CN113155306B - High-voltage power cable joint built-in passive wireless temperature sensor - Google Patents

Abstract

A passive wireless temperature sensor built into a high-voltage power cable joint belongs to the technical field of power cables. The purpose of the present invention is to directly add a built-in passive wireless temperature sensor in the high-voltage power cable joint to the high-voltage power cable joint according to the characteristics of the structural part of the high-voltage cable, which can directly measure the cable temperature at the joint part. The invention includes a SAW temperature sensor and a temperature reader; the SAW temperature sensor is mainly composed of a half-wave dipole antenna and a surface acoustic resonator; the temperature reader includes a DSP control and data processing module, a radio frequency transceiver switch, a signal generator, Transmitting signal processing module and receiving signal processing module. The invention has a simple structure, and because the copper sheet is in direct contact with the inside of the cable, the actual temperature of the cable can be obtained more accurately, so that the safety factor of the cable can be grasped in a more timely manner.

Description

Built-in passive wireless temperature-sensing sensor of high-voltage power cable joint

Technical Field

The invention belongs to the technical field of power cables.

Background

The power cable can produce heat when the operation, and because the regional temperature of every probably is different for multiple reason, in order to protect the safety of cable, can cladding multiple protection in the outside, just so can only gather the inside temperature of cable through the outside, the rate of accuracy is lower, because the inaccuracy of temperature measurement, probably causes unnecessary danger.

Disclosure of Invention

The invention aims to directly add a high-voltage power cable joint built-in passive wireless temperature sensor for directly measuring the temperature of a cable at a joint part in the high-voltage power cable joint according to the characteristics of the structural part of the high-voltage cable.

The invention includes a SAW temperature sensor and a temperature reader; the SAW temperature sensor mainly comprises a half-wave dipole antenna and an acoustic surface resonator; the temperature reader comprises a DSP control and data processing module, a radio frequency receiving and transmitting switch, a signal generator, a transmitting signal processing module and a receiving signal processing module;

SAW temperature sensor: the built-in SAW temperature sensor is in a circular ring shape in appearance, and is directly clamped on a circular copper wire core of a tested cable connector during installation, a soft copper sheet is arranged on the inner side of the sensor, and the soft copper sheet is connected with the back copper coating of the acoustic surface resonator;

DSP control and data processing module: the DSP adopts a TMS320F28335 main control chip, and selects 19.2MHz external active crystal oscillator as a system clock source;

radio frequency transmit-receive switch: the DSP controls a single-pole double-throw radio frequency switch RF6504 and two single-pole single-throw radio frequency switches ADG901 to perform excitation signal transmission and echo receiving path switching RF6504 to be a transceiver front-end module, a TX port is a power amplifier, an Rx port is a straight-through path, the two ports are connected with a single antenna port through an SP2T switch, and a transmitting mode is as follows: c_tx=1, c_rx=0; reception mode: c_tx=0, c_rx=1; ADG901 is an absorptive switch terminating the shunt pins, turned on and off by CMOS control pin CTRL control path;

a signal generator: the signal source adopts an integrated VCO+PLL chip Si4112 to generate two paths of intermediate frequency signals, one path is used as a transmitting excitation signal, the other path is used as a receiving local oscillation signal, the signal source is the intermediate frequency output frequency of AD608, the inside of Si4112 is mainly a programmable DDS system, and the numerical control frequency is realized by N, R two frequency dividing registersAfter the register value is obtained by utilizing the Si4112 programming tool, the DSP completes the configuration of the internal register of Si4112 through the SPI interface, when +.>The pins and PDIB enable, si4112 can generate a spectrum-pure analog sine wave output; the VCO has a nominal capacitance C _NOM In parallel with the total inductance, therefore, the center frequency is

