A railway signal cable insulation low-voltage rapid online testing device and method

Abstract

The present invention relates to a low-voltage rapid online test device and method for railway signal cable insulation, which is used for low-voltage rapid and accurate measurement of railway signal cable insulation resistance. The test device is respectively connected to an external cable to be tested and an external insulation leakage test device, and the test device includes: a signal sampling and filtering circuit, which is connected to the external cable to be tested and is used to collect data from the external cable to be tested; an ADC chip and a communication isolation circuit, which are connected to the signal sampling and filtering circuit, and are used to convert the analog signal used by the signal sampling and filtering circuit into a digital signal and output it; a main MCU circuit, which is respectively connected to the signal sampling and filtering circuit and the ADC chip and the communication isolation circuit; and a communication circuit, which is respectively connected to the main MCU circuit and the external insulation leakage test device. Compared with the prior art, the present invention has the advantages of low output voltage, short measurement time, and high precision.

Description

Technical Field

[0001] The invention relates to a detection device for railway signal equipment, in particular to a low-voltage rapid online testing device and method for railway signal cable insulation. Background Art

[0002] Signal equipment is divided into indoor equipment and outdoor equipment, which are connected by signal cables. If the cable is not well insulated from the ground, it may affect the normal operation of the equipment, or even cause power supply abnormality on the power panel, leading to systemic equipment failure. Therefore, signal cable insulation testing is one of the important functions of CSM.

[0003] There are two disadvantages of existing signal cable insulation monitoring equipment. First, the measuring voltage is DC500V. When measuring online, it will cause the lightning protection equipment to operate, limiting the use of the equipment. Second, the measuring internal resistance is large, which makes the equivalent capacitance charging time of the measured cable long, resulting in a measurement time ≥10S. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a railway signal cable insulation low-voltage rapid online testing device and method with low output voltage, short measurement time and high accuracy.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A railway signal cable insulation low-voltage rapid online test device is used to quickly and accurately measure the insulation resistance of the railway signal cable at low voltage. The test device is respectively connected to an external cable to be tested and an external insulation leakage test device. The test device includes:

[0007] A signal sampling and filtering circuit is connected to the external cable to be tested and is used to collect data from the external cable to be tested;

[0008] ADC chip and communication isolation circuit, and signal sampling and filtering circuit, used to convert the analog signal used by the signal sampling and filtering circuit into a digital signal and output it;

[0009] The main MCU circuit is connected to the signal sampling and filtering circuit and the ADC chip and the communication isolation circuit respectively, and is used to perform sampling enable control on the signal sampling and filtering circuit, and receive the digital signal output by the ADC chip and the communication isolation circuit and reset and feedback the ADC chip and the communication isolation circuit;

[0010] The communication circuit is connected to the main MCU circuit and the external insulation leakage current test device respectively, and is used to send the signal processed by the main MCU circuit to the external insulation leakage current test device.

[0011] Preferably, the device also includes a power supply circuit, the input end of which is connected to a 24VDC power supply output by an external insulation leakage test device, and the output end is respectively connected to a signal sampling and filtering circuit, an ADC chip and a communication isolation circuit, a main MCU circuit and a communication circuit.

[0012] Preferably, the communication circuit is connected to a main control board of an external insulation leakage current test device via an RS485 serial port to perform serial port data communication.

[0013] Preferably, the main MCU circuit is connected to the ADC chip and the communication isolation circuit via SPI communication, and the main MCU circuit is connected to the communication circuit via a UART circuit.

[0014] Preferably, the signal sampling and filtering circuit samples the cable insulation resistance data of the connected cable by outputting 48VDC, and transmits the collected data to the ADC chip and the communication isolation circuit after filtering. The ADC chip and the communication isolation circuit convert the analog quantity into a digital quantity and transmit it to the main MCU circuit.

[0015] Preferably, the signal sampling and filtering circuit includes a sampling circuit, which includes a sampling resistor R59, an input isolation circuit, and an input protection circuit. The sampling resistor R59 is connected to the input isolation circuit and the input protection circuit respectively.

