Temperature compensation method of ultrasonic analog circuit

Abstract

The invention discloses a temperature compensation method for an ultrasonic analog circuit, and the method comprises the steps: firstly carrying out the temperature characteristic test of the ultrasonic analog circuit, and obtaining the test data of an experimental sample; then temperature compensation is carried out on the circuit according to a temperature characteristic test result; specifically, a circuit gain compensation mode is adopted for an analog circuit, firstly, a component with good temperature characteristics is selected, then a matching gain compensation circuit is designed, a temperature sensor chip is introduced to convert real-time temperature into voltage, and the voltage is loaded to a variable gain amplifier; the gain design of the amplifier is also determined by test data of an experimental sample, and the variable gain amplifier needs to additionally provide a gain with a corresponding amplitude to complete temperature compensation of the analog circuit when the analog circuit outputs a response reduction amplitude at a low temperature. According to the invention, a corresponding gain compensation module is added during design, dynamic real-time adjustment can be carried out according to environment temperature change, and problems caused by uncontrollable variables in a signal link are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of partial discharge ultrasonic monitoring of electric power equipment, and in particular relates to a temperature compensation method for an ultrasonic simulation circuit. Background Art

[0002] Under the extremely cold conditions in Northeast my country, temperature has become a key factor in the increased failure rate of power equipment condition monitoring devices. According to the "extreme cold" standard defined by meteorology, that is, when the temperature is below -40°C, the physical, mechanical and electrical properties of the sensor equipment will change significantly. Under the continuous influence of the low temperature environment, the condition monitoring devices in the power system show the characteristics of reduced accuracy and stable operation, and frequently face the risk of functional abnormalities of electronic components and circuit boards due to low temperatures. At the same time, the materials used for sealing show signs of performance degradation, and the cable material becomes more fragile at low temperatures, increasing the possibility of breakage. In addition, in a low temperature environment, the battery charging and discharging performance of the monitoring device is severely degraded, usually only about 30% of that at normal temperature, which constitutes a major constraint on the stable operation of the transmission line condition monitoring device in low temperature areas.

[0003] At present, although comprehensive research has been conducted on the intelligence and communication transmission of online monitoring systems at home and abroad, specific research on the characteristics of online monitoring systems and fault resolution in low-temperature environments is relatively scarce, and no in-depth research on reliability improvement has been conducted on the above-mentioned low-temperature faults. The detection methods for partial discharge of equipment in the power grid mainly use ultrasonic method, geoelectric wave method, ultra-high frequency method, high-frequency current method and other technologies for detection. The present invention takes the partial discharge ultrasonic monitoring device as the main research object, and proposes a temperature compensation method specifically for the performance degradation problem of partial discharge ultrasonic sensors caused by changes in various parameters in low-temperature environments. Summary of the invention

[0004] The technical solution adopted by the present invention to solve the technical problem is: a temperature compensation method for an ultrasonic analog circuit, the method comprising the following steps: S100, performing a temperature characteristic test on the ultrasonic simulation circuit to obtain experimental sample test data; S200, using the experimental sample test data to design a matching gain compensation module to complete the temperature compensation of the analog circuit.

[0005] Preferably, the temperature characteristic test in step S100 includes: testing the center frequency of the ultrasonic simulation circuit at different temperatures to obtain a variation pattern of the center frequency with temperature.

[0006] Preferably, the temperature characteristic test in step S100 further includes: based on the variation pattern of the center frequency with temperature, testing the amplitude-frequency characteristic of the ultrasonic simulation circuit at different temperatures to obtain its variation pattern with temperature.

[0007] Preferably, the temperature characteristic test in step S100 further includes: based on the variation pattern of the amplitude-frequency characteristic with temperature, testing the output gain characteristic of the ultrasonic simulation circuit at different temperatures, and obtaining its variation pattern with temperature as a basis for temperature compensation.

[0008] Preferably, the gain compensation module comprises: a variable gain amplifier.

[0009] Preferably, the variable gain amplifier is located at the back end of the entire analog signal link.

[0010] Preferably, the gain compensation module further includes: a temperature acquisition circuit.

[0011] Preferably, the temperature acquisition circuit provides a control voltage for the variable gain amplifier.

