Conversion circuit for long-distance transmission of output signal of current sensor

Abstract

The utility model discloses a conversion circuit for long-distance transmission of output signals of a current sensor. The conversion circuit comprises analog signal generation equipment, namely a high-power rectification power supply, a sensor, an analog signal sampling resistor, a V / F conversion circuit, an optical fiber link, an F / V conversion circuit and a power supply control system. An analog signal optical fiber transmission system composed of a V / F conversion circuit, an optical fiber link and an F / V conversion circuit is utilized to convert an analog signal into a voltage signal with an interval of 0-10V, then the voltage signal is converted into a square wave pulse train with a certain frequency through the V / F conversion circuit, and the square wave pulse train is transmitted to a remote signal processing system through the optical fiber link. And then the pulse train is sent to an F / V conversion circuit to be restored into an analog voltage signal. The scheme of the utility model can effectively transmit low-intermediate frequency analog signals, and has the characteristics of high isolation voltage level, strong anti-interference capability, wide input signal range, 100-meter transmission distance and the like.

Description

Technical Field

[0001] The utility model relates to the technical field of signal processing and transmission, in particular to a conversion circuit for long-distance transmission of output signals of a current sensor. Background Art

[0002] In the process of intelligent signal control, telemetry and storage, the analog signal output by the current sensor is usually low in frequency, weak in signal, susceptible to interference, and generally far away from the signal receiving and processing equipment, and the signal will be further weakened during the transmission process. In some high voltage, electromagnetic coupling and other environments, the signal will be greatly interfered; especially in the field of nuclear fusion, there is a strong magnetic field around the device, and the control object and the control system often need to be separated by a long distance. At this time, the analog signal collected by the sensor needs to be transmitted to the control center for analog-to-digital conversion and then sent to the controller for processing; similarly, in order to avoid high voltage damage to the detection and control equipment, it is necessary to ensure that the signal is transmitted correctly and the input and output ends are completely isolated electrically. Using optical fiber to transmit analog signals is a simple and practical method. At the same time, the use of V / F and F / V conversion technology can better solve the problem of photoelectric isolation of analog signals. The analog signal optical fiber transmission system composed of V / F, optical fiber link and F / V has the characteristics of high isolation voltage level, strong anti-interference ability and wide input signal range. Utility Model Content

[0003] The utility model aims to solve the problem of long-distance transmission of output signals of current sensors, and for this purpose provides a conversion circuit for long-distance transmission of output signals of current sensors.

[0004] The utility model is realized by the following technical solutions:

[0005] A conversion circuit for long-distance transmission of current sensor output signals includes an analog signal generating device, i.e., a high-power rectifier power supply, a sensor, an analog signal sampling resistor, a V / F conversion circuit, an optical fiber link, an F / V conversion circuit, and a power control system. The specific contents are as follows:

[0006] The analog signal generating device, i.e., the high-power rectifier power supply, adopts the ITER PF high-power rectifier power supply. The ITER PF high-power rectifier power supply generates a high-current and high-voltage analog signal when working.

[0007] Sensor, analog signal sampling resistor: Install the sensor at the output end of the ITER PF high-power rectifier power supply. When the ITER PF high-power rectifier power supply is working normally, there will be a corresponding high voltage and high current flowing out of the power supply output end. At this time, the sensor will collect an analog signal, and after sampling by the analog signal sampling resistor, an interval of 0 will be obtained. The 10V voltage signal is sent to the V / F conversion circuit as the input signal;

[0008] V / F conversion circuit: The voltage signal sampled by the current sensor is linearly converted into a square wave pulse train of a certain frequency through voltage-frequency conversion, and then transmitted to the optical fiber link;

[0009] Fiber optic link: Fiber optic link consists of fiber optic transmitter, fiber optic, fiber optic receiver and corresponding connectors; the transmitter converts electrical pulse signals into optical signals, which are then transmitted over long distances at high speed via optical fibers to the frequency-voltage conversion part located in the control center. The receiver converts the optical signals transmitted by the optical fibers into electrical signals, so there is no direct electrical connection between the two ends of the optical fibers, achieving electrical isolation;

[0010] F / V conversion circuit: restores the pulse train into an analog voltage signal through frequency-voltage conversion.

[0011] The V / F conversion circuit and the F / V conversion circuit both use the chip AD650 to realize voltage-frequency conversion and frequency-voltage conversion.

[0012] The V / F conversion is specifically that the input voltage signal is converted into a current signal through the input resistor, and the integrating capacitor is charged through the integrator. At the same time, the capacitor voltage value is compared with the internal reference voltage. Once the threshold is reached, the internal switch disconnects the integration loop, and the internal constant current source reversely integrates the capacitor, and still compares it with the threshold voltage until the reference voltage is reached. Repeat the above process again, and at the same time output a pulse train to achieve voltage-frequency conversion. The larger the voltage, the higher the frequency of the pulse train.

[0013] F / V conversion is specifically the frequency signal f after photoelectric conversion in Through 200PF capacitor, 500 The differential circuit composed of resistors is added to the inverting input terminal of the input comparator. When the falling edge of the input pulse arrives, the input comparator outputs a high level, and the monostable multivibrator is triggered to output a high level. At this time, the current source is applied to the integral capacitor C int The charging time is determined by the capacitor C os The higher the frequency of the input pulse, the larger the integral capacitor C int The more charge is accumulated on the photoelectric converter, the higher the frequency signal Through 200PF capacitor, 500 The differential circuit composed of resistors is added to the inverting input terminal of the input comparator. When the falling edge of the input pulse arrives, the input comparator outputs a high level, and the monostable multivibrator is triggered to output a high level. At this time, the current source is applied to the integral capacitor. The charging time is determined by the capacitor The higher the frequency of the input pulse, the higher the integral capacitance The more charge accumulates on the capacitor, the higher the output voltage (capacitor The higher the voltage across the two ends), the higher the input frequency and output voltage become a linear function relationship, achieving frequency-voltage conversion.

[0014] Beneficial effects of the utility model:

[0015] In the computer measurement and control system of industrial sites or larger devices, the objects to be detected and controlled are often high-power devices with high voltage and strong magnetic field. In order to avoid damage and interference to the detection signal and detection instrument caused by high voltage and strong magnetic field, it is necessary to have a signal transmission device that can not only ensure long-distance transmission of the signal, but also ensure that the input and output ends are completely electrically isolated and have good anti-interference ability. Ordinary signal transmission devices can generally only transmit for tens of meters, and the signal has a certain attenuation, and the isolation voltage level cannot meet the harsh occasions of tens of thousands of volts. At this time, using optical fiber to transmit analog signals is a simple and practical method. At the same time, the use of V / F and F / V conversion technology can better solve the problem of photoelectric isolation and long-distance transmission of analog signals. This article uses the analog signal optical fiber transmission circuit composed of V / F, optical fiber link and F / V, which has the characteristics of high isolation voltage level, strong anti-interference ability, wide input signal range, and transmission distance up to 100 meters. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the structure of the utility model;

[0017] Figure 2 This is the circuit diagram of the V / F conversion part;

[0018] Figure 3 is the working circuit diagram of the integrating capacitor, where: Figure 3 (a) is the circuit diagram of the integration process; Figure 3 (b) is the circuit diagram of the reset process;

[0019] Figure 4 This is the circuit diagram of the F / V conversion part;

[0020] Figure 5 It is the connection circuit diagram of V / F conversion and F / V conversion;

[0021] Figure 6 Input and output waveforms when the input signal frequency is less than 1kHz;

[0022] Figure 7 Input and output waveforms when the input signal frequency is 5kHz. DETAILED DESCRIPTION

[0023] like Figure 1As shown, a conversion circuit for long-distance transmission of the output signal of a current sensor includes an analog signal generating device, i.e., a high-power rectifier power supply, a sensor, an analog signal sampling resistor, a V / F conversion circuit, an optical fiber link, an F / V conversion circuit and a power control system. The specific contents are as follows:

[0024] Analog signal generating equipment: The high-power rectifier power supply adopts ITER PF high-power rectifier power supply, which generates high-current and high-voltage signals when working.

[0025] Sensor, analog signal sampling resistor: Install the sensor at the output end of the ITER PF high-power rectifier power supply. When the ITER PF high-power rectifier power supply is working normally, there will be a corresponding high voltage and high current flowing out of the power supply output end. At this time, the sensor will collect an analog signal, and after the resistor sampling, an interval of 0 will be obtained. The 10 V voltage signal is sent to the V / F conversion circuit as an input signal.

[0026] V / F conversion circuit: 0 The 10V voltage signal is linearly transformed into a square wave pulse train of a certain frequency through voltage-frequency conversion, and then sent to the optical fiber transmitter in the optical fiber link part. There is no direct electrical connection between the two ends of the optical fiber, achieving electrical isolation.

[0027] Fiber optic link: The fiber optic transmitter converts the square wave pulse signal into an optical signal, which is then sent to the F / V conversion circuit via the optical fiber and the fiber optic receiver.

[0028] F / V conversion circuit: converts the optical signal into an analog voltage signal through frequency-voltage conversion.

[0029] The V / F conversion circuit and the F / V conversion circuit both use the chip AD650 to realize voltage-frequency conversion and frequency-voltage conversion.

[0030] At present, there are many voltage-frequency conversion chips, which are generally selected based on function, frequency range, and conversion linearity. This design requires high operating frequency, good linearity, and wide input voltage range. Based on this, the AD650 chip is selected. The AD650 circuit can be used as both a voltage-frequency conversion part and a frequency-voltage conversion part.

[0031] The V / F conversion circuit can linearly convert the input voltage into a pulse frequency signal, and its functional relationship is:

[0032] (1)

[0033] In the formula, is the input voltage; k is the transformation coefficient; is the output pulse signal frequency.

[0034] When the V / F conversion circuit input is 0 When the voltage signal is 10V, the corresponding output pulse signal frequency is 0 1MHz. This chip is a precision single-chip voltage-frequency converter that can perform both V / F and F / V conversions. It has a large dynamic range and a maximum operating frequency of 1MHz. At the same time, the device is small in size, high in precision, and has few peripheral components.

[0035] Input signal Provided by voltage sampling, Through input resistor Generate input current. Through 1mA internal current source switch control, the integral capacitor The current on the amplifier and the internal feedback current of the operational amplifier form a loop to achieve accurate balance of the current source. The current flows as follows: Figure 3 As shown, this current pulse can be regarded as composed of precise charge groups. The number of charge groups required for each pulse generated by the open collector transistor depends on the amplitude of the input current signal. The amount of charge at both ends of the circuit is linearly related to the input signal current amplitude, so V / F conversion can be achieved. The collector open transistor provides a frequency output terminal. When the monostable multivibrator outputs a high level, the current source controls the switch s 1 To the left of the operational amplifier Figure 3 (b), this process is called the reset process; when the integrator output voltage reaches the predetermined value, the current source controls the switch s 1 To the right of the operational amplifier Figure 3 (a), this process is called an integration process.

[0036] The positive input voltage is converted into a current to the integrating capacitor When the integral capacitor is charged, the slope of the integrator output voltage is downward. When the integrator voltage is greater than the comparator comparison voltage, the comparator triggers the monostable multivibrator. This time is called the trigger time. , which consists of a trigger capacitor The capacitance value is determined by the following calculation formula:

[0037] (2)

[0038] When the integrator voltage is greater than the comparator voltage, the reset process begins. At this time, the slope of the integrator is upward, and the calculation formula is as follows:

[0039] (3)

[0040] The reset process ends, the integration process begins, and the slope of the integrator goes down again. The time it takes for the integrator voltage to reach the comparator comparison voltage is calculated as follows:

[0041] (4)

[0042] The V / F conversion formula is as follows:

[0043] (5)

[0044] When the external contact capacitor and input resistance When determined, the output frequency and input voltage form a linear function relationship; its characteristic frequency Proportional to and is related to the resistance and capacitance values ​​in the circuit.

[0045] There are three main parameters that need to be determined in the V / F conversion circuit, namely, input resistance , Integral capacitor , trigger capacitor . Input resistance The input voltage range will be limited. Generally, the input current does not exceed 1mA and satisfies the following formula:

[0046] (6)

[0047] Input resistance and the integrating capacitor Determines the frequency of going online. The higher the value, the smaller the input current. The larger the value, the better the linearity and the lower the online frequency; After calculation, and given the set upper frequency, the capacitor is triggered at this time The capacitance of the integral capacitor is determined. The capacitance value can be determined by formula (7).

[0048] (7)

[0049] Optical fiber is an excellent insulator, and there is no direct electrical connection between the sending and receiving ends of a fiber optic link; a simple fiber optic link consists of a fiber optic transceiver, optical fiber, and a fiber optic connector.

[0050] Figure 2 This is the circuit diagram of the V / F conversion part. Its main function is to realize the conversion between voltage and frequency. In order to give full play to the performance of the AD650 chip, the peripheral components of the chip must be well selected. The parameters of the peripheral components will directly affect the conversion accuracy of the AD650 chip. The specific parameter design of the V / F conversion circuit is as follows Figure 2 shown.

[0051] There are three main parameters to be selected in the F / V conversion circuit, namely the integral resistor , Integral capacitor C int , trigger capacitor Before selecting parameters, the maximum and minimum input frequencies should be determined. , , maximum output voltage , the required response time The trigger capacitor It can be obtained from formula (8):

[0052] (8)

[0053] Integral resistor It can be obtained from formula (9):

[0054] (9)

[0055] Integral capacitor It can be obtained from formula (10):

[0056] (10)

[0057] In formula (10), N=6, and the output voltage of the F / V conversion circuit can be obtained by formula (11):

[0058] (11)

[0059] Figure 4 This is the F / V conversion circuit diagram. Its main function is to realize the conversion between frequency and voltage. AD650 can also be used for F / V conversion, and has very good performance. The specific circuit parameter design is as follows Figure 4 As shown, the voltage signal after F / V conversion is conditioned to obtain the original voltage signal.

[0060] Figure 5 This is the connection circuit diagram of V / F conversion and F / V conversion. From this diagram, it can be seen that the measurement signals collected in the equipment placement area can be transmitted to the remote control room through optical fiber, realizing electrical isolation and long-distance transmission of signals.

[0061] In order to test the performance of the designed circuit transmission method, a sinusoidal signal with a waveform frequency less than 1kHz is connected to the circuit. After modulation V / F and F / V conversion and restoration, the input and output waveform phases and amplitudes remain basically the same. The output waveform is as follows Figure 6As shown; while testing the linearity, the response time was tested. Another sine wave signal with a waveform frequency of 5kHz was connected to the transmission system. The input and output waveform phases were about 40us and the amplitude was slightly smaller, which met the requirements. The test waveform is as follows Figure 7 . By waveform Figure 6 and Figure 7 It can be seen that the designed circuit can effectively transmit low-intermediate frequency analog signals, and has the characteristics of high isolation voltage level, strong anti-interference ability, wide input signal range, and transmission distance of up to 100 meters.

Claims

1. A conversion circuit for long-distance transmission of current sensor output signals, characterized in that: The conversion circuit includes a high-power rectifier power supply, a sensor, an analog signal sampling resistor, a V / F conversion circuit, an optical fiber link, an F / V conversion circuit and a power control system; The high-power rectifier power supply adopts ITER PF high-power rectifier power supply, which generates high-current and high-voltage analog signals when working; The sensor is installed at the output end of the ITER PF high-power rectifier power supply. When the ITER PF high-power rectifier power supply works normally, the corresponding high voltage and high current flow out of the power supply output end. At this time, the sensor will collect an analog signal, and after sampling by the analog signal sampling resistor, a voltage signal in the range of 0~10 V is obtained, which is sent to the V / F conversion circuit as an input signal; The voltage signal sampled by the sensor is linearly transformed into a square wave pulse train of a certain frequency through voltage-frequency conversion, and then transmitted to the optical fiber link; The fiber optic link consists of a fiber optic transmitter, an optical fiber, a fiber optic receiver, and corresponding connectors. The transmitter converts the electrical pulse signal into an optical signal, which is then transmitted over a long distance at high speed via the optical fiber to the frequency-voltage conversion part located in the control center. The receiver converts the optical signal transmitted by the optical fiber into an electrical signal. Therefore, there is no direct electrical connection between the two ends of the optical fiber, achieving electrical isolation. The F / V conversion circuit is used to restore the pulse train into an analog voltage signal after frequency-voltage conversion.

2. The conversion circuit according to claim 1, characterized in that: The V / F conversion circuit and the F / V conversion circuit both use the chip AD650 to realize voltage-frequency conversion and frequency-voltage conversion.

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