Phase comparison detection method for air tightness of cavity

Abstract

The invention relates to a phase comparison detection method for cavity airtightness, and the method comprises the following steps: respectively detecting the air pressure of a test piece and a standard piece through a frequency output type pressure sensor, obtaining a standard piece frequency signal f1 and a test piece frequency signal f2, shaping the two signals into pulse signals, and carrying out the phase discrimination, the phase difference of the specific width between the two signals is subjected to pulse sampling to form a switch of a frequency measurement counting gate, in the counting gate, the frequency signal of the standard component and the frequency signal of the test piece are in full-period synchronization, the counted pulse numbers are n and m respectively, and differential pressure calculation is completed. The counting error of + / -1 pulse is overcome, and the detection precision of the air tightness of the cavity is improved.

Description

Technical Field

[0001] The invention relates to a phase comparison detection method for cavity air tightness, belonging to the technical field of cavity air tightness detection using a phase comparison method. Background Art

[0002] The air tightness of the cavity can be tested by connecting the test piece and the standard piece respectively with a pressure sensor. The standard piece is sealed as the basic condition. By detecting the pressure difference between the test piece and the standard piece, the leakage amount and leakage rate of the test piece can be obtained. This detection method has the advantages of simple structure, easy operation and low cost, and can be widely used in the air tightness detection of various airtight parts.

[0003] The use of frequency output pressure sensors can convert pressure signals into frequency signals, which is beneficial for signal transmission and digital processing. At this time, the pressure difference detection of the test piece and the standard piece for cavity air tightness becomes the frequency difference detection of two frequency signals. The commonly used frequency measurement method is the direct pulse counting frequency measurement by the microprocessor. Since the counting error of the general counter is ±1 pulse, it greatly affects the detection accuracy of cavity air tightness. In more serious cases, the frequency measurement errors of the test piece and the standard piece may be superimposed. The fundamental reason is that the frequency measurement counting gate is not synchronized with the frequency signals of the test piece and the standard piece during the detection time. Summary of the invention

[0004] The purpose of the present invention is to provide a phase comparison detection method for cavity air tightness, which utilizes the phase comparison relationship between the frequency signal of the standard part and the frequency signal of the test part to perform phase comparison between the signals and phase difference sampling to achieve high-precision cavity air tightness detection. The pulse count is controlled by utilizing the phase difference between the frequency signals of the standard part and the test part, so that the frequency measurement counting gate is synchronized with the frequency signals of the test part and the standard part, thereby greatly eliminating the counting error of ±1 pulse. The present invention has high measurement accuracy, simple circuit structure, and is easy to implement. It solves the problem of low phase comparison detection accuracy of cavity air tightness due to the ±1 pulse counting error and the failure of the frequency measurement counting gate to synchronize with the frequency signals of the test part and the standard part during the detection time in the background technology.

[0005] The technical solution of the present invention is:

[0006] A phase comparison detection method for cavity airtightness comprises the following steps:

[0007] Step 1: Use a frequency output type pressure sensor to detect the air pressure of the test piece and the standard piece respectively, and obtain the standard piece frequency signal f1 and the test piece frequency signal f2.

[0008] In the cavity air tightness detection system of the present invention, the standard part frequency signal f1 in the detection process is a reference signal with a frequency value of f1, and the frequency value of the test part frequency signal f2 is f2, and there is a small frequency deviation value from the frequency value f1. In the actual production process, the qualified test parts have little difference in air tightness from the standard parts, that is, when the standard part frequency signal f1 and the test part frequency signal f2 have the same nominal frequency, there is only a small frequency difference between the two signals.

[0009] The present invention utilizes the physical characteristics of phase comparison between frequency signals to achieve high-precision detection under the conditions of common devices. When there is only a small frequency difference between the standard component frequency signal f1 and the test component frequency signal f2, the phase difference between the two frequency signals is a monotonic periodic characteristic.

[0010] like Figure 1 As shown, taking the rising edge of the frequency signal as the phase comparison moment, assuming that the signals f1 and f2 coincide in phase at the initial moment, then the phase differences obtained by the phase comparison of every frequency signal cycle are △φ1, △φ2, △φ3, △φ4 respectively, then the signals f1 and f2 coincide in phase again, and then the phase difference changes are △φ1, △φ2, △φ3, △φ4 again.

[0011] Step 2: Shape the standard component frequency signal f1 and the test component frequency signal f2 into pulse signals, and use a phase detector to detect the phase difference between the two pulse signals.

[0012] The rising edges of the standard component frequency signal f1 and the test component frequency signal f2 are used as phase-detection trigger signals. The CPLD is used to convert the rising edges of the two frequency signals into pulse signals with the same frequency. Through this pulse shaping processing, the pulse widths of the standard component frequency signal f1 and the test component frequency signal f2 can be adjusted to improve the phase-detection accuracy.

[0013] Step 3: Use a pulse sampler to extract a phase difference of a specific width between the standard component frequency signal f1 and the test component frequency signal f2. This phase difference constitutes the switch of the frequency measurement counting gate.

[0014] Step 4: In the counting gate, the standard component frequency signal f1 and the test component frequency signal f2 are synchronized in full cycle.

[0015] The present invention utilizes the physical property of the stable change of the phase difference between frequency signals, extracts the same phase difference to form the switch signal of the frequency counting gate, can overcome the counting error of ±1 pulse, synchronizes the frequency signal of the test piece and the standard piece, and thus completes the high-precision cavity airtightness detection. Figure 1As shown, △φ1 is used as the counting gate switch signal. Since the switch signals have the same phase difference, and this phase difference is formed by comparing the standard component frequency signal f1 with the test component frequency signal f2, the full cycle synchronization of the standard component frequency signal f1 and the test component frequency signal f2 is achieved in this counting gate.

