Pressure sensor with improved drift compensation

Abstract

To provide a pressure sensor.SOLUTION: An exemplary pressure sensor disclosed herein includes a first body defining a reference pressure cavity; a second body defining a measurement pressure cavity and having an inlet configured to receive a fluid; a diaphragm disposed between the reference pressure cavity and the measurement pressure cavity; an electrode separated from the diaphragm by a gap and configured to form a capacitance between the electrode and the diaphragm; a measurement circuit configured to determine a pressure in the measurement pressure cavity based on the capacitance; and a contamination shield configured to reduce contamination on a first surface of the diaphragm. The contamination shield includes a first portion configured to block a direct path between the inlet and the diaphragm, and a second portion configured to occupy a volume within the measurement pressure cavity.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] [Related Applications] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 618,635, filed on January 8, 2024, entitled "PRESSURE SENSORS HAVING IMPROVED DRIFT COMPENSATION". The entire disclosure of U.S. Provisional Patent Application No. 63 / 618,635 is hereby incorporated by reference in its entirety to form a part of this application.

[0002] The present disclosure generally relates to pressure sensors, and more specifically to pressure transducers with improved drift compensation.

Background Art

[0003] A pressure sensor or pressure transducer measures the pressure of a fluid input to the sensor that is compared to a reference pressure. A pressure sensor can be constructed to compare the input pressure to a fixed reference pressure or a variable reference pressure.

Summary of the Invention

[0004] A pressure sensor with improved drift compensation is disclosed, substantially as shown by at least one of the drawings and described in connection therewith, as more fully set forth in the claims.

[0005] These features, aspects, and advantages of the present disclosure, as well as other features, aspects, and advantages, will be better understood when the following detailed description is read in conjunction with the accompanying drawings, in which like reference numerals represent like parts throughout.

Brief Description of the Drawings

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Figure 1A

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Figure 1B

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Figure 2

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Figure 3

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Figure 4

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Figure 5A

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Figure 5B

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Figure 6

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Figure 7

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Figure 8A

Figure 8B

[0016] The drawings are not necessarily to scale. Like or the same reference numerals are used to indicate like or the same components, where appropriate.

DETAILED DESCRIPTION OF THE INVENTION

[0017] For the purpose of promoting an understanding of the principles of the claimed technology and presenting its presently understood best mode of operation, reference is made herein to the embodiments illustrated in the drawings and this is described using specific terms. However, it will be understood that this is not intended to limit the scope of the claimed technology, and such changes and further modifications in the illustrated devices and such further applications of the principles of the claimed technology as described herein would typically occur to those skilled in the art relevant to the claimed technology.

[0018] Over time, conventional pressure sensors are exposed to contaminants, which can accumulate and cause a change in the measured capacitance for the same input pressure. This change in the measured capacitance over time (due to particulate accumulation and / or other causes) is known as "drift" of the pressure sensor. After sufficient time has elapsed, drift can cause a sufficient error in the output of the pressure sensor, which may require replacement of the pressure sensor. Drift is unpredictable from device to device and can be highly application-dependent, so it is not possible to reliably predict drift during manufacturing.

[0019] The disclosed exemplary pressure sensors and methods reduce contamination on the diaphragm, thereby reducing drift within the pressure sensor. In some examples, the pressure sensor includes a contamination shield that reduces the amount of contaminants present within the measured pressure cavity and increases the amount of contaminants captured or blocked before reaching the diaphragm. The disclosed exemplary pressure sensors and methods provide improved contamination shielding capabilities and reduced wet volume to improve the lifespan of the pressure sensor.

[0020] The disclosed exemplary pressure sensors and methods compensate for drift occurring within the pressure sensor by measuring the drift rate over an interval and using the determined drift rate to predict drift for subsequent intervals. In some examples, the pressure sensor is calibrated at a fixed reference pressure, at which point the drift rate can be measured and predicted for subsequent intervals. The disclosed exemplary pressure sensors and methods eliminate temperature-based errors in determining the drift rate so that errors due to temperature do not affect the determination of the current drift rate. The pressure sensor and method then use the drift rate to compensate the pressure measurement. As a result, the disclosed pressure sensors and methods have reduced measurement errors over time.

[0021] As used herein, the term "fluid" includes substances in both liquid and gaseous states.

[0022] The disclosed exemplary pressure sensor includes a first body defining a reference pressure cavity, a second body defining a measurement pressure cavity and having an inlet configured to receive fluid, a diaphragm between the reference pressure cavity and the measurement pressure cavity, an electrode separated from the diaphragm by a gap and forming a capacitance with the diaphragm, a measurement circuit configured to determine the pressure in the measurement pressure cavity based on the capacitance, and a contamination shield configured to reduce contamination on a first surface of the diaphragm and including a first portion configured to block a direct path between the inlet and the diaphragm and a second portion configured to occupy a volume within the measurement pressure cavity.

[0023] In some exemplary pressure sensors, the first portion includes a first surface facing the inlet, and the first surface is configured to provide a serpentine path for fluid between the inlet and the diaphragm. Some exemplary pressure sensors further include a housing external to the first body and the second body, and the first portion is configured to cooperate with the housing to provide the serpentine path.