[0016] Preferably, the input isolation circuit includes an operational amplifier U21, a diode D3, a diode D4, a diode D5 and a diode D6; the positive input terminal of the operational amplifier U21 is respectively connected to one end of the sampling resistor R59, the positive electrode of the diode D4, and the negative electrode of the diode D5, the negative electrode of the diode D4 is connected to the negative electrode of the diode D3, the positive electrode of the diode D3 is grounded, the positive electrode of the diode D5 is connected to the positive electrode of the diode D6, the negative electrode of the diode D6 is grounded, and the negative input terminal of the operational amplifier U21 is connected to the output terminal.

[0017] Preferably, the operational amplifier U21 is connected to the sampling resistor R59 through operational amplifier protection resistors R57 and R56 in sequence.

[0018] Preferably, the input protection circuit comprises a fuse R51, a fuse R45, a protection resistor R46, a protection resistor R47 and a protection resistor R48 connected in series in sequence, the fuse R51 is connected to a sampling resistor R59, and the protection resistor R48 is connected to an external cable to be tested.

[0019] A method for a low-voltage rapid online testing device for railway signal cable insulation, wherein the insulation resistance measurement of the method introduces a time parameter, and by establishing an equivalent model of the cable, according to the RC charging formula, an accurate resistance value can be obtained based on a short-time charging curve change.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1. Short measurement time: Different from the ordinary volt-ampere resistance measurement, the new insulation resistance measurement of the present invention introduces a time parameter. By establishing an equivalent model of the cable and according to the RC charging formula, a more accurate resistance value can be obtained based on the short-time charging curve change, which effectively speeds up the data processing speed and greatly shortens the measurement time.

[0022] 2. Good safety performance: The excitation output voltage of the present invention is low, the internal resistance is large, the short-circuit current is small, and it has high safety performance.

[0023] 3. High measurement accuracy: The present invention also has high accuracy when measuring cables with insulation resistance less than 1MΩ, which is convenient for accurately judging whether the insulation of the cable is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of the present invention;

[0025] Figure 2 It is a work flow chart of the present invention;

[0026] Figure 3 is a specific circuit diagram of the sampling circuit of the present invention;

[0027] Figure 4 It is a schematic diagram of a simplified measurement circuit model of the present invention. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0029] like Figure 1 As shown, a railway signal cable insulation low-voltage rapid online test device is used to quickly and accurately measure the insulation resistance of the railway signal cable at low voltage. The test device is respectively connected to an external cable to be tested and an external insulation leakage test device. The test device includes:

[0030] The signal sampling and filtering circuit 1 is connected to the external cable to be tested and is used to collect data from the external cable to be tested;

[0031] ADC chip and communication isolation circuit 2, and signal sampling and filtering circuit, used to convert the analog signal used by the signal sampling and filtering circuit into a digital signal and output it;

[0032] The main MCU circuit 3 is connected to the signal sampling and filtering circuit and the ADC chip and the communication isolation circuit respectively, and is used to perform sampling enable control on the signal sampling and filtering circuit, and receive the digital signal output by the ADC chip and the communication isolation circuit and reset and feedback the ADC chip and the communication isolation circuit;

[0033] The communication circuit 4 is connected to the main MCU circuit and the external insulation leakage current test device respectively, and is used to send the signal processed by the main MCU circuit to the external insulation leakage current test device.

[0034] The power supply circuit 5 has an input end connected to a 24VDC power supply output by an external insulation leakage current test device, and an output end connected to a signal sampling and filtering circuit, an ADC chip and a communication isolation circuit, a main MCU circuit and a communication circuit.

[0035] The external insulation leakage test device can perform precise test of insulation resistance to ground, AC leakage test to ground, DC leakage test to ground, AC voltage test to ground, DC voltage test to ground, quick test of insulation resistance to ground, and test of built-in standard resistance.

