, the well being a substantially black body; and, at least one insert which is selectively insertable in the well to adapt the body to allow said body to be used in the calibration of a selected one of said plurality of different types of temperature sensors, said at least one insert including at least one of the following inserts: (a) a block having at least one recess for receiving a temperature sensor to be calibrated; (b) a substantially solid block; (c) a hollow container containing a liquid; and, (d) a fixed point cell.
In this aspect, the well is already a black body and can be used immediately in the calibration of optical or radiation pyrometers. Various inserts can be used to adapt the apparatus for use in calibrating other types of temperature sensors.
Said recessed block may include a plurality of recesses of different sizes for respectively receiving different size temperature sensors to be calibrated.
The body preferably includes means operable to cause rotation of stirrer provided in said hollow container when said hollow container is inserted in the well.
Said well is conveniently cylindrical. Said well preferably has a circular cross-sectional shape.
In either aspect, a standard calibrated temperature sensor may be provided for making a calibrated measurement of the temperature of an insert in the well.
An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a longitudinal cross-sectional view of an example of temperature calibration apparatus according to the present invention showing the main working components; Fig. 2 is a plan view from above of the components of the apparatus shown in Figure 1; Fig. 3A and Fig. 3B are respectively a longitudinal cross-sectional view and an end view of a first example of an insert for the apparatus of Figure 1; Figs. 4A and 4B are respectively a longitudinal cross- sectional view and an end view of a second example of an insert for the apparatus of Figure 1; Figs. 5A and 5B are respectively a longitudinal cross- sectional view and an end view of a third example of an insert for the apparatus of Figure 1;
Fig. 5C is a cross-sectional view through a lid for the third example of an insert; Figs. 6A and 6B are respectively a longitudinal cross- sectional view and an end view of a fourth example of an insert for the apparatus of Figure 1; Fig. 7 is a side elevation of a fifth example of an insert for the apparatus of Figure 1; Fig. 8 is a front elevation of the apparatus; and, Fig. 9 is a plan view from above of the apparatus.
Referring to the drawings, there is shown an example of temperature calibration apparatus 1 according to the present invention having a body 2. In the example shown, the body 2 is a hollow cylinder of circular cross-sectional shape. The body 2 provides a cylindrical side wall 3 which defines a central hollow well 4 which is closed at a first, lower end by an end wall 5 of the body 2. In one specific example, the well 4 has a length of 160mm and a diameter of 35mm. Other sizes for the well 4 are within the scope of the present invention.
The body 2 is surrounded by and in thermal-contact with heating/cooling modules 6 in a manner which is known in itself. The heating/cooling modules 6 are heated or cooled to create a volume of constant temperature within the body 2, the temperature being controlled by an internal controller (which may include a computer running suitable
software) which can adjust the temperature over the working range of the apparatus 1 as required. An end ring 7 is fixed around the open mouth 8 of the well 2. The end ring 7 has a through hole 9 positioned radially outwardly of the side wall 3 of the body 2 which can receive if desired a standard thermometer 10 during calibration of a temperature sensor. The standard thermometer 10 accurately measures the temperature of the body 2 or of an insert placed in the well 4 as will be discussed further below.
As indicated schematically by dashed lines in Figure 1, the interior surface of the side wall 3 of the body 2, i. e. that part of the side wall 3 which faces the well 4, is coated so that the side wall 3 acts as a black body.
For example, the side wall 3 may be painted with a black paint having a high emissivity. As an alternative, where the body 2 is made of aluminium, the interior surface of the side wall 3 may be black anodised. In one embodiment, the interior surface of the end wall 5 is also black coated. However, in the preferred embodiment, a separate insert for the end of the well 4 is provided, as will be discussed further below.
The basic apparatus 1 is adapted by inserting one of a choice of inserts so that the apparatus 1 can be adapted to allow it to be used in the calibration of a plurality of different types of temperature sensors. In the-following description, the actual use of the apparatus 1 when adapted as discussed is in itself well known and will therefore not be described in detail. Furthermore, it will be appreciated that inserts other than those specifically
shown and described herein may be provided within the scope of the present invention.
Referring to Figures 3A and 3B, there is shown a first example of an insert 20 for use with the apparatus 1 shown in Figures 1 and 2. The first example of an insert 20 is a massive metal block which is sized to fit snugly in the well 4. The block 4 is provided with plural longitudinal blind recesses 21 which extend from a first, upper end face 22 of the block 20 almost to the opposite closed end 23 of the block 20. Each recess 21 is of the same length and may be for example 140mm long where the length of the well 4 is 160mm. The various recesses 21 have different diameters in order to accommodate a wide range of sizes for the temperature sensor or sensors to be calibrated. A central short tapped recess 24 may be provided to facilitate extraction of the block 20 from the well 4. When inserted in the well 4, the recessed block 20 adapts the apparatus 1 to be used as a dry block bath, the usage of which is known in itself and will not be described in detail. Briefly, in the preferred usage, an approximate temperature of the insert 20 is set using the controller which controls the heating/cooling modules 6 to heat or cool the insert 20 as required. The controller has its own temperature display 15. The standard thermometer 10 in this example is inserted in one of the recesses 21 so that the true temperature of the block 20 can be measured and-displayed on a second display 16. The temperature sensor (not shown) to be calibrated is inserted in an appropriate one of the other recesses 21 and the temperature measured by that temperature sensor compared with the true temperature as measured by the standard thermometer 10. The temperature
sensor to be calibrated can then be calibrated as necessary. It will be appreciated that several temperature sensors can be calibrated simultaneously using the recessed block 20 shown in Figures 3A and 3B.
