Response bandwidth measuring device of capacitive tip clearance measuring system based on analog switch

Abstract

The utility model discloses a response bandwidth measuring device of a capacitive tip clearance measuring system based on an analog switch, the capacitive tip clearance measuring system is composed of a capacitive sensor, a measuring system host and an upper computer which are connected in sequence, and the measuring system host comprises a signal demodulation module and an acquisition module. The capacitive sensor consists of a sensor probe and a three-coaxial cable which are connected with each other; the response bandwidth measuring device replaces the sensor probe and is connected with the tri-coaxial cable through an SMA connector, and the response bandwidth measuring device adopts an analog switch to simulate capacitance change caused by the fact that the tip of the rotating blade sweeps the sensor probe and simulate input of the capacitive tip clearance measuring system; the response bandwidth measuring device is composed of an analog switch, a first capacitor C1 and a second capacitor C2, the analog switch is connected with the first capacitor C1 in series after being connected with the second capacitor C2 in parallel, and the analog switch is simplified into a single-pole double-throw switch S and an equivalent capacitor Cs (off).

Description

Technical Field

[0001] The utility model relates to the field of blade tip clearance measurement, in particular to a bandwidth measuring device of a capacitive blade tip clearance measurement system based on an analog switch. Background Art

[0002] In rotating machinery such as aircraft engines, gas turbines, and steam turbines, the tiny distance between the top of the rotor blade and the inner wall of the casing is called the tip clearance, which is one of the important parameters affecting the performance of rotating machinery. The tip clearance measurement technology is of great significance to improving the performance of rotating machinery and ensuring the safe operation of rotating machinery. The capacitive tip clearance measurement method is widely used in engineering test tests of tip clearance because of its advantages such as high temperature resistance, gas corrosion resistance, low intervention, non-contact, online, and real-time.

[0003] The capacitive tip clearance measurement system consists of a capacitive sensor, cable, gap signal demodulation module, acquisition and processing module, and host computer software. It is based on the principle of parallel plate capacitors and measures the capacitance between the sensor core and the rotor blade tip to achieve tip clearance measurement. Since the capacitive tip clearance measurement system is an online measurement, in order to ensure the measurement accuracy and resolution when the blade rotates to the highest speed, the measurement system is required to have a high response bandwidth. How to accurately measure the system response bandwidth has become a key issue that needs to be solved.

[0004] In order to measure the system response bandwidth range, test signals of different frequencies are generally generated to simulate the system input, and the amplitude change of the system output signal is observed. However, the input signal of the capacitive tip clearance measurement system is the capacitance signal of the change between the sensor core and the rotor blade, and the existing devices and methods cannot generate a standard capacitance signal to simulate the system input. If the voltage test signal is used as the input signal, the system capacitance-voltage conversion process will be ignored, resulting in low measurement accuracy of the system response bandwidth. Utility Model Content

[0005] The purpose of the utility model is to overcome the shortcomings of existing devices that cannot generate standard capacitance signals to simulate system inputs, directly using standard voltage signals as inputs will ignore the influence of system capacitance-voltage conversion on response bandwidth, resulting in low measurement accuracy of response bandwidth, and provide a measurement device that can directly generate standard capacitance signals and achieve high-precision measurement of system response bandwidth.

[0006] The purpose of this utility model is achieved through the following technical solutions:

[0007] A device for measuring the response bandwidth of a capacitive blade tip clearance measurement system based on analog switches. The capacitive blade tip clearance measurement system consists of a capacitive sensor, a measurement system host, and a host computer connected in sequence. The measurement system host includes a signal demodulation module and an acquisition module. The capacitive sensor consists of a sensor probe and a triaxial cable connected to each other. The triaxial cable includes a long section and a short section. The short section of the triaxial cable is fixed to the tail of the sensor probe and connected to the long section of the triaxial cable through an SMA connector, so as to apply the triaxial cable to different sensor probes. The measurement is based on the principle of parallel plate capacitance. The core electrode of the sensor probe constitutes one plate of the variable capacitor, and the rotating blade constitutes the other plate of the variable capacitor. The blade tip clearance signal is obtained by measuring the capacitance change between the two plates. The blade tip clearance signal obtained by the sensor probe is transmitted to the measurement system host through the triaxial cable.

[0008] The signal demodulation module demodulates the blade tip clearance signal output by the capacitive sensor and converts the blade tip clearance signal into a voltage signal. The acquisition module performs data acquisition and preliminary processing on the above voltage signal and transmits the data to the host computer. The host computer further processes the data to obtain the blade tip clearance value, and at the same time performs data storage and numerical display.

