A cable length measurement system

Abstract

This invention relates to the field of electrical measurement technology and provides a cable length measurement system, including a control unit, a power supply module, a square wave generator module, test channel circuits, an oscilloscope, and the control unit itself. Under the control of the control unit, the power supply module provides positive or negative high voltage to several test channel circuits. The square wave generator module generates PWM square wave signals and, under the control of the control unit, connects them to the corresponding test channel circuits. Each of the several test channel circuits has a working mode selection switch group and self-test capability, measuring the length of the cable connected to its probe based on the PWM square wave signal and the voltage provided by the power supply module. The control unit sets the specific working mode of the relevant test channel circuit through the working mode selection switch group and outputs the test signal to the oscilloscope for observation to determine the integrity or cable length of the corresponding test channel. The working modes include a short-circuit self-test mode, a first length measurement mode, and a second length measurement mode.

Description

Technical Field

[0001] This invention relates to the field of electrical measurement technology, and more specifically to a cable length measurement system. Background Technology

[0002] With the rapid development of the communications and power industries, the application scale of cables has also expanded dramatically. From simple telephone and telegraph cables of the past, they have evolved into a wide variety of high-performance cables with thousands of pairs, including electronic cables, radio frequency cables, data cables, and combined communication cables. During cable production, only the length of each batch of cables manufactured on the production line is measured and printed to specifications. In the process of outdoor cable installation and connection, sometimes a significant amount of cable needs to be cut. Currently, this is usually done by measuring with a ruler before cutting. However, if cutting long sections of cable, this method will introduce errors, waste cable resources, and is extremely inconvenient during measurement.

[0003] Currently, mainstream cable testers measure cable length by applying a swept-frequency test signal to the cable. Specifically, the swept-frequency test signal is a series of increasingly frequent sine waves applied to one end of the cable; these sine waves propagate to the other end of the cable and are reflected back to the transmitting end. The cable tester uses a frequency domain reflectometer (“FAR”) system to measure the cable length based on the frequency response of the swept-frequency reflected signal. Existing cable testing methods have the following shortcomings:

[0004] 1. Existing cable testers have complex circuits, high costs, and no self-test function, which means that when an abnormality occurs during measurement, a lot of time is spent determining whether the problem is with the cable or with the tester itself.

[0005] 2. Existing cable testers require each test signal to be connected to a separate port of the observation / metering equipment, which limits the number of ports on the observation / metering equipment and results in a limited number of internal test channels.

[0006] 3. Performing a frequency sweep test signal from its lowest frequency (e.g., 1MHz) to its highest frequency (e.g., 256MHz) scans at 400 frequency points, which takes too long. Summary of the Invention

[0007] To address the aforementioned shortcomings of existing technical solutions for measuring cable length, this application provides a technical solution for measuring cable length. This solution features a simple test circuit designed in conjunction with an oscilloscope. It not only measures cable length and performs self-checks on the integrity of the test channel circuit, but also enables time-division observation of two observation signals from the same oscilloscope input port using a minimally simplistic circuit configuration, reducing the occupancy of the oscilloscope port.

[0008] The technical solution provided in this application is a cable length measurement system, including a control unit, a power module, a square wave generator module, several test channel circuits, an oscilloscope, and a control unit;

[0009] Under the control of the control unit, the power module provides positive voltage or negative high voltage to the plurality of test channel circuits;

[0010] The square wave generator module is used to generate PWM square wave signals and is connected to the corresponding test channel circuit under the control of the control unit.

[0011] Each of the several test channel circuits has a working mode selection switch group and self-test capability, and measures the length of the cable connected to its probe based on the PWM square wave signal and the voltage provided by the power module.

[0012] The control unit sets the specific operating mode of the relevant test channel circuit through the operating mode selection switch group, and outputs the corresponding test signal to an oscilloscope for observation to determine the integrity or cable length of the corresponding test channel. The operating modes include short-circuit self-test mode, first length measurement mode, and second length measurement mode.

[0013] Preferably, the PWM square wave generated by the square wave generation module is amplified and then connected to the corresponding test channel circuit, and the frequency of the PWM square wave is 32.767k.

