Pressure measurement device

Abstract

To ensure high accuracy by constituting a plurality of inexpensive pressure sensors, and to perform pressure measurement with guaranteed reliability even when measured at multiple points.SOLUTION: In a pressure measurement device, a plurality of pressure sensors 4-1, 4-2, 4-3, ...4-n are arranged in the device, and measurement data collected from the plurality of pressure sensors at predetermined synchronous timing are subjected to averaging processing 7 to obtain a measurement value. In the pressure measurement device, the range in which the plurality of pressure sensors are arranged is determined according to the pressure resolution of the wave to be measured.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a pressure measuring device comprising a plurality of pressure sensors. [Background technology]

[0002] By measuring infrasound (ultrasound), which is sound with a frequency lower than the human audible frequency (approximately 20Hz to 20KHz), research is being conducted to predict natural disasters such as earthquakes and volcanic activity, as well as to evaluate the structure of buildings and explore for resources. As a pressure gauge capable of measuring these infrasounds, for example, a high-precision pressure gauge using a quartz crystal oscillator manufactured by Paro Scientific is known. This pressure gauge can achieve a resolution of one billionth and an accuracy of 0.01%FS, but it is an expensive measuring instrument.

[0003] Incidentally, capacitance sensors manufactured using MEMS (Micro Electro Mechanical Systems) technology are inexpensive, compact, and energy-saving devices that are used in a variety of fields. However, using them as a standalone device to measure the above-mentioned infrasound is not practical due to insufficient signal-to-noise ratio and dynamic range. As a means for solving such problems, for example, a technique has been disclosed in which a plurality of MEMS acceleration sensors are used in a seismometer (eg, Patent Document 1).

[0004] The problem of Patent Document 1 is to reduce noise due to thermal noise contained in the output of a MEMS acceleration sensor and to reduce quantization error by an A / D converter. To reduce noise due to thermal noise, each analog output signal from the sensor is added to reduce the noise components, and noise in unnecessary frequency ranges is removed through a band-pass filter. To reduce quantization error, noise is removed in real time using an IIR (infinite impulse response) low-pass filter after oversampling. As described above, in order to reduce noise, it is preferable to increase the number (N) of sensors because the noise component caused by addition processing is proportional to the inverse of the square root of the number of sensors (N). However, when the number of sensors is increased, the mounting area also increases, and sensors that are far apart will detect different waves even if the measurement timing is the same, which causes a problem of reducing the resolution of the measuring instrument.

[0005] Infrasound is also used in scientific research and applications, and taking advantage of its ability to propagate long distances through the atmosphere, it is used to monitor earthquakes and volcanic eruptions, observe meteorological phenomena, monitor tsunamis, etc. Because the frequency of sound waves is low, they are also used to evaluate the structure of buildings and underground facilities and to explore underground resources. In such a case, when observations need to be made at multiple points, it becomes necessary to make observations at each observation point at precisely synchronized times. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2009-31032 A Summary of the Invention [Problem to be solved by the invention]

[0007] The problem to be solved is that although measuring infrasound is important for observing natural phenomena, high-performance pressure measurement devices are expensive, and particularly when observations need to be made at multiple points, this entails significant costs. [Means for solving the problem]

[0008] The main feature of the present invention is that a plurality of inexpensive, compact and power-saving capacitance sensors manufactured by MEMS (Micro Electro Mechanical Systems) technology are used as pressure sensors, and the range of placement of these sensors on a substrate is determined according to the required resolution. Also, the reliability of synchronized measurement data is guaranteed even when the sensor is used at multiple points. Effect of the Invention

[0009] The pressure measuring device of the present invention is configured to obtain the required resolution by using multiple inexpensive capacitance sensors. In addition, by using GPS (Global Positioning System) to synchronize the timing of the multiple sensors and adding a timestamp to the measurement data, the reliability of the measurement data synchronized at multiple points can be guaranteed. [Brief description of the drawings]

[0010] [Figure 1] 3A and 3B are diagrams illustrating the arrangement of pressure sensors on a substrate of the pressure measuring device according to the present invention. [Diagram 2] 4 is a diagram for explaining the distance between pressure sensors corresponding to the pressure resolution of the wave to be measured according to the present invention. FIG. [Diagram 3] 1 is a conceptual diagram showing an overall configuration of a pressure measuring device according to the present invention. [Figure 4] FIG. 4 is a diagram illustrating a process flow of the pressure measuring device according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] We have created a pressure measurement device that can obtain the required resolution with an inexpensive configuration and can acquire synchronized measurement data at multiple points. Hereinafter, an embodiment of the present invention will be described with reference to the drawings. EXAMPLES

[0012] FIG. 1 is a diagram for explaining the arrangement of pressure sensors on a substrate of a pressure measuring device according to the present invention, in which 1 is a substrate on which a circuit pattern is printed, and 2-1, ... 2-8 are capacitance sensors as pressure sensors manufactured by MEMS technology and arranged on the substrate 1. Each capacitance sensor has the same performance, and is arranged in a horizontal row of four sensors at equal intervals and two vertical rows of eight sensors in total. The distance X between the capacitance sensors is the longest between the sensor 2-1 and the sensor 2-8 or between the sensor 2-4 and the sensor 2-5. In this state, when each capacitance sensor measures a constant frequency, the measured value will differ depending on the distance between the sensors, even if each sensor starts measurement at the same timing. In other words, the values ​​measured by each sensor should be the same, but the amount of deviation is reflected in the resolution. The sensor outputs with the largest deviation are between sensors 2-1 and 2-8, and between sensors 2-4 and 2-5, which is the limit of the resolution.

[0013] 2 is a diagram for explaining the distance between pressure sensors according to the present invention, which corresponds to the pressure resolution of the wave to be measured. For example, when the wave 3 to be measured has an amplitude A=100 Pa, a frequency=5 Hz, and is measured with a pressure resolution (dA) of 0.1 Pa, if the wave propagation speed is 340 m / s, the wavelength λ is 340÷5=68 m. Here, when the wave in λ / 2 interval is linearly approximated, the relationship A:dA=λ / 2:X is satisfied, so that X=34 mm. In other words, the wavelength shift at this pressure resolution of 0.1 Pa is a maximum of 34 mm, which means that the distance between the pressure sensors must be within 34 mm. In this way, the range (distance) in which multiple pressure sensors are arranged can be determined, and by narrowing the range X in which the sensors are arranged so as to shorten the section in which the wave is linearly approximated and increasing the density of the mounting positions, the wave to be measured can be more closely approximated and the accuracy (pressure resolution) can be improved.

[0014] FIG. 3 is a conceptual diagram showing the overall configuration of a pressure measuring device according to the present invention, in which 4-1, 4-2, 4-3, . . . 4-n denote n capacitance sensors manufactured by MEMS technology, 5-1, 5-2, 5-3, . . . 5-n denote n A / D converters that convert output signals from the n capacitance sensors into digital signals, 6-1, 6-2, 6-3, . . . 6-n denote n signal processing units that perform oversampling or the like on the digital signals output from the n A / D converters described later, 7 denotes a calculation unit that averages data obtained from the n signal processing units, 8 denotes an IIR low pass filter (LPF) that cuts off the high frequency components of the averaged signal, and 9 denotes a GPS (Global Positioning System) that sends a signal to a synchronization circuit 10 described later and adds a timestamp to a measurement value. Reference numeral 10 denotes a synchronization circuit that simultaneously activates n A / D converters 6-1, 6-2, 6-3, ... 6-n at a predetermined sampling period to convert the output signal into a time-series digital signal, and reference numeral 11 denotes an output unit that outputs a measurement value at a predetermined timing.

[0015] As explained in Figure 1, the range in which the n capacitance sensors can be placed is determined so as to obtain a predetermined accuracy (pressure resolution), and the sensors are placed within that range on a substrate configured in a planar or three-dimensional shape. The pressure signals measured by these sensors are converted into digital signals by n A / D converters. The timing at which conversion starts is determined by sending a synchronization signal (every 0.1 ms in this embodiment) to each A / D converter by a synchronization circuit 10 based on a pulse 1 PPS output from the GPS 9 every second.

[0016] The signals output from the n A / D converters, sampled at a predetermined timing based on a synchronization signal from the synchronization circuit 10, are input to the signal processing unit 6-1, etc. In the signal processing units 6-1, ..., 6-n, since the MEMS capacitance sensor has a large noise due to thermal noise, the temperature is simultaneously measured and the input pressure signal is corrected. In other words, the pressure signal and temperature measurement value sampled at a predetermined timing are oversampled, and the arithmetic average of the pressure signal corrected by the temperature measurement value is calculated, and the inherent noise components contained in each sensor output are reduced in proportion to the inverse of the square root of the number of oversamplings. Here, the condition is that each sensor has the same performance, but there is a deviation in the frequency response performance of each sensor, and when sampling is performed at a period within the frequency band, a sensor with a long time constant and low response performance with respect to air pressure displacement tends to always measure an underestimated displacement. Therefore, the output of each sensor must be reduced to a frequency band that is not affected by the measurement period by oversampling processing.

[0017] The signals output from each of the signal processing units 6-1, 6-2, 6-3, . . . 6-n are averaged by the calculation unit 7, so that noise components among the n sensor outputs are reduced. In other words, by taking the arithmetic average of a total of n capacitance sensors, the noise components between the outputs of each sensor are reduced in proportion to the inverse of the square root of n, thereby expanding the dynamic range of measurement.

[0018] The output signal averaged by the calculation unit 7 passes through a low-pass filter 8, which removes unnecessary noise components in a high frequency range. The low-pass filter 8 is an IIR filter, and processes continuously in real time. The cutoff frequency of the low-pass filter 8 can be set as a parameter taking into consideration the measurement band required depending on the application.

[0019] 4 is a diagram for explaining the flow of processing in the pressure measuring device according to the present invention, in which temperature measurement (S10) and pressure measurement (S20) are performed using capacitance sensors 4-1, 4-2, 4-3, ..., 4-n and temperature sensors (not shown) built into them, and each measurement data is oversampled (S30). Digital signals output from n A / D converters 5-1, 5-2, 5-3, ..., 5-n are converted by signal processing units 6-1, 6-2, 6-3, ..., 6-n into pressure data in which noise components dependent on the temperature of each capacitance sensor have been corrected in accordance with the measurement data obtained by temperature measurement (S40).

[0020] The corrected pressure data (measurement data) from each sensor is averaged by the calculation unit 7 (S50) and output to the output unit 11 via the low-pass filter 8 (S60). Here, depending on the desired period to be outputted externally, the above processes such as temperature measurement (S10), pressure measurement (S20), etc. are repeated in sequence (S70) from the measurement data converted into a digital signal based on the sample period from the synchronization circuit 10 until that period is reached (N), and the measurement value is stored in the output unit 11 at each timing.

[0021] Then, when the predetermined period for outputting to the outside is reached (Y), the measurement values ​​stored in the output unit 11 up to that point are averaged (S80). This essentially achieves the same effect as oversampling the desired period for outputting and taking an arithmetic average. This makes it possible to obtain a highly accurate pressure measurement value. Next, a time stamp at that point is added by the GPS 9 (S90), and the pressure measurement value is output to the outside from the output unit 11 in a predetermined format (S100).