[0024] In some exemplary pressure sensors, the second portion of the contamination shield is dimensioned to provide a gap between the second portion of the contamination shield and the second body to allow fluid flow. In some exemplary pressure sensors, the gap is less than 1.3 millimeters (0.05 inches) around the outer periphery of the second portion of the contamination shield.

[0025] Some exemplary pressure sensors further comprise a housing external to the housing configured to provide a serpentine path for fluid between an inlet and a diaphragm. In some exemplary pressure sensors, a second body provides a serpentine path for fluid between an inlet and a diaphragm. Some exemplary pressure sensors further comprise a temperature sensor and a measurement circuit configured to record a first pressure measured via an electrode, a first timestamp, and a first temperature measurement taken via the temperature sensor in response to a first calibration trigger, record a second pressure measured via the electrode, a second timestamp, and a second temperature measurement via the temperature sensor in response to a second calibration trigger, determine a temperature-compensated second measured pressure by removing a first thermal shift from the second pressure, calculate a first sensor drift rate as a first curve between the first measured pressure and the temperature-compensated second measured pressure, and compensate pressure measurements after the second timestamp based on the calculated first sensor drift rate.

[0026] In some exemplary pressure sensors, the temperature sensor is configured to measure ambient temperature. In some exemplary pressure sensors, the measurement circuit is configured to compensate pressure measurements after the second timestamp based on the calculated first sensor drift rate. In some exemplary pressure sensors, the measurement circuit is further configured to record a third pressure measured via the electrode, a third timestamp, and a third temperature measurement via the temperature sensor in response to a third calibration trigger, determine a temperature-compensated third measured pressure by removing a second thermal shift from the third pressure, and calculate a second sensor drift rate as a second curve between the temperature-compensated third measured pressure and at least one pressure prior to the third timestamp.

[0027] In some exemplary pressure sensors, the measurement circuit section is configured to compensate the pressure measurement value after the third time stamp based on the calculated second sensor drift rate. In some exemplary pressure sensors, the measurement circuit section is configured to determine a curve as a linear gradient from the temperature-compensated second measured pressure and the temperature-compensated third measured pressure, and is configured to compensate the pressure measurement value after the third time stamp based on the second gradient. In some exemplary pressure sensors, the measurement circuit section is further configured to calculate an additional sensor drift rate based on a corresponding calibration trigger and compensate subsequent pressure measurement values based on the most recent sensor drift rate.

[0028] In some exemplary pressure sensors, the first calibration trigger signal and the second calibration trigger signal are received via an operator input device. In some exemplary pressure sensors, the first calibration trigger signal and the second calibration trigger signal are generated by an external controller based on an external measurement sensor that determines that the input pressure is a predetermined reference pressure.

[0029] In some exemplary pressure sensors, the first thermal shift is based on the difference between the first temperature measurement value and the second temperature measurement value. In some exemplary pressure sensors, the measurement circuit section is configured to determine the temperature-compensated second measured pressure based on a stored thermal model for the pressure sensor.

[0030] In some exemplary pressure sensors, the measurement circuit section is configured to determine the drift rate as a linear gradient. In some exemplary pressure sensors, the measurement circuit section is configured to determine the drift rate as a polynomial curve. In some exemplary pressure sensors, the pressure measurement assembly includes at least one of a capacitive diaphragm gauge (CDG), a piezoresistive pressure sensor, a magnetic pressure sensor, a resonant frequency pressure sensor, an optical pressure sensor, or a piezoelectric pressure sensor.

[0031] Some exemplary pressure sensors further include a measurement circuit configured to record a first pressure and a first timestamp measured via an electrode in response to a first calibration trigger, record a second pressure and a second timestamp measured via the electrode in response to a second calibration trigger, calculate a first sensor drift rate as a first curve between the first measured pressure and a temperature-compensated second measured pressure, and compensate pressure measurements after the second timestamp based on the calculated first sensor drift rate.

[0032] In some exemplary pressure sensors, the contamination shield includes one or more circumferentially disposed passages and one or more direct passages. In some examples, each of the one or more circumferentially disposed passages provides a longer flow path and a larger flow area than the direct passages. In some examples, the contamination shield includes a body and a plurality of fins extending from the body for taking in contaminants.

[0033] FIG. 1A is a block diagram of an exemplary process control system 100 including a pressure sensor 102. The exemplary process control system 100 of FIG. 1 includes a process chamber 104, and the pressure sensor 102 is fluidly coupled to the process chamber 104 via a fluid input line 106 to measure the pressure of the process chamber 104.

[0034] The exemplary process chamber 104 can receive one or more inputs, such as process feed materials, via a corresponding number of supply lines 108a, 108b that can be controlled via mass flow controllers 110a, 110b.

[0035] The exemplary system 100 can include a vacuum pump 112 or other pressure control pump, and a valve 114 that controls the flow rate between the vacuum pump 112 and the process chamber 104. The valve 114 is controlled by a controller 116, a computing device, and / or any other control technique, and can maintain the pressure within the process chamber 104 within a desired range. The exemplary pressure sensor 102 is communicatively coupled to the controller 116 and supplies pressure feedback to the controller 116 (e.g., for use in a pressure control loop). For example, when the pressure within the process chamber 104 increases, the pressure sensor 102 measures the pressure and supplies a signal representative of the pressure to the controller 116, which then controls the valve 114 to increase the flow rate from the process chamber 104 to the vacuum pump 112. The vacuum pump 112 can have an output to any suitable location, based on the nature of the process.

