A Portable Intelligent Detector and Detection Method for Testing Tiny Current Multi-Core Cables

Abstract

The present invention discloses a portable intelligent detector for testing a multi-core cable with a tiny current, which comprises a housing. Inside the housing, a channel board, a test board and a capacitive screen are sequentially arranged from bottom to top. The inner surface of the capacitive screen is embedded in the test board, and its outer surface is located on the housing. The channel board integrates a 128-channel test point module and a driver. The channel board is used for switching 128 test channels and driving each module to work. The sampling module on the test board is used for collecting the test path voltage and uploading it to the microprocessor. The resistance detection module and the conduction detection module perform the conduction and resistance tests on the cable under test through the 128-channel test point module. The programmed control gear module is used for receiving the resistance and conduction test results fed back by the cable under test and uploading them to the microprocessor. The microprocessor is connected to the capacitive screen to realize human-computer interaction according to the communication protocol. The present invention also discloses a method for detecting the conduction and resistance of the cable under test by using this detector.

Description

Technical Field

[0001] The present invention belongs to the technical field of measurement and control, and particularly relates to a portable intelligent detector and a detection method for testing a multi-core cable with a small current. Background Art

[0002] A cable is a communication bridge for signal transmission between electronic devices and sub-units of the devices, and is an indispensable component in missile weapon equipment and systems. The conduction performance of the cable is the basic guarantee for various tests, directly affecting the comprehensive test performance of the missile weapon system and the accuracy of the test results. To ensure the reliability of the missile weapon system and avoid the catastrophic consequences caused by design errors or production errors, it is necessary to comprehensively and accurately detect the complex cable connection relationships on the missile. The traditional detection method is to manually use a multimeter or a buzzer to perform point-by-point tests and manually read and record the data. This method is only applicable to the conventional detection of cables with a small quantity and a small number of cores, and has disadvantages such as poor accuracy and low test efficiency. To meet the detection requirements of large quantities of multi-core cables, improve the test efficiency and automation level of missile cables, it is particularly important to carry out research on cable automatic test technology, improve cable test means, and enhance the maintenance and support capabilities of logistics support and technical support departments.

[0003] Foreign countries started early and developed rapidly in the research field of cable automatic test technology. The development of their test systems, especially military automatic test systems, is mainly characterized by generalization, standardization, modularization, digitization, intelligence, and networking. The products have stable performance, high functional integration, and the overall technology is in a leading position compared with that in China. For example, Adaptronic (Germany) has a series of cable test equipment widely used in industries such as automobiles, trains, communications, instrument manufacturing, aerospace, etc. The test speed is as high as 15,600 points / minute, and the measurement accuracy is 0.001Ω. Its products are used in many domestic units. The NX series cable tester of Dynalab Company in the United States can not only test the short circuit and open circuit of the cable, but also perform high-voltage resistance test, low-voltage and high-voltage insulation test, and test functions such as resistance, capacitance, diode, and twisted pair contained in the cable. The detection speed of the conduction test is 1024 points / second, the maximum conduction resistance test range is 2MΩ, the maximum insulation test voltage is 1500V, the supporting hardware equipment is rich, the programming is easy, and the expansion and networking are convenient. The 9500 series instruments of DITMCO adopted by international large companies such as Boeing Aircraft Company can provide a full-aircraft test with more than 30,000 points, based on bus technology and scalable.

[0004] After years of development, the cable testing technology in China has become increasingly mature. There are more and more cable testing methods, with a wider coverage range, and higher testing accuracy and precision. However, in comparison, many domestic cable testing devices are borrowed from foreign counterparts of the same kind, and most of them are for a specific detection object, being relatively backward in terms of appearance design, technical performance, and manufacturing process, with relatively low levels of digitalization, intelligence, modularization, integration, and automation. The reliability index is also lower than that of foreign counterparts of the same kind. The reliability index of domestic testing instruments is generally about 3000 hours, while that of foreign ones is generally above 10000 hours, and the average trouble-free working time is 20000 - 30000 hours. Therefore, many high-end testing devices in China still rely on imports. However, due to the relatively specialized and fixed software and hardware functions of these imported devices, it is difficult to meet the specific and special requirements of missile cable testing (such as realizing the storage and management of detection data). Moreover, due to reasons such as confidentiality, there are fewer reference materials and interfaces for secondary development provided, the application scope is limited, and the cost of replacement and upgrade is high and subject to others.

