Patent Description:
Vacuum gauges are commonly used to measure the pressure in a vacuum system. The pressure measurement can be used to check that the system has a vacuum of sufficiently low pressure for its intended purpose. If the measurement indicates that the pressure of the vacuum in the system is insufficiently low this can be used to indicate and detect a leak or defect in the system and/or provide feedback to aid control of a vacuum pump evacuating the system.

A common type of vacuum gauge used for this purpose is a thermal conductivity vacuum gauge.

Thermal conductivity vacuum gauges utilize the thermal conductivity of gases for the purpose of pressure measurements, and may also be known as heat-loss vacuum gauges. In general, these gauges utilise the relationship between the thermal conductivity of a gas and its pressure in order to arrive at a pressure measurement.

One such thermal conductivity vacuum gauge is a Pirani gauge.

In a Pirani gauge, a heater element (usually in the form of a filament or wire) is placed in contact with the working gas in the vacuum system and is connected into an electrical circuit that allows it to be heated using electrical energy. As gas molecules collide with the heater element they will transfer (i.e., conduct) heat away from it. If the gas is of a higher pressure, then there will be more molecules colliding with the heater element and so more heat will be transferred away from the heater element (i.e., the gas has a higher thermal conductivity).

If the heater element is held at a constant current or voltage, then changes in the amount of heat transferred from the heater element due to changing gas pressure will cause its temperature (and thus resistance) to change a proportional amount. By measuring this change in resistance, the change in pressure of the gas can be measured. Alternatively, the heater element can be held at a constant temperature (and thus resistance), and the change in voltage needed to maintain this constant temperature depending on the gas pressure can be measured.

In this manner, the pressure of the gas is measured as a function of its thermal conductivity.

As will be appreciated by the skilled person, a common way to implement this in a Pirani gauge is to include the heater element as an arm in a Wheatstone bridge circuit.

In order to determine a more accurate pressure measurement in a thermal conductivity gauge, a thermal compensation element is generally necessary.

The thermal compensation element is an element or component that measures the ambient temperature of the gauge itself. This allows the pressure measurement to be compensated for this.

This can be achieved, for example, by using the thermal compensation element to provide a reference resistance or voltage according to the ambient temperature of the gauge for comparison to that of the heater element. This can help minimise measurement inaccuracies and inconsistencies associated with the ambient temperature of the gauge unintentionally affecting the resistance or voltage reading of the heater element.

As will be appreciated by the skilled person, one way to implement this thermal compensation in a Pirani gauge is to include the thermal compensation element (e.g., a temperature-dependent resistor) as an arm in the same Wheatstone bridge circuit as the heater element.

The thermal compensation element is generally placed on the surfaces of a body or tube of the gauge assembly, and relies on thermal conduction through the body to determine the ambient temperature of the gauge assembly for the comparison to the heater element.

The gauge body will often experience a temperature gradient across its length. This is due to one end of the body normally containing active electronics (e.g., to power the gauge and measure and display pressure therein) that can act to heat the tube, and an opposite end being attached to the vacuum system, which can act as a heat sink.

Due to the often corrosive nature of process gases used in vacuum systems, the gauge assembly body is generally made of stainless steel (or other suitable corrosion resistant material). Although such a material provides acceptable corrosion properties for the gauge assembly, it has a relatively low thermal
conductivity. For example, stainless steel has a thermal conductivity in the region of around <NUM> W/mK.

The relatively low thermal conductivity of the gauge assembly body means it can be relatively slow to communicate and equalise temperature gradients across the gauge body. This can result in a varying and inaccurate temperature compensation measurement during use of the gauge assembly, which can provide potential inaccuracies and inconsistencies in the resulting pressure measurement.

Previously, to try to reduce these inaccuracies and inconsistencies in pressure measurement, the thermal compensation element has been positioned at a particular position along the length of the body that represents the best 'average' temperature of the gauge body (e.g., such as half-way along the body). Unfortunately, this solution has some limitations, as the most accurate temperature position will change if e.g., the dissipation of heat from the electronics, ambient air temperature or vacuum system temperature changes, as occurs regularly during different stages of vacuum system operation. These changes will thus again introduce errors into the pressure measurement.