[0009] Replace the sensor probe with the response bandwidth measurement device and connect it to the long section of the triaxial cable through an SMA connector. The response bandwidth measurement device uses an analog switch to simulate the capacitance change caused by the blade tip of the rotating blade sweeping across the sensor probe, simulating the input of the capacitive blade tip clearance measurement system.

[0010] The response bandwidth measurement device consists of an analog switch, a first capacitor C1, and a second capacitor C2. The analog switch is connected in parallel with the second capacitor C2 and then connected in series with the first capacitor C1. The first capacitor C1 is connected to the long section of the triaxial cable. The analog switch is simplified to a single-pole double-throw switch S and an equivalent capacitor C s(off) 。

[0011] Furthermore, the first capacitor C1 and the second capacitor C2 are used as voltage dividing capacitors, and the capacitance value of the overall response bandwidth measurement device is adjusted by changing the capacitance values of the first capacitor C1 and the second capacitor C2. The first capacitor C1 has a DC blocking function.

[0012] Furthermore, the analog switch is a single-pole double-throw switch. Among them, VIH is the minimum voltage for the input control signal to achieve a high level, and VIL is the maximum voltage for the input control signal to achieve a low level. A square wave signal with a high voltage of VH, a low voltage of VL, and a frequency of f is generated by a digital signal generator and input to the response bandwidth measurement device. When VH > VIH, the analog switch is placed at S1, and when VL < VIL, the switch is placed at S2; when the analog switch is placed at the S1 end, its equivalent capacitance C TEST1 = C1; when the analog switch is placed at the S2 end, its equivalent capacitance

[0013] The capacitive tip clearance measurement system requires that the capacitance change before and after the blade passes the sensor probe is 0<|C TEST |<1pF, where C TEST =C TEST1 -C TEST2 , so C1 and C2 meet the requirements:

[0014]

[0015] Simplifying the formula inside the absolute value, we get:

[0016]

[0017] C TEST Derivative of the expression to obtain the effect of C1 and C2 on C TEST Impact trends:

[0018]

[0019] because Therefore, when C1 is larger and C2 is smaller, C TEST The larger the value, the better. Select the value of C1 and C2 according to the actual application requirements.

[0020] Compared with the prior art, the beneficial effects brought about by the technical solution of the utility model are:

[0021] 1. Improve measurement accuracy: The utility model avoids the error in the capacitance-voltage conversion process in the traditional method by generating a standard capacitance signal directly as input, thereby significantly improving the accuracy of the system response bandwidth measurement.

[0022] 2. Enhanced adaptability: The device can be applied to various types of capacitive blade tip clearance measurement systems and is widely used in blade tip clearance measurement in rotating machinery such as aircraft engines, gas turbines, and steam turbines, thus improving the scope of application and practicality of the system.

[0023] 3. Simplify the measurement process: The utility model simplifies the process of response bandwidth measurement, does not require additional conversion devices or complex signal processing procedures, and makes the measurement process more intuitive and efficient.

[0024] 4. Real-time online measurement: The measuring device of the utility model supports real-time online measurement and can dynamically monitor the changes in the blade tip clearance during the operation of the rotating machinery, thereby ensuring the safe operation of the rotating machinery.

[0025] 5. Improve system stability: Since the utility model directly generates a standard capacitance signal to simulate the system input, it avoids the system instability problem caused by conversion errors in traditional methods and improves the stability and reliability of the overall measurement system. In addition, the frequency and amplitude of the generated standard capacitance signal are adjustable.

[0026] 6. Economical and efficient: The device of this utility model has a reasonable design, simple structure, easy miniaturization, and convenient carrying, which can effectively reduce the overall cost of the system, while improving the measurement efficiency and convenience of system maintenance. It can also be designed according to user needs and application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of a capacitive tip clearance measurement system is shown.

[0028] Figure 2 The following is a schematic diagram showing the structure of the response bandwidth measuring device of the present invention.

[0029] Figure 3 An equivalent circuit diagram of the utility model in which the analog switch is placed at the S1 end is shown.

[0030] Figure 4 An equivalent circuit diagram of the utility model in which the analog switch is placed at the S2 end is shown.

[0031] Figure 5 A diagram showing a bandwidth measurement scheme for a blade tip clearance measurement system using the utility model is shown.

[0032] Figure 6 The utility model is used to carry out the bandwidth measurement flow chart of the blade tip clearance measurement system.