[0036] In the example of FIG. 1A, the pressure sensor 102 is configured to have a fixed pressure 118, and the input pressure of the fluid received via the fluid input line 106 is compared to the fixed pressure 118 to output a pressure signal. For example, as will be described in more detail below, the pressure sensor 102 can be provided with a sealable exhaust port that can be sealed when a desired pressure is supplied within the pressure sensor 102, and / or the pressure sensor 102 can be assembled and sealed with a volume having a desired reference pressure. The fixed pressure 118 can be a vacuum pressure, or another predetermined fixed reference pressure that is lower than, equal to, or higher than the nominal atmospheric pressure. In the configuration of FIG. 1A, the pressure sensor 102 can be used as an absolute pressure sensor.

[0037] Figure 1B is a block diagram of another exemplary process control system 150. The exemplary process control system 150 includes the exemplary pressure sensor 102, process chamber 104, fluid input line 106, supply lines 108a, 108b, mass flow controllers 110a, 110b, vacuum pump 112, valve 114, and controller 116 of Figure 1A. In the example of Figure 1B, the pressure sensor 102 is coupled to a variable source 152 of reference pressure that is external to the pressure sensor 102. For example, the pressure sensor 102 can be connected to a reference pressure source and operate as a pressure sensor having a variable reference, and / or can have a port (e.g., a selectively sealable exhaust port) that is vented to ambient pressure and operates as a pressure gauge.

[0038] Figure 2 is a schematic diagram of an exemplary pressure sensor 200 that can be used to implement the pressure sensor 102 of Figure 1A and / or Figure 1B. The exemplary pressure sensor 200 includes a pressure measurement assembly 202, an inner housing 204, and an outer housing 206. The pressure sensor 200 receives fluid via a fluid input line 208 (e.g., the fluid input line 106 of Figure 1), measures the absolute pressure of the received fluid, and outputs one or more signals representative of the measured pressure.

[0039] The pressure measurement assembly 202 is a capacitive diaphragm gauge (CDG) sensor attached to the fluid input line 208. The pressure measurement assembly 202 is sometimes referred to as a "sensor core" in that it performs the measurement that is converted into an output signal by the pressure measurement assembly 202. The pressure measurement assembly 202 is at least partially surrounded by the inner housing 204. The inner housing 204 can provide thermal insulation and / or physical protection to the pressure measurement assembly 202. Both the pressure measurement assembly 202 and the inner housing 204 are at least partially surrounded by the outer housing 206. The outer housing 206 can provide thermal insulation and / or physical protection to the pressure measurement assembly 202.

[0040] In the illustrated example, the pressure measurement assembly 202 is a capacitance pressure sensor in which a flexible diaphragm 210 is separated from an electrode 212 by a gap 214. The pressure measurement assembly 202 includes a first body 216 that defines a reference pressure cavity 218 and a second body 220 that defines a measurement pressure cavity 222. The second body 220 is coupled to the fluid input line 208 such that the measurement pressure cavity 222 has the same pressure as the fluid in the fluid input line 208. For example, the second body 220 can be sealed to the fluid input line 208 by welding, brazing, or other means to provide a hermetic seal.

[0041] When the pressure in the fluid input line 208 changes with respect to the reference pressure (e.g., vacuum pressure) in the reference pressure cavity 218, the diaphragm 210 moves or flexes, changing the capacitance at the measurement electrode 212 by an amount corresponding to the pressure in the fluid input line 208 and / or the measurement pressure cavity 222.

[0042] In the example of FIG. 2, the pressure measurement assembly 202 further includes a reference electrode 226 that similarly measures capacitance as the diaphragm 210 moves in response to pressure. The electrodes 212, 226 are metallized and form two capacitances with the flexible diaphragm 210. The signals generated by both electrodes 212, 226 change with pressure but at different rates. The signal from the reference electrode 226 is output via a signal port 228 and can be used to measure and offset common mode errors (e.g., temperature-induced errors).

[0043] The capacitance signal is output from the pressure measurement assembly 202 via a signal port 228 coupled to a measurement circuit section 238 that converts capacitance into a measurement signal and / or outputs the capacitance signal to an external signal conversion device. The measurement circuit section 238 can correct the measurement signal(s). The measurement signal(s) representing the measured pressure within the pressure measurement assembly 202 may then be transmitted by the measurement circuit section 238 (e.g., to the controller 116 of FIG. 1A or FIG. 1B, another control and / or data collection device, etc.) via a communication circuit section 240 (e.g., a connector). In the example of FIG. 2, the exemplary measurement circuit section 238 and communication circuit section 240 are mounted within the pressure sensor 200 on one or more circuit boards.

