Response bandwidth measuring device and method for analog switch-based capacitive tip-turbine clearance measuring system

Abstract

The application discloses a response bandwidth measuring device and method of 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, a measurement system host and an upper computer connected in sequence, the measurement system host comprises a signal demodulation module and an acquisition module, and the capacitive sensor is composed of a sensor probe and a three-coaxial cable connected with each other; the response bandwidth measuring device is used for replacing the sensor probe and is connected with the three-coaxial cable through an SMA joint, the response bandwidth measuring device adopts an analog switch to simulate the capacitance change caused by the blade tip sweeping through the sensor probe, and the analog capacitance type blade tip clearance measurement system is simulated as an input; 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 in parallel with the second capacitor C2 and then connected in series with the first capacitor C1, and the analog switch is simplified as a single-pole double-throw switch S and an equivalent capacitor C s(off) .

Description

TECHNICAL FIELD

[0001] The present application relates to the field of tip clearance measurement, and in particular to a bandwidth measurement device and design method of a capacitive tip clearance measurement system based on analog switch. BACKGROUND

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

[0003] The capacitive tip clearance measurement system is composed of a capacitive sensor, a cable, a gap signal demodulation module, an acquisition and processing module, and a host computer software. Based on the parallel plate capacitor principle, the measurement of tip clearance is realized by measuring the capacitance between the sensor core and the rotor blade tip. Since the capacitive tip clearance measurement system is an online measurement, in order to ensure the measurement accuracy and resolution at the highest rotational speed of the blade, the measurement system is required to have a high response bandwidth. Therefore, how to accurately measure the response bandwidth of the system becomes a key problem to be solved.

[0004] In order to measure the response bandwidth of the system, different frequency test signals 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 varying capacitance signal between the sensor core and the rotor blade, and the existing devices and methods cannot generate standard capacitance signals 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. SUMMARY

[0005] The present application aims to overcome the shortcomings of the existing devices and methods that cannot generate standard capacitance signals to simulate the system input, and directly using standard voltage signals as input will ignore the influence of system capacitance-voltage conversion on response bandwidth, resulting in low measurement accuracy of response bandwidth. The present application provides a measurement device and method that can directly generate standard capacitance signals to realize high-precision measurement of system response bandwidth.

[0006] The present application is achieved by the following technical solutions:

[0007] A response bandwidth measuring device of a simulation switch-based capacitive blade tip clearance measurement system, the capacitive blade tip clearance measurement system being composed of a capacitive sensor, a measurement system host and an upper computer connected in sequence, the measurement system host comprising a signal demodulation module and an acquisition module, the capacitive sensor being composed of a sensor probe and a three-coaxial cable connected with each other, the three-coaxial cable comprising two sections of long and short lengths, the three-coaxial cable of the short length being fixed at the tail of the sensor probe and connected with the three-coaxial cable of the long length through an SMA joint, so as to apply the three-coaxial cable to different sensor probes; the measurement is based on the flat plate capacitive principle, the core pole of the sensor probe constitutes one pole plate of the variable capacitor, the rotating blade constitutes the other pole plate of the variable capacitor, the blade tip clearance signal is obtained by measuring the capacitance change between the two pole plates, and the blade tip clearance signal obtained by the sensor probe is transmitted to the measurement system host through the three-coaxial cable;

[0008] The signal demodulation module demodulates the blade tip clearance signal output by the capacitive sensor to convert the blade tip clearance signal into a voltage signal; the acquisition module acquires and preliminarily processes the voltage signal and transmits the data to the upper computer; the upper computer further processes the data to obtain the blade tip clearance value, and simultaneously stores and displays the data value;

[0009] The response bandwidth measuring device is replaced with the sensor probe and connected with the three-coaxial cable of the long length through the SMA joint, the response bandwidth measuring device simulates the capacitance change caused by the rotating blade tip sweeping the sensor probe to simulate the input of the capacitive blade tip clearance measurement system;

[0010] 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 in parallel with the second capacitor C2 and then connected in series with the first capacitor C1, the first capacitor C1 is connected with the three-coaxial cable of the long length, and the analog switch is simplified as a single-pole double-throw switch S and an equivalent capacitor C s(off) .

[0011] Further, the first capacitor C1 and the second capacitor C2 serve as a voltage dividing capacitor, the capacitance values of the first capacitor C1 and the second capacitor C2 are changed to adjust the capacitance value of the whole response bandwidth measuring device; the first capacitor C1 has a direct current isolation function.

[0012] Further, the analog switch is a single-pole double-throw switch, VIH is the minimum voltage of the input control signal to realize the high level, VIL is the maximum voltage of the input control signal to realize the low level, a digital signal generator is adopted to generate a square wave signal with a high voltage VH, a low voltage VL and a frequency f, the square wave signal is input to the response bandwidth measuring device, the analog switch is placed at S1 when VH>VIH, and the analog switch is placed at S2 when VL<VIL; when the analog switch is placed at the S1 end, the equivalent capacitor C TEST1 =C1; when the analog switch is placed at the S2 end, the equivalent capacitor C

[0013] Capacitive tip clearance measurement system requires the amount of capacitance change 0 < |C TEST | < 1 pF, where C TEST = C TEST1 -C TEST2 Therefore, C1 and C2 meet the requirements:

[0014]

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

[0016]

[0017] The expression of C TEST is derived to obtain the influence trend of C1 and C2 on C TEST :

[0018]

[0019] Since Therefore, when C1 takes a larger value, C2 takes a smaller value, C TEST is larger, and according to the actual application requirements, the values of C1 and C2 are selected.

[0020] The application also provides a measurement method based on the response bandwidth measurement device, characterized in that, comprising:

[0021] The response bandwidth measurement device is used to measure the bandwidth of the capacitive tip clearance measurement system, the response bandwidth measurement device generates a variable capacitance test signal with different frequencies, the signal is transmitted to the signal demodulation module through a long three coaxial cable to output a voltage signal, then the corresponding output voltage signal is collected and stored, finally the amplitudes of the output signals under different frequencies are compared to obtain the bandwidth of the tip clearance measurement system.

[0022] Specifically, the steps are as follows:

[0023] S1. Install and debug the experimental equipment to be measured;

[0024] S2. Select N different frequency points to be measured in the frequency band range to be measured of the experimental equipment to be measured;

[0025] S3. Adjust the control signal frequency of the response bandwidth measurement device in turn to the frequencies of the N frequency points to be measured, record the output voltage of the signal demodulation module under different test frequencies, compare the output signal amplitude, when the output signal amplitude decreases to 0.707 times of the maximum amplitude, the upper limit value minus the lower limit value of the frequency obtained is the bandwidth of the tip clearance measurement system; if the signal amplitude output by the experimental equipment to be measured meets the requirements, the bandwidth of the experimental equipment to be measured is the selected working frequency band range, if the amplitude does not meet the requirements, the bandwidth of the experimental equipment to be measured is less than the working frequency band range, and the experimental equipment to be measured does not meet the requirements.

[0026] Compared with the prior art, the technical scheme of the present application has the beneficial effects that:

[0027] 1. Improve measurement accuracy: the present application directly generates a standard capacitance signal as input, avoiding errors in the capacitance-voltage conversion process in traditional methods, thereby significantly improving the accuracy of system response bandwidth measurement.

[0028] 2. Enhance adaptability: the device and method can be applied to various types of capacitive tip clearance measurement systems, widely applicable to tip clearance measurement in rotating machinery such as aero-engines, gas turbines, steam turbines, etc., improving the system's scope of application and practicality.

[0029] 3. Simplify the measurement process: the measurement method of the present application simplifies the process of response bandwidth measurement, eliminating the need for additional conversion devices or complex signal processing procedures, making the measurement process more intuitive and efficient.

[0030] 4. Real-time online measurement: the measurement device and method of the present application support real-time online measurement, enabling dynamic monitoring of tip clearance changes during rotating machinery operation, ensuring safe operation of the rotating machinery.

[0031] 5. Improve system stability: since the present application directly generates a standard capacitance signal to simulate system input, avoiding the system instability problem caused by conversion errors in traditional methods, it improves the stability and reliability of the overall measurement system. The generated standard capacitance signal frequency is adjustable, and the amplitude is adjustable.

[0032] 6. Economical and efficient: the device of the present application is designed rationally, with simple structure, easy miniaturization, convenient portability, which can effectively reduce the overall cost of the system, improve the measurement efficiency and the convenience of system maintenance. And can be designed according to user demand and application scene. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 A schematic diagram of a capacitive tip clearance measurement system is shown.

[0034] Figure 2 A structure principle diagram of the response bandwidth measurement device in the present application is shown.

[0035] Figure 3 The equivalent circuit diagram of the analog switch in the application is shown in the S1 end.

[0036] Figure 4 The equivalent circuit diagram of the analog switch in the application is shown in the S2 end.

[0037] Figure 5 The scheme diagram of the bandwidth measurement of the tip clearance measurement system using the application is shown.

[0038] Figure 6 The flow chart of the bandwidth measurement of the tip clearance measurement system using the application is shown.

[0039] The figure shows the following: 1-capacitance sensor, 11-sensor probe, 12-three coaxial cable, 13-SMA joint, 2-measurement system host, 21-signal demodulation module, 22-acquisition module, 3-upper computer, 4-analog switch DETAILED DESCRIPTION

[0040] The application will be further described in detail below in combination with the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and do not limit the application.

[0041] The embodiment provides a response bandwidth measurement device of a capacitance type tip clearance measurement system based on an analog switch. The capacitance type tip clearance measurement system is composed of a capacitance sensor 1, a measurement system host 2 and an upper computer 3 connected in sequence, as shown in Figure 1 The measurement system host 2 comprises a signal demodulation module 21 and an acquisition module 22. The capacitance sensor 1 is composed of a sensor probe 11 and a three coaxial cable 12 connected to each other. The three coaxial cable 12 comprises two sections of long and short lengths. The short section of the three coaxial cable is fixed at the tail of the sensor probe 11 and is connected to the long section of the three coaxial cable through an SMA joint, so as to apply the three coaxial cable to different sensor probes 11. The measurement is based on the flat plate capacitance principle. The core pole of the sensor probe 11 constitutes one pole plate of the variable capacitance, and the rotating blade constitutes the other pole plate of the variable capacitance. The tip clearance signal is obtained by measuring the capacitance change between the two pole plates. The tip clearance signal obtained by the sensor probe 11 is transmitted to the measurement system host 2 through the three coaxial cable.

[0042] The signal demodulation module 21 in the measurement system host 2 demodulates the variable capacitance signal output by the capacitance sensor 1, and converts the capacitance signal into a voltage signal. The acquisition module 22 collects and preliminarily processes the voltage signal, and transmits the data to the upper computer 3. The upper computer 3 further processes the data, calculates the tip clearance value, and simultaneously stores and displays the data.

[0043] The response bandwidth measuring device of the embodiment of the capacitive tip clearance measurement system adopts analog switch 4 to simulate the capacitance change caused by the rotating blade tip sweeping the capacitive sensor probe 11, and simulates the input of the capacitive tip clearance measurement system. Since the working frequency of the capacitive tip clearance measurement system can reach 230 kHz, the analog switch 4 should select a high-frequency analog switch with small on-resistance. Taking a single-pole double-throw analog switch as an example, the device structure principle is as shown in Figure 2

[0044] Further, the response bandwidth measuring device mainly consists of analog switch 4, capacitors C1 and C2. The analog switch 4 can be simplified as 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 capacitance value of the whole response bandwidth measuring device is adjusted by changing the capacitance values of C1 and C2. In addition, capacitor C1 also has a direct current blocking function.

[0045] Preferably, the analog switch 4 is a single-pole double-throw switch, wherein VIH is the minimum voltage of the input control signal to realize high level, and VIL is the maximum voltage of the input control signal to realize low level. A digital signal generator is used to generate a square wave signal (Uc) with high voltage VH, low voltage VL and frequency f, which is input to the response bandwidth measuring device. When VH>VIH, the analog switch is in S1, and when VL<VIL, the switch is in S2. When the switch is in S1, the simplified circuit diagram is as shown in Figure 3 When the switch is in S2, the simplified circuit diagram is as shown in Figure 4 When the analog switch 4 is in S1, its equivalent capacitor C TEST1 =C1. When the analog switch 4 is in S2, its equivalent capacitor

[0046] It is known that the capacitive tip clearance measurement system requires that the capacitance change before and after the blade sweeps the capacitive sensor probe is 0<|C TEST |<1 pF, wherein C TEST =C TEST1 -C TEST2 Therefore, C1 and C2 meet the requirements:

[0047]

[0048] Further, the formula inside the absolute value is simplified, and the following can be obtained:

[0049]

[0050] Further, the derivative of the expression of C TEST is taken to obtain the influence trend of C1 and C2 on C TEST :

[0051] ​

[0052] Further, since Therefore, when C1 takes a larger value, C2 takes a smaller value, C TEST becomes larger.

[0053] According to the actual application needs of the aero-engine measurement, the capacitance change C TEST is about 0.5pF, based on the common capacitance standard value, C1=8pF, C2=100pF is selected, and C TEST =0.45pF can be obtained through calculation.

[0054] The response bandwidth measurement device of the application is used to measure the bandwidth of the capacitive tip clearance measurement system, and the system bandwidth measurement scheme is as shown in 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 three coaxial cable 12 to output a voltage signal, and the output voltage signal is collected, stored, and compared with the amplitude of the output signal at different frequencies to obtain the bandwidth of the tip clearance measurement system.

[0055] Specifically, the experimental process of measurement is as shown in Figure 6 The experimental equipment to be measured is installed and debugged, 13 frequency test points are set, 5Hz and 230kHz are selected as the frequency test points, and 11 other test points are selected as 100Hz, 1kHz, 10kHz, 30kHz, 50kHz, 70kHz, 101kHz, 121kHz, 151kHz, 181kHz, 202kHz, the control signal frequency of the response bandwidth measurement device based on the analog switch 4 is adjusted, the output voltage of the signal demodulation module at the above different test frequencies is recorded, the output signal amplitude is compared, and the bandwidth of the tip clearance measurement system is obtained. If the signal amplitude output by the experimental equipment to be measured meets the requirements, the bandwidth of the experimental equipment to be measured is the selected working frequency band range, if the amplitude does not meet the requirements, the bandwidth of the experimental equipment to be measured is smaller than the working frequency band range, and the experimental equipment to be measured does not meet the requirements.

[0056] The application is not limited to the above-described embodiments. The above description of the specific embodiments is intended to describe and illustrate the technical solutions of the application, and the specific embodiments described above are merely illustrative and not restrictive. Without departing from the purpose of the application and the scope protected by the claims, those skilled in the art can make many forms of specific changes under the inspiration of the application, and these all belong to the protection scope of the application.

Claims

1. A response bandwidth measurement device for an analog switch-based capacitive tip clearance measurement system, the capacitive tip clearance measurement system being composed of a capacitive sensor, a measurement system host and an upper computer connected in sequence, the measurement system host comprising a signal demodulation module and an acquisition module, the capacitive sensor being composed of a sensor probe and a triaxial cable connected to each other, the triaxial cable comprising a long section and a short section, the triaxial cable of the short section being fixed to the tail of the sensor probe and connected to the triaxial cable of the long section through an SMA joint so as to apply the triaxial cable to different sensor probes; the measurement being based on the principle of a flat plate capacitor, the core of the sensor probe constituting one plate of the variable capacitor, the rotating blade constituting the other plate of the variable capacitor, the tip clearance signal being obtained by measuring the capacitance change between the two plates, the tip clearance signal obtained by the sensor probe being transmitted to the measurement system host through the triaxial cable; the signal demodulation module demodulating the tip clearance signal output by the capacitive sensor to convert the tip clearance signal into a voltage signal; the acquisition module collecting and preliminarily processing the voltage signal and transmitting the data to the upper computer; the upper computer further processing the data to obtain the tip clearance value, and simultaneously performing data storage and numerical display; characterized in that, the response bandwidth measurement device is used to replace the sensor probe and is connected to the triaxial cable of the long section through the SMA joint, the response bandwidth measurement device simulating the capacitance change caused by the tip of the rotating blade sweeping across the sensor probe to simulate the input of the capacitive tip clearance measurement system; The response bandwidth measuring device is composed of an analog switch, a first capacitor and a second capacitor , the analog switch is connected in parallel with the second capacitor and connected in series with the first capacitor , the first capacitor is connected with a long section of three coaxial cables, the analog switch is simplified as a single-pole double-throw switch S and an equivalent capacitor ; the response bandwidth measurement device is used to measure the bandwidth of the capacitive tip clearance measurement system, the response bandwidth measurement device generating variable capacitance test signals of different frequencies, the variable capacitance test signals being transmitted to the signal demodulation module through the triaxial cable of the long section to output voltage signals, the corresponding output voltage signals being then collected and stored, and finally the amplitudes of the output signals at different frequencies being compared to obtain the bandwidth of the tip clearance measurement system.

2. The response bandwidth measuring device for an analog switch-based capacitive tip-turbine clearance measuring system according to claim 1, characterized in that The first capacitor and the second capacitor As a voltage division capacitor, the capacitance value of the first capacitor and the second capacitor is changed to adjust the overall capacitance value of the response bandwidth measuring device; the first capacitor has a direct current blocking function.

3. The response bandwidth measuring device for a switched-capacitor tip-turbine clearance measurement system according to claim 1, wherein The analog switch is a single-pole double-throw switch, wherein VIH is the minimum voltage of an input control signal to realize a high level, VIL is the maximum voltage of the input control signal to realize a low level, a digital signal generator is used to generate a square wave signal with a high voltage VH, a low voltage VL and a frequency f, the square wave signal is input to the response bandwidth measuring device, when VH>VIH, the analog switch is placed at S1, when VL<VIL, the switch is placed at S2; when the analog switch is placed at the S1 end, the equivalent capacitance ; when the analog switch is placed at the S2 end, the equivalent capacitance ; Capacitive tip clearance measurement systems require a change in capacitance before and after the blade sweeps past the sensor probe wherein therefore and meets the requirements: ； The formula inside the absolute value is simplified as follows: ； Taking the derivative of the expression for , we obtain and Taking the derivative of the expression for , we obtain the influence trend: ； ； Since , , when is greater, the value of is smaller, and the value of is greater, the values of and are selected according to actual application requirements.

4. A measuring method based on the response bandwidth measuring apparatus according to any one of claims 1 to 3, characterized by, including: S1. Installing and debugging the experimental equipment to be tested; S2. Selecting N different frequency points in the frequency band range of the experimental equipment to be tested; S3. Adjusting the control signal frequency of the response bandwidth measurement device to the frequencies of the N frequency points to be tested in sequence, recording the output voltage of the signal demodulation module at different test frequencies, comparing the amplitudes of the output signals, and when the amplitude of the output signal is reduced to 0.707 times the maximum amplitude, the upper limit value minus the lower limit value at the obtained frequency is the bandwidth of the tip clearance measurement system; if the amplitude of the signal 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 smaller than the working frequency band range, and the experimental equipment to be tested does not meet the requirements.

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