[0033] Reference numerals: 1-capacitive sensor, 11-sensor probe, 12-triaxial cable, 13-SMA connector, 2-measuring system host, 21-signal demodulation module, 22-acquisition module, 3-host computer, 4-analog switch DETAILED DESCRIPTION

[0034] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0035] This embodiment provides a response bandwidth measurement device for a capacitive blade tip clearance measurement system based on an analog switch. The capacitive blade tip clearance measurement system is composed of a capacitive sensor 1, a measurement system host 2, and a host computer 3 connected in sequence. Figure 1, the host computer 2 of the measurement system includes a signal demodulation module 21 and an acquisition module 22; the capacitive sensor 1 is composed of a sensor probe 11 and a triaxial cable 12 which are connected to each other. The triaxial cable 12 includes a long section and a short section. The short section of the triaxial cable is fixed at the tail of the sensor probe 11 and is connected to the long section of the triaxial cable through an SMA connector so as to apply the triaxial cable to different sensor probes 11; the measurement is based on the flat capacitance principle. The core electrode of the sensor probe 11 constitutes one plate of the variable capacitor, and the rotating blade constitutes the other plate of the variable capacitor. The tip clearance signal is obtained by measuring the capacitance change between the two plates. The tip clearance signal obtained by the sensor probe 11 is transmitted to the host computer 2 of the measurement system through the triaxial cable.

[0036] The signal demodulation module 21 in the host computer 2 of the measurement system demodulates the variable capacitance signal output by the capacitive sensor 1 and converts the capacitance signal into a voltage signal; the acquisition module 22 performs data acquisition and preliminary processing on the voltage signal and transmits the data to the upper computer 3; the upper computer 3 performs further processing of the data, calculates the tip clearance value, and simultaneously stores the data and displays the value.

[0037] For the response bandwidth measurement device of the capacitive tip clearance measurement system in this embodiment, an analog switch 4 is used to simulate the capacitance change caused by the tip of the rotating blade sweeping across the capacitive sensor probe 11, simulating the input of the capacitive tip clearance measurement system. Since the operating frequency of the capacitive tip clearance measurement system can reach 230 kHz, the analog switch 4 should select a high-frequency analog switch with a small on-resistance. Taking the single-pole double-throw analog switch as an example, the structural principle of the device is as Figure 2 shown.

[0038] Furthermore, the response bandwidth measurement device mainly consists of an analog switch 4, capacitors C1 and C2. The analog switch 4 can be simplified to a single-pole double-throw switch S and an equivalent capacitor C s(off) . Capacitors C1 and C2 are used as voltage-dividing capacitors, and the overall capacitance value of the response bandwidth measurement device is adjusted by changing the capacitance values of C1 and C2. In addition, capacitor C1 also has a DC blocking function.

[0039] Preferably, the analog switch 4 is a single-pole double-throw switch, where VIH is the minimum voltage for the input control signal to achieve a high level, and VIL is the maximum voltage for the input control signal to achieve a low level. A digital signal generator is used to generate a square wave signal (Uc) with a high voltage of VH, a low voltage of VL, and a frequency of f and input it to the response bandwidth measurement device. When VH > VIH, the analog switch is placed at S1, and when VL < VIL, the switch is placed at S2. When the switch is placed at S1, the simplified circuit diagram is as Figure 3 shown, and when the switch is placed at S2, the simplified circuit diagram is as Figure 4 shown. When the analog switch 4 is placed at the S1 end, its equivalent capacitor C TEST1=C1. When analog switch 4 is placed at S2, its equivalent capacitance

[0040] It is known that the capacitive tip clearance measurement system requires the capacitance change before and after the blade sweeps the capacitive sensor probe to be 0<|C TEST |<1pF, where C TEST =C TEST1 -C TEST2 , so C1 and C2 meet the requirements:

[0041]

[0042] Further simplifying the formula inside the absolute value, we can get:

[0043]

[0044] Furthermore, for C TEST Derivative of the expression to obtain the effect of C1 and C2 on C TEST Impact trends:

[0045]

[0046] Furthermore, due to Therefore, when C1 is larger and C2 is smaller, C TEST The bigger.

[0047] According to the actual application needs of aircraft engine measurement, the capacitance change C is proposed TEST About 0.5pF. Based on the common standard values ​​of capacitance, select C1=8pF, C2=100pF. After calculation, we can get C TEST =0.45pF.

[0048] The bandwidth of the capacitive blade tip clearance measurement system is measured using the response bandwidth measurement device of the utility model. The system bandwidth measurement scheme is as follows: Figure 5 The response bandwidth measurement device based on the analog switch 4 can generate a variable capacitance test signal of different frequencies, which is transmitted to the signal demodulation module 21 through a long section of the triaxial cable 12 to output a voltage signal, collect and store the output voltage signal, compare the amplitude of the output signal at different frequencies, and obtain the bandwidth of the blade tip clearance measurement system.