[0044] To perform the measurement and processing, the measurement circuit section 238 may be implemented using at least one controller or processor that controls the operation of the pressure sensor 200. The measurement circuit section 238 receives and processes multiple inputs. The measurement circuit section 238 may include one or more microprocessors, such as one or more “general-purpose” microprocessors, one or more dedicated microprocessors and / or ASICs, and / or any other type of processing device. For example, the measurement circuit section 238 may include one or more digital signal processors (DSPs). The measurement circuit section 238 may further include a memory device and / or a data storage device.

[0045] The pressure sensor 200 can include a contamination shield 230 positioned between the fluid input line 208 and the diaphragm 210 to block contaminants, thereby reducing the accumulation of contaminants on the diaphragm 210. FIG. 5A is a first perspective view of an exemplary contamination shield 230, and FIG. 5B is a second perspective view of the exemplary contamination shield 230.

[0046] The exemplary contamination shield 230 of FIGS. 2, 5A, and 5B includes a first portion 232 and a second portion 234. The first portion 232 blocks the direct path between the fluid input line 208 and the diaphragm 210. For example, the first portion 232 has a first surface 236 facing the fluid input line 208 and extends around the inner housing 204.

[0047] The exemplary first surface 236 forms a serpentine path 246 (shown in FIG. 5A) for fluid to cross between the fluid input line 208 and the diaphragm 210. The serpentine path 246 provides additional surface area to deposit contaminants in the input fluid on the surface of the first surface 236, thereby reducing the deposition of contaminants on the surface of the diaphragm 210 and reducing the drift of the pressure sensor 200.

[0048] The second portion 234 of the contamination shield 230 occupies most of the remaining volume of the measurement pressure cavity 222. By reducing the wet volume of the measurement pressure cavity 222 that includes the input fluid, the second portion 234 reduces the amount of contaminants to which the diaphragm is exposed while still allowing the pressure in the fluid input line 208 to be applied to the diaphragm 210.

[0049] The first portion 232 and the second portion 234 are dimensioned to provide one or more gaps 248 between the first portion 232 and the inner housing 204 and / or between the second portion 234 and the second body 220 to allow fluid to reach the diaphragm 210. The total surface area of the gaps 248 can affect the response time of the pressure sensor 200 to changes in pressure in the fluid input line 208. In some examples, the gaps 248 are less than about 1.3 millimeters (0.05 inches) wide around the outer perimeter of the contamination shield 230.

[0050] In some other examples, the second body 220 may be configured to reduce the volume within the measurement pressure cavity 222 occupied by the second portion 234 of the contamination shield 230 in the example of FIG. 2. FIG. 6 is a schematic diagram of an exemplary pressure sensor 600 that may be used to implement the pressure sensor 102 of FIGS. 1A and / or 1B, and the second body 620 is constructed to reduce the wet volume of the measurement pressure cavity 222.

[0051] The pressure sensor 600 is similar to the pressure sensor 200 of FIG. 2, except that the second body 620 reduces the wet volume of the measurement pressure cavity 222. For example, the second body 620 may be a continuous piece of material with holes 650, openings, or other paths provided through the second body 620 to allow the input fluid to reach the diaphragm 210 by following the serpentine path 246 and / or gap 248 between the first portion 232 of the contamination shield 230 and the inner housing 204.

[0052] In some examples, the serpentine path 246 may be implemented by the inner housing 204 and / or the second housing 220.

[0053] Exemplary materials that may be used to construct the first body 216, the second body 220, and / or the contamination shield 230 include corrosion-resistant alloys such as nickel alloys (e.g., Inconel™ alloys) and / or superalloys, cobalt superalloys, iron superalloys, aluminum, copper alloys, titanium, and / or stainless steel.

[0054] To set a fixed reference pressure, the first body 216 can include an exhaust port 242 (e.g., a pinch tube or a pinch-off tube). The exhaust port 242 is in fluid communication with a reference pressure cavity 218. During manufacturing and after sealing of the pressure measurement assembly 202, the pressure (e.g., a vacuum or another set pressure) within the reference pressure cavity 218 is drawn through the exhaust port 242 that is pinched to seal the reference pressure cavity 218 when the desired pressure level is reached. In some other examples, the pressure measurement assembly 202 may be constructed and sealed within a volume where a desired reference pressure exists, which fixes the desired reference pressure within the reference pressure cavity 218 when the exhaust port 242 is sealed within the fixed pressure chamber via welding or pinch-off cold welding.

[0055] In some examples where a fixed reference pressure is set, a getter can be installed within the reference pressure cavity 218 and can be activated during manufacturing, such as when the fixed reference pressure is established but before the reference pressure cavity 218 is sealed. Additionally or alternatively, the inner surface of the reference pressure cavity 218 (e.g., the first body 216 adjacent to the reference pressure cavity 218, the electrode 212) is coated with a substance that reduces or prevents gas outgassing. An exemplary coating that can be used is parylene-C.

[0056] In some other examples, the exhaust port 242 may remain open to ambient pressure and / or may be connected to a variable source of reference pressure.

[0057] The inner housing 204 is attached to the second body 220 (e.g., using an adhesive, welding, press-fitting, etc.). The outer housing 206 is fixed to the measurement circuit section 238 and / or the inner housing 204 (e.g., via fasteners, adhesives, welding, etc.).