[0014] The test channel circuit further includes a filter circuit, a charging capacitor, and a rectifier circuit. The operating mode switch group includes a first switch, a second switch, and a third switch; the first, second, and third switches are double-pole double-control relay switches. One end of the charging capacitor is connected to a high-voltage power supply controlled by a control unit, via a current-limiting resistor, and to the second end of the filter circuit. The first end of the filter circuit is connected to a probe or left floating via the first switch, and the probe is grounded or left floating via the second switch and the current-limiting resistor. The other end of the charging capacitor is connected to the first end of the rectifier circuit, and the second end of the rectifier circuit is connected to the oscilloscope port via the third switch. The oscilloscope port is grounded via a resistor. The rectifier circuit consists of a resistor and a diode connected in parallel, with the anode of the diode being its first end and the cathode being the second end of the rectifier circuit. The probe is also directly connected to the oscilloscope port via the first switch, a wire, and the third switch.

[0015] Furthermore, the PWM square wave generated by the square wave generation module is connected to the test channel circuit through a third switch.

[0016] Furthermore, each of the aforementioned test channel circuits forms a port circuit in pairs; two test channel circuits within the same port circuit share a rectifier circuit, and the test signals share a single output line connected to the oscilloscope port. To ensure that the test signals of the two test channel circuits can be distinguished on the oscilloscope, the cable length difference between the probes of the two test channels must be greater than 5 meters.

[0017] Furthermore, when any test channel circuit is in short-circuit self-test mode, the control unit provides a negative high voltage to the test channel circuit via the control power module, and controls the first switch and the third switch to charge the charging capacitor. After the charging capacitor has been charged for a predetermined time, it is discharged through the first switch, the second switch, and the third switch using the filter circuit and the rectifier circuit. The integrity of the test channel circuit is determined by observing whether a short pulse is output at the second terminal of the rectifier circuit during the discharge process.

[0018] Furthermore, when the test channel circuit is in the first length measurement mode, the PWM square wave generated by the square wave generation module is input to the oscilloscope through the third switch and output to the cable under test (TUT) on the probe through the wire and the first switch. The length of the TUT is calculated by observing the delay corresponding to the reflection signal (reflection of electric field or electromagnetic wave at the interface of the medium) of the PWM square wave signal at the break point of the TUT using the oscilloscope. At this time, the PWM square wave signal and its reflection signal do not pass through any inductor or capacitor in any of the test channel circuits.

[0019] Furthermore, when any test channel circuit is in the second length measurement mode, the cable under test is connected to the probe of the test channel circuit. The control unit controls the power module to provide a negative high voltage to the test channel circuit and controls the first and third switches to charge the charging capacitor. After the charging capacitor has been charged for a predetermined time, it is discharged through the first, second, and third switches using the filter circuit and rectifier circuit. The length of the cable under test is calculated by observing the delay between the discharge pulse generated at the second end of the rectifier circuit and the reflected pulse generated at the break point of the cable under test on the probe (the delay rt of the filter circuit needs to be subtracted).

[0020] The technical solution provided in this application has a simpler circuit structure and more reliable operation compared to existing cable measurement solutions. It can not only perform self-testing, but also display the test signals of two test channel circuits using one port of an oscilloscope, reducing the number of oscilloscope ports occupied and thus increasing the number of cables that can be measured simultaneously. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 A schematic diagram of the structure of the circuit for measuring cable length provided in this application in one embodiment.

[0023] Figure 2 A schematic diagram of the port circuit in the cable length measuring circuit provided in this application in one embodiment;

[0024] Figure 3 for Figure 2 A partially enlarged structural diagram;

[0025] Figure 4 for Figure 2 Another enlarged structural diagram. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0027] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0028] like Figure 1 In the illustrated embodiment, the circuit for measuring cable length provided in this application includes: a power module 102, a square wave generator module 103, several test channel circuits 121, 122...128, an oscilloscope 11, and a control unit 101; each test channel circuit is connected to a probe 13. The control unit 101, the power module 102, and the square wave generator module 103 are all mounted on the same board 10.