[0036] The power supply circuit 5 converts the input 24VDC power supply into 3.3VDC, 5VDC, isolated ±5VDC, isolated ±2.5VDC, isolated 2.048V voltage reference, and provides it to other functional modules as working power supply. It converts it into isolated 48VDC for cable insulation resistance measurement.

[0037] The communication circuit 4 is connected to the main control board of the external insulation leakage current test device through the RS485 serial port to perform serial port data communication.

[0038] The main MCU circuit 3 performs SPI communication with the ADC chip and the communication isolation circuit 2, and its function is to reset and feedback the ADC chip. The main MCU circuit 3 is connected to the communication circuit 4 through the UART circuit, and the main MCU circuit 3 performs sampling enable control on the signal sampling and filtering circuit 1. The main MCU circuit can realize functions such as online upgrade, upload version number and hardware self-test status.

[0039] The signal sampling and filtering circuit 1 is connected to the external measurement cable, and samples the cable insulation resistance and other data of the connected cable by outputting 48VDC. The collected data is filtered and transmitted to the ADC sampling / communication isolation circuit. The ADC circuit then converts the analog quantity into a digital quantity and transmits it to the main MCU circuit.

[0040] The method can realize the function of measuring the 0Ω and 1MΩ resistance of the main control board of the external insulation leakage current test device, and is used for the measurement calibration function.

[0041] like Figure 2 As shown, the measurement process is based on the communication protocol of the monitoring station, receiving the test command issued by the station, connecting the measurement power supply, starting the charging time recording, starting the ADC sampling recording, the sampling frequency is 500Hz, collecting the charging data within 1.9S, disconnecting the measurement power supply, filtering the ADC sampling raw data, calculating multiple resistance values ​​at different times according to the measurement principle, filtering the multiple resistance values, taking the average value to obtain the final resistance value, judging the resistance insulation according to the final measured resistance value, outputting the measurement result to the station, and ending this measurement.

[0042] Since the interference in the measurement circuit comes from power frequency interference, the frequency of the interference is fixed at 50Hz, so the measurement object is sampled at a frequency of 500Hz, and then digital filtering is performed to filter out this interference.

[0043] From the analysis of the measurement principle, it can be known that due to the existence of capacitors, ordinary volt-ampere resistance measurement must be performed after the capacitor is fully charged to obtain a more accurate resistance value. Different from ordinary volt-ampere resistance measurement, the insulation resistance measurement of this method introduces a time parameter. By establishing an equivalent model of the cable, according to the RC charging formula, a more accurate resistance value can be obtained based on the short-term charging curve change. Since the time parameter is introduced during the measurement, the absorption coefficient can be calculated based on the sampling values ​​at different charging time points: such as the ratio between the voltage value corresponding to the sampling value at 1s or 1.5s and the estimated sampling voltage value when fully charged.

[0044] Measuring principle

[0045] like Figure 4 The following is a simplified measurement circuit model without considering interference signals, where U is the measurement excitation voltage source, R n is the equivalent resistance of the sum of all resistances inside the measuring board, C x and R x It is the insulation resistance to ground and distributed capacitance of the cable to be tested.

[0046] Assume the measured excitation voltage is U, and R n The voltage across the two ends is u n , C x and R xThe voltage across the two ends is u x ,Right now From the KVL theorem, we know that:

[0047] u n +u x =U 2-(1)

[0048] From the KCL theorem, we know that:

[0049]

[0050] According to Ohm's law:

[0051] u n =i×R n 2-(3)

[0052] Combining 2-(1), 2-(2), and 2-(3), we can obtain:

[0053]

[0054] Solving this differential equation yields:

[0055]

[0056] In formula 2-(5), C * is the constant term of the general solution of Equation 2-(4).

[0057] At t = 0, Substituting into 2-(5) we get:

[0058]

[0059] Substituting 2-(6) into 2-(5) yields:

[0060]

[0061] Formula 2-(7) describes Figure 1 Model cable The law of change, t are all known measured quantities, U, R n is a constant. If C can be measured x The value of R can be directly calculated according to this formula. x . But in the model circuit, C x cannot be solved at the same time. Therefore, we use another transformation technique to solve this problem.