[0005] With the development of cable testing technology, domestic cable testing devices have been developing in the direction of functional integration, expandable test capacity, automation, and intelligence. However, there are not many varieties of general cable testing devices for main battle weaponry, the supporting ability is weak, the replacement is slow, and the technical performance still needs to be improved. Summary of the Invention

[0006] In view of the above-mentioned existing technical problems, the present invention provides a portable intelligent detector for testing multi-core cables with tiny current, which combines the upper computer and the lower computer of traditional testing into one, with a small volume and light weight, effectively improving the convenience of use, maintenance, and management of the cable detector.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A portable intelligent detector for testing multi-core cables with tiny current,

[0009] comprising a housing, inside which a channel board, a test board, and a capacitive screen are sequentially arranged from bottom to top. The inner surface of the capacitive screen is embedded in the test board, and its outer surface is located on the housing. The channel board is integrated with a 128-channel test point module and a driver; the test board is integrated with a microprocessor, a communication module, a sampling module, a resistance detection module, a conduction detection module, and a programmed control gear module;

[0010] The channel board is used to switch 128 test channels and drive each module to work. The sampling module is used to collect the voltage of the test path and upload it to the microprocessor. The resistance detection module and the conduction detection module perform the conduction and resistance tests on the cable under test through the 128 test point module. The program-controlled gear module is used to receive the resistance and conduction test results feedback from the cable under test and upload them to the microprocessor. The microprocessor is connected to the capacitive touch screen through the communication module to achieve human-computer interaction according to the communication protocol.

[0011] Preferably, the microprocessor is connected to the capacitive touch screen, the sampling module, the resistance detection module, the conduction detection module and the program-controlled gear module. The microprocessor is used to receive the control instructions input through the capacitive touch screen, send the gear selection control signal to the program-controlled gear module, send the resistance detection control signal to the resistance detection module, and send the conduction test control signal to the conduction test module. The sampling module is used to collect the voltage of the resistance of the cable under test and the voltage of the standard resistance and upload them to the microprocessor. The microprocessor calculates and outputs the resistance value and the conduction result according to the test circuit and displays them through the capacitive touch screen.

[0012] Preferably, the program-controlled gear module is also connected to the resistance detection module and the conduction detection module. The program-controlled gear module receives the gear selection control signal from the microprocessor and the test results feedback from the cable under test and uploads them to the microprocessor.

[0013] The program-controlled gear module has 4 gears. Each gear includes relays (K15, K23), precision resistors (R35), resistors (R27) and LED lights (D20). Each of the relays (K15, K23) has 2 pins connected to the precision resistor (R35), resistor (R27) and LED light (D20) to form a four-wire test circuit. The precision resistor (R35) and resistor (R27) are used to calculate the resistance value of the cable under test, and the LED light is used for test debugging.

[0014] Each gear represents a different order of magnitude of resistance, and its gear shifting is controlled by the microprocessor. The relays in the program-controlled gear module use AGQ200A4H type relays.

[0015] Preferably, the test circuits of the resistance detection module and the conduction detection module both include a constant current source circuit, a signal conditioning circuit, an AD converter and a single-chip microcomputer. The constant current source circuit collects the voltage signals at both ends of the cable under test and sends them to the signal conditioning circuit. The signal conditioning circuit performs differential amplification processing on the voltage signals to obtain the amplified voltage analog signals and sends them to the AD converter. The AD conversion circuit converts the analog signals into digital signals and sends them to the single-chip microcomputer, and the single-chip microcomputer processes the digital signals to obtain the resistance value of the cable under test.

