Wide-threshold uniform pressure calibration method for flexible fabric pressure sensor

Abstract

The invention discloses a wide-threshold uniform pressure calibration method for a flexible fabric pressure sensor. The wide-threshold uniform pressure calibration method comprises the following steps: S1, preprocessing the flexible fabric pressure sensor; s2, constructing a wide-threshold uniform pressure calibration platform; s3, graded pressure application and data acquisition are carried out; s4, calibration data processing and model establishment; s5, verifying and correcting a calibration result; according to the method, the wide pressure threshold range of 0-200 kPa is set, grading calibration is carried out in the low pressure section, the medium pressure section and the high pressure section, the problem that only narrow threshold calibration can be achieved through a traditional method is solved, and the use requirements of more scenes are met; the flexible pressure applying assembly is matched with the pressure distribution monitoring module to ensure that the surface pressure of the sensor is uniform in the pressure applying process, the pressure difference value is smaller than or equal to 1kPa, the problem of uneven pressure caused by a traditional rigid pressure head is avoided, and the calibration precision is improved.

Description

Technical Field

[0001] This invention belongs to the field of flexible fabric pressure sensor calibration technology, specifically a method for calibrating a flexible fabric pressure sensor with wide threshold uniform pressure. Background Technology

[0002] Flexible fabric pressure sensors are widely used in various fields due to their excellent flexibility, breathability, and fit. However, the pressure detection threshold range of these sensors is difficult to accurately control due to the characteristics of the fabric material. Furthermore, traditional calibration methods often use rigid indenters, which can lead to uneven pressure distribution on the sensor surface, achieving only a narrow threshold calibration of 0-50 kPa. This fails to meet the wide threshold requirements of 0-200 kPa in some scenarios, and the calibration accuracy is low, often exceeding 8%, severely impacting the actual detection performance of the sensor. Therefore, there is an urgent need for a calibration method that can achieve a wide threshold and uniform pressure, overcoming the shortcomings of existing technologies. Summary of the Invention

[0003] In view of the above situation and to overcome the shortcomings of the prior art, the present invention provides a wide threshold uniform pressure calibration method for flexible fabric pressure sensors, which effectively solves the problems raised in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a method for calibrating a flexible fabric pressure sensor with a wide threshold uniform pressure, comprising the following steps: Step S1: Preprocessing of flexible fabric pressure sensor; Step S2: Construction of a wide threshold uniform pressure calibration platform; Step S3: Tiered pressure application and data collection; Step S4: Calibration data processing and model establishment; Step S5: Verification and correction of calibration results.

[0005] Preferably, step S1, the preprocessing of the flexible fabric pressure sensor, includes the following steps: S1.1 Place the flexible fabric pressure sensor to be calibrated in a constant temperature and humidity environment for 24 hours. The ambient temperature is controlled at 23±2℃ and the relative humidity is controlled at 50±5%RH to eliminate the influence of ambient temperature and humidity fluctuations on the initial performance of the sensor. S1.2. Use a pressure loading device with an accuracy of 0.01 kPa to apply a pre-pressure of 10 kPa to the sensor and keep the pre-pressure stable for 30 minutes to eliminate the initial residual stress of the sensor fabric substrate and avoid calibration errors caused by residual stress in the subsequent calibration process. S1.3 After the pre-pressure is completed, remove the pre-pressure and keep the sensor in the constant temperature and humidity environment for 1 hour to allow the sensor to return to its initial stable state.