[0058] The pressure sensor 200 further includes a temperature sensor 244 coupled to the measurement circuit section 238. The temperature sensor 244 measures the ambient or other environmental temperature that can affect the measurement by the electrodes 212, 226. For example, a change in temperature can change the size of the gap 214 and / or the tension of the diaphragm 210.

[0059] As described above, the exemplary measurement circuit section 238 can compensate for drifts that occur over time in the pressure sensor 200. To compensate for the drift, the measurement circuit section 238 can be calibrated at regular or irregular intervals to determine the measured output at a given input pressure, as described in more detail below. The exemplary measurement circuit section 238 can use sequential calibration to determine the drift rate and compensate the measured value based on the determined drift rate.

[0060] Since the temperature of the pressure sensor 200 can contribute to measurement errors in addition to drift, the exemplary measurement circuit section 238 compensates the calibration of the pressure sensor 200 to reduce or eliminate temperature-based errors from the determination of the drift rate.

[0061] The measurement circuit section 238 records the timestamp, the pressure output voltage, and the ambient temperature T at a given fixed pressure P0 that can be any pressure. The measurement circuit section 238 can record the data in response to a trigger input that can be an automatic trigger or an input device (e.g., a calibration button) accessible to the operator.

[0062] FIG. 3 is a graph 300 showing an exemplary current drift rate calculation that can be performed by the pressure sensor 200 of FIG. 2. The graph 300 shows a set of calibration measurements 302, 304, 306 taken at different times (t1, t2, t3) at the same given pressure. The given pressure is separate from the pressure sensor 200 and can be determined based on a pressure sensor fluidly coupled to the input line 208.

[0063] At the first time t1 and a predetermined pressure P0, the measurement circuit unit 238 records the time stamp t1, the output V1 of the electrode 212, and the temperature T1 measured by the temperature sensor 244 as the calibrated measurement value 302. V1 and T1 are stored as base or reference measurement values.

[0064] At the second time t2 and the predetermined pressure P0, the measurement circuit unit 238 records the time stamp t2, the output V2 of the electrode 212, and the temperature T2 measured by the temperature sensor 244 as the calibrated measurement value 304. Using the stored temperature coefficients at multiple temperatures (e.g., % of maximum sensitivity per degree Celsius) (e.g., TZS for the temperature coefficient at zero output and TSS for the temperature coefficient at maximum sensitivity), and the maximum sensitivity output (VFS), the measurement circuit unit 238 calculates the thermal shift VT2 between the first time t1 and the second time t2 using Equation 1. VT2 = TZS * VFS * (T2 - T1) + TSS * V1 * (T2 - T1) (Equation 1)

[0065] To compensate subsequent measurement values, the measurement circuit unit 238 determines the estimated drift rate (S12) from t1 to t2 using Equation 2. S12 = (V2’ - V1) / (t2 - t1) (Equation 2)

[0066] In Equation 2, V2’ is the temperature-compensated output and is calculated as V2’ = V2 - VT2. After t2 and until t3, the measurement circuit unit 238 compensates the pressure measurement values using the estimated drift rate S12. The measurement circuit unit 238 removes an estimated drift amount that increases according to the estimated drift rate S12 as time elapses from t2 from the measurement values after t2 to compensate the measurement values of the pressure. The measurement circuit unit 238 compensates the pressure measurement values occurring after t2 to determine the compensated output V’ using Equation 3. V’ = V - (V2’ - V1) - S12 * (t - t2) - VT (Equation 3)

[0067] In Equation 3, V is the measured pressure output from the electrode 212, t is the time of the measured pressure output, and the thermal shift VT is determined according to Equation 4. VT = TZS * VFS * (T - T1) + TSS * V * (T - T1) (Equation 4)

[0068] At the third time t3 and a predetermined pressure P0, the measurement circuit unit 238 records the time stamp t3, the output V3 of the electrode 212, and the temperature T3 measured by the temperature sensor 244 as the calibrated measurement value 306. Using the stored temperature coefficients TZS, TSS, and the maximum sensitivity output VFS, the measurement circuit unit 238 calculates the thermal shift VT3 between the first time t1 and the third time t3 using Equation 5. VT3 = TZS * VFS * (T3 - T1) + TSS * V1 * (T3 - T1) (Equation 5)

[0069] The measurement circuit unit 238 is configured again to make the output value of the pressure P0 equal to V1 to calibrate the output signal from the electrode 212. To compensate for subsequent measured values following the time t3, the measurement circuit unit 238 determines the estimated drift rate (S23) from t2 to t3 (which may be different from the drift rate from t1 to t2 and / or from t1 to t3) using Equation 6. S23 = (V3’ - V2’) / (t3 - t2) (Equation 6)

[0070] In Equation 6, V3’ is calculated as V3 - VT3. The measurement circuit unit 238 continues to compensate the pressure measurement values occurring after t3, substitutes the current drift rate S23 and the most recent compensated output and the time t3, and determines the compensated output V’ using the above Equation 3.

[0071] The measurement circuit unit 238 can repeat calibration, drift rate calculation, and compensation for additional time after t3 to reduce the output error caused by the drift of the pressure sensor 200 over the operating life of the pressure sensor 200.

[0072] Graph 300 shows the total drift 310 from t1 to t2, the estimated drift 312 from t2 to t3, the total compensated drift 314 at t3, and the remaining uncompensated drift 316 at t3.

[0073] Instead of a linear drift rate as shown in the example of FIG. 3, the exemplary measurement circuit section 238 can calculate other drift curves such as a polynomial drift curve. The drift curve can be obtained based on fitting a predetermined drift curve trend to the observed temperature-compensated output and time stamps. For example, the measurement circuit section 238 can perform regression analysis and / or any other type of analysis to determine the drift curve.

[0074] Additionally or alternatively, the measurement circuit section 238 can store all calibration data (e.g., time stamps, output signals, measured temperatures, etc.) in a storage device for later retrieval. For example, the calibration data can be stored permanently, or at least for a predetermined or configurable time, and / or up to the memory limit of the measurement circuit section 238. The stored calibration data can be output to a maintenance system (e.g., via the communication circuit section 240). The maintenance system can analyze the calibration data for the pressure sensor 200 and update the approximate curve coefficients (e.g., for performing curve fitting) based on, for example, the observed data and / or for a particular application or use of the pressure sensor 200. The maintenance system can then load and return the updated coefficients to the measurement circuit section 238 for storage and updated drift compensation determination. The coefficients determined based on the first pressure sensor 200 can be further loaded into a replacement pressure sensor 200, and thus the new pressure sensor 200 can have more accurate curve fitting coefficients for the same or similar applications.

[0075] FIG. 4 is a flowchart representing exemplary machine-readable instructions 400 that may be executed by the pressure sensor 200 of FIG. 2 to compensate pressure measurement values for sensor drift. The exemplary instructions 400 are described below with reference to the measurement circuit section 238. In the following instructions 400, baseline measurement values of pressure V1, time t1, and temperature T1 may be pre-captured at the startup or initialization of the pressure sensor 200.

[0076] In block 402, the measurement circuit section 238 determines whether to calibrate the pressure sensor 200. For example, the measurement circuit section 238 can receive an input signal from a control device (e.g., via the communication circuit section 240) or via a user input device (e.g., a calibration button). If calibration is to be performed (block 402), the measurement circuit section 238 inputs a predetermined pressure into the fluid input line 208. For example, a known input pressure source may be connected to the input line 208, or the connected system may be configured to input a predetermined input pressure.

[0077] In block 406, the measurement circuit section 238 captures a pressure measurement value, a timestamp, and a temperature measurement value. For example, the measurement circuit section 238 can receive a signal from the electrode 212 to represent one of the calibration measurement values 302, 304, 306 of FIG. 3, a timestamp from a timer or clock, and a temperature measurement value of the ambient temperature or environmental temperature from the temperature sensor 244. In block 408, the measurement circuit section 238 determines a temperature-compensated current pressure measurement value. For example, the measurement circuit section 238 can determine a temperature-compensated current pressure measurement value V2' based on the thermal shift calculated using Equation 1 above.

[0078] In block 410, the measurement circuit unit 238 determines the current sensor drift rate (e.g., S12, S23, etc.) as a curve based on the previous measured pressure (e.g., baseline or temperature-compensated) and the temperature-compensated current pressure measurement value. For example, the measurement circuit unit 238 may use Equation 2 or Equation 6 to determine the linear drift rate, or may determine a polynomial drift curve or other non-linear drift curve.

[0079] After determining the sensor drift rate (block 410), or if the pressure sensor is not calibrated (block 402), in block 412, the measurement circuit unit 238 determines whether a pressure measurement value has been captured. For example, the measurement circuit unit 238 can determine the pressure measurement signal V from the electrode 212 at regular or irregular intervals and / or in response to a trigger or event. If the pressure measurement value is not captured (block 412), the control returns to block 412.

[0080] If the pressure measurement value is not captured (block 412), in block 414, the measurement circuit unit 238 captures the temperature measurement value via the temperature sensor 244.

[0081] In block 416, the measurement circuit unit 238 compensates the pressure measurement signal V using the current sensor drift rate, the time stamp of the pressure measurement value, and the temperature measurement value. For example, the measurement circuit unit 238 can use Equation 3 to determine the corrected pressure output. Then, the control returns to block 402.

[0082] FIG. 7 is a schematic diagram of another exemplary pressure sensor 700 that can be used to implement the pressure sensor of FIGS. 1A and / or 1B. FIGS. 8A and 8B are other views of the exemplary contamination shield 730 of FIG. 7 coupled to the pressure sensor 700. The exemplary pressure sensor 700 includes a pressure measurement assembly 202, an inner housing 204, an outer housing 206, a fluid input line 208, a diaphragm 210, electrodes 212, a gap 214, a first body 216, a reference pressure cavity 218, a second body 220, a measurement pressure cavity 222, a reference electrode 226, a signal port 228, a measurement circuit section 238, a communication circuit section 240, an exhaust port 242, and a temperature sensor 244, as described above with reference to FIG. 2.

[0083] The exemplary pressure sensor 700 of FIG. 7 further includes a contamination shield 730 positioned between the fluid input line 208 and the diaphragm 210 to block contaminants, thereby reducing the accumulation of contaminants on the diaphragm 210. The exemplary contamination shield 730 improves the response time by reducing the free volume between the fluid input line 208 and the diaphragm 210 in a manner similar to the contamination shield of FIG. 2. The contamination shield 730 can provide an improved conductance compared to the contamination shield 230 of FIG. 2, thereby further improving the response time compared to the contamination shield 230.

[0084] The exemplary contamination shield 730 is positioned within the second body 220 and includes a shield body 732. The shield body 732 includes a first portion 732a that blocks the direct path between the fluid input line 208 and the diaphragm 210 and a second portion 732b that occupies the volume between the fluid input line 208 and the diaphragm 210.

[0085] The shield body 732 includes a circumferentially disposed passage 734 and a central passage 736 that allow fluid to pass between the fluid input line 208 and the diaphragm 210. The circumferentially disposed passage 734 provides more flow through a longer flow path between the fluid input line 208 and the diaphragm 210, which promotes the deposition of particulate contaminants onto the body 732 (e.g., onto the fins 738 and / or onto the inner and / or outer surfaces of the body 732). The circumferentially disposed passage 734 can be configured to provide more controlled flow, for example, to direct the gas flow along a desired flow path and / or to direct surface contact with the body 732 and / or the fins 738.

[0086] The central passage 736 provides a smaller and more direct flow path between the fluid input line 208 and the diaphragm 210, which improves conductance and response time. The exemplary central passage 736 can also promote turbulence around the shield body 732 during pressure changes and further improve the entrainment of contaminant particles onto the shield body 732.

[0087] The exemplary shield body 732 includes three exemplary circumferentially disposed passages 734, but in other examples, the shield body 732 can include one, two, four, or more circumferentially disposed passages 734. Additionally or alternatively, the circumferentially disposed passages 734 can be arranged evenly or unevenly spaced around the outer perimeter of the body 732.

[0088] The exemplary shield body 732 includes a single central passage 736, but in other examples, the shield body 732 can include a plurality of central passages 736 disposed on the surface of the shield body 732 (e.g., facing the fluid input line 208 and the diaphragm 210). In other examples, the shield body 732 can omit the central passage 736 and the circumferentially disposed passages 734 are the only passages fluidly coupling the fluid input line 208 and the diaphragm 210.

[0089] The examples disclosed above have been described with reference to CDG sensors, but the disclosed exemplary systems and methods are applicable to other types of pressure sensors that are subject to drift, such as piezoresistive pressure sensors, magnetic pressure sensors, resonant frequency pressure sensors, optical pressure sensors, piezoelectric pressure sensors, and / or any other type of pressure sensor.

[0090] In some examples, the pressure sensor 200 omits the temperature sensor 244 and does not compensate for temperature variations in the pressure measurements (e.g., pressure measurements 302, 304, 306). Instead, the measurement circuitry 238 can capture calibration measurements at substantially consistent pressures and substantially consistent temperatures (e.g., within a predetermined pressure range of a target calibration pressure and within a predetermined temperature range of a target calibration temperature). In such an example, the measurement circuitry 238 can record a first pressure measured via the electrodes, record a first timestamp in response to a first calibration trigger, record a second pressure measured via the electrodes, and record a second timestamp in response to a second calibration trigger. The measurement circuitry 238 can then calculate a first sensor drift rate as a first curve between the first measured pressure and the temperature-compensated second measured pressure, and then compensate pressure measurements after the second timestamp based on the calculated first sensor drift rate. The measurement circuitry 238 can perform additional calibrations and subsequent corrections in a similar manner.

[0091] As used herein, "and / or" means any one or more of the items in the list connected by "and / or". By way of example, "x and / or y" means any element of the three-element set {(x), (y), (x, y)}. In other words, "x and / or y" means "one or both of x and y". As another example, "x, y and / or z" means any element of the seven-element set {(x), (y), (z), (x, y), (x, z), (y, z), (x, y, z)}. In other words, "x, y and / or z" means "one or more of x, y and z". As used herein, the term "exemplary" serves as a non-limiting example, instance or illustration. As used herein, the term "for example" begins a list of one or more non-limiting examples, instances or illustrations.

[0092] The method and / or system has been described with reference to certain embodiments, but those skilled in the art will understand that various changes can be made and equivalents substituted without departing from the scope of the method and / or system. For example, the blocks and / or components of the disclosed examples can be combined, divided, rearranged, and / or otherwise changed. Additionally, many modifications can be made to adapt the teachings of the present disclosure to particular situations or materials without departing from the scope of the present disclosure. Accordingly, the method and / or system is not limited to the particular embodiments disclosed. Instead, the method and / or system includes all embodiments that fall within the scope of the appended claims, literally or under the doctrine of equivalents.

Claims

1. A pressure sensor, comprising: a first body defining a reference pressure cavity; a second body defining a measurement pressure cavity, the second body having an inlet configured to receive a fluid; a diaphragm between the reference pressure cavity and the measurement pressure cavity; an electrode spaced from the diaphragm by a gap to form a capacitance between the electrode and the diaphragm; a measurement circuit configured to determine a pressure in the measurement pressure cavity based on the capacitance; a contamination shield configured to reduce contamination on a first surface of the diaphragm, the contamination shield comprising: a first portion configured to block a direct path between the inlet and the diaphragm; and a second portion configured to occupy a volume within the measurement pressure cavity; and a contamination shield; a pressure sensor comprising the above.

2. The pressure sensor according to claim 1, wherein the first portion has a first surface facing the inlet, and the first surface is configured to provide a meandering path for the fluid between the inlet and the diaphragm.

3. The pressure sensor according to claim 2, further comprising a housing outside the first body and the second body, wherein the first portion is configured to cooperate with the housing to provide the meandering path.

4. The pressure sensor according to claim 1, wherein the second portion of the contamination shield is dimensioned to provide a gap between the second portion of the contamination shield and the second body to allow flow of the fluid.

5. The pressure sensor according to claim 4, wherein the gap is less than about 1.3 millimeters (0.05 inches) around an outer periphery of the second portion of the contamination shield.

6. The pressure sensor according to claim 1, further comprising a housing, wherein the housing is configured to provide a meandering path for the fluid between the inlet and the diaphragm outside the housing.

7. The pressure sensor according to claim 1, wherein the second body is configured to provide a meandering path for the fluid between the inlet and the diaphragm.

8. The pressure sensor according to claim 1, further comprising a temperature sensor and a measurement circuit, wherein the measurement circuit... In response to a first calibration trigger, record a first pressure measured via the electrode, a first timestamp, and a first temperature measurement value measured via the temperature sensor. In response to a second calibration trigger, record a second pressure measured via the electrode, a second timestamp, and a second temperature measurement value via the temperature sensor. A first sensor drift rate By removing a first thermal shift from the second pressure, determine a temperature-compensated second measured pressure. Determine the first sensor drift rate as a first curve between the first measured pressure and the temperature-compensated second measured pressure. Calculate by Based on the calculated first sensor drift rate, compensate pressure measurement values after the second timestamp. The pressure sensor according to claim 1, which is configured to perform the above.

9. The pressure sensor according to claim 8, wherein the temperature sensor is configured to measure ambient temperature.

10. The pressure sensor according to claim 8, wherein the measurement circuit unit is configured to compensate pressure measurement values after the second timestamp based on the calculated first sensor drift rate.

11. The measurement circuit unit further In response to a third calibration trigger, record a third pressure measured via the electrode, a third timestamp, and a third temperature measurement value via the temperature sensor. A second sensor drift rate By removing a second thermal shift from the third pressure, determine a temperature-compensated third measured pressure. Determine the second sensor drift rate as a second curve between the temperature-compensated third measured pressure and at least one pressure before the third timestamp. Calculate by The pressure sensor according to claim 8, which is configured to perform the above.

12. The pressure sensor according to claim 11, wherein the measurement circuit unit is configured to compensate pressure measurement values after the third timestamp based on the calculated second sensor drift rate.

13. The measurement circuit unit is configured to determine the curve as a linear gradient from the temperature-compensated second measured pressure and the temperature-compensated third measured pressure, and to compensate the pressure measurement value after the third time stamp based on the second gradient. The pressure sensor according to claim 12.

14. The measurement circuit unit is further configured to calculate an additional sensor drift rate based on a corresponding calibration trigger and to compensate subsequent pressure measurement values based on the most recent sensor drift rate. The pressure sensor according to claim 11.

15. The first calibration trigger signal and the second calibration trigger signal are received via an operator input device or are generated by an external controller based on an external measurement sensor that determines that the input pressure is a predetermined reference pressure. The pressure sensor according to claim 8.

16. The first thermal shift is based on the difference between the first temperature measurement value and the second temperature measurement value. The pressure sensor according to claim 8.

17. The measurement circuit unit is configured to determine the temperature-compensated second measured pressure based on a stored thermal model for the pressure sensor. The pressure sensor according to claim 16.

18. The measurement circuit unit is configured to determine the drift rate as a linear gradient. The pressure sensor according to claim 8.

19. The measurement circuit unit is configured to determine the drift rate as a polynomial curve. The pressure sensor according to claim 8.

20. The pressure measurement assembly includes at least one of a capacitive diaphragm gauge (CDG), a piezoresistive pressure sensor, a magnetic pressure sensor, a resonant frequency pressure sensor, an optical pressure sensor, or a piezoelectric pressure sensor. The pressure sensor according to claim 1.

21. Furthermore, it includes a measurement circuit unit, and the measurement circuit unit records the first pressure measured via the electrode and the first time stamp in response to a first calibration trigger; records the second pressure measured via the electrode and the second time stamp in response to a second calibration trigger; calculates a first sensor drift rate as a first curve between the first measured pressure and the temperature-compensated second measured pressure; Compensating the pressure measurement value after the second timestamp based on the calculated first sensor drift rate; The pressure sensor according to claim 1, configured to perform the above.

22. The pressure sensor according to claim 1, wherein the contamination shield includes one or more circumferentially arranged passages and one or more direct passages.

23. The pressure sensor according to claim 22, wherein each of the one or more circumferentially arranged passages provides a longer flow path and a larger flow area than the direct passage.

24. The pressure sensor according to claim 1, wherein the contamination shield includes a main body and a plurality of fins extending from the main body for taking in contaminants.

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