[0062] From 2-(7), we can see that is a function of time t, which changes with time. We select different measurement moments t1 and t2 during the measurement process and measure the corresponding Thus, a system of equations is established:

[0063]

[0064] The only unknown variable in equation 2-(8) is R. x and C x , the resistance to be measured R can be obtained through numerical calculation x The value of .

[0065] like Figure 3 As shown, the signal sampling and filtering circuit includes a sampling circuit, which includes a sampling resistor R59, an input isolation circuit, and an input protection circuit. The sampling resistor R59 is connected to the input isolation circuit and the input protection circuit respectively. The input isolation circuit includes an operational amplifier U21, a diode D3, a diode D4, a diode D5, and a diode D6; the positive input terminal of the operational amplifier U21 is respectively connected to one end of the sampling resistor R59, the positive electrode of the diode D4, and the negative electrode of the diode D5, the negative electrode of the diode D4 is connected to the negative electrode of the diode D3, the positive electrode of the diode D3 is grounded, the positive electrode of the diode D5 is connected to the positive electrode of the diode D6, the negative electrode of the diode D6 is grounded, and the negative input terminal of the operational amplifier U21 is connected to the output terminal. The operational amplifier U21 is connected to the sampling resistor R59 through the operational amplifier protection resistors R57 and R56 in sequence. The input protection circuit includes a fuse R51, a fuse R45, a protection resistor R46, a protection resistor R47 and a protection resistor R48 connected in series in sequence, the fuse R51 is connected to a sampling resistor R59, and the protection resistor R48 is connected to an external cable to be tested.

[0066] The sampling circuit uses a 2KΩ / 3W resistor as the sampling resistor, an extremely low bias current op amp is used as input isolation at the back end, and two extremely low leakage clamping diodes are used at the front end of the op amp as protection against input overshoot voltage. Two resistor-type fuses are used as input protection at the sampling signal input point, and multiple high-power resistors are connected in series inside the circuit to increase the internal resistance of the circuit to ensure that the measurement signal will not affect the normal working signal of the cable under test.

[0067] Select DC48V as the measurement voltage. Under normal circumstances, the DC 48V measurement excitation current flows out of the measurement board. The specific path is: DC 48V measurement excitation power positive pole → Fn (intrinsic safety fuse inside the board) → R1 (internal resistance of the measurement board) → cable under test → target signal equipment → another cable of the target signal equipment → R2 (insulation resistance of the other cable to ground) → earth → measurement board Rm → DC48V measurement excitation power negative pole.

[0068] The current in this path flows into the target signal device, forming an interference current. In the most unfavorable case, assuming that the other cable of the target device is completely short-circuited to the ground and the DC internal resistance of the target device is zero, the interference current is less than 0.1mA. This interference energy is very limited: the impact on signal devices such as signal machines and switch machines that require higher working voltages can be ignored. It does not affect the sensitive ZPW-2000A track circuit either, because the measurement process applies a stable DC excitation voltage, there is no AC component, and there is no periodic on-off control, so the interference noise spectrum component is zero, and it does not affect the ZPW-2000A track circuit receiver. For the 25Hz track circuit, the trigger relay action depends on the phase information of the AC power, and the DC leakage current of the insulation measurement does not work. For the 480 track circuit, a slight insulation measurement DC leakage current is connected in series with the receiving end loop, which can act on the coil through the rectifier bridge inside the JZXC-480 relay, and the impact is also extremely limited. The pick-up voltage of the relay is ≥8V, and the excitation current flowing is ≥17mA. This current threshold is much larger than the maximum value of 0.1mA that the entire insulation measurement device can output, so it will not cause the track relay to be erroneously picked up.