[0016] Preferably, the constant current source circuit is a programmable precision constant current source circuit composed of dual operational amplifiers. The programmable precision constant current source circuit includes a first-stage follower (U8), a second-stage operational amplifier (U11), and precision resistors (R64, R66, R35, R67). The positive input terminals of the first-stage follower (U8), the precision resistor (R64), the second-stage operational amplifier (U11), and the precision resistor (65) are connected in sequence. The precision resistor (35) is connected in series with the resistor (R40) and is connected in parallel across the second-stage operational amplifier (U11) and the precision resistor (65). The precision resistor (R67) is connected to the precision resistor (R66) and is connected in parallel across the second-stage operational amplifier (U11) and the precision resistor (65). The precision resistor (R66) is coupled to the negative input terminal of the second-stage operational amplifier (U11). The resistor (R40) is connected to the resistor test loop to provide a constant current to the load, and this constant current ≤ 1 mA;

[0017] The first-stage follower (U8) is used to provide buffering for the reference pin of the second-stage operational amplifier (U11). The output voltage of the second-stage operational amplifier (U11), that is, the programmable voltage DAC1, is the voltage across the resistor (R40). The resistor (R40) converts it into a current. After subtracting the input bias current of the second-stage operational amplifier (U11), it provides a constant current to the resistor test loop.

[0018] Preferably, the acquisition module includes an AD8421 chip and three-way relays. The AD8421 chip cooperates with the three-way relays to switch the precision resistors. The AD8421 chip is connected to pins 2 and 3 of the second-stage operational amplifier (U11) to achieve gain control of the acquired voltage.

[0019] Preferably, the 128-channel test point module is composed of 128 test points. Each test point is composed of four MOS transistors, for a total of 512 MOS transistors. The arrangement method: divide the 512 MOS transistors into 8 groups, with 2 MOS transistor boards in each group. There are 32 MOS transistors at the beginning and end of each MOS transistor board, forming 8 MOS transistor matrix units.

[0020] Preferably, heat dissipation holes and channel output interfaces are provided on the side wall of the housing. At least two channel output interfaces are provided. The 128-channel test point module is connected to the cable under test through the channel output interfaces.

[0021] Preferably, it further includes a first power module and a second power module. The first power module is integrated on the channel board and is used to provide a constant current source to the driver. The second power module is integrated on the test board and is used to provide a constant current source to the microprocessor, the acquisition module, the conduction detection module, the resistance detection module, and the programmable gear module.

[0022] A detection method for a portable intelligent detector used for testing multi-core cables with tiny current, the detection method including resistance detection and conduction detection;

[0023] Conduction detection process:

[0024] The conduction detection module receives instructions from the microprocessor, analyzes and performs conduction detection according to the instructions. A DC low-voltage signal is applied to the input bus of the conduction test loop. This low-voltage signal is switched to different test loops through any MOS transistor on the channel board to achieve the conduction test of the internal lines of the cable under test;

[0025] The conduction test loop consists of a 1.5V constant voltage excitation source, a standard resistor R with a value of 100Ω, and the cable under test. After passing through the signal conditioning circuit, the AD converter measures the resistance R1 and the voltage values U1 and U2 at the same moment on the cable under test. Among them, U1 is the voltage on the standard resistor, and U2 is the voltage on the resistor under test. Then, it can be obtained that:

[0026]

[0027] That is

[0028]

[0029] The on-off resistance value R2 of the cable to be tested is calculated using the known standard resistance value R1, and it is sent to the microprocessor. The actual resistance of the cable under test is compared with the standard resistance value to determine whether the cable under test is conducting;

[0030] Resistance detection process:

[0031] (1) Single-core cable

[0032] The resistance detection module receives instructions from the microprocessor, analyzes and performs resistance detection according to the instructions. Before detection, the microprocessor controls the program-controlled gear module to select the middle gear. During detection, the test point one d1_1 terminal and the test point two d2_2 terminal are driven by the driver. The constant current source passes through the program-controlled gear module, flows in from L1 of the test point one, passes through the cable under test, and flows out to the ground from L3 of the test point two. The signal conditioning circuit collects the voltage signal of the cable under test, sends the voltage signal to the AD converter to be converted into a digital signal and sent to the single-chip microcomputer. The single-chip microcomputer calculates the resistance value, sends it to the program-controlled gear module, compares it with the resistance of the program-controlled gear module, and sends the comparison result and the resistance value to the microprocessor. The microprocessor controls whether to shift gears according to the comparison result; Repeat the above process 10 times, send the measured resistance value to the microprocessor, calculate its average value, and display the result on the capacitive screen;

[0033] (2) Multi-core cable

[0034] Since the continuity of each core has been measured during the continuity test, when measuring the resistance of a certain core, the test points measured during the continuity test can be closed at one end and the other end to obtain the resistance value of the core.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention designs a program-controlled precision constant current source circuit composed of dual operational amplifiers, ensuring that the test current is less than 1 mA, effectively eliminating the measurement error caused by the fluctuation of the test excitation source, ensuring both test safety and maintaining the accuracy of test data; On the basis of meeting the requirements of multi-core cable continuity and resistance testing, the present invention comprehensively considers economic costs and performance requirements, selects components with small volume and light weight, integrates them on a detector, realizes portable and mobile detection, reduces the working intensity at the same time, and only one person can complete the cable continuity and resistance detection, improving work efficiency; The present invention separates the excitation source circuit from the measurement circuit, designs a four-wire connection method test circuit, eliminates the resistance of some patch cords, effectively excludes the influence of lead resistance on measurement, and improves the measurement accuracy of the system; The present invention adopts a four-wire non-contact MOS transistor electronic switch circuit to realize the automatic switching of 128 test points. While saving costs and reducing volume, it can also eliminate the interference of the impedance of wiring and contact resistance on the test results, ensure that the feedback signal is less likely to be distorted, has better detected performance when measuring voltage or current, and can effectively improve the cable test accuracy. Description of the Drawings

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0037] Figure 1 It is a schematic structural diagram of a portable intelligent detector for testing multi-core cables with tiny current of the present invention;

[0038] Figure 2 It is a schematic diagram of the principle of use of a portable intelligent detector for testing multi-core cables with tiny current of the present invention;

[0039] Figure 3 It is a MOS transistor switch circuit;

[0040] Figure 4 It is a MOS transistor circuit of the channel board;

[0041] Figure 5 It is a sampling circuit;

[0042] Figure 6 It is a program-controlled gear shifting circuit;

[0043] Figure 7 This is the connection diagram of the conduction and resistance test circuit in the present invention;

[0044] Figure 8 is the AD signal conditioning circuit;

[0045] Figure 9 is the constant current source test circuit;

[0046] Figure 10 is the constant current source conduction test circuit;

[0047] Figure 11 is the constant current source resistance test circuit;

[0048] Figure 12 is the constant current source circuit for microampere range;

[0049] Figure 13 is the conduction test excitation source circuit;

[0050] Figure 14 is the conduction detection circuit;

[0051] Figure 15 is the power supply switching circuit;

[0052] Figure 16 is the circuit diagram of the program-controlled gear module;

[0053] Figure 17 is the ADC acquisition gain circuit diagram;

[0054] Figure 18 This is the module connection block diagram of the detector of the present invention;

[0055] Among them, 1 - test board; 101 - microprocessor; 102 - acquisition module; 103 - resistance detection module; 104 - conduction detection module; 105 - program-controlled gear module; 106 - communication module; 107 - second power supply module; 2 - channel board; 201 - 128-channel test point module; 202 - driver; 203 - first power supply module; 3 - capacitive screen. Specific embodiments

[0056] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Generally, the components of the embodiments of the present invention described and illustrated herein can be arranged and designed in various different configurations.

[0057] Accordingly, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0058] The present invention specifically provides a portable intelligent detector for testing a multi-core cable with a small current, as Figure 1-2 and Figure 18 shown, which includes a housing. Inside the housing, a channel board 2, a test board 1, and a capacitive screen 3 are sequentially arranged from bottom to top. The inner surface of the capacitive screen 3 is embedded in the test board 2, and its outer surface is located on the housing. The channel board 2 is integrated with a 128-channel test point module 201 and a driver 202; the test board 1 is integrated with a microprocessor 101, a sampling module 102, a resistance detection module 103, a conduction detection module 104, a programmed control gear module 105, and a communication module 106.

