Heat conduction vacuum gauge

Abstract

This invention provides a thermal conduction pressure gauge and a method for measuring thermal conduction pressure that improve the accuracy, reproducibility, and repeatability of pressure measurements while minimizing the influence of ambient temperature changes on pressure readings. [Solution] Process-critical thermal conduction vacuum gauge (PCTCG) instruments provide improved accuracy and heat resistance through reduced and linearized temperature coefficients based on gauge chamber wall ambient temperature supercontrol (AATC). The sensor resistance is exposed to the gas pressure within the gauge chamber. AATC is provided by controlling a heater that heats the chamber wall to control the temperature difference between the sensor resistance and the chamber wall. An exemplary application of this technology is for endpoint detection in freeze-drying, where a thermal conduction pressure gauge is used to track the partial pressure of water in a two-energy mixture.

Description

[Technical Field]

[0001] Related applications This application claims the advantages of U.S. Provisional Patent Application No. 63 / 114,287, filed on November 16, 2020. All teachings of the above application are incorporated herein by reference. [Background technology]

[0002] A thermal conductivity gauge (TCG) measures pressure based on the relationship between the temperature of a heated sensor resistor and the amount of heating power applied to the sensor resistor. For example, a thin wire (sensor resistor) is heated to a constant temperature (T s The amount of heating power required to maintain the wire at a certain temperature may be monitored. As the gas pressure increases, the thermal conductivity of the gas increases, and the gas removes more heat from the heated wire, increasing the heating power required to maintain the wire at a constant temperature. Calibration curves that relate heating power to pressure enable pressure measurement. Calibration is typically performed in factories against pure nitrogen gas. This is an indirect pressure measurement where heating power is proportional to the gas pressure.

[0003] This principle is used in the well-known Pirani gauge, where heat loss is measured in a Wheatstone bridge network that serves both to heat the sensing element and to measure its resistance. In the Pirani gauge, the temperature-sensing resistor is connected as one arm of the Wheatstone bridge. The temperature-sensing resistor is mounted in a chamber exposed to a vacuum environment where pressure is measured.

[0004] Conventional Pirani gauges are calibrated to several known pressures to determine the relationship between gas pressure and power loss to the gas or bridge voltage. In this case, assuming end losses and radiation losses remain constant, the unknown pressure of the gas may be directly determined by the power lost to the gas or associated with the bridge voltage in the bridge balance. Pirani gauges using Wheatstone bridges and alternative TCG circuits are described in U.S. Patent Application Publication 2007 / 0186658 and U.S. Patent Application Publication 2019 / 0316981A1.

[0005] A common problem addressed by many TCGs is that the actual heating power is affected by the temperature T of the sensor wire. s Rather, the chamber wall (T w The calibration depends on the temperature difference between the chamber wall and the sensor wire; in other words, the calibration curve depends on the wall temperature, which is also dependent on the ambient temperature. w As the pressure rises, the amount of power required to heat the filament decreases, and unless ambient temperature compensation is performed, this is interpreted as a pressure drop. Ambient temperature severely affects accuracy. Standard TCG designs require complex algorithms / calibration procedures that measure the wall temperature and also compensate for ambient temperature changes, keeping the sensor wire at a constant temperature, or require an additional, expensive compensation wire scheme built into the gauge that adjusts the temperature of the sensor wire to maintain a constant temperature difference between the sensor wire and the wall. TCGs tend to self-heat as the pressure rises, and T w Since it changes the temperature, such a scheme is necessary even if the room temperature is stable.

[0006] TCGs are seeing increasing use in process-critical applications where data provided by TCGs is needed to make critical decisions, and gauge users are beginning to demand performance improvements that cannot be met by current commercial products, including improvements in accuracy, repeatability, and temperature stability. Process-critical thermal conduction vacuum gauges (PCTCGs) need to meet the requirements of, for example, modern freeze-drying processes.