When measuring lower vacuum pressures and using a more compact Pirani gauge (which has a smaller filament and thus has lower sensitivity), the variance and errors found in the temperature compensation due to the thermal gradients and changes therein across the gauge body can be great enough to mask any pressure-related changes for the process gas being measured within the gauge. Thus, this issue can place a restriction on the size and pressure measurement sensitivity of the gauge that can be practically implemented.

Accordingly, a need exists to provide a thermal conductivity vacuum gauge assembly that improves on the above aspects. This can not only lead to a thermal conductivity vacuum gauge of increased accuracy and sensitivity, but can also allow more compact vacuum gauges to be realised.

Although this description generally exemplifies a Pirani gauge assembly, it is to be understood that any other suitable type of thermal conductivity vacuum gauge assembly (where a heater element with a temperature compensation element) may also benefit from this disclosure and are accordingly within the scope thereof. Such other thermal conductivity vacuum gauges may include, for example, a thermistor gauge assembly or a thermocouple gauge assembly.

Known vacuum gauges are described in <CIT>, <CIT>, <CIT> and <CIT>.

From one aspect, the present disclosure provides a thermal conductivity vacuum gauge assembly. The gauge assembly comprises a body defining an internal chamber for receiving working gas, a heater element disposed within the chamber, a thermal compensation element in thermal communication with the body; and a thermal equalisation element in thermal communication with the body. The body is defined by a wall having an outer facing wall surface and an opposing inner facing wall surface, and the body is made of a material with a first thermal conductivity, and the thermal equalisation element is made of a material with a second thermal conductivity that is higher than the first thermal conductivity.

The thermal equalisation element helps conduct heat across the body more quickly. This can help reduce the size of temperature gradients between different parts of the body and reduce variation and inaccuracy in the ambient body temperature communicated to the thermal compensation element. This can result in a more accurate pressure measurement being realised.

The thermal compensation element is an element for providing a measurement indicative of an ambient temperature of the body. In one example, the thermal compensation element is a resistance temperature detector (RTD). In other examples, the thermal compensation element is a thermistor (such as a positive temperature co-efficient (PTC) thermistor or a negative temperature co-efficient (NTC) thermistor).

In an embodiment of the above, the thermal equalisation element at least partially surrounds the internal chamber and is in thermal contact with the body.

In a further embodiment of the above, the thermal equalisation element at least partially surrounds the outer facing wall surface, and in yet a further embodiment, the thermal equalisation element forms an outer sleeve around the body. In such an embodiment, the thermal equalisation element fully surrounds the circumference of the body.

In another embodiment, the thermal equalisation element comprises at least one strip extending along the body.

In another embodiment, the thermal equalisation element is enclosed within the wall between the inner and outer facing wall surfaces. In further embodiments, the thermal equalisation element disposed within the wall is at least one strip or a sleeve disposed within the wall.

These embodiments provide configurations of the thermal equalisation element that provide good thermal contact with the body to reduce the size of temperature gradients between different parts of the body. It will be appreciated from the description below that certain ones of these configurations have manufacturing and assembly advantages over others.

In a further embodiment of any of the above, the second thermal conductivity is at least <NUM> times (or an order of magnitude) greater than the first thermal conductivity.

This gives the thermal equalisation element sufficient thermal conductivity compared to the body to conduct heat quickly enough to reduce the size of temperature gradients between different parts of the body to help reduce variation and inaccuracy in the ambient body temperature communicated to the thermal compensation element.

In certain suitable embodiments, the thermal equalisation element is made of a material that has a thermal conductivity of greater than or equal to <NUM> W/mK, greater than or equal to <NUM> W/mK, or greater than or equal to <NUM> W/mK.

According to the invention, the body is made of stainless steel and the thermal equalisation element is made of aluminium. In another embodiment, that is not covered by the claims, the thermal equalisation element is made of copper.

According to the invention, the thermal compensation element is located within a cavity defined in the wall.