[0059] The channel board 2 is used to switch 128 test channels and drive each module to work. The sampling module 102 is used to collect the test path voltage and upload it to the microprocessor 101; the resistance detection module 103 and the conduction detection module 104 perform the conduction and resistance tests on the cable under test through the 128-channel test point module 201; the programmed control gear module 105 is used to receive the resistance and conduction test results fed back by the cable under test and upload them to the microprocessor 101. The microprocessor 101 is connected to the capacitive screen 3 through the communication module 106 to realize human-computer interaction according to the communication protocol.

[0060] Specifically, the microprocessor 101 is connected to the communication module 106, the sampling module 102, the resistance detection module 103, the conduction detection module 104, and the programmed control gear module 105. The microprocessor 101 is used to receive the control instructions input through the capacitive screen 3, send a gear selection control signal to the programmed control gear module 105; send a resistance detection control signal to the resistance detection module 103, and send a conduction test control signal to the conduction test module 104; the sampling module 102 is used to collect the voltage of the resistance of the cable under test and the voltage of the standard resistance and upload them to the microprocessor 101. The microprocessor 101 calculates and outputs the resistance value and the conduction result according to the test circuit and displays them through the capacitive screen 3.

[0061] On the upper end face of the housing of the present invention, a power button, an operation button, and an alarm display lamp are also provided. On the side of the housing, a channel output interface, a switch button, and heat dissipation holes are also provided. The switch button and the heat dissipation holes are located on the mutually symmetrical planes of the housing. The channel output interface is located on the front side wall of the housing. The channel output interface is used to connect the cable under test to realize the connection between the cable under test and the internal channel board.

[0062] The channel board 2 in the present invention is a substrate structure for conduction and resistance testing. All tests of the cable are carried out relying on each test point on the channel board. The cable to be tested needs to select 128 test points of the four-wire system for testing. In order to realize the automatic measurement of the resistance between these test points, a multiplexing circuit needs to be designed. The present invention uses a MOS transistor electronic switch circuit to replace the relay matrix circuit. The MOS transistor is small in size and relatively inexpensive compared to the relay, and has a higher cost performance. The connection relationship of the MOS transistor switch circuit is as Figure 3 shown. The constant current source is added from L1 to L3 grounded, so that the purpose of adding the constant current source to each core of the cable can be realized. The voltages at both ends of the cable core need to be measured by another two wires L2 and L4, and a total of four buses are required. During the test, the test point one d1_1 end (the first end) and the test point two d2_2 (the last end) are driven by the driver. If there is a conduction relationship in the cable to be tested, the conduction signal flows into the cable to be tested from L1 of the test point one and flows out from L3 of the test point two to the conduction detection module. For a multi-core cable, the single-chip microcomputer controls the operation of the first end of one "test point 1" of many cores and the operation of all the "test point 2" last ends. If there is no conduction relationship, or if there is an abnormality in this core, then there will be no voltage signal on the bus L3. And if there is a conduction relationship, then there is a voltage signal on L3. At this time, the other corresponding end is found by using the dichotomy method.

[0063] Therefore, each test point on the channel board 2 is composed of four MOS transistors (model number FDV303N). Then 128 test points mean 512 MOS transistors. The arrangement method: divide the 512 MOS transistors into 8 groups, each group has 2 MOS transistor boards, and there are 32 MOS transistors at the first and last ends of each MOS transistor board, forming 8 MOS transistor matrix units. The MOS transistors are specifically as Figure 4 shown. The main body of the entire channel board is 128 test points, and the communication module, the driver, and the second power supply all serve the test points.

[0064] In the present invention, there is more than one cable to be tested and it is a multi-core cable. If the test points are directly inserted into the core pins or core holes of the cable to be tested, it is not only difficult and requires a lot of manpower, but also easy to cause poor contact and affect the measurement result. In order to ensure the accurate and reliable connection of the cable and achieve quick plugging and unplugging, and ensure that the detection wiring does not change due to the change of the conduction relationship of the cable, a single-end or two-end adapter cable transfer method is designed for testing.

[0065] During single - end testing, one end of the adapter cable is a European socket pin connected to the tester, and the other end is the pin of the cable under test. One end of the cable under test is fixed to the corresponding pin of the adapter cable, and the other end is scattered. In this way, the system test points can be reduced to 27 points. Four 26 - core components under test can be measured at one time, which can improve the test speed to a certain extent. However, this method cannot determine whether the conduction relationship of the core wires at both ends of the cable is correct, and can only measure the conduction resistance of the current cable.

[0066] Two - end testing means testing by connecting both ends of the cable under test simultaneously. Using this method, the number of points to be tested is large, a total of 52 points, which is nearly twice the number of test points required for single - end testing. At most, two 26 - core cables under test can be measured at one time, and the test speed is reduced. However, using this testing method, not only can the conduction resistance of the current cable be tested, but also whether the conduction relationship of the current cable is correct can be accurately tested, which better meets the cable testing requirements.

[0067] In the present invention, the microprocessor is the control and processing core of the entire detector. It mainly realizes the logical control of the entire device and displays the detection results through the capacitive screen to achieve human - machine interaction. The STM32F107 single - chip microcomputer microprocessor is used in the present invention. Compared with the ARM microprocessor, this processor supports a variety of low - power operation modes, which means that under the same working conditions, the chip has lower power consumption, and STM32F107 has its own function library.

[0068] In the present invention, the sampling environment during the cable testing process is relatively complex. To improve the sampling accuracy, the following measures are mainly taken: First, a higher sampling frequency is adopted to broaden the frequency domain of the original signal to ensure that the original signal can be sampled with minimal distortion; second, a high - precision and high - linearity A / D conversion chip is selected to ensure the high - precision A / D conversion quantization value; third, the two channels start sampling simultaneously to measure the phase angle difference; fourth, a trigger circuit is designed to achieve fixed - frequency sampling. The sampling trigger circuit is as Figure 5 shown.

[0069] In the present invention, the program - controlled gear module 105 is respectively connected to the microprocessor 101, the resistance detection module 103, and the conduction detection module 104. The program - controlled gear module 105 receives the gear - selection control signal from the microprocessor 101 and the test results fed back from the cable under test, and uploads them to the microprocessor.

[0070] As Figure 16As shown, the programmable gear module 105 has a total of 4 gears. Each gear includes relays (K15, K23), precision resistors (R35), resistors (R27), and LED lights (D20). Each of the relays (K15, K23) has 2 pins connected to the precision resistor (R35), resistor (R27), and LED light (D20) to form a four-wire test circuit. The precision resistor (R35) and resistor (R27) are used to calculate the resistance value of the cable under test, and the LED light is used for test debugging. Each gear represents a different order of magnitude of resistance and is shifted by the microprocessor. The relays in the programmable gear module use AGQ200A4H type relays. This relay has a total of eight pins and is suitable for circuits with more pins in the programmable shift module. When the relay is turned on, the current from the constant current source passes through the resistors in the programmable shift module and then to the channel board to ground, forming a closed loop. Then, the sampling circuit collects the voltage across the resistors in the programmable gear module and sends it to the microprocessor for comparison with the resistance of the tested cable to determine whether they are of the same order of magnitude and whether they meet the accuracy requirements. Then, the microprocessor determines whether to shift gears. Its circuit diagram is as shown in Figure 6 shown.

[0071] According to the principle of conduction and resistance testing, the on-resistance is measured by building an A / D acquisition circuit and calculating it after collecting the voltage across the resistor under test. Therefore, the test circuits of the conduction detection module and resistance detection module designed in the present invention (as shown in Figure 7 shown) both include a constant current source circuit, a signal conditioning circuit, an AD converter, and a single-chip microcomputer. The constant current source circuit collects the voltage signal across the cable under test and sends it to the signal conditioning circuit. The signal conditioning circuit performs differential amplification processing on the voltage signal to obtain an amplified voltage analog signal and sends it to the AD converter. The AD conversion circuit converts the analog signal into a digital signal and sends it to the single-chip microcomputer, and the single-chip microcomputer processes the digital signal to obtain the resistance value of the cable under test.

[0072] Among them, the AD converter uses the AD7609 chip of ADI Company, with a sampling rate of 200ks / s. It can input either single-point or differentially. The isolation and conditioning at the front end of the A / D conversion are completed by an AD follower circuit, as shown in Figure 8 shown. The amplitude of the signal V to be measured is less than 5V and is input to the IN+ terminal and IN_COM terminal of AD204JY. After passing through the AD204JY isolation operational amplifier, an isolation voltage equal to the input voltage is generated at the output terminal HI / LO, and then a voltage follower output is generated through the OP07 operational amplifier and input to the analog-to-digital converter AD7609 for analog-to-digital conversion.

[0073] In the present invention, the cable under test is a multi-core cable, and the conduction resistance of each core of the cable needs to be tested one by one. How to apply a constant current source to each cable core is the key to the design of the conduction test circuit. A relatively simple method is to connect both ends of the cable with a wire and separate the cores with normally open contacts of a relay. When testing a certain cable core, close the corresponding normally open contact, so that the purpose of applying the constant current source to each core of the cable can be basically achieved, and the prototype of the four-wire system is initially formed. As Figure 9 shown.

[0074] According to the above principle, a constant current source conduction test circuit is designed as Figure 10 shown. The conduction detection module receives instructions from the microprocessor, analyzes and executes the resistance test function according to the instructions, applies a DC constant current source on the bus, and this DC constant current source is switched to different test circuits through any electronic switch on the channel board to realize the acquisition of the voltage drops across the internal wires of the DUT and both ends of the standard resistor in the test circuit. The embedded microprocessor uploads the AD values of the cable under test and the standard resistor collected to the upper computer. The upper computer compares and calculates the measured cable AD value and the set standard resistor AD value, obtains the actual resistance value of the cable under test, and then compares it with the standard resistance value to give a conclusion on whether it is qualified or not.

[0075] The constant current source conduction circuit adopts a highly stable and programmable adjustable constant current source. The maximum test current is 1 mA, and the test resistance range is 10 mΩ to 10 Ω. The test channels are switched in a four-wire system using electronic switches. One path passes through the constant current source, and the other path collects the voltage of the cable under test, which can ensure the accuracy of the test value to the greatest extent. At the same time, in the signal processing stage, a high-precision low-temperature drift operational amplifier is used, and the single-chip microcomputer used has an 18-bit high-resolution AD conversion function to further improve the resistance test accuracy.

[0076] The constant current source resistance test circuit is as Figure 11 shown. Before detection, the microprocessor controls the programmable range module to select the second gear (an intermediate gear can be determined according to the number of gears). During detection, the test point one d1_1 terminal and the test point two d2_2 terminal are driven by a driver. The constant current source flows through the programmable range module from L1 of the test point one, through the cable under test, and out from L3 of the test point two to the ground. The signal conditioning circuit collects the voltage signal of the cable under test, sends the voltage signal to the AD converter to be converted into a digital signal and sends it to the single-chip microcomputer. The single-chip microcomputer calculates to obtain the resistance value, sends it to the programmable range module, compares it with the resistance of the programmable range module, and sends the comparison result and the resistance value to the microprocessor. The microprocessor controls whether to shift gears according to the comparison result. Repeat the above process 10 times, send the measured resistance value to the microprocessor, and calculate its average value.

[0077] For a multi-core cable, the resistance detection process is the same as that of a single-core cable. Since the continuity of each core has been detected in the continuity test, when detecting the resistance of a certain core, only need to close the test points measured in the continuity test - one end - the other end to obtain the resistance value of this core.

[0078] In the continuity resistance test circuit, the AD analog input voltage range is ±5V. When the cable is broken or the continuity resistance value is very large, the sampling voltage will be close to the test excitation source voltage. If the test voltage is too large, the sampling voltage will exceed the AD input range; if the test voltage is too small, the sampling voltage will also decrease accordingly. At this time, the influence of temperature drift and noise will cause a large error in the test result. In addition, there are certain gain errors and offset errors in the AD converter. The AD conversion value and the input voltage are not a straight line passing through the origin, so there is a conversion voltage blind area. Therefore, a voltage too close to the boundary value is very likely to get an incorrect conversion result during AD conversion. Therefore, the test voltage of the excitation source must be designed appropriately to ensure the test accuracy. In the present invention, the cable under test is connected to the seeker and the initiator, and it is required that the test voltage be as small as possible. However, considering the requirements of AD conversion accuracy, the test voltage cannot be too small. Considering the above factors comprehensively, the test voltage is designed to be 1.5V, which can not only meet the needs of resistance testing but also meet the accuracy requirements.

