WO2001036930A1

WO2001036930A1 - Method and apparatus for pressure measurement

Info

Publication number: WO2001036930A1
Application number: PCT/JP2000/008144
Authority: WO
Inventors: Yasuhiro Komai; Yukio Masuda
Original assignee: Nt Engineering Kabushiki Kaisha
Priority date: 1999-11-18
Filing date: 2000-11-17
Publication date: 2001-05-25
Also published as: JP2001147172A

Abstract

A pressure detection apparatus (10) uses an absolute pressure measurement system, in which a pressure detector (22) is provided in a channel (16) through which compressed fluid, such as compressed air, is supplied from an air supply (12) to a workpiece (14). The apparatus includes an oscillating and modulating sensor (18) that converts changes in pressure of compressed air directly into changes in frequency, and a counter circuit (20) that directly receives the converted frequencies as digital signals. The apparatus provides accurate measurements of very small changes in pressure while using a simple configuration and a simple process.

Description

Description Pressure detection method and device Technical field

The present invention relates to a pressure detecting method and apparatus for supplying a pressurized fluid to a work and detecting pressure leak of the work. Background art

For example, if a small hole is formed in a machined container-shaped work, or if there is a small gap in the fitting part when assembling the work, the gas supplied into the work is Gas such as oil or liquid such as oil (hereinafter, referred to as fluid) force may leak from the hole or the gap.

Therefore, a leak tester is used to detect whether or not there is a fluid leakage in such a container-like work. In general, a leak tester employs a pressure detection method using air pressure as a medium, and the determination of whether or not there is fluid leakage is performed by measuring the pressure of 0.5 to 5 atmospheres in the object (work). This is done by sealing the air pressure under pressure and detecting how the air pressure changes.

Specifically, a typical leak tester uses a sensor that combines a diaphragm and a strain gauge to detect pressure. Then, when the pressure acting on the diaphragm changes while the reference voltage for measurement is applied to the strain gauge, the strain gauge changes accordingly, and the voltage value applied to the strain gauge changes. Therefore, the pressure is detected by extracting the change in voltage applied to the strain gauge as a change in pressure.

In recent years, with the rise of environmental problems, very small leaks, which were previously regarded as allowable values, have become a problem. For this reason, the leakage of fluid from the work tends to be regulated very strictly, and the demand for the detection accuracy of the leak tester is also increasing. However, the conventional leak tester has a problem with the pressure detection method, There is a problem that the demand for high detection accuracy cannot be satisfied.

That is, in a sensor combining a diaphragm and a strain gauge, in order to achieve high-precision pressure detection, a reference voltage to the strain gauge, which is a reference for the measurement, must be stable with high accuracy. However, the reference voltage is made of a so-called bridge circuit, which is liable to change over time due to a change in resistance due to heat, etc., and the pressure is detected based on the voltage causing the change over time. Therefore, the detected value includes an error such as power.

In addition, a so-called digital circuit operation is used to determine whether to read the detected voltage value. Here, the detected voltage is an analog value, and it is necessary to perform a so-called analog / digital (AZD) conversion process of converting the detected voltage into a digital value. However, the pressure change to be detected is a very small value, and in order to obtain a sufficient digital value in the conversion process, the detected voltage value must be greatly amplified by an amplifier circuit. At that time, if the voltage value is greatly amplified, the noise component and the drift component are naturally included in the voltage value, and the measured value also includes an amplification error.

On the other hand, if the detection voltage is not amplified by the amplifier circuit, a voltage having a very small change width is converted into a digital signal, and a small change may not be converted into a digital signal. This makes it impossible to judge the force due to a large change in pressure, and consequently raises a problem that a small change in pressure cannot be detected unless the detected value is amplified.

Even if there is a deviation, the detection of pressure change by the combination of the diaphragm and the strain gauge will include a conversion error in the process of converting the analog detection value to digital, and will also add the drift of the strain gauge reference voltage, etc. It is pointed out that high-precision measurement cannot be performed.