[0012] The technical advantages of the present invention are as follows: 1) The present invention adds a corresponding gain compensation module during design, which can be dynamically adjusted in real time according to changes in ambient temperature to solve the problem caused by uncontrollable variables in the signal link; 2) The variable gain amplifier in the present invention is located at the back end of the entire analog signal chain, and its location will not cause deterioration of the noise coefficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A flow chart of a temperature compensation method for an ultrasonic simulation circuit in one embodiment of the present invention; Figure 2 (a) is a common-mode amplifier circuit in an ultrasonic analog circuit; Figure 2 (b) is an active narrowband filter circuit in an ultrasonic simulation circuit; FIG3( a ) is a diagram showing the center frequency of a simulation circuit at different temperatures in one embodiment of the present invention; FIG3( b ) is an amplitude-frequency response of a simulation circuit at different temperatures in one embodiment of the present invention; FIG3( c ) is an output gain characteristic of an analog circuit at different temperatures in one embodiment of the present invention; Figure 4 A circuit diagram of a temperature sensor in one embodiment of the present invention; Figure 5 A circuit diagram for adjusting the gain factor in one embodiment of the present invention; Figure 6 A gain compensation circuit diagram in one embodiment of the present invention; FIG. 7( a ) is a graph showing the relationship between gain compensation and temperature in one embodiment of the present invention; FIG. 7( b ) is a diagram showing the relationship between the compensated channel gain and the temperature in one embodiment of the present invention. DETAILED DESCRIPTION

[0014] The following will refer to the attached Figure 1 7 (b) to describe in detail a specific embodiment of the present invention. Although specific embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0015] It should be noted that certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. This specification and claims do not use the difference in nouns as a way to distinguish components, but use the difference in the functions of the components as the criterion for distinction. As mentioned throughout the specification and claims, "including" or "comprising" is an open term, so it should be interpreted as "including but not limited to". The subsequent description of the specification is a preferred embodiment of the present invention, but the description is based on the general principles of the specification and is not intended to limit the scope of the present invention. The scope of protection of the present invention shall be determined by the attached claims.

[0016] To facilitate understanding of the embodiments of the present invention, further explanation will be given below by taking specific embodiments as examples in conjunction with the accompanying drawings, and each of the accompanying drawings does not constitute a limitation on the embodiments of the present invention.

[0017] The present invention provides a temperature compensation method for an ultrasonic simulation circuit, comprising the following steps: First, the temperature characteristics of the ultrasonic analog circuit are tested to obtain experimental sample test data; then temperature compensation is performed based on the temperature characteristics test results; specifically, for the analog circuit, the circuit gain compensation method is adopted, and firstly, components with good temperature characteristics should be selected, and then a matching gain compensation circuit is designed, and a temperature sensor chip is introduced to convert the real-time temperature into a voltage, and then loaded onto a variable gain amplifier; the gain design of the amplifier is determined by the experimental sample test data, and the output response of the analog circuit is reduced at low temperature, and the variable gain amplifier needs to provide an additional gain of the corresponding amplitude to complete the temperature compensation of the analog circuit.

[0018] General design process: (1) First, the gain of the AE analog circuit decreases with temperature; (2) Confirm the control voltage Vctl the scope of change; (3) Determine the temperature range and confirm V T Range of variation; (4) The circuit is adjusted by the amplification factor so that the voltage V representing the temperature T Converted into the control voltage V of the gain compensation circuit ctl ; Calculate the resistance value of each resistor and the bias voltage to complete the parameter design of the amplification factor adjustment circuit.

[0019] (5) Set the control voltage V ctl Input to the gain compensation circuit and test the compensation effect.

[0020] Refer to Figures 2 (a) and 2 (b), which are the circuit diagrams of the ultrasonic simulation module used in this patent. Figure 2 (a) is a common-mode amplifier circuit in the ultrasonic simulation circuit, which amplifies the weak local discharge ultrasonic signal (mV level) into a measurable signal (hundreds of mV level) with a certain gain. According to the ideal op amp equation, assuming that the open-loop gain A ol is infinite, the current entering the two input terminals of the op amp is 0, and the input voltage U i With output voltage U The relationship of 0 is: (1) By adjusting the resistance values ​​of resistors R1 and R2, the gain of the amplifier circuit can be changed, but it will be affected by the external temperature. In addition, the input offset voltage and input offset current of the operational amplifier will also drift due to the influence of temperature, affecting the output accuracy of the amplifier.