[0049] Specifically, the experimental process of measurement is as follows Figure 6As shown. Install and debug the experimental equipment to be tested, set up 13 frequency points to be tested, take 5Hz and 230kHz as frequency test points, and select another 11 test points of 100Hz, 1kHz, 10kHz, 30kHz, 50kHz, 70kHz, 101kHz, 121kHz, 151kHz, 181kHz, 202kHz, adjust the control signal frequency of the response bandwidth measurement device based on analog switch 4, record the output voltage of the signal demodulation module at the above different test frequencies, compare the output signal amplitude, and obtain the blade tip clearance measurement system bandwidth. If the signal amplitude output by the experimental equipment to be tested meets the requirements, the bandwidth of the experimental equipment to be tested is the selected working frequency band range. If the amplitude does not meet the requirements, the bandwidth of the experimental equipment to be tested is less than the working frequency band range, and the experimental equipment to be tested does not meet the requirements.

[0050] The present invention is not limited to the implementation methods described above. The above description of the specific implementation methods is intended to describe and illustrate the technical solution of the present invention. The above specific implementation methods are merely illustrative and not restrictive. Without departing from the scope of protection of the present invention and the claims, ordinary technicians in this field can also make many forms of specific changes under the enlightenment of the present invention, which all fall within the protection scope of the present invention.

Claims

1. A response bandwidth measurement device for a capacitive blade tip clearance measurement system based on an analog switch, wherein the capacitive blade tip clearance measurement system is composed of a capacitive sensor, a measurement system host and a host computer connected in sequence, wherein the measurement system host includes a signal demodulation module and an acquisition module, and the capacitive sensor is composed of a sensor probe and a triaxial cable connected to each other, wherein the triaxial cable includes two sections, one long and one short, wherein the short section of the triaxial cable is fixed at the tail of the sensor probe and connected to the long section of the triaxial cable through an SMA connector, so that the triaxial cable can be applied to different sensor probes; the measurement is based on the principle of flat plate capacitance, and the sensor probe The core electrode constitutes one plate of the variable capacitor, and the rotating blade constitutes the other plate of the variable capacitor. The tip clearance signal is obtained by measuring the capacitance change between the two plates. The tip clearance signal obtained by the sensor probe is transmitted to the measurement system host via a triaxial cable; the signal demodulation module demodulates the tip clearance signal output by the capacitance sensor and converts the tip clearance signal into a voltage signal; the acquisition module performs data acquisition and preliminary processing on the above voltage signal, and transmits the data to the host computer; the host computer further processes the data to obtain the tip clearance value, and simultaneously performs data storage and numerical display; it is characterized in that The sensor probe is replaced by a response bandwidth measurement device and connected to a long section of triaxial cable through an SMA connector, wherein the response bandwidth measurement device uses an analog switch to simulate the capacitance change caused by the tip of a rotating blade sweeping across the sensor probe, simulating the input of a capacitive tip clearance measurement system; The response bandwidth measurement device is composed of an analog switch, a first capacitor C1 and a second capacitor C2. The analog switch is connected in parallel with the second capacitor C2 and then in series with the first capacitor C1. The first capacitor C1 is connected to a long section of triaxial cable. The analog switch is simplified to a single-pole double-throw switch S and an equivalent capacitor C s(off) .

2. The response bandwidth measurement device of the capacitive blade tip clearance measurement system based on analog switches according to claim 1, characterized in that: The first capacitor C1 and the second capacitor C2 are used as voltage-dividing capacitors. The capacitance value of the entire response bandwidth measurement device is adjusted by changing the capacitance values ​​of the first capacitor C1 and the second capacitor C2. The first capacitor C1 has a DC isolation function.

3. The response bandwidth measurement device of the capacitive blade tip clearance measurement system based on analog switch according to claim 1, characterized in that: The analog switch is a single-pole double-throw switch, where VIH is the minimum voltage for the input control signal to achieve a high level, and VIL is the maximum voltage for the input control signal to achieve a low level. A digital signal generator is used to generate a square wave signal with a high voltage of VH, a low voltage of VL, and a frequency of f and input it into the response bandwidth measurement device. When VH > VIH, the analog switch is placed at S1, and when VL < VIL, the switch is placed at S2; when the analog switch is placed at the S1 terminal, its equivalent capacitance C TEST1 = C1; when the analog switch is placed at the S2 terminal, its equivalent capacitance The capacitive tip clearance measurement system requires that the capacitance change before and after the blade passes the sensor probe is 0<|C TEST |<1pF, where C TEST =C TEST1 -C TEST2 , so C1 and C2 meet the requirements: Simplifying the formula inside the absolute value, we get: C TEST Derivative of the expression to obtain the effect of C1 and C2 on C TEST Impact trends: because Therefore, when C1 is larger and C2 is smaller, C TEST The larger the value, the better. Select the value of C1 and C2 according to the actual application requirements.

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