The present invention is to solve this kind of problem, and to provide a pressure detection method and apparatus capable of detecting a small pressure change with high accuracy and smoothness by a simple process and configuration. With the goal. Disclosure of the invention

After the pressure change of the pressurized fluid for detecting the pressure leak of the work is directly converted into the frequency change, the converted frequency is directly supplied to the counter circuit as a digital signal. Further, a pressure change is obtained as a count value by performing a counting process in the counter circuit. This avoids errors during amplification and conversion, such as when pressure is detected as an analog value, and makes it possible to detect pressure changes for leak detection with high accuracy and reliability.

Further, the oscillation modulation type sensor includes a high frequency oscillating means for generating a MHZ (megahertz) band reference frequency, a winding coil connected to the high frequency oscillating means, and a retractable coil disposed in the winding coil. And a probe that directly modulates the reference frequency by engaging and displacing the diaphragm that is deformed by the pressure change. For this reason, the change in pressure directly changes the frequency, and the pressure can be detected with high accuracy. In addition, since a high frequency is used, it is possible to reliably and quickly detect a small change in pressure.

Here, the high frequency oscillation means includes a crystal oscillation circuit and a battery power supply connected to the crystal oscillation circuit. The crystal oscillation circuit can obtain a stable reference frequency and can accurately and stably detect a pressure change. The battery power supply is not affected by noise and drift unlike a commercial power supply, and by using this battery power supply, a more stable and accurate reference frequency can be obtained. At that time, by using a temperature compensation circuit, it becomes possible to generate a stable oscillation frequency with a small drift error even with a temperature change.

Furthermore, the modulated reference frequency can be directly applied to so-called FM transmission or PM transmission, and this can be sent directly to the counter circuit as a detection signal. In this case, in order to send the detection signal to a relatively distant counter circuit, a high-frequency amplification output circuit that performs frequency processing of the reference frequency is provided.By directly performing digital amplification, conversion errors and delivery errors can be prevented. Can be avoided. The transmission method may be a wired method or a wireless method.

Also, mixed frequency processing is performed to facilitate reading of the detection signal. In this mixed frequency processing, a mixer signal having a frequency close to the transmitted detection signal is generated by another oscillation circuit, and the detection signal and the mixer signal are transmitted to a mixer circuit. In the mixer circuit, a converted frequency signal is generated by subtracting the high-frequency carrier component from the detection signal.

Further, in order to read the converted frequency signal by the counter method, first, the converted frequency signal is subjected to half-wave processing to obtain a half-wave shape detection signal. On the other hand, for the counter, a very high-precision high-frequency reference signal is oscillated from the clock oscillation circuit to generate a clock signal, and then this clock signal is mixed with the half-wave shape detection signal. A counting signal is obtained. Next, the count signal is subjected to count reading processing by a counter circuit, whereby a pressure change is detected as a count value. In this way, by using a frequency signal that is a digital signal as the detection signal and performing digital reading processing on the detection signal, high-precision reading processing without conversion errors can be reliably performed. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an explanatory diagram of an overall configuration of a pressure detecting device according to a first embodiment of the present invention. FIG. 2 is an explanatory diagram of a crystal oscillation circuit constituting the pressure detecting device according to the first embodiment. is there.

FIG. 3 is an explanatory diagram of frequency characteristics of a temperature compensation circuit provided in the crystal oscillation circuit.

FIG. 4 is an explanatory diagram of a circuit constituting the pressure detecting device according to the first embodiment. FIG. 5 is an explanatory diagram of the entire configuration of the pressure detecting device according to the second embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is an explanatory diagram of an overall configuration of a pressure detection device 10 for performing a pressure detection method according to a first embodiment of the present invention. This pressure detecting device 10 is an absolute type in which a pressure detector 22 is arranged in communication with an air pipe 16 for supplying a pressurized fluid, for example, pressurized air from an air supply source 12 to a work 14. An oscillation modulation type sensor 18 that directly converts a pressure change of the pressurized air into a frequency change, and a counter that directly supplies the converted frequency as a digital signal. Circuit 20.