[0007] One of the biggest factors affecting the accuracy of the TCG is the temperature coefficient of the pressure reading. Most products specify the accuracy and temperature range in which they operate. However, products are not able to meet the accuracy requirements over the entire operating temperature range. It has become standard to refer to accuracy specifications for operation in a single or narrow temperature range. Some of the more modern products have made better progress towards proper compensation of the pressure reading for ambient temperature changes by performing specific temperature compensation calibrations of the gauges in the factory. The compensation calibration measurements rely on temperature chambers that are time-consuming, prone to failure, and tend to have high maintenance costs, and even such measures only specify accuracy at a single temperature and have no prospect of addressing the entire temperature range. Even when there are no large temperature changes in the room temperature, the TCG is also affected by self-heating depending on the pressure, so temperature compensation is still necessary even under a stable room temperature.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] In the vacuum industry, there is a need to improve the accuracy, reproducibility, and repeatability of pressure measurements while minimizing the influence of ambient temperature changes on pressure readings for the TCG.

Means for Solving the Problems

[0010] The proposed solution is based on the precise temperature control of the chamber wall of the sensor above the ambient temperature. When the sensor wire and the wall temperature are properly stabilized, the influence of the room temperature on the pressure reading decreases. Optimization of the sensor and wall temperature with respect to the process conditions can also be achieved.

[0011] A thermal conductivity pressure gauge includes a sensor resistance and a sensor chamber having a chamber wall spaced apart from the sensor resistance. A heater heats the chamber wall. The electronics applies power to the sensor resistance and determines the pressure of the gas in the sensor chamber based on the relationship between the resistance of the sensor resistance and the applied power. The electronics also applies power to the heater to heat the chamber wall and control the temperature difference between the sensor resistance and the chamber wall.

[0012] In a method of measuring thermal conductivity pressure, a sensor resistance is provided in a chamber having a chamber wall spaced apart from the sensor resistance. The chamber wall is heated to control the temperature difference between the sensor resistance and the chamber wall. Power is applied to the sensor resistance and the pressure of the gas in the chamber is determined based on the relationship between the resistance of the sensor resistance and the applied power.

[0013] The power applied to the sensor resistance may maintain a constant temperature T S and the power applied to the heater may maintain a constant chamber wall temperature T w . The temperature T S may be greater than T W . The power applied to the sensor resistance to maintain a constant temperature may determine the pressure in the chamber. Alternatively, the power applied to the sensor resistance may be kept constant and the detected temperature determines the pressure.

[0014] The temperature T S may be controllable to different constant temperatures. Similarly, the wall temperature T w may be controllable to different constant temperatures. <00。00107> The heater may be located within the insulation surrounding the chamber walls. The heater may also be a ribbon heater bonded to the inner surface of the insulation surrounding the chamber.

[0016] The heater may be connected to electronic equipment that supplies power to the heater, and the chamber wall and sensor resistor may be inserted into the heater for inserting sensor leads into the electronic equipment, thereby electrically connecting the sensor resistor and the electronic equipment.

[0017] The chamber wall temperature may be in the range of 45°C to 110°C. The sensor resistance temperature may be greater than the chamber wall temperature by an amount in the range of 30°C to 110°C (in a Pirani-type sensor, the sensor wire is always hotter than the wall, and the upper limit of 110°C for the wall is selected to be above the boiling point of water).

[0018] The sensor resistance may be a thin sensor wire, as in the case of a conventional Pirani gauge. Alternatively, the sensor resistance may be on the surface of the cavity, and the chamber wall may be the wall on the opposite side of the cavity.

[0019] The electronic equipment may be configured to heat the heater to a temperature that cleans the heater wall. Having available heating power allows for control of the chamber temperature to absorb ambient changes, dry the inside of the gauge after exposure to droplets, prevent the accumulation and adhesion of dirt inside the sensor, and degas contaminants through burning.

[0020] The baffle may be provided into the process chamber across an opening in the chamber wall.

[0021] The foregoing will be evident from the following more specific description of the exemplary embodiments shown in the attached drawings. Throughout the different drawings, similar reference letters refer to the same part. The drawings are not necessarily to scale, but rather focus on illustrating the embodiments. [Brief explanation of the drawing]

[0022] [Figure 1] This is an explanatory diagram of a prior art heat conduction vacuum meter. [Figure 2] This is a cross-sectional view of a deformation of the gauge in Figure 1, according to the principle of the present invention. [Figure 3] This is a cross-sectional view of an alternative embodiment of the present invention, associated with a control device for providing total pressure and partial pressure measurement. [Figure 3A] Figure 3 is a top view of the sensor. [Figure 4] This is an explanatory diagram of the assembly shown in Figure 3 in the freeze-drying system. [Figure 5] This is an exploded perspective view of a MEMS thermal conduction sensor that embodies the present invention. [Figure 6] Figure 3 is a cross-sectional view of the gauge deformation. [Modes for carrying out the invention]

[0023] Exemplary embodiments are described below.

[0024] All patents, published applications, and references cited herein are incorporated in their entirety by reference.

[0025] Figure 1 shows a TCG 12 having a sensor wire 10 in a sensor chamber 13 connected by a pipe 18 to a process chamber where its pressure is measured. The wire 10 is heated by power E from a power source 16. The heat output radiated from the wire into the gas is proportional to the gas pressure and such (indirect measurement), such that E ∝ Pgas. The heating power required to maintain the wire at a constant temperature increases proportionally to the gas pressure. However, its fixed temperature T s The heating power E required to maintain the sensor wire 10 of TCG 12 is the sensor wire (T s ) and the temperature of the sensor chamber wall 14 (T w It is also related to the temperature difference with ): E∝(T s -T w ). This is T w When it becomes larger, the heating power requirement E decreases, T wUnless the change is explained as being due to temperature compensation calibration and algorithms, the decrease could be mistaken for a pressure drop. Since it is determined, T is not adequately explained by the temperature compensation algorithm. w Changes in this can cause errors in pressure measurements and impair the accuracy of the device. Self-heating is typically performed under high pressure. w Because this affects the pressure readings, it could also affect the accuracy of the pressure readings.

[0026] Wall temperature T w Above Ambient Temperature Correction (AATC) improves the accuracy of the pressure sensor. The outer chamber wall of the gauge may be stabilized within a very narrow temperature range above the ambient temperature, preferably with a variation not exceeding 0.1°C. The chamber wall temperature is maintained above room temperature, for example, using a heating jacket, providing a constant temperature difference between the sensor wire and the chamber wall, regardless of pressure and ambient temperature. Strict temperature control of the temperature difference between the chamber wall and the wire results in a very small temperature coefficient for pressure readings, closer to linear behavior, and additional compensation wires may no longer be necessary to achieve high-precision pressure readings.

[0027] An embodiment of chamber wall ambient temperature supercontrol (AATC) allows the TCG to do the following:

[0028] 1. Provides more accurate pressure readings that are independent of room temperature. The instrument can meet accuracy specifications over a wider temperature range.

[0029] 2. Provides more accurate pressure readings unaffected by self-heating.

[0030] 3. By instantaneously raising the temperature of the wall, it provides the ability to dry the gauge after exposure to wet chemical reactions.

[0031] 4. Reduce the accumulation of precursor chemicals on the gauge chamber during the process.

[0032] 5. By instantaneously raising the chamber temperature, it provides the ability to decontaminate the gauge after exposure to sticky precursors.

[0033] 6. Provides the ability to burn out gauges for UHV compliance.

[0034] 7. Improved zero-point fluctuation performance for pressure measurements at the bottom of the operating pressure range, reducing the need to perform routine re-zeroing of pressure reading output.

[0035] One embodiment of a heating system for controlling the chamber temperature is shown in Figure 2. The heating element 22 is attached around the chamber wall 14. The heating element 22 may be a resistance heater filament in a tape, which may contain an adhesive for bonding the tape to the chamber or the surrounding insulator 24. Power to the heater 22 is provided by a power supply 26.

[0036] A preferred embodiment is a wall temperature T that is higher than the ambient temperature. w The goal is to maintain this. If the operating ambient temperature range is expected to be 0°C to 40°C, T w The preferred temperature range is 45°C to 110°C. A controlled chamber temperature of 45°C must remain above the ambient temperature and enable highly accurate pressure measurements across the entire temperature range. Temperatures above 110°C are not recommended for the wall, as this would require the sensor wire to become too hot, leading to increased degradation due to contamination (i.e., through the thermal decomposition of precursor chemicals). Most modern TCG gauges operate with their sensor wires at a fixed temperature of 30°C to 110°C above the ambient temperature. A preferred embodiment uses a fixed sensor wire temperature of 30°C to 110°C above the wall temperature. The precise temperatures of the sensor and the wall may be adjusted to provide optimal sensitivity at controlled process pressures.

[0037] A wall temperature of 100°C to 110°C may be required, for example, to provide rapid drying of the sensor's inner surface after a freeze-drying process that results in water droplets reaching inside the sensor. The highest wall temperatures can also be used to burn and clean the inner wall surface during process execution.

[0038] The sensor wire and chamber wall temperatures are customer-accessible variables that can be modified throughout the process to adapt to changes in gas and process conditions, thereby decontaminating and drying the gauge. The user can switch operating conditions via commands or digital input. LEDs may indicate oven status, such as standard, degassed, or dried.

[0039] One new application of TCG is the detection of the endpoint of freeze-drying. In this case, the total pressure, as measured by a capacitance diaphragm gauge, is fixed somewhere between 0.1 and 1 Torr. Throughout the drying process, the gaseous composition of the two-energy mixture changes, but the pressure is kept constant through the introduction of nitrogen purging by a gas mass flow controller connected to the capacitance diaphragm gauge. The TCG gauge used under this application does not need to provide operation over the entire pressure range, but rather must be optimized to provide the best possible resolution in pressure measurements at and per controlled process pressures. The freeze-drying comparative pressure measurement (CPM) method uses the difference between the pressure measurement provided by the TCG and the pressure measurement of the capacitance manometer to provide the partial pressure of water: for a mixture of pure nitrogen and water, PPH2O = [(P Pirani) - (P cdg)] / 0.4. See U.S. Patent Application Publication 2018 / 0306763 and U.S. Patent Application Publication 2019 / 0346328. The wire and wall temperature conditions may be optimized to provide the highest resolution for this partial pressure measurement.

[0040] Process-critical TCGs must include the flexibility to adjust both chamber wall and sensor wire temperatures to adapt to different applications or stages of a single process. For example, the wall temperature may be increased to dry the TCG if water droplets approach the sensor, to eliminate the accumulation of certain precursors, or to clean the gauge between processes (burn off contaminants). The sensor temperature may also be fine-tuned based on process pressure conditions. For example, for freeze-drying at a constant pressure, the gas pressure may be fixed somewhere between 0.1 and 1 Torr, and the sensor wire temperature may be optimized to provide optimal sensitivity and resolution at those pressures.

[0041] Another embodiment of the TCG, packaged with controller electronics particularly suited for freeze-drying applications, is shown in Figure 3. In the TCG system 302, the controller electronics 312 are mounted within a module housing 309. The housing also supports a TCG sensor, which includes a sensing wire 314 within a chamber wall 316. The sensor is removable from the assembly for repair or replacement. A heater oven 304 for heating the sensor's chamber (envelope) wall 316 is fixed within the housing 309 and positioned to receive the gauge wall 316. The oven 304 comprises an insulator 306 and a heating tape 308 fixed to the inner surface of the insulator 306. The heating tape is connected to the controller electronics by leads 310, which maintain power to the heating tape to maintain a desired chamber wall temperature. The insulation protects the electronics from the high temperatures the oven can reach. The heater may be part of the electronics module, or the heater may be part of a removable gauge. Placing the heater on the controller simplifies the sensor design and reduces replacement costs. Placing the heater on the sensor may also provide more accurate temperature control.

[0042] A lead 318 to the sensor wire 314 is joined to the base of the chamber wall 316 through an electrical insulator 319. The lead 318 is connected to controller electronics for applying power to maintain the temperature of the sensing wire and to detect the pressure inside the chamber. The sensor assembly of the sensor wire 314 and wall 316 may be removed from the heater oven 304 by sliding the chamber axially, upward as viewed in Figure 3, and disconnecting the lead 318 from the controller electronics. This configuration of the heating oven with the controller module and connectable sensor assembly as a single unit allows for reduced sensor replacement costs, as it does not involve costly heater replacement. The chamber may be connected by a flange 320 to a process chamber, such as a freeze-drying process chamber.

[0043] When temperature compensation is an integral part of an electronics module, the electronics themselves may also be heated for additional temperature compensation. If the wall temperature is controlled between 45 and 70°C, it makes sense to include the temperature-sensitive components of the electronics in the same oven to obtain temperature control for both the sensors (which provide the signals) and the electronics (which receive and process the signals). This is unlikely if there is an intention to heat above 70°C, as special high-temperature electronics may be required. If electronics are included in the oven, it is not necessary to include all the electronics in the module. Analog processing components would likely be the best candidates for temperature control.

[0044] The baffle 322 may be suspended by a support column 324 (Figure 3A) across the end opening of the envelope 316 to block contaminants and radiation. The contaminants may be gases, sputtered material in the line of sight, and even droplets. The baffle is thermally connected to the heated temperature wall 316 to eliminate condensation and provide axial thermal boundary conditions. In normal operation, the assembly is inverted relative to the orientation shown in Figure 3 such that the baffle 322 faces downward into the process chamber. It has a conical shape to drain liquid from inside the chamber and from the sensor wire.

[0045] The gauge assembly 302 is configured to receive a gas-independent pressure input from a capacitance diaphragm gauge. To this end, the system receives an analog input from the capacitance diaphragm gauge at input 330 and passes its pressure reading to analog output 332. The controller electronics 312 also determines the total pressure, which is gas-dependent and read from the TCG. As described above, the controller electronics combine the gas-independent total pressure read from the capacitance diaphragm gauge and the gas-dependent total pressure read from the TCG to calculate the partial pressure of water, and provides an analog output of that partial pressure at 336.

[0046] A series of digital inputs or digital commands 338 are preset for different process steps (T w , T s It allows switching between sets of ) for, for example, one for measurement and the other for drying. w This is the AATC wall temperature, which may be variable between 45 and 110°C. The lower limit is higher than the maximum operating temperature of 40°C, and the upper limit is above the boiling point of water. s This is the sensor wire temperature. s -T w It will probably be between 30 and 110 degrees Celsius. Multiple (T w , T s There may be calibration information that matches the combination of the sets.

[0047] Dial 340 is adjusted to inform the instrument of the full range of the CDG. Digital command 338 can also be used.

[0048] Digital In Calibrate 342 allows the TCG to read nearly the entire range of the CDG, similar to the CDG, when pure nitrogen is present as a gas. This ensures that both the CDG and TCG are properly calibrated and pure N2 is present in the system. It is used to ensure that the divided voltage reading is zero when present.

[0049] The Digital In Zero 344 zeros the Pirani and CDG readings when a high vacuum pressure level is achieved. While there may be two separate inputs, one per sensor, this example provides a combined input. Once the pressure reaches a high vacuum level, both the CDG and TCG can be zeroed again.

[0050] Digital Input (T s , T w )338 is for operation (T s , T w Select a set of (T). This may change during the process. Digital commands are also available. The calibration table for heating power versus gas pressure readings is for multiple (T w , T s It must be usable by the group.

[0051] LEDs may be used to indicate the oven status, such as standard, degassed, or dry.

[0052] Figure 4 shows the introduction of assembly 302 of Figure 3 into the freeze-drying process system. Gauge assembly 302 is inverted and coupled to the freeze-drying chamber 402. Capacitance diaphragm gauges, for example, 404, are typically already included in such systems. A process controller 406 is also included. Assembly 302 is coupled to its controller through the inputs and outputs described above to provide the total pressure to be read from the CDG and to acquire and provide the partial pressure readings described above.

[0053] While the provided explanation focuses on conventional TCG designs including sensor wires, the ambient temperature control described above is also applicable to MEMS-scale devices. MEMS sensors are sensitive to temperature changes, partly and often due to residual stress accumulated within the device. Sometimes, even minimal temperature changes can cause abrupt changes in performance due to mechanical stress mechanisms. Temperature stabilization of small sensors is highly practical and can significantly improve performance.

[0054] The MEMS sensor shown in Figure 5 comprises a silicon chip 502 having a heated sensor resistance element 504 suspended in a cavity (gauge chamber) of a silicon cover 510. A silicon cover 506 on the chip forms the surface opposite the cavity. A heater 508 is formed on the upper or lower surface of the silicon cover 506 that forms the cavity (chamber) wall. Alternatively, the entire die may be heated using thermal conductivity to heat the cover. A temperature measuring resistor 512 is mounted on the silicon cover 510. Due to the geometric shape of the sensor, convection cannot occur within the cavity, and consequently, the sensor is not affected by its mounting position. Gas molecules are delivered by diffusion only to the heated element where the heat loss of the gas is measured. The sensor element is extremely robust and can withstand high G forces and instantaneous air inflow.

[0055] Figure 6 shows a variation of the thermal conduction vacuum gauge. In this embodiment, the heater is a winding 602 in an insulator 604 surrounding the chamber wall 316. Controller electronics 606, which may include a microprocessor, controls the heating of the sensing wire 314 to a constant temperature via a sensor circuit 608. The sensor circuit 608 may include a conventional Wheatstone bridge, for example, as shown in the prior art of published PCT application International Publication 2019 / 203929A1 and U.S. Patent No. 10,845,263. However, the sensor circuit 608 may be one of the novel circuits shown in those applications and patents. These novel circuits enable temperature compensation when the target wire temperature is reached and the wall temperature changes.

[0056] The heater circuit 610 controls the heating of the chamber wall 316. The closed-loop circuit 610 heats the wall to a preset fixed temperature under the control of the electronic equipment 606. A temperature sensor 612, such as a thermistor, monitors the temperature of the chamber wall 316. The heater circuit 610 senses this temperature through a lead 614 and compares the detected temperature to a temperature setpoint provided by the electronic equipment 606. The circuit 610 controls the power input to the heating coil 602 through the lead 616 to maintain the temperature of the chamber wall 316 at the set temperature. The temperature detected by the sensor 612 may also be supplied to the electronic equipment 606 for use in the electronic equipment for temperature compensation to obtain more accurate pressure readings.

[0057] The advantages of TCG chamber wall temperature control include the following:

[0058] a. Improved accuracy. Ambient temperature-stabilized heat dissipation at any pressure, resulting in accurate room temperature-dependent pressure measurements.

[0059] b. Significant reduction in the temperature coefficient. Modern TCGs cannot maintain their specified accuracy over a wide pressure range. Temperature control of the chamber wall temperature is a solution.

[0060] c. Improved repeatability. A stable AATC ensures improved repeatability of pressure measurements.

[0061] d. Self-heating resistance. Insensitivity to changes in power dissipation when the system pressure changes. TCGs self-heat at high pressure due to the higher heating power transmitted to the walls. Thermally stabilized walls of the chamber eliminate self-heating at high pressure and eliminate the need for compensating wires and trim resistors.

[0062] e. No need for internal compensation wires or resistance trimming. Simpler design, reduced internal surface area, and lower cost construction.

[0063] f. Complex temperature compensation algorithms including nonlinear influence coefficients are not required. Algorithmic temperature compensation may still be applied in the presence of AATC, and if applied, the temperature dependence is close to linear behavior. Current temperature compensation algorithms rely on simplified linear temperature coefficients. Unfortunately, ignoring higher-order temperature coefficients is the reason why accuracy is not good over the wide temperature range of commercially available products. The AATC of the chamber must provide accuracy that matches the published specifications over the entire temperature range.

[0064] g. For example, use of an external heater for chamber wall temperature control to dry the TCG exposed to liquid mist between SIP and CIP for freeze-drying. Incomplete drying between processes is a problem, especially in wet processes. Adding a hydrophobic coating inside the gauge can also help minimize the amount of water droplets adhering to the walls.

[0065] h. Use of an external heater for wall temperature control to generate temperature correction coefficients. Use of an existing heater to simulate changes in ambient temperature. No complex temperature boxes, which are cumbersome and prone to failure, are required.

[0066] i. Use high wall temperatures to reduce the deposition of precursor molecules on the chamber walls. This extends sensor life and reduces the operator's sensor replacement costs and tool downtime.

[0067] j. Use of high-temperature chambering to clean the gauge of moisture and contaminants during process execution. Degassing / burning of the sensor wall is possible.

[0068] k. This involves heating the chamber to eliminate degassing at high vacuum pressures and to burn out the chamber, making the sensor suitable for UHV applications without worrying about excessive degassing.

[0069] l. Improved zero-point fluctuation. The zero-point fluctuation of the TCG (at the lowest end of the pressure range or in high vacuum) is greatly affected by wall temperature. Radiation loss outweighs heat loss from the sensor wire in high vacuum, and radiation heat loss is (T s 4 -T w 4 (T s -T w This is compared to the gas loss proportional to the temperature. This improvement in zero-point fluctuation should contribute to improved accuracy and temperature range of the TCG. The AATC of the wall temperature should improve accuracy at the lower end of the sensor and, in some cases, expand the range of pressures over which it may be used.

[0070] m. The ability to change temperature conditions during process step switching.

[0071] n. For optimal total and partial resolution in a constant pressure process, the temperature difference T s -T w The ability to control.

[0072] From the perspective of developing endpoint detectors for freeze-drying, the AATC approach offers many opportunities to improve the performance of both sensors and electronics, providing several advantages for commercially available products.

[0073] Improvements to TCG sensors for freeze-drying: - Ambient temperature ultracontrol - Improved accuracy, repeatability, and stability (i.e., reduced variability) - Active heating for drying after CIP and SIP, and between processes. - Reduced contamination due to buildup. - Heaters integrated into electronic devices to reduce sensor replacement costs.

[0074] • Improved drainage of liquids - Improved wastewater treatment of water and hydrogen peroxide through mechanical design - Proposed use of hydrophobic coatings (such as perfluoro coatings) on the internal surface. - Improved baffles protect the sensor wires from droplets.

[0075] • Optimized sensitivity at process pressure - Sensitivity optimized for typical process pressures, based on (1) sensor wire design (material and size), (2) wall and sensor wire temperature, and (3) chamber design (material and size). - It is not necessary to cover a wide pressure range outside of the use cases.

[0076] • Improved resolution - Greater sensitivity at typical process pressures can provide higher electronic resolution for pressure measurement.

[0077] Improvements to TCG electronics for freeze-drying: CDG connectivity: - CDG-Analog Input: The TCG accesses the CDG output via the analog input. - CDG Range Dial: The user can adjust the pressure range of the CDG (0.1, 1, 10, and 1 The value (00 Torr) can be set using the dial. - CDG-Analog Output: Pass-through mode for CDG readings.

[0078] • Calibration for CDG. - Calibration - Digital input: Signal calibration of TCG to CDG readings in the presence of a purer N2. - Zero-digital input: Signal zeroing of CDG and TCG readings in the presence of a high vacuum.

[0079] • Heater with ultra-precise ambient temperature control. - The heater enables temperature control of the chamber. The heater is essential to the controller. The temperature range is 45-110°C. - The heater temperature is programmable and can be changed throughout the process. - The heater can be used to dry the TCG sensor after CIP and SIP. - Temperature - Digital Input: Select different chambers and sensor wire temperature sets. LEDs indicate heater status (i.e., standard, dry, etc.).

[0080] • Adjustable sensor wire temperature. - Select different sensor wire temperatures depending on the process conditions.

[0081] • TCG total pressure output. - TCG Analog Output: Both linear and logarithmic analog outputs supported by the controller. Linear output of 0-10V that conforms to the CDG output range, preferred by system integrators.

[0082] • Partial pressure water output: - PPH2O-Analog Output: The controller provides an analog signal that reflects the amount of water measured via comparative pressure measurement (CPM). This supports endpoint detection (EPD). - EPD - Digital Output, Relay, and LED: The user can specify EPD thresholds for primary and secondary drying. When the thresholds cross, the system integrator can use a digital output, relay activation, or LED to detect the EPD. This separates the levels at which primary and secondary drying are available.

[0083] While exemplary embodiments have been illustrated and described in detail, it will be understood by those skilled in the art that various modifications may be made to the form and details without departing from the scope of the embodiments included in the appended claims.

Claims

1. Sensor resistance and A sensor chamber having a chamber wall spaced apart from the sensor resistor, A heater configured to heat the chamber wall, An electronic device configured to apply power to the sensor resistor to determine the pressure of the gas in the sensor chamber based on the relationship between the resistance of the sensor resistor and the applied power, and to apply power to the heater to heat the chamber wall and control the temperature difference between the sensor resistor and the chamber wall. Equipped with, Thermal conduction pressure gauge.

2. To provide the sensor resistor in a chamber having a chamber wall spaced apart from the sensor resistor, To control the temperature difference between the sensor resistance and the chamber wall, the chamber wall is heated, By applying power to the sensor resistor, the pressure of the gas in the chamber is determined based on the relationship between the resistance of the sensor resistor and the applied power. including, Method for measuring thermal conduction pressure.

3. Power at a constant temperature T ｓ To maintain the sensor resistance, power is applied to a constant chamber wall temperature T ｗ A pressure gauge according to claim 1, or the method according to claim 2, which is applied to the heater in order to maintain the temperature.

4. T ｓ However, T ｗ A larger pressure gauge according to claim 1 or 3, or the method according to claim 2 or 3.

5. The temperature T ｓ A pressure gauge according to claim 1, 3, or 4, or the method according to claim 2, 3, or 4, which is controllable to different constant temperatures.

6. The wall temperature T ｗ A pressure gauge according to any one of claims 1 and 3 to 5, or the method according to any one of claims 2 to 5, which is controllable to different constant temperatures.

7. The pressure gauge according to any one of claims 1 and 3 to 6, or the method according to any one of claims 2 to 6, wherein the heater is positioned within the insulating material surrounding the chamber wall.

8. The pressure gauge according to any one of claims 1 and 3 to 7, or the method according to any one of claims 2 to 7, wherein the heater is a ribbon heater bonded to the inner surface of the insulating material surrounding the chamber.

9. A pressure gauge according to any one of claims 1 and 3 to 8, or the method according to any one of claims 2 to 8, wherein the heater is connected to an electronic device that supplies power to the heater, and when a sensor lead is inserted into the electronic device to electrically connect the sensor resistor to the electronic device, the chamber wall and the sensor resistor are inserted into the heater.

10. A pressure gauge according to any one of claims 1 and 3 to 9, wherein the chamber wall temperature is in the range of 45°C to 110°C, or the method according to any one of claims 2 to 9.

11. The chamber wall temperature is greater than the sensor resistance temperature by an amount within the range of 30°C to 110°C. A pressure gauge according to any one of claims 1 and 3 to 10, or the method according to any one of claims 2 to 10.

12. The pressure gauge according to any one of claims 1 and 3 to 11, wherein the sensor resistance is a sensor wire, or the method according to any one of claims 2 to 11.

13. A pressure gauge according to any one of claims 1 and 3 to 12, wherein the sensor resistance is the resistance on the surface of a chip in a cavity, and the chamber wall forms the wall opposite to the cavity, or the method according to any one of claims 2 to 12.

14. A pressure gauge according to any one of claims 1 and 3 to 13, or the method according to any one of claims 2 to 13, wherein the electronic device is configured to heat the heater to a temperature that cleans the heater wall.

15. A pressure gauge according to any one of claims 1 and 3 to 14, or the method according to any one of claims 2 to 14, wherein the electronic device is configured to heat the heater to a temperature that dries the heater wall.

16. A pressure gauge according to any one of claims 1 and 3 to 15, further comprising a baffle extending to a process chamber across an opening in the chamber wall, or the method according to any one of claims 2 to 15.

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