In a further embodiment of any of the above, the assembly further comprises an electrical connection member mounted to the thermal compensation element, wherein at least some of a first portion of the electrical connection member is surrounded by the thermal equalisation element and a second portion of the electrical connection member protrudes out from the body.

The placement of the thermal compensation element in the cavity and/or the use of an electric connection member can help support the thermal compensation element in better thermal contact with the body to improve the accuracy of the temperature measurement thereof.

In a further embodiment of any of the above, the body extends along a longitudinal axis between a base and a top and has a sidewall extending between the base and the top, and the thermal equalisation element at least partially surrounds the sidewall and extends axially along the longitudinal axis.

Surrounding the sidewall surrounds a larger surface area of the body for improved thermal communication therewith.

In a further embodiment of the above, the body includes a radially extending shoulder that abuts the thermal equalisation element.

The shoulder can help support the thermal equalisation element in place, e.g., without the need for additional joining or bonding agents. This can facilitate the assembly and replaceability of the thermal equalisation element on the body.

In a further embodiment of the above, the base defines an inlet passage in fluid communication with the chamber, and includes a radially extending flange with a recess therein for receiving a seal.

The flange allows for a more secure fit of the assembly to a vacuum system and the recess (allowing for an O-ring seal therein) provides a better seal to be formed between the assembly and the vacuum system when in use.

In a further embodiment of any of the above, the heater element is a filament for heating by an electrical power source. In examples, the filament may be made of Platinum or Tungsten. Such an assembly may be known generally as a Pirani gauge assembly.

In another aspect, the present disclosure provides a thermal conductivity vacuum gauge. The gauge comprises the assembly of any of the embodiments of the above aspect, and a housing receiving and at least partially surrounding the body and the thermal equalisation element.

The housing and the connections thereto facilitated by the embodiments of the assembly allow for improved modularity and replaceability for the thermal conductivity vacuum gauge.

In an embodiment of the above, the housing includes a control circuit for providing electrical control of the heater element and the thermal compensation element.

The control circuit can allow the housing to act as a replaceable, modular add-on to the assembly that allows interrogation of the assembly pressure measurement.

Although certain advantages have been discussed in relation to certain features above, other advantages of certain features may become apparent to the skilled person following the present disclosure, the matter for which protection is sought being defined by the claims.

Referring to <FIG>, a thermal conductivity vacuum gauge assembly <NUM> is shown. The assembly <NUM> includes a body <NUM> that has a sidewall <NUM> that extends axially along a longitudinal axis X between a base <NUM> and a top <NUM>. The body <NUM> includes a shoulder <NUM> that projects radially outward from the sidewall <NUM> at the base <NUM>.

In the depicted embodiment, the body <NUM> is generally annular, but with a chamfered section <NUM> around a portion of the circumference. As discussed below, this chamfered section <NUM> can aid attachment and orientation of the assembly with other component parts of a thermal conductivity vacuum gauge (e.g., a housing or covering (not shown)).

Although a specific shape of body <NUM> is depicted, it should be understood that within the scope of this disclosure any other suitable shape of body <NUM> can be used (e.g., square or rectangular cross-section).

An inlet passage <NUM> extends axially from the base <NUM> and includes a flange <NUM> that extends radially therefrom. In one example, the flange <NUM> has a <NUM> nominal bore specification. In another example, the flange <NUM> has a <NUM> nominal bore specification. Although, any suitable type and dimension of flange <NUM> may be used within the scope of this disclosure.

The top <NUM> includes an end cap <NUM> through which electrical connector <NUM> and support features <NUM> for a heater element <NUM> protrude (discussed in more detail below with reference to <FIG>), and are secured therein.

The end cap <NUM> is fixed within an opening <NUM> defined in the top <NUM>.

In some embodiments, the end cap <NUM> may be fixedly attached to the top <NUM>, for example, by being welded into the opening <NUM>, or by being press-fit therein. In other embodiments, the end cap <NUM> may be removably fixed into the top <NUM> by threaded engagement therewith. Such removable fixation methods may facilitate repair and replacement of the heater element <NUM> and connection and support features. In yet further embodiments, the end cap <NUM> may be omitted and the top <NUM> extends radially across the top <NUM> without an opening <NUM> therein. In such embodiments, the connection and support features would extend through the top <NUM> itself.