The oscillation modulation type sensor 18 is provided with a pressure detector 22 communicating with the air line 16 on the downstream side of the on-off valve 21, and the pressure detector 22 is provided with a pressure fluctuation in the air line 16. A diaphragm 24 deformed by the diaphragm 24, a measuring element 26 that is displaced by engaging with the diaphragm 24, and a winding coil 28 in which the measuring element 26 is disposed so as to be able to move forward and backward are provided. The wound coil 28 is connected to the oscillation modulation circuit 30, and the oscillation modulation circuit 30 is connected to high-frequency oscillation means 32 that generates a reference frequency in the MHZ (megahertz) band.

The high-frequency oscillation means 32 includes a crystal oscillation circuit 34 and a battery power supply (DC power supply) 36 connected to the crystal oscillation circuit 34. As shown in FIG. 2, the crystal oscillation circuit 34 includes a crystal oscillator 38 and an oscillation transistor 40, and a temperature compensation circuit 42 is provided in order to avoid a change in the oscillation frequency due to a temperature change. Provided. This temperature compensating circuit 42 includes a kind of inverse characteristic circuit, for example, a temperature compensating capacitor. As shown in FIG. 3, the frequency characteristic with respect to temperature has a characteristic opposite to that of the crystal oscillator 38. This cancels out changes due to temperature.

As shown in FIG. 1, the oscillation modulation circuit 30 extracts a change in pressure as a high-frequency signal f 1 and sends the high-frequency signal ί 1 to a high-frequency amplification output circuit 44. As shown in FIG. 4, the high-frequency amplification output circuit 44 supplies a mixer circuit 46 that processes the amplified and output detection signal f 2 and the mixer signal f 3 at a mixed frequency to generate a converted frequency signal f 4. At the same time, the mixer circuit 46 is connected to a mixer signal oscillation circuit 48 that generates the mixer signal f3 having a frequency close to the detection signal f2.

The mixer circuit 46 is connected to a conversion frequency amplification circuit 50 that amplifies the conversion frequency signal f 4 to generate an amplified conversion frequency signal f 5. The conversion frequency amplification circuit 50 includes the amplification conversion frequency Half-wave processing of the signal f5 to obtain the half-wave shape detection signal ί6 The wave circuit 52 is connected. The clock oscillation circuit 54 that generates the high-frequency clock signal f7 is connected to the counter mixer 56 together with the half-wave circuit 52. In the counter mixer 56, the half-wave shape detection signal f6 and the clock are output. The count signal f8 is obtained by mixing the signal f7, and the count signal f8 is sent to the counter circuit 20. The counter circuit 20 includes a display 58 for displaying the detected value.

The operation of the pressure detecting device 10 thus configured will be described below. First, in a state where the work 14 is connected to the air line 16, after the caro-pressure air is supplied from the air supply source 12 to apply the measurement pressure to the work 14, the opening / closing valve 21 is opened. Closed. Here, when the work 14 has a leak and the measurement pressure applied to the work 14 is reduced, the diaphragm 24 constituting the pressure detector 22 is deformed. A measuring element 26 is connected to the diaphragm 24. When the diaphragm 24 is deformed due to a change in pressure, the measuring element 26 is displaced in the winding coil 28.

At this time, a reference frequency in the MHZ (megahertz) band is applied to the wound coil 28 from the crystal oscillation circuit 34, and when the measuring element 26 moves in the wound coil 28, The load inductance of the coil 28 changes. For this reason, the reference frequency is modulated, and this modulation frequency is directly taken out by the oscillation modulation circuit 30 as the high frequency signal f 1, and the high frequency signal f 1 is sent to the high frequency amplification output circuit 44. The high-frequency amplification output circuit 44 amplifies the high-frequency signal f1 so that it can be sent to a distant place, and outputs the detection signal f2.

Next, mixed frequency processing is performed to facilitate reading of the detection signal f2. That is, as shown in FIG. 4, the mixer signal oscillation circuit 48 generates a mixer signal ί3 having a frequency close to the transmitted detection signal ί2, and outputs the detection signal f2 and the mixer signal f3. Is sent to the mixer circuit 46. The mixer circuit 46 generates a converted frequency signal ί4 in the KHZ (kilohertz) band obtained by subtracting the high-frequency carrier component from the detection signal f2.