A transmission signal processing module: DSP through timerThe enable terminal control Si4112 outputs a sine pulse signal. The signal is attenuated by a digital attenuator RFSA2644, then is amplified by a low noise amplifier LNA and an internal PA of RF6504, RFSA2644 is a 6-bit digital step attenuator, DSP adjusts the signal intensity by configuring a 6-bit gain register in RFSA2644 through SPI time sequence, and PUP is connected with high level; a high performance low noise RF front end amplifier RF2373 is employed;

a received signal processing module: the antenna receives echo signals, the echo signals are subjected to band-pass filtering through a passive sound surface filter SJKT435 with a simple structure, weak signals after the band-pass filtering are amplified through two-stage LNAs, the LNAs are used as a first-stage active circuit of a wireless receiving front end, and an LNA application circuit, namely an RF2373 application circuit is adopted; and accessing the local oscillation signal and the amplified echo signal output by the second signal source into the receiver IF subsystem AD608, carrying out frequency mixing, intermediate frequency low-pass filtering, amplifying and other processing, outputting two paths of analog quantities of the RSSI and the intermediate frequency signal limited by hardware, and finally, controlling the on-chip AD module to complete sampling and data processing by the DSP.

The invention has simple structure, and the copper sheet is in direct contact with the inside of the cable, so that the actual temperature of the cable is obtained more accurately, and the safety coefficient of the cable can be mastered more timely.

Drawings

FIG. 1 is a schematic diagram of a SAW temperature sensor of the present invention;

FIG. 2 is a pictorial view of a SAW temperature sensor of the present invention;

FIG. 3 is a hardware frame diagram of a temperature reader of the present invention;

FIG. 4 is a circuit diagram of an RF6504 application of the present invention;

FIG. 5 is a functional block diagram of the AD901 of the present invention;

FIG. 6 is a block diagram of the IF synthesis of the present invention;

FIG. 7 is a circuit diagram of the Si4112 application of the present invention;

FIG. 8 is a circuit diagram of an RFSA2644 application of the present invention;

FIG. 9 is a circuit diagram of an RF2373 application of the present invention;

FIG. 10 is a functional block diagram of the AD608 of the present invention;

FIG. 11 is a circuit diagram of an AD608 intermediate frequency digital system application of the invention;

FIG. 12 is a software flow chart of the present invention;

FIG. 13 is a diagram of an excitation pulse sequence;

FIG. 14 is an echo signal plot;

FIG. 15 is a diagram of a full scan mode;

FIG. 16 is a partial swept mode diagram;

FIG. 17 is a graph of measured temperature versus center frequency;

fig. 18 is a graph of temperature versus center frequency.

Detailed Description

The acquisition front end of the invention consists of a circular ring-shaped SAW temperature sensor, a temperature reader and a reading antenna. The SAW temperature sensor is responsible for receiving sweep frequency signals sent by the reader in real time and returning the collected temperature signals to the reader. The temperature reader is the core of system operation, can transmit the wireless sweep frequency signal and carry on receiving, analyzing and identifying to SAW sensor return signal through it, and upload the temperature information to the monitoring upper computer through the industrial bus; the reading antenna is a channel for wireless signal transmission, and the working frequency band is 433MHz. When the temperature exceeds a set threshold, the upper machine can perform early warning through an alarm lamp and a message popup window so as to instruct operation and maintenance personnel to timely treat potential safety hazards. And meanwhile, according to the alarm information, carrying out comprehensive analysis, confirmation, processing and other operations on the real-time temperature data and the historical temperature curve.

Fig. 1 and 2 are schematic circuit diagrams and real objects of SAW temperature sensors, respectively. It mainly consists of half-wave dipole antenna and acoustic surface resonator. The center frequency of the acoustic watch resonator is 430.5MHz, and the frequency precision is +/-75 kHz.

The built-in SAW temperature sensor is circular in appearance and is directly clamped on a circular copper wire core of a tested cable connector during installation. The inside of the sensor is provided with a soft copper sheet which is connected with the copper coating on the back of the sound meter resonator, so that the heat at the temperature measuring point can be ensured to be quickly transferred into the sound meter resonator.