[0016] Step 5: In the counting gate, the number of pulses of the standard component frequency signal f1 is counted as n, and the number of pulses of the test component frequency signal f2 is counted as m, and the pressure difference calculation is completed.

[0017] The main innovation of the present invention is: when there is only a small frequency difference between the standard component frequency signal f1 and the test component frequency signal f2, a pulse counting switch is formed by utilizing a stably changing phase difference signal, and pulses of the standard component frequency signal f1 and the test component frequency signal f2 are counted separately in this counting switch, so that high-precision pulse counting can be performed on the changing test component frequency signal.

[0018] The positive effects of the present invention are: the instrument has a simple structure and is easy to implement. It utilizes the physical characteristics of phase comparison between frequency signals to achieve high-precision detection under the conditions of common devices. The pulse counting gate switch signal is controlled by detecting the steadily changing phase difference between the two pulse signals, thereby greatly eliminating the counting error of ±1 pulse. The full cycle synchronization of the standard part frequency signal f1 and the test part frequency signal f2 is achieved in this counting gate. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of frequency signal phase comparison in pressure difference measurement of the present invention;

[0020] Figure 2 It is a block diagram of the phase comparison pressure difference measurement system of the present invention. DETAILED DESCRIPTION

[0021] The purpose of the present invention is to provide a phase comparison detection method for cavity air tightness, which utilizes the phase comparison relationship between the frequency signal of the standard part and the frequency signal of the test part to perform phase comparison and phase difference sampling to achieve high-precision cavity air tightness detection, and utilizes the phase difference between the frequency signals of the standard part and the test part to control the pulse count, so that the frequency measurement counting gate is synchronized with the frequency signals of the test part and the standard part, thereby greatly eliminating the counting error of ±1 pulse. The present invention has high measurement accuracy, simple circuit structure, and is easy to implement, and solves the problem of low phase comparison detection accuracy of cavity air tightness due to ±1 pulse counting error and the failure of the frequency measurement counting gate to synchronize with the frequency signals of the test part and the standard part during the detection time in the background technology.

[0022] The present invention will be further described below by way of examples.

[0023] like Figure 2 As shown:

[0024] In this cavity air tightness detection system, compressed air is injected into the standard part and the test part for air tightness detection, with the air tightness of the standard part as a reference. The system uses a frequency output pressure sensor to detect the air pressure of the standard part and the test part respectively, and outputs the standard part frequency signal f1 and the test part frequency signal f2. Under the same nominal frequency, there is only a small frequency difference between the standard part frequency signal f1 and the test part frequency signal f2. The system makes full use of this relationship between the standard part and the test part in the actual cavity production and air tightness detection, which is different from the complex frequency conversion in other frequency measurement methods.

[0025] The detection system converts the rising edges of the standard component frequency signal f1 and the test component frequency signal f2 into pulse signals of the same frequency through a pulse shaping processing circuit. During the pulse shaping process, the common delay adjustment module in CPLD is used to control the pulse width of the standard component frequency signal f1 and the test component frequency signal f2 to improve the measurement resolution of the phase comparison.

[0026] The detection system uses CPLD to generate a phase-error detector module to perform phase comparison between the pulse signals of the standard component frequency signal f1 and the test component frequency signal f2. When the standard component frequency signal f1 and the test component frequency signal f2 have the same nominal frequency and a small frequency difference, the phase-error detector outputs a periodically monotonically changing phase difference signal.

[0027] The detection system uses a pulse sampling module controlled by a CPLD to set a phase difference of a specific width to generate a trigger pulse signal, and this pulse trigger signal constitutes a pulse counting gate for the standard component frequency signal f1 and the test component frequency signal f2. Therefore, the periodically appearing phase difference signal constitutes a synchronous counting switch signal for the signal f1 and the signal f2.

[0028] During pulse counting, the standard part frequency signal f1 and the test part frequency signal f2 have an integer synchronization relationship, which greatly eliminates the counting error of ±1 pulse and improves the detection accuracy. The number of pulses of the standard part frequency signal f1 is counted as n, and the number of pulses of the test part frequency signal f2 is counted as m, completing the pressure difference calculation.

[0029] The present invention utilizes the physical characteristics of the phase comparison between the standard component frequency signal f1 and the test component frequency signal f2 to achieve high-precision detection under the conditions of common devices. The phase difference between the two signals changes periodically and monotonically. The same phase difference is used as the pulse counting gate switch signal to achieve synchronization of the signals f1 and f2, eliminate the counting error influence of ±1 pulse, and can quickly respond to the changing test component frequency signal.

Claims

1. A phase comparison detection method for cavity airtightness, characterized in that: The method comprises the following steps: Step 1: Use a frequency output type pressure sensor to detect the air pressure of the test piece and the standard piece respectively, and obtain the standard piece frequency signal f1 and the test piece frequency signal f2; Step 2: shaping the standard component frequency signal f1 and the test component frequency signal f2 into pulse signals, and using a stray phase detector to detect the phase difference between the two pulse signals; Step 3: Use a pulse sampler to extract a phase difference of a specific width between the standard component frequency signal f1 and the test component frequency signal f2. This phase difference constitutes the switch of the frequency measurement counting gate. Step 4: In the counting gate, the standard component frequency signal f1 and the test component frequency signal f2 are synchronized in full cycle; Step 5: In the counting gate, the number of pulses of the standard component frequency signal f1 is counted as n, and the number of pulses of the test component frequency signal f2 is counted as m, and the pressure difference calculation is completed.

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