Further, in order to read the converted frequency signal f 4 in the counter method, first, the converted frequency signal f 4 is amplified by the converted frequency amplifying circuit 50 and the amplified converted frequency signal f 4 is amplified. After generating the signal f5, the half-wave circuit 52 half-processes the amplified converted frequency signal 半 5 to obtain a half-wave shape detection signal f6. On the other hand, after the clock oscillation circuit 54 oscillates a very high-precision high-frequency reference signal to generate a clock signal f7, the clock signal f7 becomes a half-wave shape. The count signal f 8 is obtained by mixing with the detection signal f 6.

Next, the count signal f8 is subjected to count reading processing by the counter circuit 20, whereby a pressure change is detected as a count value. At this time, the counter method counts the number of signals to be measured within a fixed time, and the change in pressure detected as a high-frequency signal f 1 by this reading process is minute 1 Hz (Hertz). In addition, it can read accurately to the order of 1 HZ (hertz) or less. Note that the shorter the time axis of the clock signal f7, which is the counted component, becomes, the more accurate the counting becomes possible. For example, several tens of MHz (megahertz) to 200 MHz (megahertz) Are used.

As described above, in the first embodiment, the diaphragm 24, the measuring element 26 that is displaced by engaging with the diaphragm 24, and the winding in which the measuring element 26 is disposed so as to be able to advance and retreat. An oscillation modulation type sensor 18 having a coil 28 is used to directly change a change in pressure of the work 14 into a change in frequency to perform a pressure leak test on the work 14. As a result, the pressure can be detected not by an analog value but by a digital value. By digitally reading a frequency signal which is a digital signal, a high-precision reading process without an amplification error or a conversion error can be performed. The effect that the high-precision pressure leak inspection of 14 is surely performed is obtained.

Further, the high-frequency oscillating means 32 includes a crystal oscillating circuit 34, so that a stable reference frequency can be obtained, and a pressure change can be accurately and stably detected. In addition, since a high frequency in the MHZ (megahertz) band is used as the reference frequency, there is an advantage that even a small change in pressure can be detected reliably and quickly. Furthermore, since the battery power supply 36 is used, it is possible to obtain a more stable and accurate reference frequency without being affected by noise and drift as in a commercial power supply. At this time, by using the temperature compensation circuit 42, On the other hand, a stable oscillation frequency with little drift error can be generated. Furthermore, since the high-frequency signal f1 is amplified through the high-frequency amplification output circuit 44 to obtain the detection signal f2, the detection signal f2 can be reliably sent to the counter circuit 20 which is relatively far away. become. The detection signal ί2 is obtained by directly digitally amplifying the high-frequency signal f1, and can avoid occurrence of a conversion error or a delivery error.

FIG. 5 is an explanatory diagram of the overall configuration of a pressure detection device 80 for performing the pressure detection method according to the second embodiment of the present invention. The same components as those of the pressure detection device 10 according to the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. The pressure detection device 80 is a pressurized fluid, for example, A differential pressure measurement method is provided in which a pressure detector 22 is disposed in communication with an air pipeline 82 that supplies pressurized air from an air supply source 12 to a work 14 and a master 84. A work 14 and a master 84 are connected to the air line 82, and the work 14 and the master 84 can be shut off via a bypass valve 86. The master 84 has the same volume and the same shape as the work 14 to be measured, and it is previously detected that there is no pressure leak. The master 84 may not have the same volume and the same shape as the work 14 in some cases.

In the pressure detection device 80 configured as described above, the work 14 to be subjected to the pressure leak inspection and the master 84 are connected to the air line 82 and the compressed air is supplied from the air supply source 12. Then, after the measured pressure is applied to the work 14 and the master 84, the open / close valve 21 and the bypass valve 86 are closed. Here, if a leak exists in the work 14, a pressure difference (P 2 −P 1) occurs between the work 14 and the master 84, and the diaphragm 24 constituting the pressure detector 22 is deformed.

