Temperature probe with improved response time

Abstract

A temperature probe includes a sheath, a temperature-sensitive element, and an insert. The sheath has sidewalls defining an internal space. The temperature-sensitive element is disposed within the internal space of the sidewalls and has temperature-dependent electrical properties. An insert, formed of silicon carbide, is operatively inserted between the sidewalls and the temperature-sensitive element. A method for manufacturing the temperature probe is also provided. A temperature sensing system employing the temperature probe is also provided.

Description

Technical Field

[0001] This disclosure relates to temperature probes, and more particularly to temperature probes with improved response times. Background Technology

[0002] Temperature probes are used in a variety of industries and environments to provide an indication of the temperature of a substance or surface, such as a process fluid flowing in a process fluid conduit (e.g., a pipe). Temperature probes typically include an outer sheath formed of metal, ceramic, or glass, which protects the temperature-sensitive element located within the sheath from impacts and exposure to the process fluid. Non-conductive powders such as magnesium oxide (MgO) or ceramics (e.g., alumina – Al₂O₃) are often used to fill the space between the inner surface of the sheath and the temperature-sensitive element.

[0003] Temperature probes involve a number of design considerations that must be taken into account to suit specific applications. These considerations include accuracy, thermal operating range, and response time. Fast response time is a critical consideration in many high-precision industries, such as pharmaceuticals, food and beverage production, and cargo transport monitoring. Providing temperature probes with improved response times will allow for their use in a wider range of applications, especially those requiring fast response times. Summary of the Invention

[0004] A temperature probe includes a sheath, a temperature-sensitive element, and an insert. The sheath has sidewalls defining an internal space. The temperature-sensitive element is disposed within the internal space of the sidewalls and has temperature-dependent electrical properties. An insert, formed of silicon carbide, is operatively inserted between the sidewalls and the temperature-sensitive element. A method for manufacturing the temperature probe is also provided. A temperature sensing system employing the temperature probe is also provided. Attached Figure Description

[0005] Figure 1 This is a schematic diagram of a portion of an RTD-based temperature probe based on existing technology.

[0006] Figure 2A and Figure 2B This is a schematic cross-sectional view of a portion of a temperature probe based on an RTD (Real-Time Difference) according to existing technology.

[0007] Figure 3 This is a schematic perspective view of a thermal insert for a temperature probe based on an RTD according to an embodiment of the present invention.

[0008] Figure 4 This is a schematic diagram of a heat-insertion member disposed within a stainless steel sheath according to an embodiment of the present invention.

[0009] Figure 5This is a schematic diagram of a temperature probe based on RTD according to an embodiment of the present invention.

[0010] Figure 6A and Figure 6B This is a schematic cross-sectional view of a portion of a temperature probe based on an RTD according to an embodiment of the present invention.

[0011] Figure 7 This is a flowchart of a method for manufacturing an RTD-based temperature probe according to an embodiment of the present invention.

[0012] Figure 8 This is a schematic diagram of a heat-insertion component applied to a sleeve according to an embodiment of the present invention. Detailed Implementation

[0013] Figure 1 This is a schematic diagram of a portion of a prior art RTD-based temperature probe. Probe 100 typically includes an RTD element 102 disposed within a metal sheath 104 having a metal end 106. Sidewalls 108 and the end 106 together form an end assembly of the temperature probe 100. The end assembly is welded to or otherwise coupled to the sheath sidewall 110 at a weld 112. An insulating powder, such as magnesium oxide (MgO), is disposed within the sheath 104 and typically holds the RTD element 102 in place within the sheath 104. The RTD element 102 can be formed according to any suitable RTD element forming process, such as thin-film technology or wire-wound technology. In either case, a circuit formed of a metal having a resistance that typically varies in response to temperature changes is provided. Examples of such metals include platinum, copper, and nickel. Two or more conductors 116, 118 extend through the insulating powder 114 and couple the element 102 to a suitable measuring circuit (not shown).

[0014] Figure 2A and Figure 2B This is a cross-sectional view of a temperature probe based on RTD (Real-Time Difference) technology, according to existing technology. For example... Figure 2A As shown, the rectangular RTD element 120 is located within MgO powder 114 within the sheath 104. The rectangular RTD element 120 can be formed according to thin film deposition techniques, wherein metal is sputtered or otherwise deposited on a non-conductive substrate such as silicon. Figure 2BIn this configuration, a circularly wound RTD sensor element 122 is positioned within MgO powder 114 inside a sheath 104. In each case, to detect the temperature from a surface outside the sheath 104 or the environment, thermal energy must flow through the metal sheath 104 (which can be made of stainless steel or an Inconel alloy) and through the MgO powder 114 to induce a detectable temperature change in the RTD element. It can be understood that thermal energy can flow in either direction depending on whether the temperature change is hotter or colder. In either case, the time required for heat transfer will affect the response time of the RTD. Figure 2A and Figure 2B As shown, the thermal conductivity of MgO powder is approximately 18 W / C. It can be considered that the thermal conductivity of MgO powder, plus the distance heat must travel through the powder, provides an opportunity to improve thermal response characteristics (i.e., reduce response time) by setting an insulating structure with a higher thermal conductivity than that of MgO powder.

[0015] Figure 3 This is a schematic diagram of a silicon carbide insert for a temperature probe according to an embodiment of the present invention. The silicon carbide insert 200 typically has a cylindrical shape 202, the outer diameter of which is designed to fit within a stainless steel sheath 104 (e.g., ...). Figure 1 The insert 200 includes an inner diameter within the specified inner diameter (as shown). Furthermore, the insert 200 also includes an inner bore 204, the dimensions of which are designed to receive a temperature-sensitive element (e.g., an RTD sensor element), schematically indicated by reference numerals 120 or 122. Figure 2A and Figure 2B (As shown in the diagram). Temperature-sensitive elements have electrical properties that change with temperature. In the case of an RTD, the property is resistance, while in the case of a thermocouple, the property is voltage. When using a thin-film RTD sensor element (e.g., a square thin-film element 120), the size of the hole 204 in the insert 200 is designed to circumscribe the square shape of the sensor 120. Similarly, when using a wire-wound RTD sensor element 122, the size of the hole 204 is designed such that the outer diameter of the wire-wound RTD sensor 122 will pass through the inner hole 204 of the insert 200.

[0016] Figure 4This is a schematic diagram of a silicon carbide insert 200 disposed within a stainless steel sheath 104 according to an embodiment of the present invention. In the structure of the sheath 10, the end cap portion defined by the end cap 106 is typically welded to the cylindrical sidewall 110 at weld 112. This is a potentially weak area in the sheath. According to one aspect of the invention, the insert 200 extends from the end cap 106 beyond weld 112. In this way, the rigidity of the carbide insert 200 also provides strength for the temperature probe at the location of weld 112. This provides a more robust structure, as weld 112 is sometimes a source of wear or breakage in prior art equipment.

[0017] Figure 5 This is a schematic diagram of an RTD-based temperature probe according to an embodiment of the present invention. A thin-film RTD sensor element 120 is disposed within a hole 204 of a silicon carbide insert 200. Furthermore, a certain amount of MgO powder 114 is disposed between the inner diameter 204 of the silicon carbide insert 200 and the outer surface 205 of the thin-film RTD sensor element 120. Additionally, the additional MgO powder 114 is positioned below the RTD sensor element 120 and supports the lower surface 220 of the RTD sensor element 120 above the end cap 106.

[0018] The selection of silicon carbide as the material for insert 200 was based on a careful balance of various design constraints. The material within the temperature probe must be able to withstand considerably high temperatures, must not form galvanic cells with the sheath material, and must be able to withstand significant thermal and mechanical shocks. Furthermore, such a material must be cost-effective to maintain the economic viability of the overall design. Silicon carbide meets the stringent material property requirements for applications such as temperature probes, providing a thermal conductivity of 200 W / m*K, which significantly exceeds that of materials commonly used in RTD probe structures. In comparison, MgO powder has a thermal conductivity of 60 W / m*K. At 20°C, MgO powder has a specific heat of 0.880 J / g*K and a resistivity greater than 10 Ω·cm. 14 The density of MgO powder is approximately 3.6 grams per cubic centimeter (cm³). 3 In contrast, at 20 degrees Celsius, silicon carbide has a thermal conductivity of 200 W / m*K, a specific heat of 0.67 J / g*K, and a resistivity of 10⁻⁶. 8 ohms*Cm. The density of silicon carbide is 3.2 grams / cm³. 3 .

[0019] Formulas 1-3 listed below are useful in the following analysis comparing response times.

[0020]

[0021] In Equation 1, Q represents the total thermal resistance R when the temperature difference is t2-t1. total The heat flow.

[0022]

[0023] In Formula 2, R cylinder It is the thermal resistance through the walls of a cylinder with an inner radius r1 and an outer radius r2, where L is the length of the cylinder and k is the thermal conductivity of the material.

[0024]

[0025] Formula 3 defines the total thermal conductivity C. total and total thermal resistance R total The reciprocal of.

[0026] Regarding heat flow comparison, in the prior art, heat from the environment typically flows through the thermal resistance of the sheath, then through the thermal resistance of the MgO powder, and into the RTD sensor element. In the embodiments of the present invention employing a thin-film RTD sensor element, the heat flow passes through the sheath, through the silicon carbide insert, and through a relatively small amount of MgO powder between the inner hole of the silicon carbide insert and the thin-film sensor.

[0027] In the wire-wound sensor embodiment of the present invention, the heat flow of MgO in the prior art is simply replaced by the heat flow of the silicon carbide insert.

[0028] For comparison, specific prototypes and dimensions are used to illustrate the differences in heat flux and response time. In the following embodiments, a stainless steel sheath with an outer diameter of 5.95 mm, an inner diameter of 5.35 mm, and a length of 28 mm is used. This provides a thermal resistance R through the sheath of 0.0403 C / W. sheath .

[0029] For comparison with the thin film examples, the prior art MgO powder also has an outer diameter of 5.35 mm, an inner diameter of 3.0 mm, and a length of 28 mm, with a thermal resistance of 0.0548 C / W. In contrast, a silicon carbide insert with the exact same dimensions has a thermal resistance of 0.0164 C / W, or in other words, a thermal conductivity of 60.7934. This reduces the overall thermal resistance by 70%.

[0030] Using a silicon insert with an inner diameter of 3.0 mm still requires a small amount of MgO powder to fill the space between the rectangular sensor element and the inner diameter of the silicon insert. The outer diameter of this MgO is the same as the inner diameter of the insert (3.0 mm), and the inner diameter of the MgO is 2.95 mm. This results in a thermal resistance of 0.0016 C / W for the MgO, which is added to the thermal resistance of the silicon carbide insert (0.0164 C / W) and R...sheath (0.0403), providing a total thermal resistance R of 0.0583C / W. total .like Figure 6A As shown, this represents a 38.67% reduction compared to thin-film-based RTD sensors that use only MgO powder and do not employ silicon carbide inserts.

[0031] Comparing the wire-wound embodiments, the improvement provided by the silicon carbide insert is more significant. A sheath with an outer diameter of 5.95 mm, an inner diameter of 5.35 mm, and a length of 47 mm is used. This sheath has a thermal resistance of 0.0240 C / W. MgO powder with an outer diameter of 5.35 mm, an inner diameter of 2.60 mm, and a length of 47 mm provides a thermal resistance of 0.0407 C / W. Therefore, the total thermal resistance of the prior art system is 0.0647 C / W. When using a silicon carbide insert with the same dimensions as the MgO powder, the insert's thermal resistance is 0.0122 C / W, and the total thermal resistance is 0.0362 C / W. Figure 6B As shown, this makes R total This represents a 44.05% reduction. These reductions in thermal resistance, as described in embodiments of the present invention, provide a faster response time for the entire RTD-based temperature probe.

[0032] Silicon carbide is composed of tetrahedra of carbon and silicon atoms, strongly bonded in its crystal lattice. This results in an extremely hard and robust material. Silicon carbide is resistant to corrosion from any acid, alkali, or molten salt at temperatures up to 800°C. In air, silicon carbide forms a protective silicon oxide coating at 1200°C and can be used at temperatures up to 1600°C. Its high thermal conductivity, coupled with low thermal expansion and high strength, gives this material excellent thermal shock resistance. Silicon carbide ceramics with few or no grain boundary impurities retain their strength without loss even at very high temperatures approaching 1600°C. Its chemical purity, resistance to chemical corrosion at temperature, and strength retention at high temperatures make it highly desirable for use as wafer tray supports and paddles in semiconductor furnaces. Its electrical conductivity makes it suitable for resistance heating elements in electric furnaces and for use as a key component in thermistors and varistors.

[0033] return Figure 5A silicon carbide insert 200 is typically pressed into the hot-end sheath of the temperature probe. The outer diameter of the insert 200 matches the inner diameter of the probe sheath, and the inner diameter of the silicon carbide insert is designed to be slightly larger than that of the sensor element (thin-film or wire-wound). For thin-film elements, the remaining volume is filled with MgO powder to hold the sensing element at the center of the assembly. In some embodiments, a solid blank can be selected, allowing for customization of the pocket relative to the geometry of each individual element. This customization can be implemented later in the manufacturing process. This allows for the collection of waste MgO powder and its reuse to fill the cavity. Furthermore, if a solid insert is used, it can be used in conjunction with a check valve or blind hole to improve the consistency and repeatability of element placement. Setting MgO (standard magnesium oxide powder) in the remaining voids after the RTD element is installed provides thermal continuity and a rigid internal structure. MgO will also compensate for any geometric changes in the sensing element.

[0034] Figure 7 This is a flowchart of a method for manufacturing an RTD-based temperature probe according to an embodiment of the present invention. Method 300 begins at block 302, in which the end of a sheath is provided. Figure 1 As shown, the end has an end cap 106. Next, at frame 304, the silicon carbide insert is pressed into or otherwise positioned within the sheath. In one embodiment, the length of the silicon carbide insert is selected to extend from the end cap of the sheath to a position beyond any end cap / sidewall weld in the sheath. Next, at frame 306, the RTD element or blank is disposed within the silicon carbide insert. Figure 7 As shown, the RTD element can be a thin-film element 308 or a wire-wound element 310, or a suitable solid blank whose shape and size are designed to resemble one of elements 308 / 310. In an embodiment employing the thin-film sensor 310, MgO powder is disposed at frame 312 to fill the area between the inner diameter of the silicon carbide insert and the outer surface of the thin-film RTD sensor element.

[0035] While embodiments of the present invention are particularly suitable for providing silicon carbide inserts within conventional stainless steel sheaths, it is also clearly anticipated that the wall thickness of stainless steel or other suitable metals can be reduced, thereby further reducing the response time of the temperature probe, given the strength of the silicon carbide inserts.

[0036] While embodiments of the invention have been described with respect to temperature probes, these embodiments can also be used to improve the thermal conductivity and response time of the sleeve. This can be achieved by replacing a portion of the sleeve's material with a silicon carbide insert at the bottom of the sleeve and implementing the idea of ​​inserting the probe's outer diameter.

[0037] Figure 8This is a schematic diagram of a heat-insertion device applied to a sleeve according to an embodiment of the present invention. The sleeve system 400 includes a sleeve 402 having a distal portion 404 extending into a process fluid conduit or other suitable structure for temperature measurement. The distal portion is typically cylindrical and has a temperature probe assembly 408 capable of receiving a temperature probe (e.g., a heat-insertion probe). Figure 1 The interior of the prior art probe assembly shown herein, or the silicon carbide-based arrangement described herein. According to another aspect of the invention, the distal portion 404 of the sleeve 402 may further include a silicon carbide insert 406 to further reduce the response time of the sleeve system 400.

[0038] Furthermore, the embodiments described herein can also be implemented for sanitary sensors, which have a similar insert sensor placement at the tip of the sensor. Additionally, improvements over conventional sensors can be provided at minimal cost, and these improvements can be used with a wide range of sensor configurations and components.

[0039] Although the invention has been described with reference to preferred embodiments, those skilled in the art will recognize that modifications in form and detail may be made without departing from the spirit and scope of the invention. For example, while embodiments have generally been described with respect to RTDs, the embodiments described herein are applicable to any type of temperature-sensitive element, including but not limited to thermocouples, thermistors, and semiconductor-based integrated circuits.

Claims

1. A temperature measurement system, comprising: A sleeve having a distal end and a cylindrical sidewall extending from said distal end; RTD temperature probe, having a metal sheath disposed within the sleeve; A silicon carbide insert is positioned within the sleeve and arranged around the temperature probe; as well as The RTD temperature probe includes: The metal sheath has sidewalls that define the internal space; An RTD element, disposed within the internal space of the sidewall, the RTD element having a resistance that varies with temperature; and An insert, operably inserted between the sidewall and the RTD element, is formed of silicon carbide.

2. The temperature measurement system according to claim 1, wherein, The RTD element is a thin-film RTD element.

3. The temperature measurement system according to claim 2 further includes insulating powder disposed in the space between the rectangular surface of the thin-film RTD element and the inner diameter of the silicon carbide insert.

4. The temperature measurement system according to claim 1, wherein, The RTD element is a wire-wound RTD element.

5. The temperature measurement system according to claim 1, wherein, The temperature probe is a thermocouple probe.

6. The temperature measurement system according to claim 1, wherein, The end cap of the temperature probe is configured to contact the distal end of the sleeve.

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