[0006] Preferably, step S2, the construction of the wide threshold uniform pressure calibration platform, includes the following steps: S2.1 Build a calibration platform consisting of a flexible pressure application component, a pressure control module, a signal acquisition module, and a pressure distribution monitoring module; S2.2 The flexible pressure application component adopts a double-layer structure. The upper layer is an elastic buffer layer, which is made of silicone material with a hardness of 50-70 Shore A and a thickness of 5mm. The lower layer is a flexible contact layer, which is made of cotton fabric of the same material as the sensor fabric substrate and has a thickness of 2mm, to ensure that the pressure on the sensor surface is uniformly transmitted during the pressure application process. S2.3 The pressure control module uses a servo motor driven pressure loading device with a pressure adjustment range of 0-250kPa and a pressure control accuracy of ±0.1kPa, which can realize continuous and stable pressure adjustment. S2.4 The signal acquisition module uses a 16-bit precision data acquisition card with a sampling frequency of 100Hz to acquire the output voltage signal of the sensor under different pressures in real time. S2.5 The pressure distribution monitoring module uses an array-type pressure sensor with a detection accuracy of 0.1 kPa and a detection range of 0-200 kPa. It is attached and fixed under the flexible contact layer of the flexible pressure application component to monitor the pressure distribution on the sensor surface in real time and ensure that the pressure difference at each point on the pressure application surface is ≤1 kPa.

[0007] Preferably, step S3, graded pressure application and data acquisition, includes the following steps: S3.1 Fix the pre-treated flexible fabric pressure sensor to the test station of the calibration platform, ensuring that the sensor's detection surface is completely in contact with the flexible contact layer of the flexible pressure application component, without wrinkles or offset. S3.2. Pressure is applied according to the preset pressure levels by the pressure control module. The pressure levels are divided into low pressure, medium pressure and high pressure. The low pressure level is 0-50 kPa, with a calibration pressure point set every 5 kPa; the medium pressure level is 50-150 kPa, with a calibration pressure point set every 10 kPa; and the high pressure level is 150-200 kPa, with a calibration pressure point set every 20 kPa. S3.3 For each calibration pressure point, the pressure control module smoothly loads the target pressure at a rate of 0.5 kPa / s. After loading, the pressure is kept stable for 10 seconds. After the sensor output signal stabilizes, the sensor output voltage signal at that pressure point is acquired through the signal acquisition module. The acquisition is repeated 5 times for each pressure point, and the average value of the 5 acquisition results is taken as the reference value of the sensor output signal corresponding to that calibration pressure point. S3.4 During the pressure holding process at each pressure point, the pressure distribution on the sensor surface is monitored in real time by the pressure distribution monitoring module. If the pressure difference between any two points on the pressure surface is greater than 1 kPa, the calibration of that pressure point is stopped immediately, the contact state between the flexible pressure application component and the sensor is adjusted, and the pressure application and data acquisition at that pressure point are repeated until the pressure distribution meets the uniformity requirements.

[0008] Preferably, step S4, calibration data processing and model establishment, includes the following steps: S4.1. Compile the pressure values ​​of all calibrated pressure points collected in step S3 with the corresponding sensor output signal reference values, and eliminate abnormal data caused by equipment interference; the criterion for judging abnormal data is: the deviation of a certain collected value from the average value of that pressure point is >5%; S4.2. A piecewise fitting method is used to establish a model relating pressure values ​​to sensor output signals, wherein: For the low pressure range of 0 ~ 50 kPa, a linear fitting algorithm is used, and the fitting formula is: ; in, Where x is the sensor output voltage and x is the pressure value. The fitting coefficients for the low-pressure range are 0.02 to 0.03. This is the intercept for the low-pressure range, with a value ranging from 0.1 to 0.2. For the pressure range of 50-150 kPa, a quadratic polynomial fitting algorithm is used, and the fitting formula is as follows: ; in, The range of values ​​is ~ , The value range is 0.01 ~ 0.02. The value range is 0.3 ~ 0.5; For the 150-200 kPa high-pressure range, a cubic polynomial fitting algorithm is used, and the fitting formula is as follows: ; in, The range of values ​​is ~ , The range of values ​​is ~ , The value range is 0.005~0.01. The value range is 0.8 to 1.0; S4.3 Calculate the calibration error of the fitting model for each pressure range. The formula for calculating the calibration error is as follows: ; in, This represents the actual applied pressure value. To ensure that the calibration error of each pressure range is ≤5% for the pressure values ​​calculated by fitting the model.