As a result, the tracing stylus 26 is displaced in the coil 28 and the change in the pressure of the work 14 is directly changed to the change in the frequency. The same effect as that of the first embodiment can be obtained, for example, a highly accurate pressure leak inspection of the work 14 can be reliably performed. Industrial applicability

In the pressure detection method and device according to the present invention, after the pressure change of the pressurized fluid for detecting the pressure leak of the work is directly converted into the frequency change, the converted frequency is directly converted into the digital value. Since the pressure change is supplied to the counter circuit as a signal and the pressure change is obtained as a count value, errors during amplification and conversion, such as when pressure is detected as an analog value, are avoided, and pressure changes for leak detection are accurately and accurately detected. It will be possible to detect it reliably. As a result, with a simple process and configuration, the pressure leakage inspection processing of the work is efficiently and accurately performed.

Claims

The scope of the claims

1. A pressure detecting method for detecting a pressure leak of the work by supplying a pressurized fluid to the work,

Directly converting the pressure change of the pressurized fluid into a frequency change; and supplying the converted frequency directly to a counter circuit as a digital signal.

A step of obtaining the pressure change as a count value by performing a counting process in the counter circuit;

A pressure detection method comprising:

2. The pressure detecting method according to claim 1, wherein after modulating a reference frequency in an MHZ (megahertz) band by a change in pressure of the pressurized fluid, the modulated reference frequency is subjected to frequency processing and sent to the counter circuit. A pressure detector characterized by the above-mentioned.

3. A pressure detecting device for supplying a pressurized fluid to a work to detect a pressure leak of the work,

An oscillation modulation type sensor for directly converting a pressure change of the pressurized fluid into a frequency change,

A counter circuit to which the converted frequency is directly supplied as a digital signal.

A pressure detecting device comprising:

4. The pressure detecting device according to claim 3, wherein the oscillation modulation type sensor includes a high frequency oscillation unit that generates a reference frequency in an MHZ (megahertz) band;

A winding coil connected to the high-frequency oscillation means,

A tracing stylus that is arranged in the wound coil so as to be able to advance and retreat, and directly modulates the reference frequency by engaging and displacing a diaphragm that is deformed by the pressure change;

A pressure detecting device comprising:

5. The pressure detection device according to claim 4, wherein the high-frequency oscillation means includes a temperature compensation circuit.

6. The pressure detection device according to claim 4, further comprising a high-frequency amplification output circuit for amplifying the modulated reference frequency at a high frequency and sending the amplified reference frequency to the power counter circuit.

7. The pressure detection device according to claim 6, wherein a mixer circuit that performs a mixed frequency process on a high frequency signal and a mixer signal obtained by modulating the high frequency amplified reference frequency to generate a converted frequency signal,

A half-wave circuit that performs half-wave processing on the converted frequency signal to obtain a half-wave shape detection signal; a clock oscillation circuit that generates a high-frequency clock signal;

A counter mixer for mixing the half-wave shape detection signal and the cook signal to obtain a count signal;

A pressure detecting device comprising:

8. The pressure detection device according to claim 4, wherein the high-frequency oscillating means includes a crystal oscillation circuit,

A battery power supply connected to the crystal oscillation circuit;

A pressure detecting device comprising:

9. The pressure detection device according to claim 8, wherein the high-frequency oscillation means includes a temperature compensation circuit.

10. The pressure detection device according to claim 8, further comprising a high-frequency amplification output circuit for high-frequency amplifying the modulated reference frequency and sending the amplified reference frequency to the power counter circuit.

11. The pressure detector according to claim 10, wherein the high frequency signal and the mixer signal obtained by modulating the high frequency amplified reference frequency are subjected to mixed frequency processing to generate a converted frequency signal. Circuit and

A half-wave circuit that performs half-wave processing on the converted frequency signal to obtain a half-wave shape detection signal; a clock oscillation circuit that generates a high-frequency cut-off signal;

A counter mixer for mixing the half-wave shape detection signal and the clock signal to obtain a count signal;

A pressure detecting device comprising: