Response bandwidth measuring device of capacitance type tip clearance measuring system based on variable capacitance diode

Abstract

The utility model discloses a response bandwidth measuring device of a capacitance type blade tip clearance measuring system based on a variable capacitance diode, the capacitance type blade tip clearance measuring system is composed of a capacitance 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 capacitance sensor is composed of a sensor probe and a tri-coaxial cable which are connected with each other, the response bandwidth measuring device is connected with the tri-coaxial cable through an SMA connector after replacing the sensor probe, and a variable capacitance diode is adopted to simulate capacitance change caused by the fact that a blade tip of a rotating blade sweeps the capacitance sensor probe; the response bandwidth measuring device is composed of a variable capacitance diode D, a resistor R1, a capacitor C1 and a capacitor C2. Two ends of the capacitor C2 connected in parallel with the variable capacitance diode D are respectively connected in series with the resistor R1 and the capacitor C1, the capacitor C1 is connected with the tri-coaxial cable, and the input end of the response bandwidth measuring device is connected with the resistor R1.

Description

TECHNICAL FIELD

[0001] The utility model relates to tip clearance measurement field especially relates to a capacitive tip clearance measurement system bandwidth measuring device. BACKGROUND

[0002] In rotating machinery such as aero-engine, gas turbine and steam turbine, the tiny distance between the rotor blade top end and the inner wall of the casing is called tip clearance, which is one of the important parameters affecting the performance of rotating machinery, and the 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 tip clearance engineering test due to its advantages of high temperature resistance, gas corrosion resistance, low intervention, non-contact, online and real-time.

[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, and is based on the parallel plate capacitor principle. The tip clearance is measured by measuring the capacitance between the sensor core and the rotor tip. Since the capacitive tip clearance measurement system is an online measurement, in order to ensure the measurement accuracy and resolution at the highest speed of the rotating blade, the measurement system requires a high response bandwidth, and how to accurately measure the system response bandwidth becomes a key problem to be solved.

[0004] In order to measure the response bandwidth of the system, 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 between the sensor core and the rotor blade, and the existing devices and methods cannot generate standard capacitance signals to simulate 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 utility model aims at overcoming the shortcomings of the prior art that the existing devices cannot generate standard capacitance signals to simulate 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, and provides a measuring device capable of directly generating standard capacitance signals to realize high-precision measurement of system response bandwidth.

[0006] The utility model aims at overcoming the shortcomings of the prior art that the existing devices cannot generate standard capacitance signals to simulate 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, and provides a measuring device capable of directly generating standard capacitance signals to realize high-precision measurement of system response bandwidth.

[0007] The application discloses a response bandwidth measuring device of a capacitance type blade tip clearance measuring system based on a varactor, and the capacitance type blade tip clearance measuring system is composed of a capacitance sensor, a measuring system host and an upper computer which are sequentially connected.

[0008] The signal demodulation module demodulates the blade tip clearance signal output by the capacitance sensor and converts the blade tip clearance signal into a voltage signal; the acquisition module collects and preliminarily processes the voltage signal and transmits data to the upper computer; the upper computer further processes the data to obtain a blade tip clearance value, and simultaneously performs data storage and numerical display.

[0009] The response bandwidth measuring device is used to replace the sensor probe and is connected to the long three-coaxial cable through an SMA joint, and a varactor is used to simulate the capacitance change caused by the blade tip sweeping the capacitance sensor probe; the response bandwidth measuring device is composed of a varactor D, a resistor R1, a first capacitor C1 and a second capacitor C2; the two ends of the second capacitor C2 in parallel connection with the varactor D are respectively connected with the resistor R1 and the first capacitor C1 in series connection, the first capacitor C1 is connected with the long three-coaxial cable, and the input end of the response bandwidth measuring device is connected with the resistor R1.

[0010] Further, the input voltage V of the response bandwidth measuring device is V=V0+V', wherein V0 is a direct current voltage, and V' is a sinusoidal alternating current voltage with a frequency of f, and the capacitance of the varactor D changes with the change of the voltage.

[0011] Further, the resistor R1 plays a role of protecting the power supply and prevents the power supply from being short-circuited to the ground when the varactor D is broken down, and the value range of the resistor R1 is 1-10kΩ.

[0012] Further, the first capacitor C1 and the second capacitor C2 are used as a voltage dividing capacitor, and the capacitance value of the whole response bandwidth measuring device is adjusted by changing the capacitance values of the first capacitor C1 and the second capacitor C2; the first capacitor C1 also has a direct current isolation function.

[0013] Further, under the input of the voltage V, the varactor D is equivalent to a capacitor C xand the capacitance AC x in parallel, where C x is determined by the DC voltage Vo, AC x varies with the sinusoidal AC voltage V', the variation frequency of AC x is the frequency f of the sinusoidal AC voltage V', and let the capacitance of the varactor diode D vary linearly in the range [-Δ, Δ];

[0014] The capacitance value C TEST of the circuit in the response bandwidth measurement device is:

[0015]

[0016] Let the capacitance C0=C x +C2, then

[0017] Further, the selection of the first capacitance C1 and the second capacitance C2 includes:

[0018] 1) To achieve long cable signal transmission, the measurement system host connects an AC voltage V1' with a frequency of f1 between the core and the shell of the three coaxial cables, the frequency and amplitude of V1' are determined by the signal demodulation module and cannot be eliminated, to reduce the interference of the AC voltage V1' on the bandwidth measurement, adjust the values of the first capacitance C1 and the second capacitance C2, so that the effect of the AC voltage V1' is less than 1 / 10 of the effect of the input voltage V, therefore the sum of the capacitance C0 and the variable capacitance AC x of the varactor diode is greater than 10 times the capacitance value of the first capacitance C1, that is:

[0019] C0+ΔC x >10C1

[0020] 2) Increase the variable capacitance AC x of the varactor diode D to increase the influence on C TEST , let AC x ∈[-Δ, Δ], Δ>0, and let then:

[0021]

[0022] If the change amount of C TEST takes the maximum value, the value of C needs to be increased, and the value of C also needs to be increased;

[0023] 3) The capacitance type tip clearance measurement system requires that the capacitance change amount before and after the simulated blade sweeps the sensor probe be 0pF<|C TEST |<1pF, where C TEST =C TEST，max -C TEST，min , then:

[0024]

[0025] Derivation C TEST The relationship with the change of C1 is:

[0026]

[0027] Since C0>>Delta, therefore That is, increase the value of C1;

[0028] Derivation C TEST The relationship with the change of C0 is:

[0029]

[0030] Therefore, reduce the value of C0;

[0031] Derivation C TEST The relationship with the change of Delta is:

[0032]

[0033] Therefore, increase the value of Delta;

[0034] Before carrying out the response bandwidth measurement experiment, the maximum value of the capacitance change in the process of the blade sweeping the sensor probe is estimated, so as to select the values of C1 and C2.

[0035] Compared with the prior art, the technical scheme of the utility model brings the beneficial effects that:

[0036] 1. Improve the measurement accuracy: the utility model directly generates a standard capacitance signal as input, avoiding the error in the capacitance-voltage conversion process in the traditional method, thereby significantly improving the accuracy of the system response bandwidth measurement.

[0037] 2. Enhance adaptability: the device can be applied to various types of capacitive tip clearance measurement systems, and is widely applicable to tip clearance measurement in rotating machinery such as aero-engines, gas turbines, steam turbines, etc., improving the application range and practicality of the system.

[0038] 3. Simplify the measurement process: the utility model simplifies the process of response bandwidth measurement, without the need for additional conversion devices or complex signal processing procedures, making the measurement process more intuitive and efficient.

[0039] 4. Real-time online measurement: the measurement device of the utility model supports real-time online measurement, which can dynamically monitor the change of tip clearance during the operation of rotating machinery, ensuring the safe operation of rotating machinery.

[0040] 5. Improve system stability: the utility model directly generates standard capacitance signal simulation system input, avoids the system instability problem caused by conversion error in traditional method, improves the stability and reliability of overall measurement system. And the generated standard capacitance signal frequency is adjustable, the amplitude is adjustable.

[0041] 6. Economic and efficient: the device of the utility model is reasonable in design, simple in structure, easy to miniaturize, convenient to carry, can effectively reduce the overall cost of the system, at the same time 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

[0042] Figure 1 The schematic diagram of the capacitive tip clearance measurement system is shown.

[0043] Figure 2 The structure principle diagram of the response bandwidth measurement device in the utility model is shown.

[0044] Figure 3 The equivalent circuit diagram of the response bandwidth measurement device in the utility model is shown.

[0045] Figure 4 The bandwidth measurement scheme diagram of the tip clearance measurement system in the utility model is shown.

[0046] Figure 5 The bandwidth measurement flow chart of the tip clearance measurement system in the utility model is shown.

[0047] Reference signs: 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-response bandwidth measurement device DETAILED DESCRIPTION

[0048] The utility model will be further described in detail in combination with the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the utility model, and are not used to limit the utility model.

[0049] The embodiment provides a response bandwidth measurement device of a capacitive tip clearance measurement system based on varactor, and the capacitive 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 1The measurement system host 2 includes a signal demodulation module 21 and an acquisition module 22; the capacitance sensor 1 consists of interconnected sensor probes 11 and a triaxial cable 12. The triaxial cable 12 includes two sections, one long and one short. The short section of the triaxial cable is fixed to the tail of the sensor probe 11 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 11; the measurement is based on the principle of parallel plate capacitor. The core of the sensor probe 11 forms one plate of a variable capacitor, and the rotating blade forms the other plate of the variable capacitor. The blade tip gap signal is obtained by measuring the capacitance change between the two plates. The blade tip gap signal obtained by the sensor probe 11 is transmitted to the measurement system host 2 via the triaxial cable 12.

[0050] The signal demodulation module 21 in the host computer 2 of the measurement system demodulates the changing capacitance signal output by the capacitance sensor 1 and converts the capacitance signal into a voltage signal; the acquisition module 22 acquires and performs preliminary processing of the voltage signal and transmits the data to the host computer 3; the host computer 3 performs further processing of the data, calculates the blade tip clearance value, and simultaneously stores and displays the data.

[0051] The response bandwidth measuring device 4 of the capacitive blade tip clearance measuring system of this invention uses a varactor diode to simulate the capacitance change caused by the rotating blade tip sweeping across the capacitive sensor probe. The structural principle of the device is as follows: Figure 2 As shown, the response bandwidth measuring device 4 mainly consists of a varactor diode D, a resistor R1, and capacitors C1 and C2. After replacing the sensor probe, the response bandwidth measuring device 4 is connected to a long section of three-coaxial cable via an SMA connector. The varactor diode simulates the capacitance change caused by the tip of a rotating blade sweeping across the capacitance sensor probe. The response bandwidth measuring device consists of a varactor diode D, a resistor R1, and capacitors C1 and C2. The two ends of capacitor C2, connected in parallel with the varactor diode D, are connected in series with resistor R1 and capacitor C1, respectively. Capacitor C1 is connected to the long section of three-coaxial cable. The input terminal of the response bandwidth measuring device is connected to resistor R1. V = V o +V′ is the input voltage of the response bandwidth measuring device 4, where V o V is a DC voltage, ensuring the varactor diode is in reverse bias; V′ is a sinusoidal AC voltage with frequency f, controlling the capacitance of the varactor diode D to change with the voltage. Resistor R1 protects the power supply, preventing it from short-circuiting to ground in the event of a breakdown in the varactor diode D; a value of 1kΩ or 10kΩ can be selected.

[0052] Preferably, capacitors C1 and C2 are used as voltage divider capacitors, and the overall capacitance value of the response bandwidth measuring device is adjusted by changing the capacitance values ​​of C1 and C2. Capacitor C1 also has a DC blocking function.

[0053] When selecting a varactor diode D, a model with a larger linear operating region and stronger voltage withstand capability should be preferred. Under an input voltage V, the varactor diode D is equivalent to a capacitor C. x and changing capacitance ΔC x Parallel connection, such as Figure 3 As shown, the capacitor C x Determined by the DC voltage V0, ΔC x ΔC varies with the alternating current voltage V′. x The frequency of change is the frequency f of the AC voltage V′, and the linear range of the capacitance of the varactor diode is assumed to be [-Δ, Δ].

[0054] Calculate along the direction of the arrow Figure 3 The capacitance value C of the response bandwidth measurement device TEST for:

[0055]

[0056] Let C o =C x +C2, then

[0057] Specifically, the selection of capacitors C1 and C2 in a varactor diode-based response bandwidth measurement device needs to consider the following points:

[0058] 1) To achieve signal transmission over long cables, the measurement system host connects an AC voltage V1′ with frequency f1 between the core and outer shell of the triaxial cable. The frequency and amplitude of V1′ are determined by the signal demodulation module and cannot be eliminated. To reduce the interference of AC voltage V1′ on bandwidth measurement, the values ​​of capacitors C1 and C2 are adjusted to make the AC voltage V1′... 1′ The effect of the capacitor C0 is less than 1 / 10 of the effect of the input voltage V, therefore the change in capacitance ΔC of the varactor diode is less than 1 / 10. x The sum of these values ​​is greater than 10 times the capacitance value of the first capacitor C1, that is:

[0059] C0+ΔC x >10C1

[0060] 2) Change the capacitance ΔC of the varactor diode. x As large as possible, so that it can affect C TEST It has a significant impact. Let ΔC x ∈[-Δ, Δ], Δ>0, we can assume but:

[0061]

[0062] If C TEST If the change is taken to its maximum value, then it is necessary to Take as large a value as possible, and at the same time The value is as large as possible.

[0063] 3) The capacitive tip clearance measurement system requires the analog leaf blade to sweep the capacitance sensor probe before and after the capacitance change amount 0 < Δ < 1 pF, wherein C TEST < 1 pF, wherein C TEST = C TEST，ma x-C TEST，min :

[0064]

[0065] Derive the change relationship of C TEST with C1:

[0066]

[0067] Since C o >> Δ, therefore That is, C1 should be as large as possible.

[0068] Derive the change relationship of C TEST with C o :

[0069]

[0070] Therefore, C o should be as small as possible.

[0071] Derive the change relationship of C TEST with Δ:

[0072]

[0073] Therefore, Δ should be as large as possible.

[0074] Before carrying out the response bandwidth measurement experiment, estimate the maximum value of the capacitance change in the process of the leaf blade sweeping the capacitance sensor probe, so as to select the values of C1 and C2.

[0075] When the gap value is 0.5 mm, the capacitance change amount C TEST is about 0.28 pF, the linear working area of the selected variable capacitance diode is Δ = 20 pF, and C x = 60 pF. Based on common capacitance standard values, C1 = 22 pF and C2 = 181 pF are selected, and C TEST = 0.2815 pF is calculated.

[0076] The response bandwidth measurement device 4 of the embodiment is used to measure the bandwidth of the capacitive tip clearance measurement system, and the system bandwidth measurement scheme is as follows: Figure 4The response bandwidth measuring device 4 based on the varactor diode can generate a variable capacitance test signal of different frequencies, which is transmitted to the signal demodulation module 21 through the three coaxial cables 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.

[0077] Specifically, the bandwidth measurement experiment process of the capacitive tip clearance measurement system is as shown in the figure. Figure 5 The experimental equipment to be measured is installed and debugged, and there are 13 frequency points to be measured, 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 and 202kHz. The control signal frequency of the response bandwidth measuring device 4 based on the varactor diode is adjusted, the output voltage of the signal demodulation module 21 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 amplitude of the signal 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.

[0078] The utility model is not limited to the above-mentioned embodiment. The above description of the specific embodiment is intended to describe and illustrate the technical scheme of the utility model, and the above-mentioned specific embodiment is only illustrative and is not restrictive. Without departing from the purpose of the utility model and the scope of the claims, those skilled in the art can make many forms of specific changes under the guidance of the utility model, and these are within the protection scope of the utility model.

Claims

1. A response bandwidth measurement device for a variable capacitance diode-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 capacitive sensor probes; the measurement being based on a flat plate capacitance principle, a core pole of the sensor probe constituting one pole plate of a variable capacitance, a rotating blade constituting another pole plate of the variable capacitance, a tip clearance signal being obtained by measuring the capacitance change between the two pole 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 a 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, and a variable capacitance diode is used to simulate the capacitance change caused by the rotating blade tip sweeping across the capacitive sensor probe; the response bandwidth measurement device is composed of a variable capacitance diode D, a resistor R1, a first capacitor C1 and a second capacitor C2; the two ends of the second capacitor C2 in parallel connection with the variable capacitance diode D are respectively connected in series with the resistor R1 and the first capacitor C1, the first capacitor C1 is connected to the triaxial cable of the long section, and the input end of the response bandwidth measurement device is connected to the resistor R1.

2. The response bandwidth measuring device for a varactor-diode-based capacitive tip-turbine-blade-clearance measuring system according to claim 1, characterized in that The input voltage V of the response bandwidth measurement device is V=V0+V', wherein V0 is a direct current voltage, ensuring that the variable capacitance diode D is in a reverse bias state; V' is a sinusoidal alternating current voltage, the frequency being f, and the capacitance of the variable capacitance diode D changes with the change of the voltage.

3. The response bandwidth measuring device for a varactor-diode-based capacitive tip-turbine-blade-clearance measuring system according to claim 1, characterized in that The resistor R1 plays a role of protecting the power supply, preventing the power supply from being short-circuited to the ground when the variable capacitance diode D is broken down, and the value range is 1-10 kΩ.

4. The response bandwidth measuring device for a varactor-diode-based capacitive tip-turbine-blade-clearance measuring system according to claim 1, characterized in that The first capacitor C1 and the second capacitor C2 are used as a voltage dividing capacitor, and the capacitance value of the whole 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 also has a direct current blocking function.

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