[0009] Preferably, step S5, calibration result verification and correction, includes the following steps: S5.1. Within the pressure range of 0-200 kPa, randomly select 10 verification pressure points; Among them, three low-pressure ranges were selected: 10 kPa, 25 kPa, and 40 kPa. Four medium-pressure ranges were selected: 60 kPa, 80 kPa, 120 kPa, and 140 kPa. Three high-pressure ranges were selected: 160 kPa, 180 kPa, and 190 kPa. S5.2. Apply pressure to each verification pressure point according to the pressure application method in step S3, collect the sensor output signal, and calculate the corresponding calibration pressure value through the piecewise fitting model established in step S4. S5.3 Compare the actual applied verification pressure value with the calculated calibration pressure value; If the error of all verification pressure points is ≤5%, the calibration is deemed qualified, and the wide threshold uniform pressure calibration of the flexible fabric pressure sensor is completed. If the error of any verification pressure point is greater than 5%, return to step S3, reselect the calibration pressure point within the pressure range corresponding to the error for pressure application and data acquisition, and re-execute the model building in step S4 until the error of all verification pressure points meets the requirement of ≤5%.

[0010] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention solves the problem that traditional methods can only achieve narrow threshold calibration by setting a wide pressure threshold range of 0-200kPa and performing graded calibration in low, medium and high pressure segments, thus meeting the needs of more application scenarios. 2. A flexible pressure application component is used in conjunction with a pressure distribution monitoring module to ensure uniform pressure on the sensor surface during the pressure application process, with a pressure difference ≤1kPa. This avoids the pressure unevenness problem caused by traditional rigid pressure heads and improves calibration accuracy. 3. By establishing a corresponding model between pressure and output signal through piecewise fitting, and combining it with verification and correction steps, the calibration error is made ≤5%, which significantly improves the detection accuracy of the sensor and provides a guarantee for the reliable application of flexible fabric pressure sensors. Attached Figure Description

[0011] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0012] Figure 1 This is a schematic diagram of a method for calibrating a flexible fabric pressure sensor with a wide threshold uniform pressure according to the present invention. Detailed Implementation

[0013] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0014] Example 1, by Figure 1 This invention relates to a method for calibrating a flexible fabric pressure sensor with a wide threshold uniform pressure, comprising the following steps: Step S1: Preprocessing of flexible fabric pressure sensor; Step S2: Construction of a wide threshold uniform pressure calibration platform; Step S3: Tiered pressure application and data collection; Step S4: Calibration data processing and model establishment; Step S5: Verification and correction of calibration results.

[0015] Step S1 of this embodiment, the preprocessing of the flexible fabric pressure sensor, includes the following steps: S1.1 Place the flexible fabric pressure sensor to be calibrated in a constant temperature and humidity environment for 24 hours. The ambient temperature is controlled at 23±2℃ and the relative humidity is controlled at 50±5%RH to eliminate the influence of ambient temperature and humidity fluctuations on the initial performance of the sensor. S1.2. Use a pressure loading device with an accuracy of 0.01 kPa to apply a pre-pressure of 10 kPa to the sensor and keep the pre-pressure stable for 30 minutes to eliminate the initial residual stress of the sensor fabric substrate and avoid calibration errors caused by residual stress in the subsequent calibration process. S1.3 After the pre-pressure is completed, remove the pre-pressure and keep the sensor in the constant temperature and humidity environment for 1 hour to allow the sensor to return to its initial stable state.

[0016] Step S2 of this embodiment, the construction of the wide threshold uniform pressure calibration platform, includes the following steps: S2.1 Build a calibration platform consisting of a flexible pressure application component, a pressure control module, a signal acquisition module, and a pressure distribution monitoring module; S2.2 The flexible pressure application component adopts a double-layer structure. The upper layer is an elastic buffer layer, which is made of silicone material with a hardness of 50-70 Shore A and a thickness of 5mm. The lower layer is a flexible contact layer, which is made of cotton fabric of the same material as the sensor fabric substrate and has a thickness of 2mm, to ensure that the pressure on the sensor surface is uniformly transmitted during the pressure application process. S2.3 The pressure control module uses a servo motor driven pressure loading device with a pressure adjustment range of 0-250kPa and a pressure control accuracy of ±0.1kPa, which can realize continuous and stable pressure adjustment. S2.4 The signal acquisition module uses a 16-bit precision data acquisition card with a sampling frequency of 100Hz to acquire the output voltage signal of the sensor under different pressures in real time. S2.5 The pressure distribution monitoring module uses an array-type pressure sensor with a detection accuracy of 0.1 kPa and a detection range of 0-200 kPa. It is attached and fixed under the flexible contact layer of the flexible pressure application component to monitor the pressure distribution on the sensor surface in real time and ensure that the pressure difference at each point on the pressure application surface is ≤1 kPa.

[0017] Step S3 of this embodiment, graded pressure application and data acquisition, includes the following steps: S3.1 Fix the pre-treated flexible fabric pressure sensor to the test station of the calibration platform, ensuring that the sensor's detection surface is completely in contact with the flexible contact layer of the flexible pressure application component, without wrinkles or offset. S3.2. Pressure is applied according to the preset pressure levels by the pressure control module. The pressure levels are divided into low pressure, medium pressure and high pressure. The low pressure level is 0-50 kPa, with a calibration pressure point set every 5 kPa; the medium pressure level is 50-150 kPa, with a calibration pressure point set every 10 kPa; and the high pressure level is 150-200 kPa, with a calibration pressure point set every 20 kPa. S3.3 For each calibration pressure point, the pressure control module smoothly loads the target pressure at a rate of 0.5 kPa / s. After loading, the pressure is kept stable for 10 seconds. After the sensor output signal stabilizes, the sensor output voltage signal at that pressure point is acquired through the signal acquisition module. The acquisition is repeated 5 times for each pressure point, and the average value of the 5 acquisition results is taken as the reference value of the sensor output signal corresponding to that calibration pressure point. S3.4 During the pressure holding process at each pressure point, the pressure distribution on the sensor surface is monitored in real time by the pressure distribution monitoring module. If the pressure difference between any two points on the pressure surface is greater than 1 kPa, the calibration of that pressure point is stopped immediately, the contact state between the flexible pressure application component and the sensor is adjusted, and the pressure application and data acquisition at that pressure point are repeated until the pressure distribution meets the uniformity requirements.

[0018] Step S4 of this embodiment, calibration data processing and model establishment, includes the following steps: S4.1. Compile the pressure values ​​of all calibrated pressure points collected in step S3 with the corresponding sensor output signal reference values, and eliminate abnormal data caused by equipment interference; the criterion for judging abnormal data is: the deviation of a certain collected value from the average value of that pressure point is >5%; S4.2. A piecewise fitting method is used to establish a model relating pressure values ​​to sensor output signals, wherein: For the low pressure range of 0 ~ 50 kPa, a linear fitting algorithm is used, and the fitting formula is: ; in, Where x is the sensor output voltage and x is the pressure value. The fitting coefficients for the low-pressure range are 0.02 to 0.03. This is the intercept for the low-pressure range, with a value ranging from 0.1 to 0.2. For the pressure range of 50-150 kPa, a quadratic polynomial fitting algorithm is used, and the fitting formula is as follows: ; in, The range of values ​​is ~ , The value range is 0.01 ~ 0.02. The value range is 0.3 ~ 0.5; For the 150-200 kPa high-pressure range, a cubic polynomial fitting algorithm is used, and the fitting formula is as follows: ; in, The range of values ​​is ~ , The range of values ​​is ~ , The value range is 0.005~0.01. The value range is 0.8 to 1.0; S4.3 Calculate the calibration error of the fitting model for each pressure range. The formula for calculating the calibration error is as follows: ; in, This represents the actual applied pressure value. To ensure that the calibration error of each pressure range is ≤5% for the pressure values ​​calculated by fitting the model.

[0019] Step S5 of this embodiment, calibration result verification and correction, includes the following steps: S5.1. Within the pressure range of 0-200 kPa, randomly select 10 verification pressure points; Among them, three low-pressure ranges were selected: 10 kPa, 25 kPa, and 40 kPa. Four medium-pressure ranges were selected: 60 kPa, 80 kPa, 120 kPa, and 140 kPa. Three high-pressure ranges were selected: 160 kPa, 180 kPa, and 190 kPa. S5.2. Apply pressure to each verification pressure point according to the pressure application method in step S3, collect the sensor output signal, and calculate the corresponding calibration pressure value through the piecewise fitting model established in step S4. S5.3 Compare the actual applied verification pressure value with the calculated calibration pressure value; If the error of all verification pressure points is ≤5%, the calibration is deemed qualified, and the wide threshold uniform pressure calibration of the flexible fabric pressure sensor is completed. If the error of any verification pressure point is greater than 5%, return to step S3, reselect the calibration pressure point within the pressure range corresponding to the error for pressure application and data acquisition, and re-execute the model building in step S4 until the error of all verification pressure points meets the requirement of ≤5%.

[0020] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0021] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for calibrating a flexible fabric pressure sensor with a wide threshold uniform pressure, comprising the following steps: Step S1: Preprocessing of flexible fabric pressure sensor; Step S2: Construction of a wide threshold uniform pressure calibration platform; Step S3: Tiered pressure application and data collection; Step S4: Calibration data processing and model establishment; Step S5: Verification and correction of calibration results.

2. The method for calibrating a flexible fabric pressure sensor with wide threshold uniform pressure according to claim 1, characterized in that: Step S1, the preprocessing of the flexible fabric pressure sensor, includes the following steps: S1.1 Place the flexible fabric pressure sensor to be calibrated in a constant temperature and humidity environment for 24 hours. The ambient temperature is controlled at 23±2℃ and the relative humidity is controlled at 50±5%RH to eliminate the influence of ambient temperature and humidity fluctuations on the initial performance of the sensor. S1.

2. Use a pressure loading device with an accuracy of 0.01 kPa to apply a pre-pressure of 10 kPa to the sensor and keep the pre-pressure stable for 30 minutes to eliminate the initial residual stress of the sensor fabric substrate and avoid calibration errors caused by residual stress in the subsequent calibration process. S1.3 After the pre-pressure is completed, remove the pre-pressure and keep the sensor in the constant temperature and humidity environment for 1 hour to allow the sensor to return to its initial stable state.

3. The method for calibrating a flexible fabric pressure sensor with wide threshold uniform pressure according to claim 1, characterized in that: Step S2, the construction of the wide threshold uniform pressure calibration platform, includes the following steps: S2.1 Build a calibration platform consisting of a flexible pressure application component, a pressure control module, a signal acquisition module, and a pressure distribution monitoring module; S2.2 The flexible pressure application component adopts a double-layer structure. The upper layer is an elastic buffer layer, which is made of silicone material with a hardness of 50-70 Shore A and a thickness of 5mm. The lower layer is a flexible contact layer, which is made of cotton fabric of the same material as the sensor fabric substrate and has a thickness of 2mm, to ensure that the pressure on the sensor surface is uniformly transmitted during the pressure application process. S2.3 The pressure control module uses a servo motor driven pressure loading device with a pressure adjustment range of 0-250kPa and a pressure control accuracy of ±0.1kPa, which can realize continuous and stable pressure adjustment. S2.4 The signal acquisition module uses a 16-bit precision data acquisition card with a sampling frequency of 100Hz to acquire the output voltage signal of the sensor under different pressures in real time. S2.5 The pressure distribution monitoring module uses an array-type pressure sensor with a detection accuracy of 0.1 kPa and a detection range of 0-200 kPa. It is attached and fixed under the flexible contact layer of the flexible pressure application component to monitor the pressure distribution on the sensor surface in real time and ensure that the pressure difference at each point on the pressure application surface is ≤1 kPa.

4. The method for calibrating a flexible fabric pressure sensor with wide threshold uniform pressure according to claim 1, characterized in that: Step S3, graded pressure application and data collection, includes the following steps: S3.1 Fix the pre-treated flexible fabric pressure sensor to the test station of the calibration platform, ensuring that the sensor's detection surface is completely in contact with the flexible contact layer of the flexible pressure application component, without wrinkles or offset. S3.

2. Pressure is applied according to the preset pressure levels by the pressure control module. The pressure levels are divided into low pressure, medium pressure and high pressure. The low pressure level is 0-50 kPa, with a calibration pressure point set every 5 kPa; the medium pressure level is 50-150 kPa, with a calibration pressure point set every 10 kPa; and the high pressure level is 150-200 kPa, with a calibration pressure point set every 20 kPa. S3.3 For each calibration pressure point, the pressure control module smoothly loads the target pressure at a rate of 0.5 kPa / s. After loading, the pressure is kept stable for 10 seconds. After the sensor output signal stabilizes, the sensor output voltage signal at that pressure point is acquired through the signal acquisition module. The acquisition is repeated 5 times for each pressure point, and the average value of the 5 acquisition results is taken as the reference value of the sensor output signal corresponding to that calibration pressure point. S3.4 During the pressure holding process at each pressure point, the pressure distribution on the sensor surface is monitored in real time by the pressure distribution monitoring module. If the pressure difference between any two points on the pressure surface is greater than 1 kPa, the calibration of that pressure point is stopped immediately, the contact state between the flexible pressure application component and the sensor is adjusted, and the pressure application and data acquisition at that pressure point are repeated until the pressure distribution meets the uniformity requirements.

5. The method for calibrating a flexible fabric pressure sensor with wide threshold uniform pressure according to claim 1, characterized in that: Step S4, calibration data processing and model establishment, includes the following steps: S4.

1. Compile the pressure values ​​of all calibrated pressure points collected in step S3 with the corresponding sensor output signal reference values, and eliminate abnormal data caused by equipment interference; the criterion for judging abnormal data is: the deviation of a certain collected value from the average value of that pressure point is >5%; S4.

2. A piecewise fitting method is used to establish a model relating pressure values ​​to sensor output signals, wherein: For the low pressure range of 0 ~ 50 kPa, a linear fitting algorithm is used, and the fitting formula is: ； in, Where x is the sensor output voltage and x is the pressure value. The fitting coefficients for the low-pressure range range from 0.02 to 0.

03. This is the intercept for the low-pressure range, with a value ranging from 0.1 to 0.

2. For the pressure range of 50-150 kPa, a quadratic polynomial fitting algorithm is used, and the fitting formula is as follows: ； in, The range of values ​​is ~ , The value range is 0.01 ~ 0.

02. The value range is 0.3 ~ 0.5; For the 150-200 kPa high-pressure range, a cubic polynomial fitting algorithm is used, and the fitting formula is as follows: ； in, The range of values ​​is ~ , The range of values ​​is ~ , The value range is 0.005~0.

01. The value range is 0.8 to 1.0; S4.3 Calculate the calibration error of the fitting model for each pressure range. The formula for calculating the calibration error is as follows: ； in, This represents the actual applied pressure value. To ensure that the calibration error of each pressure range is ≤5% for the pressure values ​​calculated by fitting the model.

6. The method for calibrating a flexible fabric pressure sensor with wide threshold uniform pressure according to claim 1, characterized in that: Step S5, calibration result verification and correction, includes the following steps: S5.

1. Within the pressure range of 0-200 kPa, randomly select 10 verification pressure points; Among them, three low-pressure ranges were selected: 10 kPa, 25 kPa, and 40 kPa. Four medium-pressure ranges were selected: 60 kPa, 80 kPa, 120 kPa, and 140 kPa. Three high-pressure ranges were selected: 160 kPa, 180 kPa, and 190 kPa. S5.

2. Apply pressure to each verification pressure point according to the pressure application method in step S3, collect the sensor output signal, and calculate the corresponding calibration pressure value through the piecewise fitting model established in step S4. S5.3 Compare the actual applied verification pressure value with the calculated calibration pressure value; If the error of all verification pressure points is ≤5%, the calibration is deemed qualified, and the wide threshold uniform pressure calibration of the flexible fabric pressure sensor is completed. If the error of any verification pressure point is greater than 5%, return to step S3, reselect the calibration pressure point within the pressure range corresponding to the error for pressure application and data acquisition, and re-execute the model building in step S4 until the error of all verification pressure points meets the requirement of ≤5%.

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