In the depicted embodiment, the end cap <NUM> includes a marking area <NUM>, which provides an area for the marking of various numbers or codes related to assembly manufacture (e.g., part number/bar code, batch number etc.). It should be understood that within the scope of this disclosure such a marking area <NUM> could alternatively be present on any other suitable part of the assembly <NUM> or omitted altogether.

<FIG> shows a cross-section of assembly <NUM> taken along the longitudinal axis X (along the line defined by arrows A-A) and viewed in the direction of arrows A-A. <FIG> gives a view of the internal structure and components within the body <NUM>, as discussed below.

The body <NUM> defines an internal chamber <NUM> which is configured to receive working or process gas (e.g., from a vacuum system) when the assembly <NUM> is in use. By 'working' or 'process' gas, it is meant the gas (or gases) that the assembly intends to measure the pressure of. The 'working gas' is usually the gas (or gases) that are being worked on (e.g., being evacuated) by the vacuum system. The pressure of this gas can provide an indication of the general pressure of vacuum in the system.

In the depicted example, the body <NUM> is generally tubular, and may also be known as a 'body tube'. The internal chamber <NUM> is accordingly generally cylindrical about the longitudinal axis X within the body <NUM>.

The body <NUM> is defined or formed by a wall <NUM>. The wall <NUM> is defined between an outer facing wall surface 122a and an opposing, inner facing wall surface 122b. Surfaces 122a and 122b are generally annular in accordance with the depicted shape of the body <NUM>. The outer facing wall surface 122a is radially outward of the inner facing wall surface 122b and faces the exterior of the assembly <NUM>. The inner facing wall surface 122b faces the interior of the assembly <NUM> and defines (or encloses) the internal chamber <NUM>.

As discussed above, the body <NUM> is generally made of a relatively low thermal conductivity, but corrosion resistant metal, such as a stainless steel. This allows the body <NUM> to withstand the potentially corrosive effects of the process gas.

The body <NUM> can be made from any suitable manufacturing method, such as by being moulded/cast, machined from a solid block or 3D printed.

The inlet passage <NUM> extends axially from the base <NUM> and into the chamber <NUM>. The inlet passage <NUM> is in fluid communication with the chamber <NUM>, and permits working gas (e.g., from a vacuum system) to enter and exit the chamber <NUM> during use.

A filter element <NUM> is disposed across the inlet passage <NUM> for filtering the working gas before it enters the chamber <NUM>. The filter element <NUM> passes radially across the inlet passage <NUM> relative to the longitudinal axis X, and in the depicted embodiment is secured in place with a retaining ring <NUM> positioned in the inlet passage <NUM>.

The filter element <NUM> is used to ensure contaminants do not enter the chamber <NUM>. Such contaminants may damage the assembly <NUM> (e.g., by corroding or depositing on the heater element <NUM>, wall surface 122b or electrical connections within the chamber <NUM>) and/or may interfere with the pressure measurement process and provide inaccuracies therein.

In one example, the filter element <NUM> is a stainless steel mesh, although any other suitable type (e.g., a membrane) or material for filter element <NUM> may be used within the scope of this disclosure.

The flange <NUM> includes a recess or groove <NUM> defined therein. The recess <NUM> is annular around the longitudinal axis X and permits a seal to be seated therein. This can allow a better seal to be formed between the assembly <NUM> and a vacuum system when in use, and secured in position via the flange <NUM>. The seal can be any suitable type of seal, such as an O-ring seal or a metallic seal. In other embodiments, a (e.g., metallic) gasket arrangement between the flange <NUM> and the system may be used instead.

A heater element <NUM> is disposed within the chamber <NUM>. In the depicted example, the heater element <NUM> extends generally axially into the chamber <NUM> from the top <NUM> towards the base <NUM>.

The heater element <NUM> in the depicted embodiment is a filament for heating by an electric power source. The filament may be made from any suitable material, such as Tungsten or Platinum. Platinum in particular, may be used in vacuum system environments or applications that are known to contain more corrosively aggressive agents and/or working gases.

Electrical connectors or pins 132a, 132b, 132c protrude through the end cap <NUM> and are secured therein. The heater element <NUM> is connected to certain ones of the electrical connectors 132a, 132b, 132c to permit electrical communication therewith for control of the heater element <NUM>.

In the depicted example, the connectors 132a, 132c are connected to two opposing ends of the heater assembly <NUM>, whilst the connector 132b is used for grounding purposes. The connectors 132a, 132b, 132c can be subsequently connected to a separate control circuit (not shown) that can provide electrical power to heat and control the heater assembly <NUM> when the assembly <NUM> is in use.

The heater element <NUM> can be connected in any suitable manner to connectors 132a, 132c, e.g., by being wrapped around a base of the connectors or welded or soldered thereto etc..

The heater element <NUM> is supported within the chamber <NUM> by a support structure. In the depicted example, the support structure is in the form of a spring arm <NUM> and a bar <NUM>.

The bar <NUM> protrudes through end cap <NUM> and is secured thereto. The bar <NUM> extends axially into the chamber <NUM> from the top <NUM> towards the base <NUM> substantially parallel to the heater element <NUM>. In the depicted embodiment, the bar <NUM> is a cylindrical rod.

The spring arm <NUM> is secured to the end of the bar <NUM> nearest the base <NUM>, and extends radially (relative to the longitudinal axis X) to support the heater element <NUM>.

The spring arm <NUM> features a hook <NUM> around which the heater element <NUM> is passed. The spring arm <NUM> and bar <NUM> are used to provide a tension that keep the heater element <NUM> taut and supported in use between the connectors 132a, 132c.

As will be appreciated, in the depicted embodiment, the heater assembly <NUM> provides a substantially V-shape or U-shape when hung between the connectors 132a, 132c via the hook <NUM>.

Although one particular arrangement of the heater element <NUM>, electrical connectors 132a, 132b, 132c and support structure thereof is shown, it is to be understood that within the scope of this disclosure any other suitable arrangement may be used. For example, different numbers and types of electrical connectors 132a, 132b, 132c, a different type of heater element <NUM> (e.g., a thermistor), and different numbers or types of components to bar <NUM> and spring arm <NUM> may be used.

A thermal compensation element <NUM> is held against the outer surface 122a of the wall <NUM> of the body <NUM> in a cavity <NUM> defined therein. In this manner, the thermal compensation element <NUM> is held in thermal communication with the body <NUM>. This allows the thermal compensation element <NUM> to provide a reference reading for the ambient temperature of the body <NUM> to help adjust pressure measurements due to thermal conduction through the body <NUM> to the thermal compensation element <NUM>.

For simplicity of assembly, it is desirable to maintain the thermal compensation element <NUM> against the outer surface 122a without any further joining or bonding. However, in certain examples, thermal paste could be applied between the surface 122a in the recess <NUM> and the thermal compensation element <NUM> making contact therewith, in order to improve the thermal contact between the two.

The thermal compensation element <NUM> may be of any suitable type e.g., that can provide a resistance and/or voltage indicative of an ambient temperature of the wall <NUM> against which it is disposed. In one example, the thermal compensation element <NUM> is a resistance temperature detector (RTD), such a Molybdenum or Platinum RTD. In another example, the thermal compensation element <NUM> is a thermistor, such as a positive temperature co-efficient thermistor (PTC) or a negative temperature co-efficient thermistor (NTC) made of powdered metal oxides or a polymer. In another example, the thermal compensation element <NUM> could be a solid-state temperature sensor.

Although other types of thermal compensation element <NUM> fall within the scope of the present disclosure, it is thought that the above offer certain durability, cost and accuracy advantages over others.

An electrical connection member <NUM> is mounted to the thermal compensation element <NUM> and is used to hold it in position against the body <NUM>. The electrical connection member <NUM> also allows electrical communication between the thermal compensation element <NUM> and a control circuit (not shown) that can be connected thereto.

In the depicted embodiment, the electrical connection member <NUM> is a printed circuit board (PCB) of the FR-<NUM> specification; however, any suitable type of electrical connection member <NUM> could be used instead, or a PCB of any other suitable specification. By using a PCB in the depicted embodiment, the electrical connection member <NUM> also provides a durable/rigid substrate that offers some mechanical support for the thermal compensation element <NUM>, to hold it against the wall surface 122a.

A first portion of the electrical connection member <NUM> is held in the recess <NUM>. A second portion protrudes axially out from the wall <NUM> from the top <NUM>.

The first portion of the member <NUM> and the cavity <NUM> are sized and shaped such that the first portion can be push-fit and retained firmly therein to hold the thermal compensation element <NUM> in place against the wall surface 122a of the body <NUM> and maintain good thermal communication/contact therewith. Although, the electrical connection member <NUM> with element <NUM> thereon can be retained against the body <NUM> in another suitable manner, e.g., by the first portion of the electrical connection member <NUM> being adhesively fixed in the cavity <NUM>.

The second portion of the electrical connection member <NUM> includes an electrical connector <NUM> that is suitable to provide an electrical connection between the member <NUM> and a control circuit (not shown), and allow electrical communication between such a control circuit and the thermal compensation element <NUM> to inform the pressure measurements made by the assembly <NUM>.

In the depicted embodiment, the thermal compensation element <NUM> is surface mounted to the electrical connection member <NUM>.

This permits the thermal compensation element <NUM> to be made integrally with the electrical connection member <NUM> as a one-piece component that has cost, installation and durability benefits.

Nonetheless, within the scope of this disclosure, any other suitable method of mounting thermal compensation element <NUM> to the member <NUM> may be used, such as through-hole or soldering techniques.

In other embodiments (not shown), that are not covered by the claims, the thermal compensation element <NUM> can be held against the outer surface 122a without a cavity <NUM> therein.

In other embodiments (also not shown), the thermal compensation element <NUM> and first portion of the electrical connection member <NUM> can be enclosed within the wall <NUM> (i.e., between surfaces 122a and 122b) instead being held against the outer surface 122a. This can be achieved by the cavity <NUM> being placed in the wall <NUM> between surface 122a and 122b and the thermal compensation element <NUM> and first portion of the electrical connection member <NUM> being secured therein. Such embodiments may improve the longevity/durability of the thermal compensation element <NUM> and member <NUM>, as well as improve the amount of thermal contact between the thermal compensation element <NUM> and the wall <NUM> (for improved temperature compensation accuracy).

Although the depicted embodiments show the thermal compensation element <NUM>, electrical connection member <NUM> and cavity <NUM> disposed generally in the sidewall <NUM> of the body <NUM>, it is to be understood that they may be disposed at any other suitable part or portion of the body <NUM> defined by a wall <NUM> thereof (e.g., the base <NUM> or the top <NUM>), as may suit a particular application or vacuum system.

As shown in <FIG> and <FIG>, the sidewall <NUM> of the body <NUM> is surrounded (or circumscribed) by a thermal equalisation element <NUM>. <FIG> also shows the thermal equalisation element <NUM> having been removed from the body <NUM>.

The thermal equalisation element <NUM> includes a cylindrical portion <NUM> and a chamfered portion <NUM> that corresponds to the contours of the sidewall <NUM> and the chamfered portion <NUM> of the body <NUM>, respectively.

As shown in <FIG>, the thermal equalisation element <NUM> (i.e., with portions <NUM> and <NUM>) is sized and shaped such that it forms an outer sleeve that can be slid axially over the body <NUM> and abuts (or rests against) shoulder <NUM> in use.

The thermal equalisation element <NUM> is sized and shaped such that it is push-fit over the body <NUM> and retained in place by the push-fit (i.e., due to a slight interference between the sidewall <NUM> and the thermal equalisation element <NUM>). This allows the thermal equalisation element <NUM> to make good thermal contact with the sidewall <NUM> of the body <NUM>.

The push-fit provides simplicity of assembly and facilitates removability and replacement of the element <NUM>, e.g., compared to a method that bonds or joins the element <NUM> to the body <NUM> instead. Having said this, however, any other suitable method of holding the element <NUM> to the body <NUM> is envisaged within the scope of this disclosure (such as welding or brazing or using adhesive). In certain examples, thermal paste could also be applied between the element <NUM> and the surface 122a/sidewall <NUM> of the body <NUM> in order to improve the retention and thermal contact between the two.

The thermal equalisation element <NUM> is made of a material that has a relatively high thermal conductivity compared to that of the body <NUM>. In the depicted example, the thermal equalisation element <NUM> is made of aluminium (or an alloy thereof). Aluminium has a thermal conductivity in the region of around <NUM> W/mK, which is significantly greater than the around <NUM> W/mK thermal conductivity of an exemplary stainless steel generally used to make the body <NUM>.

It is to be appreciated that the thermal equalisation element <NUM> in thermal communication with the body <NUM> will help conduct any heat generated at different points in the body <NUM> across the body <NUM> more quickly. This can help reduce problematic temperature gradients between different parts of the body <NUM> (e.g., from the heat from electronics at or near top <NUM> and a relatively cool heat sink at or near the base <NUM>/flange <NUM>), which can help reduce variation and inaccuracy in the ambient body temperature communicated to the thermal compensation element <NUM>. This results in a more accurate pressure measurement being realised.

Although aluminium is exemplified, any other suitable material of sufficient thermal conductivity can also be used within the scope of this disclosure. For example, copper may be used, which has a thermal conductivity in region of around <NUM> W/mK.

In some examples, a suitable thermal equalisation element <NUM> is made of a material that has a thermal conductivity of greater than or equal to <NUM> W/mK, greater than or equal to <NUM> W/mK, or greater than or equal to <NUM> W/mK.

In further examples, the thermal conductivity of the thermal equalisation element <NUM> is made of a material that has a thermal conductivity at least <NUM> times (i.e., an order of magnitude) higher than that of the material that the body <NUM> is made of.

The thermal equalisation element <NUM> defines a wall thickness T (i.e., in the radial direction) that is of any suitable thickness. In some examples, the wall thickness can be between <NUM>-<NUM>, or more narrowly, <NUM>-<NUM>.

In the depicted example, the thermal equalisation element <NUM> is made by extrusion, which is a relatively low cost manufacturing process that provides a consistently sized element <NUM>. Having said this, however, the thermal equalisation element <NUM> can be made by any other suitable method within the scope of this disclosure, e.g., by machining or additive manufacturing/3D printing.

The thermal equalisation element <NUM> extends axially along longitudinal axis X for a majority of the axial length L of the body <NUM> (i.e., defined between top <NUM> and base <NUM> thereof). The thermal equalisation element <NUM> can be any suitable axial length compared to the body <NUM>, as long as it has a sufficient length to thermally contact enough of the body <NUM> to effectively equal out temperature gradients thereacross. It is to be appreciated that such a sufficient length allows the element <NUM> to extend a sufficient axial length over the heater element <NUM> (e.g., over the full or a majority of the axial length of the heater element <NUM>).

In some suitable examples, the thermal equalisation element <NUM> extends between <NUM>-<NUM>%, <NUM>-<NUM>%, <NUM>-<NUM>%, <NUM>-<NUM>%, <NUM>-<NUM>%, <NUM>-<NUM>%, <NUM>-<NUM>%, <NUM>-<NUM>% or <NUM>-<NUM>% of the axial length L of the body <NUM>.

Although the depicted thermal equalisation element <NUM> wholly surrounds the sidewall <NUM> of the body <NUM> (i.e., around its circumference), it should be understood that in alternative embodiments, the thermal equalisation element <NUM> need only partially surround the sidewall <NUM> of the body <NUM> instead.

In such examples, the thermal equalisation element <NUM> would have a cut or break along its axial length, and thus be substantially C-shaped or U-shaped in axial cross-section. Such examples could advantageous be clipped around the body <NUM> rather than axially push-fit there over.

In other such examples, the thermal equalisation element <NUM> may instead be an axially extending strip of material, or a plurality thereof, that is secured to the sidewall <NUM>.

Moreover, within the scope of this disclosure, the thermal equalisation element <NUM> needn't be limited to at least partially surrounding the outside of the body <NUM> (i.e., the outer wall 122a of the body <NUM>) as depicted. The thermal equalisation element <NUM> could instead be disposed within the wall <NUM> of the body <NUM> itself (i.e., in the radial thickness of the wall <NUM> between the outer and inner wall surfaces 122a and 122b).

In such examples, as with the depicted examples, the thermal equalisation element <NUM> would still at least partially surround the chamber <NUM> (and the inner wall surface 122b of the body <NUM>).

In such an example, the thermal equalisation element <NUM> could be fitted into an axially extending cavity within the wall <NUM> of the body <NUM> (between surfaces 122a, 122b) and make thermal contact with the body <NUM> therein. Alternatively, the element <NUM> could be integrally formed within the wall <NUM> when forming the body <NUM> (e.g., using additive manufacturing/3D printing).

As shown in the depicted embodiment, the thermal equalisation element <NUM> covers the recess <NUM> in which the thermal compensation element <NUM> is located. Such positioning is advantageous, as it provides thermal equalisation of gradients in the direct vicinity of the thermal compensation element <NUM>, which can further help with providing a more accurate temperature measurement thereto. Accordingly, in some examples, the thermal equalisation element <NUM> surrounds the body <NUM> in at least the area where the thermal compensation element <NUM> is located (i.e., covers the radial cross-sectional area where the thermal compensation element <NUM> is positioned).

For example, in an alternative to the depicted embodiment, the thermal equalisation element <NUM> is a planar axial strip along the sidewall <NUM> covering the recess <NUM> containing the thermal compensation element <NUM>.

In one example, a thermal conductivity vacuum gauge (not shown) is formed using the assembly <NUM> by it being received in a further housing or cover (not shown) that at least partially surrounds and passes over the thermal equalisation element <NUM> and body <NUM>.

The housing can generally include the control circuit and/or electronics (e.g., remainder of a Wheatstone bridge circuit) that can be connected to the assembly <NUM> in order to control and operate the heater element <NUM> in combination with the thermal compensation element <NUM>.

The electrical connectors 132a, 132b, 132c, <NUM> protruding from the assembly <NUM> can facilitate ease of integration with the housing, as they can simply be connected and disconnected to ports therein when the housing receives the assembly <NUM>. This can also aid modularity and replaceability for the housing and assembly <NUM>.

The housing can feature its own electrical connections/connectors that will allow the control circuit/electronics and the assembly <NUM> to be powered and interrogated, as necessary.

The housing can also feature a screen/readout thereon. This screen/readout can display/indicate the measured pressure value or other parameters associated with the gauge/assembly <NUM> (e.g., resistance, temperature, voltage etc.) and the vacuum system it is measuring.

As discussed briefly above, the shape of the body <NUM> and the thermal equalisation element <NUM>, including chamfered sections <NUM> and <NUM>, can be used to aid attachment of the housing. For example, the chamfered sections <NUM>, <NUM> provide a flat axial surface to aid insertion and fitment of the housing on the element <NUM> and body <NUM>. It may also provide an easy visual reference to ensure the housing is inserted over the element <NUM> and the body <NUM> in the correct orientation.

Claim 1:
A thermal conductivity vacuum gauge assembly (<NUM>) comprising:
a body (<NUM>) defining an internal chamber (<NUM>) for receiving working gas, wherein the body (<NUM>) is defined by a wall (<NUM>) having an outer facing wall surface (122a) and an opposing inner facing wall surface (122b);
a heater element (<NUM>) disposed within the chamber (<NUM>);
a thermal compensation element (<NUM>) in thermal communication with the body (<NUM>) wherein the thermal compensation element (<NUM>) is located within a cavity (<NUM>) defined in the wall (<NUM>).; and
a thermal equalisation element (<NUM>) in thermal communication with the body (<NUM>);
wherein the body (<NUM>) is made of a material with a first thermal conductivity, and the thermal equalisation element (<NUM>) is made of a material with a second thermal conductivity that is higher than the first thermal conductivity;
characterised in that the body (<NUM>) is made of stainless steel and the thermal equalisation element (<NUM>) is made of aluminium.