[0021] Figure 2 (b) shows an active narrowband filter circuit in an ultrasonic analog circuit, which is used to filter out interference signals outside the main frequency band of the ultrasonic signal. C 2 = C 3 , R 2 = R 3 , R 4 = R 5 , according to the characteristics of the ideal amplifier, the transfer function H(s) of the bandpass filter is derived as follows: (2) The main performance indicators of the bandpass filter are bandwidth, center frequency and gain at the center frequency, which directly affect the reliability of the entire measurement system. According to the simulation results, the center frequency at room temperature is 37.93kHz, the gain at the center frequency is 13.47dB, and the bandwidth is 37.15~38.81kHz. It can be seen that the circuit bandwidth is narrow and has a high screening characteristic for signals of a certain frequency.

[0022] In one embodiment, the center frequency, amplitude-frequency characteristics, and output gain characteristics of the selected ultrasonic simulation circuit are first tested in a wide temperature range (-60~30°C) with temperature as a single variable factor to obtain their variation patterns with temperature, see Figures 3(a) to 3(c).

[0023] For the ultrasonic analog circuit, 8 temperature points were selected for research, and the relationship between the center frequency and temperature is shown in Figure 3 (a). It can be seen from the figure that the center frequency of the analog circuit of the ultrasonic sensor is not greatly affected by temperature, and the change of the center frequency in the range of -50℃~20℃ can be basically ignored. The center frequency changes in the experimental temperature range from 39-40kHz, which remains basically unchanged. It is clear that the center frequency of the test signal in the experiment should also be 40kHz.

[0024] Based on the determined center frequency of 40kHz, the frequency range of the standard ultrasonic signal source is changed, and the frequency sweep method is used to obtain the analog circuit amplitude-frequency characteristics within the frequency range of 20-50kHz at different temperatures. If the temperature has little effect on it or is within an acceptable range, no compensation is required; if the effect is large, circuit compensation can be used, and the change law of the output gain characteristics with temperature needs to be further obtained.

[0025] The amplitude-frequency characteristic curves of the ultrasonic analog circuit at different temperatures are shown in Figure 3 (b). As can be seen from the figure, when the ambient temperature drops, the filter center frequency of the analog circuit remains unchanged at about 40kHz, and the broadband range of its frequency response remains stable between 32kHz and 46kHz, with no significant fluctuations. However, it is worth noting that the output voltage amplitude of the circuit is significantly reduced, which clearly shows that the reduction in temperature has an adverse effect on the amplification ability of the circuit, that is, the gain performance. Therefore, the amplification performance of the analog circuit at low temperatures needs to be paid special attention. By extension, when the ambient temperature drops, the filter center frequency of the analog circuit remains unchanged at a certain value, and the broadband range of its frequency response remains stable between the certain value ±6kHz, with no significant fluctuations.

[0026] In order to more intuitively compare the gain changes under different temperatures, the voltage output peak and gain at 40kHz are selected for analysis, and the relationship between voltage output and temperature is shown in Figure 3 (c). The law of change of output gain characteristics with temperature is used as the basis for temperature compensation. As shown in Figure 3 (c), the gain decreases by 2.6dB with temperature from 20℃ to -50℃. This 2.6 is the basis for subsequent compensation. As can be seen from the figure, temperature has a great influence on the amplification function of the analog circuit. As the temperature decreases, the gain of the entire circuit also decreases, and the trend of change is roughly linear with the temperature. When it decreases from 20℃ to -50℃, the output decreases by 26.67%, which is unacceptable for the measurement results at low temperatures.

[0027] From the above conclusions, it can be seen that the low temperature environment has a significant impact on the partial discharge ultrasonic simulation circuit. It will cause the reliability of the analog circuit output to weaken and the data accuracy to decline, which in turn affects the quality of decisions made based on these measurement data, and cannot accurately show the true characteristics of partial discharge. In view of this, temperature compensation for ultrasonic simulation circuits has become an urgent and critical need.

[0028] In another embodiment, the temperature compensation of the ultrasonic analog circuit is divided into two steps: the first step is to select components with good temperature characteristics; the second step is to add corresponding gain compensation modules during design, which can be dynamically adjusted in real time according to changes in ambient temperature to solve the problems caused by uncontrollable variables in the signal link.

[0029] In another embodiment, the gain compensation module can be divided into two parts. The first part is a temperature acquisition circuit that provides a control voltage for the variable gain amplifier, which converts the temperature into voltage through a temperature sensor chip and loads it onto the variable gain amplifier. The second part is a variable gain amplifier located in the signal chain, which is located at the back end of the entire analog signal chain and its location will not cause deterioration of the noise coefficient.

[0030] In another embodiment, for the selection of the temperature sensor chip and the variable gain amplifier, the analog chip does not require a processor for digital control configuration, and has a simple structure and is easy to miniaturize. Therefore, after comprehensive consideration, the analog chip is selected as the main component of the solution.

[0031] In another embodiment, the temperature sensor chip selects the LM35 series, produced by National Semiconductor, and its output voltage is linearly related to the Celsius temperature within the operating temperature range. Among them, LM35A has a rated operating temperature of -55℃ to +150℃, an accuracy of ±0.5℃, an operating voltage range of 4V to 30V, an output voltage range of -1V to 6V, and a nonlinear error of only 0.25℃ within the range of -55℃~+150℃. The self-heating is very low, and the temperature rise in still air is only 0.08℃, which has no effect on the interference of temperature measurement and meets the module requirements.

[0032] In another embodiment, the variable gain amplifier chip of the present invention selects AD602S produced by ADI. This chip has a linear gain response in dB, and the dB gain is proportional to the control voltage. It is precisely calibrated and does not change with the power supply voltage and temperature. The gain range is -10 dB to +30 dB, and the precise absolute gain can reach ±0.3 dB. The wide bandwidth range is DC to 35MHz, and the rated operating temperature range is -55℃ to +125℃. It can be used in any scenario requiring precise gain, low noise, low distortion and wide bandwidth, which meets the requirements of the present invention. Temperature sensor circuit design reference Figure 4 .

[0033] In another embodiment, the temperature voltage transfer function of LM35 is , where T represents temperature. In its entire operating temperature range of -55℃ to 150℃, the voltage changes from -550mV to 1500mV. The slope of the AD602S gain change with temperature is 31.25mV / dB. According to the gain compensation required by different analog amplifier circuits in the corresponding temperature range, the range of control voltage change can be confirmed. For the AE analog amplifier circuit, its gain decreases by 2.6dB with temperature from 20℃ to -50℃, and the change rate is 0.037dB / ℃.

[0034] In another embodiment, the voltage output by LM35 according to the temperature needs to be processed, so the amplification factor adjustment circuit refers to Figure 5 The entire gain adjustment circuit consists of three parts: V T Reverse attenuation module, temperature signal bias V bis module and gain control voltage V ctl Adjust the module. V T The reverse attenuation module realizes the reverse attenuation of the temperature sensor output voltage. The output voltage of LM35 decreases as the temperature decreases. The gain of AD602S is positively correlated with the control voltage, so the temperature voltage needs to be inverted. Temperature signal bias V bisThe module is responsible for zero offset correction of the temperature sensor. When there is no external temperature influence, the temperature sensor may have a non-zero initial output value, that is, the output in the cold state is not zero. In order to make the output of the entire measurement system have a known and controllable reference point at the low temperature end (for example, 0V corresponds to a specific temperature, usually room temperature or 0℃), it is necessary to apply a bias voltage for zero point calibration. Gain control voltage V ctl The adjustment module realizes reasonable adjustment of the gain control voltage range through the in-phase amplifier circuit. By reasonably setting the resistance value of the resistor, the temperature compensation circuit can meet the different gain compensation requirements of the two sensors.

[0035] For the amplification factor adjustment circuit, its output voltage U 0 and V ctl The output is as follows: (3) (4) Among them, V bis is the temperature signal bias voltage, V ctl is the gain control voltage, V T is the temperature voltage. The required V ctl The range is 0~81.2mV, corresponding to V T The range is 200~-500mV, then V ctl With V T The relationship is that the resistance values ​​and bias voltages of each resistor are R1=7.6kΩ, R2=1kΩ, R3=0kΩ, R4=10kΩ, V bis =23.2mV. The amplifier of the gain adjustment circuit is the AD8022 amplifier produced by Analog Devices. It has two built-in low-noise, high-speed, voltage feedback amplifiers and an operating temperature range of -55°C to +125°C, which meets the application scenario of this module. All resistors in the circuit are 0.1% high-precision resistors. For different sensors, only R6 and R3 need to be adjusted to meet their temperature compensation requirements.

[0036] In another embodiment, the gain compensation circuit is the core part of the entire temperature compensation module, which realizes the final compensation of the output signal of the signal chain. Figure 6 , gain control voltage V ctl AD602 cannot be controlled directly, and the gain control voltage V ctl Add a -625mV offset to zero the gain of the AD602.

[0037] In another embodiment, after the analog circuit is subjected to overall temperature compensation, the gain compensation result changes with temperature as shown in FIG7 (a), and the relationship between the compensated gain and temperature is shown in FIG7 (b). It can be seen that the gain compensation is linearly related to the temperature, which meets the requirement of linear gain compensation with temperature. Combined with the uncompensated analog circuit for analysis, the gain of the compensated signal channel is improved with temperature changes, and the gain of the AE signal channel is maintained at about 65.1dB, with an error of ±0.03dB. It can be seen that the temperature compensation module effectively improves the gain temperature drift characteristics of the original circuit.

[0038] In another embodiment, the temperature compensation method design process provided by the present invention is as follows: (1) AE analog amplifier circuit test data: the gain decreases by 2.6 dB as the temperature increases from 20°C to -50°C, as shown in Figure 3(c); (2) The slope of the AD602S gain change with temperature is 31.25mV / dB. According to the gain compensation required by different analog amplifier circuits in the corresponding temperature range, it can be confirmed that the control voltage V ctl The range of change is 0-81.2mV; (3) The temperature-voltage transfer function of LM35 is: , the temperature range is from 20℃ to -50℃, then V T Variation range: 200~-500mV; (4) The function of the amplification factor adjustment circuit is to make the voltage V representing the temperature T Converted into a gain compensation circuit ( Figure 6 ) control voltage V ctl ; ①Required between 20℃ and -50℃ V ctl The range is 0~81.2mV, corresponding to V T The range is 200~-500mV, then V ctl and V T The relationship is; ②For the amplification factor adjustment circuit ( Figure 5 ), its output voltage U 0 and V ctl The calculation of is as follows:

[0039]

[0040] but ; ③ Combining the two formulas in step ① and ②, the resistance values ​​of each resistor and the bias voltage can be determined as R1=7.6kΩ, R2=1kΩ, R3=0kΩ, R4=10kΩ, V bis =23.2mV. The parameter design of the amplification factor adjustment circuit is completed.

[0041] (5) Set the control voltage V ctl Input to the gain compensation circuit ( Figure 6 ), if the compensation effect test and verification pass and meet expectations, the temperature compensation of the analog circuit is completed.

[0042] The above general description of the invention involved in this application and the description of its specific implementation methods should not be understood as limiting the technical solutions of the invention. Based on the disclosure of this application, those skilled in the art can, without violating the constituent elements of the invention involved, add, reduce or combine the disclosed technical features in the above general description or / and specific implementation methods (including examples) to form other technical solutions within the scope of protection of this application.

Claims

1. A temperature compensation method for an ultrasonic analog circuit, characterized in that: The method comprises the following steps: S100, performing a temperature characteristic test on the ultrasonic simulation circuit to obtain experimental sample test data; S200, using the experimental sample test data to design a matching gain compensation module to complete the temperature compensation of the analog circuit.

2. The method according to claim 1, characterized in that Preferably, the temperature characteristic test in step S100 includes: testing the center frequency of the ultrasonic simulation circuit at different temperatures to obtain a variation pattern of the center frequency with temperature.

3. The method according to claim 1, characterized in that The temperature characteristic test in step S100 further includes: based on the variation pattern of the center frequency with temperature, testing the amplitude-frequency characteristic of the ultrasonic simulation circuit at different temperatures to obtain the variation pattern of the amplitude-frequency characteristic with temperature.

4. The method according to claim 1, characterized in that The temperature characteristic test in step S100 also includes: based on the variation pattern of the amplitude-frequency characteristic with temperature, testing the output gain characteristic of the ultrasonic simulation circuit at different temperatures, obtaining the variation pattern of the output gain with temperature as a basis for temperature compensation.

5. The method according to claim 1, characterized in that The gain compensation module includes: a variable gain amplifier.

6. The method according to claim 5, characterized in that The variable gain amplifier is located at the back end of the entire analog signal chain.

7. The method according to claim 5, characterized in that The gain compensation module also includes: a temperature acquisition circuit.

8. The method according to claim 7, characterized in that The temperature acquisition circuit provides a control voltage for the variable gain amplifier.

Images