[0029] The power supply module 102, under the control of the control unit, provides positive or negative high voltage to the plurality of test channel circuits. The square wave generator module 103 generates PWM square wave signals and, under the control of the control unit 101, connects to the corresponding test channel circuit. Each test channel circuit has a working mode selection switch group (…). Figure 1 (Not shown in the diagram) The length of the cable connected to its probe is measured based on the input PWM square wave signal. The control unit 101 sets the corresponding test channel circuit to work in short-circuit self-test mode or cable length measurement mode by controlling the operating mode selection switch group, and outputs the corresponding test signal to the oscilloscope 11 for observation to determine the integrity of the corresponding test channel or the cable length. The control unit 101 is a microcontroller or other on-chip control system.

[0030] exist Figure 1 In the illustrated embodiment, each pair of test channel circuits constitutes a port circuit, and the two test channel circuits of the same port circuit share an output line connected to the port of oscilloscope 11. For example, test channel circuits 121 and 122 are connected to a port of oscilloscope 11 via a common signal line. To ensure that the test signals of the two test channel circuits can be distinguished on oscilloscope 11, the difference in cable length between the probes of the two test channels must be greater than 5m.

[0031] The schematic diagram of the above port circuit in one embodiment is as follows: Figure 2 As shown. One test channel circuit of the port circuit includes probe SMA100, double-pole double-throw relay switches K100, K101, and K103, an AC filter circuit composed of resistors R103 and R105 and capacitor C100, a charging circuit composed of resistor R107 and charging capacitor C102, and a rectifier circuit composed of R109 and diode D104. The other test channel circuit includes probe SMA101, double-pole double-throw relay switches K100, K102, and K103 (hereinafter referred to as relay switches K100, K102, and K103), an AC filter circuit composed of resistors R104 and R106 and capacitor C101, a charging circuit composed of resistor R108 and charging capacitor C103, and a rectifier circuit composed of R109 and diode D104. That is, the two test channel circuits of the same port circuit share the rectifier circuit, relay switches K100 and K103, and the same input port of the oscilloscope. The power supply terminal HV in the figure is connected to the power supply voltage output by the power module 102. It can be a positive voltage or a negative high voltage (-80V~-180V). The polarity of the power supply terminal HV voltage and whether a voltage is connected are controlled by the control unit 101.

[0032] like Figure 2As shown, the PWM square wave generated by the square wave generation module has a frequency of 32.767kHz, which is connected to the corresponding test channel circuit and oscilloscope via relay switch K103 (in conjunction with switches 101 and 102). Preferably, the PWM square wave generated by the square wave generation module is amplified by an amplifier before being connected to the port circuit.

[0033] Due to the strong electromagnetic interference in typical testing environments, the power module 102 employs double-layer isolation: the first layer is AC / DC isolation with an external filtered and isolated AC input; the second layer is DC / DC isolation, using a DC 24V filter. The power module 102's enclosure is made of metal and anodized to significantly shield against electromagnetic induction, and internal shielding is added to key areas to further isolate the electromagnetic environment and reduce disturbances. The power module 102 can use commercially available power chips; the required power supply can be configured according to the corresponding user manual, which will not be elaborated further here.

[0034] Figure 2 The port circuit (test channel circuit) shown achieves measurement of the cable on the probe using the first length measurement mode through the following operation:

[0035] 1) First, switch the working mode to PWM circuit mode: Connect the PWM square wave (32.768kHz) output by the square wave generator module 103 directly to contact 5 of K103 through the relay switch K103 via the wire, and connect contact 3 to contact 5 at the same time.

[0036] 2) Users need to select the appropriate test channel circuit, through... Figure 2 The relay switches K101 and K102 will perform corresponding engaging / releasing actions to switch the test channel circuit; at the same time, they will directly short-circuit the AC filter circuit in the signal path.

[0037] 3) Loosen relay switch K100 to prevent the circuit from being shorted to low (connect the input signal to the zero-level circuit through a 50Ω resistor).

[0038] 4) When relay switch K103 is activated, the signal from the front end is directly transmitted to the CH1 port of the oscilloscope. The signal at the CH1 port is connected to ground through a 50Ω resistor to form an impedance matching terminal.