[0022] In this way, attaching a timestamp to a measurement value is an effective means of locating the source of a pressure event, such as an earthquake, because, for example, when pressure is observed at multiple distant points, it is necessary to know the absolute time and synchronization timing of the measurement value at each point. That is, the pressure measuring device of the present invention uses GPS to output measured values ​​with time stamps synchronized with global time, making it possible to perform time-series synchronized measurements even in a multi-point observation network. For example, the location and scale of the source can be estimated by obtaining the time of occurrence and the amount of attenuation from a large number of infrasound measurement results measured in a distributed manner several kilometers apart.

[0023] Also, instead of the above-mentioned processing method of performing the arithmetic average, two sensors are provided as redundant sensors for the N sensors, and an initial default value of, for example, 1 atmosphere is preset, and the measurement data from each sensor is compared to obtain the maximum value and the minimum value with the largest amount of change. Then, the N measurement data excluding the maximum and minimum values ​​is averaged to obtain the measurement value at this timing. Thereafter, in the same manner, the measurement value obtained by averaging at the previous timing is compared with the measurement data of each of the (N+2) sensors to obtain the maximum and minimum values, and the arithmetic average of the N measurement data excluding these measurement data is obtained to obtain the measurement value at this timing. Note that if there are multiple identical maximum or minimum values, it is considered that the measurement data does not contain a large noise component (is close to the actual measurement value), so the arithmetic average is obtained using the measurement data of the predetermined N sensors.

[0024] Using the previous measurement value as a reference, the maximum and minimum measurement data are considered to have the greatest deviation from the current measurement value (average value) and to contain the largest noise components. Therefore, by calculating the additive average in this manner, the measurement data containing the largest noise components is excluded and then averaged, which is closer to the actual measurement value than the above processing method in which the measurement data from all sensors are averaged, thereby improving the accuracy of the measuring device. It should be noted that the present invention is not limited to the above-described embodiment, and various modifications and applications are possible within the scope of the present invention. [Industrial Applicability]

[0025] It will now be possible to realize inexpensive, highly accurate pressure measurement devices, which will enable the acquisition of useful information in fields where measuring infrasound is essential, such as natural sciences, civil engineering and construction, disaster prevention, and resource exploration. [Explanation of symbols]

[0026] 1 Board 2-1 Capacitive sensor 3 waves 4-1 Capacitive sensor 5-1 A / D converter 6-1 Signal Processing Section 7 Arithmetic section 8 Low-pass Filter 9. GPS 10 Synchronous Circuits 11 Output section

Claims

1. A pressure measuring device in which a plurality of pressure sensors are disposed within the device, and measurement data collected from the plurality of pressure sensors at a predetermined synchronous timing is averaged to obtain a measurement value, A pressure measuring device, characterized in that a range in which the plurality of pressure sensors are arranged is determined according to a pressure resolution of a wave to be measured.

2. 2. The pressure measuring device according to claim 1, wherein the measurement data after the averaging process is passed through a low-pass filter having a predetermined cutoff frequency to remove noise components.

3. 2. The pressure measuring device according to claim 1, further comprising: a synchronization signal generated at the predetermined synchronization timing based on GPS and sent to the plurality of pressure sensors; and a time stamp added to the measured value and outputted.

4. 2. The pressure measuring device according to claim 1, further comprising: a measuring section configured to measure a pressure of the pressure sensor and a measuring section configured to measure the pressure of the pressure sensor.

5. 2. The pressure measuring device according to claim 1, wherein the pressure sensors are capacitance sensors manufactured by MEMS technology.

6. 2. The pressure measuring device according to claim 1, wherein the measurement value is calculated by averaging the measurement values ​​obtained until a predetermined period for outputting the measurement value to the outside is reached.

7. The pressure measuring device according to claim 1 , wherein the wave to be measured is infrasound.

8. 2. The pressure measuring device according to claim 1, wherein the averaging process is performed by excluding from the measurement data those measurement data for which the difference between the measurement data and the measurement value obtained by the previous averaging process is maximum and minimum.

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