[0069] During the online measurement process, the working current of the target signal device will also flow into the measurement board through the above path, causing interference to the measurement. Especially when the insulation of the other cable of the target signal device is poor, a large interference or surge will be generated at both ends of the measurement board. To this end, the following measures are adopted:

[0070] The DC48V measurement excitation power module adopts a higher isolation voltage. The device model is URH2424P-6WR3. The input-output adopts reinforced insulation with 6KV isolation performance. The creepage distance is 8mm. The use of this power module effectively avoids the possibility that the input-output of the measurement excitation power module may be broken down under the impact of external measurement interference voltage, which may cause the insulation resistance of the measurement circuit to the ground to decrease or form a circuitous interference loop, affecting safety.

[0071] The fuse uses the PICO 305 intrinsically safe fuse from Littelfuse. The measuring board and the cable under test are connected through a 50mA intrinsically safe fuse. When an abnormal surge passes through, the fuse can be reliably blown, and the high temperature and burning that may be caused during the blowing process are contained inside the fire-resistant shell to ensure that they will not spread to the PCB and cause serious consequences such as smoke and burning.

[0072] The protective resistor Rn through which the measuring board and the measured cable are connected actually uses three 3W metal film power resistors connected in series to enhance the voltage resistance performance during external impact.

[0073] According to the data sheet, the maximum operating voltage of a single resistor of this specification is 350V, the maximum overload voltage is 700V, and the maximum overload voltage after three resistors are connected in series is 2100V, ensuring that they will not directly break down under a surge voltage impact and lose their current limiting protection function.

[0074] The terminals connecting the measuring board and the measured cable use 5.08mm pitch connectors, with a rated working voltage of 320V / 20A and an insulation withstand voltage of AC2500V / 1min. When an abnormal surge passes through, the connector will not be short-circuited or heated and burned.

[0075] The measurement board measurement sampling resistor R59 uses a 3W metal film power resistor 2KΩ resistor. The resistor will not be damaged due to overheating, and there is no risk of burning out due to overheating, ensuring that the subsequent circuit is always connected to the negative pole of the measurement power supply through Rm, limiting the surge voltage and avoiding the surge directly impacting the back-end circuit.

[0076] The measurement board R56 and R57 use two SMD 1210 resistors in series, and D4 and D5 diodes BASS116, which together form the input protection circuit of the op amp. When the input power supply is higher than VCC+0.3V or lower than -0.3V, D4 or D5 is turned on, limiting the input voltage to VCC+0.3V or -0.3V to prevent damage to the op amp. During the conduction period of the protection diodes D4 and D5, the current flowing through the diodes is limited by R56+R57.

[0077] When the external surge continues to impact, the current of D4 and D5 may further increase, and the voltage drop at both ends will also increase. For this reason, the circuit is equipped with TVS tubes D3 and D6 to protect the positive power supply and negative power supply respectively. When a higher surge occurs, it can be triggered in time to limit the power supply voltage to a tolerable level. The models of D3 and D6 are 1SMA10AT, with a minimum trigger threshold of 6.67V and a maximum of 7.37V. Together with the aforementioned D4 and D5, they can reliably protect the sensitive op amps of the subsequent stage.

[0078] The power supplies AVCC5V and AVCC_-5V of the op amp and ADC are provided by the isolated power module G2405S-2W. This isolated power module is similar to the measurement excitation power module and both use a 6KV isolation voltage level. The ADC isolation uses a high-grade withstand voltage optocoupler 6N137, which can withstand an overvoltage of up to 6000V.