[0039] 5) The PWM square wave enters the selected test channel circuit, passes through the probe until it reaches the break in the external cable, and returns. The returned signal is superimposed on the PWM signal propagating to the left, and a stepped test waveform can be seen on the oscilloscope. By measuring the length of the steps (i.e., the corresponding delay), the length of the cable connected to probe 1 or probe 2 can be calculated.

[0040] 6) After the measurement is completed, return the channel selection switch to the zero position.

[0041] Figure 2 The port circuit (test channel circuit) shown implements the second length measurement mode for the cable on probe 1 through the following operation:

[0042] 1. Complete the laying and connection of cables (note if...) Figure 2 If probes SMA100 and SMA101 are used to measure cables, the lengths of the cables connected to them must differ by about 5 meters; otherwise, the waveforms on the oscilloscope will overlap.

[0043] 2. When a negative high voltage (-80 ~ -180V) is applied to the power supply terminal HV of the circuit, contact 3 of relay switch K101 is left floating (disconnected), and contacts 2 and 3 of relay switch K103 are connected, allowing power supply terminal HV to pass through... Figure 2 The resistor R107 in the middle charges the capacitor C102.

[0044] 3. After capacitor C102 has been charged for a predetermined time, connect contacts 6 and 7 of relay switch K101, contacts 3 and 2 of relay switch K101, contacts 3 and 2 of relay switch K103, and contacts 6 and 5 of relay switch K100. Capacitor C102 then begins to discharge, and the resulting test signal is transmitted to channel CH1 of the oscilloscope. At this time, the charge on the negative plate of capacitor C102 flows through the filter circuit formed by resistor R105 and capacitor C100, relay switch K101, and resistor R116 to the ground terminal. From there, it flows through resistor R111 and the rectifier circuit (composed of diode D104 and resistor R109) to the positive plate of capacitor C102. In this process, the discharge of capacitor C102 first generates a discharge pulse in oscilloscope channel CH1 through a rectifier circuit composed of diode D104 and resistor R109. Then, a reflected echo (the reflection of electric field / electromagnetic wave at the dielectric break) is generated at the cable break point connected to probe 1. The reflected echo returns to the oscilloscope's display channel through the grounding point of switch K100 and resistor R111, resulting in a corresponding reflected echo pulse in the oscilloscope. The length of the cable connected to probe 1 can be calculated by calculating the delay between the discharge pulse and the emitted echo pulse.

[0045] Figure 2 The port circuit (test channel circuit) shown performs a self-test on the test channel circuit where probe 1 is located through the following operations:

[0046] 1. A negative high voltage (-80~+180V) is connected to the power supply terminal HV of the circuit. Contacts 2 and 3 of relay switch K103 are connected, while contact 3 of relay switch K101 is left floating (disconnected), allowing power supply terminal HV to pass through. Figure 2 The resistor R107 in the middle charges the capacitor C102.

[0047] 2. Select the test channel circuit for testing using relay switches K101 and K102. When the channel containing probe 1 is selected, connect contacts 3 and 2, and contacts 6 and 7 of relay switch K101.

[0048] 3. After capacitor C102 has been charged for a predetermined time, the control relay switch K100 is grounded. At this time, the charge on the negative plate of capacitor C102 will flow through the filter circuit formed by R105 and C100, and then further flow from the resistor R116 controlled by relay K100 to ground. It then flows through the ground terminal of oscilloscope channel CH1 and the rectifier circuit (composed of diode D104 and resistor R109) to the positive plate of capacitor C102. Thus, the rectified path formed by resistor R109 and D104 causes a change in the voltage at oscilloscope port CH1. A corresponding short-time pulse waveform can be observed on the oscilloscope, and a short-time discharge causing LED100 to light up can be seen.

[0049] Compared with existing cable measurement solutions, the technical solution provided by this invention has a simpler circuit structure and more flexible operating mode. It can not only realize the self-test of the test channel, but also allow two test channels to share one port and use only one port of the oscilloscope to test two cables, reducing the number of oscilloscope ports occupied and thus increasing the number of cables that can be measured simultaneously.