A second example of an insert 30 is shown in Figures 4A and 4B. This second example is a solid block of metal which has a flat top surface 31 suitable for the calibration of surface sensors. The solid block 30 is again sized so that it is snugly received in the well 4.
The solid block 30 can include its own calibrated thermometer (not shown), which may be for example a thermocouple or a resistance thermometer. Alternatively or additionally, the solid block 30 may have a lateral blind recess provided in its side just under its top surface 31 for receiving the tip of the standard thermometer 10. In any event, the true temperature of the surface 31 of the solid block 30 is measured to provide a comparison reference for the surface sensor to be calibrated. The calibration of surface sensors using solid blocks of the type shown in Figures 4A and 4B follows the process outlined above for the recessed block 20 and is in itself known and will therefore not be described further herein.
A third example of an insert 40 is shown in Figures 5A and 5B. This third example is a hollow container 40 which again is snugly received in the well 4. The hollow container 40 has one open end 41 which can be closed by a separate lid 42 when the hollow container 40 is not in use and when required or desired during calibration of a temperature sensor. When in use and inserted in the well 4, the hollow container 40 is filled with a liquid 43 which
is chosen according to the temperature or range of temperatures at which the experimental temperature sensor is to be calibrated. For example, the liquid 43 may be water which can be cooled in the apparatus 1 so that the water 43 freezes for calibration at 0°C or which can be boiled in the apparatus 1 for calibration at 100°C. Other liquids which can be used include alcohols and acetone for lower temperatures and oils of different types for higher temperatures. As indicated in Figure 5A, the hollow container 40 preferably includes a metallic stirrer rod 44 which is retained at the lower closed end 45 of the hollow container 40 by a mesh 46. The stirrer rod 44 can be caused to rotate in the hollow container 40 by a rotating magnet 11 provided below the body 2 as shown in Figure 1.
The speed of rotation of the rotating magnet 11 can be adjusted by a control knob 12. The rotating stirrer rod 44 helps ensure that the liquid 43 has the same temperature throughout. As is known, (stirred) liquid baths tend to be more accurate than dry block baths and are also useful for calibrating awkwardly shaped temperature sensors. The standard thermometer 10 can again be used to obtain an accurate measure of the true temperature of the liquid 43 by insertion into the liquid.
A fourth example of an insert 50 is shown in Figures 6A and 6B and can be used to convert the well 4 into a black body primary source. As has been mentioned above, the black body insert 50 may not be necessary if the internal surface of the closed end 5 of the well 4 is appropriately black coated. However, for greatest accuracy, it is preferred that a black body insert 50 be used if the well 4 is to be used as a black body primary
source. The black body insert 50 is in the form of a flat disc which seats snugly at the bottom of the well 4 adjacent the closed end 5 of the body 2. The uppermost surface 51 of the black body insert 50, i. e. that surface which faces into the well 4 and therefore which faces the open mouth 8 of the well 4, is provided with a matrixed surface, i. e. the surface is textured to minimise the amount of light which is reflected by the well 4. For example, the surface of the insert 50 can be provided with an array of pyramids which absorb most of the light entering the well 4 and reflect the remaining light to other pyramids, or to the side wall 3 of the well 4, where further absorption takes place. The emissivity of the well 4, which is the ratio of the radiation emitted by the well 4 to that emitted by a black body at the same temperature, may be of the order of 0.995. When acting as a black body primary source, the well 4 can be used to calibrate optical or radiation pyrometers, as is well known in itself.
Again, the standard thermometer 10 can be used as a measure of the true temperature in the well 4.
A fifth example of an insert 60 is shown in Figure 7.
The insert 60 shown in Figure 7 converts the apparatus 1 to be a fixed point cell and its construction is known in itself. The specific example shown in Figure 7 is suitable for calibrating a temperature sensor at the triple point of water, in a known manner. Other fixed point cells, which may have different designs, can be provided for other fixed points including for example the melt points of gallium and indium. Such fixed point cells are used for very accurate calibration of temperature sensors, as is well known.
The use of fixed point cells allows for accurate calibration of a temperature sensor which is a temperature sensor used"in the field". The use of fixed point cells also allows the standard thermometer 10 itself to be checked and, if necessary, recalibrated. For example, the freezing (ice) point and boiling point of water readily provide extremely accurate and stable fixed points of 0°C and 100°C respectively (adjusted as necessary to allow for variations due to variations in ambient atmospheric pressure) against which the calibration of the standard thermometer 10 can be checked. The apparatus 1 can therefore effectively be self-checking and also allows the standard thermometer 10 readily to be recalibrated. This avoids the need for a temperature calibration laboratory to have to submit their standard thermometers to an external authority for recalibration.
An embodiment of the present invention has been described with particular reference to the examples illustrated. However, it will be appreciated that variations and modifications may be made to the examples described within the scope of the present invention. For example, in applications where the apparatus is used as a liquid bath, it may be possible to put the liquid directly into the well 4 (optionally with a stirrer rod 44) without having to use the hollow container 40 mentioned above. A remote communications link via an appropriate connector 17 can be provided so that automatic or remote calibration is possible, whether of the standard thermometer 10 or of some other temperature sensor.