The temperature reader mainly comprises a signal generator, a transmitting signal processing module, a receiving signal processing module, a radio frequency receiving and transmitting switch, a DSP control and data processing module, as shown in figure 3. The signal generator generates two paths of intermediate frequency signal sources which are used as local oscillators of the excitation signal and the echo signal. The primary modes of operation of the temperature reader are the transmit and receive modes. In the transmitting mode, a specific radio frequency signal is transmitted by the transmitting signal processing module to excite the SAW sensor to generate resonance. In the receiving mode, the echo signals returned by the SAW sensor are processed by a received signal processing module. The DSP control and data processing module mainly generates control signals and measures RSSI and frequency of echo signals.

(1) DSP control and data processing module

The DSP adopts TMS320F28335 main control chip, and selects 19.2MHz external active crystal oscillator as system clock source. The DSP completes the main control and signal processing calculation work of the detection system, and specific tasks include: configuring a frequency synthesizer of the radio frequency circuit; performing time sequence control on radio frequency signal transmission and echo reception; echo signals and RSSI thereof are acquired through the on-chip AD, the resonance frequency is determined according to the intensity of the echo signals in the sweep frequency range, then the temperature value of the sensor is calculated, and the temperature value is transmitted to the upper computer software for display.

(2) Radio frequency receiving and transmitting switch

The radio frequency transceiver circuit shares an antenna, and a single-pole double-throw radio frequency switch (RF 6504) and two single-pole single-throw radio frequency switches (ADG 901) are controlled by the DSP to switch the excitation signal transmitting and echo receiving paths.

RF6504 is a 50Ω transceiver front-end module for 433MHz to 470 MHz. The TX port provides a power amplifier with a nominal output power of 30dBm and a gain of 15dB, with a maximum input power of no more than 20dBm. The Rx port is a pass-through path. Both are connected to a single antenna port through an SP2T switch. Emission mode: c_tx=1, c_rx=0; reception mode: c_tx=0, c_rx=1. And the power failure of the PA is realized by controlling the VREG direct current bias control pin, so that the power consumption is reduced. RF6504 application circuitry is shown in fig. 4.

ADG901 is an absorptive (matched) switch with a 50 Ω terminated shunt pin, with high isolation and low insertion loss characteristics and a broadband frequency up to 1 GHz. Its maximum input power does not exceed 16dBm. The paths are turned on and off by the CMOS control pin CTRL. The ADG901 functional block diagram is shown in fig. 5.

(3) Signal generator

The signal source adopts an integrated VCO+PLL chip Si4112 to generate two paths of intermediate frequency signals, one path is used for transmitting excitation signals, and the other path is used for receiving local oscillation signals. The frequency difference between the two signals is 10.7MHz, which is the intermediate frequency output frequency of the AD 608. The Si4112 is mainly a programmable DDS system, the input clock of the system is 19.2MHz, and two frequency dividing registers of N, R are used for realizing numerical control frequencyThe frequency step is 25kHz, see fig. 6. After the register value is obtained by using the Si4112 programming tool, the DSP completes the configuration of the internal register of Si4112 through the SPI interface. When->The pins and PDIB enable, si4112 produces a spectrally pure analog sine wave output.

The application circuit of Si4112 is shown in FIG. 7. The PLL of Si4112 may adjust the IF output frequency within ±5% of the VCO center frequency. The centre frequency depends on the total inductance L of the tank circuit connected to the VCO _TOT 。L _TOT In the order of nH, which is equal to the external inductance L _EXT (external inductor between pins 19IFLA and 20IFLB and PCB lead inductor in FIG. 7) and package inductor L _PAK And (3) summing. Although the external inductance value has a deviation of + -10%, si4112 can compensate the error of the inductance by a self-tuning algorithm. The VCO has a nominal capacitance (C _NOM ) In parallel with the total inductance, therefore, the center frequency is

C _NOM ＝6.5pF，L _PAK ＝2.1nH，f _CEN =434 MHz substitution (3-1), calculated

IF output frequency is lower than 500MHz, it can directly drive resistance load of 200 Ω or more.

(4) Transmitting signal processing module

In the transmit mode, the DSP passes through the timer andthe enable terminal control Si4112 outputs a sine pulse signal. The signal is first attenuated by a digital attenuator (RFSA 2644) for signal strength control. And then passes through a Low Noise Amplifier (LNA) and an RF6504 internal PA two-stage power amplification. The first stage amplifies and outputs 10dBm; the second stage amplifies the output 30dBm.

RFSA2644 is a 6-bit digital step attenuator with high linearity over the entire 31.5dB gain control range, with step accuracy of 0.5dB. The application circuit of RFSA2644 is shown in fig. 8. The DSP adjusts the signal strength by SPI timing configuration of the 6-bit gain registers inside RFSA 2644. The PUP is connected with a high level, and the power-on initialization attenuation gain is 0dB.

LNA is used for RF weak signal amplification, and low noise amplifier requires low noise and high gain in order to ensure a certain signal-to-noise ratio of the output signal and to suppress the influence of the subsequent circuit on the noise performance of the system. The LNA should also have high linearity to reduce the effect of out-of-band interference signals on the receiver. The present system employs a high performance low noise RF front end amplifier RF2373. The working bandwidth is 0.4 GHz-4 GHz. When the operating frequency is 880Hhz, operating at a high gain (21.5 dB), the Noise Figure (NF) is 1.1dB. The application circuit of RF2373 is shown in fig. 9. The RC feedback branch circuit plays a role in expanding bandwidth and improving gain stability.

(5) Received signal processing module

In the receiving mode, the antenna receives the echo signal, and the echo signal is subjected to band-pass filtering through a passive sound surface filter (SJKT 435) with a simple structure, retains 433MHz frequency band signals and filters noise in other frequency bands.

The weak signal after band-pass filtering is amplified by a two-stage LNA. The LNA is used as a first-stage active circuit of the wireless receiving front end, and noise and gain directly influence the sensitivity and noise figure of the whole system. Therefore, the LNA application circuit shown in fig. 9 is also employed. If the amplified echo signals with the main frequency of 433MHz are directly sampled, the design difficulty and the cost of the AD hardware circuit are certainly increased, so that the echo signals are further processed with the difference frequency. And (3) accessing the local oscillation signal and the amplified echo signal output by the second signal source to a receiver IF subsystem (AD 608), carrying out frequency mixing, intermediate frequency low-pass filtering, amplifying and other processing, and outputting two analog quantities of RSSI (bandwidth 2 MHz) and the intermediate frequency signal limited by hardware. Finally, the AD module in the chip is controlled by the DSP to complete sampling and data processing.

AD608 is a 3.3V receiver IF subsystem chip from AD corporation, and the functional block diagram is shown in FIG. 10. It integrates a low power, low distortion, low noise mixer and a fully integrated log/limiting amplifier with hardware limited output and RSSI functionality.

In fig. 10, the mixer implements a local oscillator signal (frequency f _c ) And echo signal (frequency f _SAW ) Mixing, which can be decomposed into f _SAW +f _c And f _SAW -f _c The two components are subjected to low-pass filtering and a 10.7MHz ceramic filter (bandwidth 180 kHz) to obtain a 10.7MHz intermediate frequency signal. The mixer can linearly work in the range of-95 dBm to-15 dBm of radio frequency input. The mixer current output may drive a 10.7MHz 330 q ceramic filter connected at the opposite end, which meets industry standards.

Since the logarithmic amplifier is dc coupled, it has a gain of more than 110dB, so that even a few μv offset at its input will saturate the output. Thus, AD608 uses a low frequency feedback loop to cancel the input offset. The loop consists of a limiter driven current source that sends 50 muA current pulses to the FDBK side.These pulses pass through the C ₁ ，R ₄ ，C ₅ The pi-type network is formed to carry out low-pass filtering. The smoothed dc voltage is subtracted from the input IFLO of the intermediate frequency amplifier. Since the amplifier is a high gain amplifier with a feedback loop, care must be taken in layout design and choice of component values to prevent oscillations from occurring.

The application circuit of an AD608 operating at 10.7MHz intermediate frequency digital system is shown in fig. 11. The hardware limited output of AD608 is 200mV (400 mVpp). The phase stability is + -3 DEG in the input range of-75 dBm to +5dBm at a frequency of 10.7 MHz. The limited output signal is amplified and DC-boosted by a homodromous adder formed by a rail-to-rail operational amplifier AD8601 and then connected to an AD input channel. AD608 also provides a high speed RSSI output with an output voltage in the range of 0.2-1.8V (20 mV/dB) and corresponding input signal power in the range of-75 dBm to +5dBm. The RSSI is directly connected to the AD input channel.

The software design is to realize a series of functions such as system initialization, output of excitation signals, excitation signal processing, setting of scanning frequency interval, receiving of response information from the SAW temperature sensor, data conversion between resonance frequency and temperature, serial communication with an upper computer and the like.

To ensure that the SAW temperature sensor is able to collect a sufficiently strong excitation signal for optimal operation after the transmitted signal has decayed through the cable joint insulation and shielding. Firstly, the VCO+PLL, the transmitting gain and the radio frequency switch are controlled by the DSP to output excitation signals with certain intensity. The power of the sensor is best between 10 and 20dbm, and the power scanning function of the upper computer can be used for testing.

The detection algorithm is to transmit signals with different frequencies and the same intensity, and then search the frequency position corresponding to the highest echo signal intensity in the sweep frequency range. For temperature T ₀ The time center frequency is f ₀ When the measured temperature is at [ T ] _min ，T _max ]The change is required in [ f ] _min ，f _max ]The range is swept in step size deltaf. The software implementation flow is shown in fig. 12.

The smaller the sweep step length is set, the frequency of sweepThe more the sweep time is, the longer the power consumption is. In order to improve the frequency sweep efficiency and reduce the power consumption, the system sets the sweep step delta f=25kHz, and adopts the following frequency sweep method: for the first sweep, the sensor frequency [ f _min ，f _max ]The full sweep frequency is carried out in the range to obtain the center frequency f of the sensor at the current temperature ₀ The method comprises the steps of carrying out a first treatment on the surface of the At the later frequency sweep, at f ₀ As reference frequency, the frequency [ f ] is divided by Δf ₀ -5Δf，f ₀ +5Δf]Local sweep frequency is performed in the range.

System testing

And a test platform of the surface acoustic wave sensor and the temperature reader. The sampling rate can reach 10GS/s at the highest by adopting a Talcum oscilloscope MSO 5024. The bandwidth of the oscilloscope voltage probe TPP0500B is 500MHz, and the observation and analysis of 433MHz signals can be satisfied.

(1) Stimulus signal testing

The frequency synthesizer Si4112 outputs 433MHz signal, observes the waveform of the transmitted signal and the FFT analysis result thereof, sets 433MHz center frequency of FFT, and scans 80MHz range. The waveform and FFT analysis result in the amplified window show that the frequency purity of the sinusoidal signal generated by Si4112 is good and is close to the set value.

As shown in fig. 13, curve (1) is the transmission enable control signal, active high. (2) The number curve represents a set of swept excitation pulse sequences with a pulse period of 13.5ms and a pulse width of 36 mus.

(2) Echo signal testing

As shown in fig. 14, a reception enable signal, a reception channel signal, an RSSI signal, a gradually decaying echo signal, and an RSSI thereof. The signal strength decay time was approximately 45 mus, which is close to the time estimated in section 2.3.1 using the equivalent circuit of the acoustic surface resonator.

(3) Frequency scanning mode and temperature measurement result

The center frequency of the tested SAW temperature sensor is about 428.55MHz at 25 ℃, when the temperature changes within the range of-25 ℃ to 120 ℃, the corresponding sweep frequency interval is 427.95MHz to 429.525Hz, and the center frequency f is calculated according to the echo intensity ₀ . Δf=25 kHz, so the number of first full sweeps is 64, as shown in fig. 15. f (f) ₀ After determinationThe local sweep mode is switched to, and the frequency of sweep is 11 times, as shown in fig. 16.

The measured data at different temperatures are read back from the temperature reader using the host computer software tool as shown in fig. 17. The data were imported into an Excel table for curve plotting and trend fitting, as shown in fig. 18, and it was seen that the linearity of the tested SAW temperature sensor was good, and the frequency resolution was 10kHz/°c.

Claims (1)

1. A high-voltage power cable joint built-in passive wireless temperature sensor is characterized in that: including SAW temperature sensors and temperature readers; the SAW temperature sensor mainly comprises a half-wave dipole antenna and an acoustic surface resonator; the temperature reader comprises a DSP control and data processing module, a radio frequency receiving and transmitting switch, a signal generator, a transmitting signal processing module and a receiving signal processing module;

SAW temperature sensor: the built-in SAW temperature sensor is in a circular ring shape in appearance, and is directly clamped on a circular copper wire core of a tested cable connector during installation, a soft copper sheet is arranged on the inner side of the sensor, and the soft copper sheet is connected with the back copper coating of the acoustic surface resonator;

DSP control and data processing module: the DSP adopts a TMS320F28335 main control chip, and selects 19.2MHz external active crystal oscillator as a system clock source;

radio frequency transmit-receive switch: the DSP controls a single-pole double-throw radio frequency switch RF6504 and two single-pole single-throw radio frequency switches ADG901 to perform excitation signal transmission and echo receiving path switching RF6504 to be a transceiver front-end module, a TX port is a power amplifier, an Rx port is a straight-through path, the two ports are connected with a single antenna port through an SP2T switch, and a transmitting mode is as follows: c_tx=1, c_rx=0; reception mode: c_tx=0, c_rx=1; ADG901 is an absorptive switch terminating the shunt pins, turned on and off by CMOS control pin CTRL control path;

a signal generator: the signal source adopts an integrated VCO+PLL chip Si4112 to generate two paths of intermediate frequency signals, one path is used as a transmitting excitation signal, the other path is used as a receiving local oscillation signal, the signal source is the intermediate frequency output frequency of AD608, the inside of Si4112 is mainly a programmable DDS system, and two frequency division registers of N, R are used for realizingNow numerical control frequencyAfter the register value is obtained by utilizing the Si4112 programming tool, the DSP completes the configuration of the internal register of Si4112 through the SPI interface, when +.>The pins and PDIB enable, si4112 can generate a spectrum-pure analog sine wave output; the VCO has a nominal capacitance C _NOM In parallel with the total inductance, therefore, the center frequency is

A transmission signal processing module: DSP through timerEnabling end control Si4112 outputs sine pulse signals, the signals are attenuated by a digital attenuator RFSA2644, then two-stage power amplification is carried out by a low noise amplifier LNA and an internal PA of RF6504, RFSA2644 is a 6-bit digital step attenuator, DSP adjusts signal intensity by configuring a 6-bit gain register in RFSA2644 through SPI time sequence, and PUP is connected with high level; a high performance low noise RF front end amplifier RF2373 is employed;

a received signal processing module: the antenna receives echo signals, the echo signals are subjected to band-pass filtering through a passive sound surface filter SJKT435 with a simple structure, weak signals after the band-pass filtering are amplified through two-stage LNAs, the LNAs are used as a first-stage active circuit of a wireless receiving front end, and an LNA application circuit, namely an RF2373 application circuit is adopted; and accessing the local oscillation signal and the amplified echo signal output by the second signal source into the receiver IF subsystem AD608, carrying out frequency mixing, intermediate frequency low-pass filtering, amplifying and other processing, outputting two paths of analog quantities of the RSSI and the intermediate frequency signal limited by hardware, and finally, controlling the on-chip AD module to complete sampling and data processing by the DSP.