[0050] The above description is merely an embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the technical solutions provided by the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A cable length measurement system, comprising a control unit, characterized in that, It also includes: a power supply module, a square wave generator module, several test channel circuits, an oscilloscope, and a control unit; Under the control of the control unit, the power module provides positive voltage or negative high voltage to the plurality of test channel circuits; The square wave generator module is used to generate PWM square wave signals and is connected to the corresponding test channel circuit under the control of the control unit. Each of the several test channel circuits has a working mode selection switch group and self-test capability, and measures the length of the cable connected to its probe based on the PWM square wave signal and the voltage provided by the power module. The control unit sets the specific operating mode of the relevant test channel circuit through the operating mode selection switch group, and outputs the corresponding test signal to the oscilloscope for observation to obtain the integrity or cable length of the corresponding test channel; the operating modes include short-circuit self-test mode, first length measurement mode and second length measurement mode; The first length measurement mode requires the PWM square wave signal generated by the square wave generator module to be connected to the corresponding test channel circuit, while the second length measurement mode and the self-test mode do not require the PWM square wave signal generated by the square wave generator module to be connected to the corresponding test channel circuit. Each of the aforementioned test channel circuits further includes a filter circuit, a charging capacitor, a direct connection wire, and a rectifier circuit; the operating mode switch group includes a first switch, a second switch, and a third switch, wherein the first switch, the second switch, and the third switch are double-pole double-control relay switches; One end of the charging capacitor is connected to a high-voltage power supply, controlled by a control unit, via a current-limiting resistor, and to the second end of the filter circuit. The first end of the filter circuit is connected to a probe or left floating via a first switch, and the probe is grounded or left floating via a second switch and a current-limiting resistor. The other end of the charging capacitor is connected to the first end of the rectifier circuit, and the second end of the rectifier circuit is connected to the port of the oscilloscope via a third switch. The port of the oscilloscope is grounded via a resistor. The rectifier circuit consists of a resistor and a diode connected in parallel, with the anode of the diode being its first end and the cathode being the second end of the rectifier circuit. The direct connection wire connects the first switch and the third switch, and the probe can be directly connected to the port of the oscilloscope by controlling the first switch and the second switch.

2. The cable length measurement system as described in claim 1, characterized in that, When the corresponding test channel circuit is in short-circuit self-test mode, the control unit provides a negative high voltage to the test channel circuit through the control power module, and controls the first switch and the third switch to charge the charging capacitor. After the charging capacitor has been charged for a predetermined time, it is discharged through the first switch, the second switch, and the third switch using the filter circuit and the rectifier circuit. The integrity of the corresponding test channel circuit is determined by observing whether a short pulse is output at the second terminal of the rectifier circuit during the discharge process.

3. The cable length measurement system as described in claim 2, characterized in that, When the corresponding test channel circuit is in the first length measurement mode, the PWM square wave generated by the square wave generation module is input to the oscilloscope through the third switch and output to the cable under test on the probe through the direct connection wire and the first switch; the length of the cable under test is calculated by observing the reflection signal of the PWM square wave signal at the break point of the cable under test through the oscilloscope and calculating the corresponding delay.

4. The cable length measurement system as described in claim 2, characterized in that, When the corresponding test channel circuit is in the second length measurement mode, after the cable under test is connected to the probe of the test channel circuit, the control unit controls the power module to provide a negative high voltage to the corresponding test channel circuit and controls the first switch and the third switch to charge the charging capacitor. After the charging capacitor is charged for a predetermined time, the first switch, the second switch, and the third switch are used to discharge the charging capacitor using the filter circuit and the rectifier circuit. By observing the time difference between the discharge pulse generated at the second end of the rectifier circuit and the reflected pulse generated at the break point of the cable under test on the probe, the time difference is subtracted from the delay rt of the filter circuit to calculate the length of the cable under test.

5. The cable length measurement system as described in claim 1, characterized in that, The test channel circuits are configured in pairs to form a port circuit; the two test channel circuits of the same port circuit share a rectifier circuit and the test signals share an output line connected to the oscilloscope port.

6. The cable length measurement system as described in claim 1, characterized in that, The PWM square wave generated by the square wave generator module is amplified and then connected to the corresponding test channel circuit.

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