[0079] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A low-voltage rapid online test method for railway signal cable insulation, which is used to quickly and accurately measure the insulation resistance of railway signal cables at low voltage. The test device used in this method is connected to an external cable to be tested and an external insulation leakage test device respectively, and is characterized in that: The testing device comprises: A signal sampling and filtering circuit is connected to the external cable to be tested and is used to collect data from the external cable to be tested; ADC chip and communication isolation circuit, and signal sampling and filtering circuit, used to convert the analog signal used by the signal sampling and filtering circuit into a digital signal and output it; The main MCU circuit is connected to the signal sampling and filtering circuit and the ADC chip and the communication isolation circuit respectively, and is used to perform sampling enable control on the signal sampling and filtering circuit, and receive the digital signal output by the ADC chip and the communication isolation circuit and reset and feedback the ADC chip and the communication isolation circuit; A communication circuit is connected to the main MCU circuit and the external insulation leakage current test device respectively, and is used to send the signal processed by the main MCU circuit to the external insulation leakage current test device; The test method includes: A simplified measurement circuit model is used without considering interference signals, where U is the measurement excitation voltage source, R n is the equivalent resistance of the sum of all resistances inside the measuring board, C x and R x The insulation resistance to ground and distributed capacitance of the cable to be tested; Assume the measured excitation voltage is U, and R n The voltage across the two ends is u n , C x and R x The voltage across the two ends is u x ,Right now From the KVL theorem, we know that: u n +u x =U2-(1) According to KCL theorem: According to Ohm's law: u n =i×R n 2-(3) Combining 2-(1), 2-(2), and 2-(3), we get: Solving this differential equation yields: In formula 2-(5), C * is the constant term of the general solution of equation 2-(4); At t = 0, Substituting into 2-(5) we get: Substituting 2-(6) into 2-(5) yields: Formula 2-(7) describes the model cable The law of change, t are all known measured quantities, U, R n is a constant. If C can be measured x numerical value, then R can be directly calculated according to this formula x ; From 2-(7), we can see that It is a function of time t, which changes with time. Different measurement moments t1 and t2 are selected during the measurement process, and the corresponding Thus, a system of equations is established: The only unknown variable in equation 2-(8) is R. x and C x , the resistance to be measured R can be obtained through numerical calculation x The value of .

2. The method according to claim 1, characterized in that The device also includes a power supply circuit, the input end of which is connected to a 24VDC power supply output by an external insulation leakage current test device, and the output end is respectively connected to a signal sampling and filtering circuit, an ADC chip and a communication isolation circuit, a main MCU circuit and a communication circuit.

3. The method according to claim 1, characterized in that: The communication circuit is connected to the main control board of the external insulation leakage current test device through the RS485 serial port to perform serial port data communication.

4. The method according to claim 1, characterized in that The main MCU circuit is connected to the ADC chip and the communication isolation circuit via SPI communication, and the main MCU circuit is connected to the communication circuit via a UART circuit.

5. The method according to claim 1, characterized in that The signal sampling and filtering circuit samples the cable insulation resistance data of the connected cable by outputting 48VDC, and transmits the collected data to the ADC chip and the communication isolation circuit after filtering. The ADC chip and the communication isolation circuit convert the analog quantity into a digital quantity and transmit it to the main MCU circuit.

6. The method according to claim 1, characterized in that The signal sampling and filtering circuit includes a sampling circuit, which includes a sampling resistor R59, an input isolation circuit, and an input protection circuit. The sampling resistor R59 is connected to the input isolation circuit and the input protection circuit respectively.

7. The method according to claim 6, characterized in that The input isolation circuit includes an operational amplifier U21, a diode D3, a diode D4, a diode D5 and a diode D6; the positive input terminal of the operational amplifier U21 is respectively connected to one end of the sampling resistor R59, the positive electrode of the diode D4, and the negative electrode of the diode D5, the negative electrode of the diode D4 is connected to the negative electrode of the diode D3, the positive electrode of the diode D3 is grounded, the positive electrode of the diode D5 is connected to the positive electrode of the diode D6, the negative electrode of the diode D6 is grounded, and the negative input terminal of the operational amplifier U21 is connected to the output terminal.

8. The method according to claim 7, characterized in that The operational amplifier U21 is connected to the sampling resistor R59 through operational amplifier protection resistors R57 and R56 in sequence.

9. The method according to claim 6, characterized in that The input protection circuit includes a fuse R51, a fuse R45, a protection resistor R46, a protection resistor R47 and a protection resistor R48 connected in series in sequence, the fuse R51 is connected to a sampling resistor R59, and the protection resistor R48 is connected to an external cable to be tested.

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