[0079] Due to the particularity of the cable under test, the current passing through the test loop should not be greater than 1mA. The present invention uses a programmable precision constant current source composed of dual operational amplifiers to provide a constant current for the test loop. The cable continuity test loop consists of a 1.5V constant voltage excitation source, a standard resistor R = 100Ω, and the cable. The programmable precision constant current source circuit is as Figure 12 shown.

[0080] Figure 12Among them, the constant current source circuit adopts a programmable precision constant current source circuit composed of dual operational amplifiers. The programmable precision constant current source circuit includes a first-stage follower (U8), a second-stage operational amplifier (U11), and precision resistors (R64, R66, R35, R67). The positive input terminals of the first-stage follower (U8), the precision resistor (R64), the second-stage operational amplifier (U11), and the precision resistor (65) are connected in sequence. The precision resistor (35) is in series with the resistor (R40) and is connected in parallel across the second-stage operational amplifier (U11) and the precision resistor (65). The precision resistor (R67) is connected to the precision resistor (R66) and is connected in parallel across the second-stage operational amplifier (U11) and the precision resistor (65). The precision resistor (R66) is coupled to the negative input terminal of the second-stage operational amplifier (U11), and the resistor (R40) is connected to the resistor test loop. The first-stage follower (U8) is used to provide buffering for the reference pin of the second-stage operational amplifier (U11). The output voltage of the second-stage operational amplifier (U11), that is, the programmable voltage DAC1, is the voltage across the resistor (R40). The resistor (R40) converts it into a current. After subtracting the input bias current of the second-stage operational amplifier (U11), the current flows to the load.

[0081] From the virtual open, it can be known that no current flows through the input terminal of the second-stage operational amplifier (U11), then

[0082] (Vi–V1) / R64=(V1–V4) / R35 (a)

[0083] (V3–V2) / R67=V2 / R66 (b)

[0084] From the virtual short, it is known that V1 = V2 (c)

[0085] If R64 = R35 and R66 = R67, then from the abc formula, V3 - V4 = Vi

[0086] Among them, V1 and V2 are the output voltages before and after the first-stage operational amplifier, V3 and V4 are the output voltages before and after the second-stage operational amplifier, and Vi is the initial voltage.

[0087] The above formula shows that the voltage across R40 is equal to the input voltage DAC1. The input bias current of the second-stage operational amplifier (U11) can be ignored. The output current calculation formula of this circuit is I = DAC1 / R40. To ensure the safety of the cable under test in the subsequent stage, it is necessary to detect the voltage drop across R40 in real time during the resistance test. The first operational amplifier has the characteristic of high input impedance, so the voltage of the subsequent resistor will not change suddenly at the moment of power-on during the test, which can protect the test data of the cable under test in the subsequent stage to be accurate and error-free.

[0088] In the present invention, the sampling module is responsible for collecting voltage information and uploading it to the microprocessor. Then, the microprocessor calculates and outputs the resistance value and conduction result according to the test circuit. The acquisition chip of the sampling module usually has a limited acquisition range. When the voltages at both ends of the measured resistor and the standard resistor are too small to be within the acquirable range, gain control is required to amplify them to the range that the acquisition chip can collect. Therefore, the AD8421 chip, whose various parameters and indicators are very suitable for gain setting, is combined with a three-way relay to perform precise resistor switching, and stable gain settings of 10 times, 100 times, and 1000 times can be achieved respectively, which can be debugged and used according to the resistance test range of the measured cable. Connecting the ADC gain control to pins 2 and 3 of the second-stage operational amplifier of the resistance test module can achieve gain control of the collected voltage. The connection is as shown in Figure 17 as shown.

[0089] In the present invention, the cable conduction test adopts the ratio method. The conduction test excitation circuit is as shown in Figure 13 as shown. The voltage of the conduction test excitation source V = 1.5V tests the voltage drop of the test loop, and the current-limiting resistor R48 is set to 100Ω. The maximum output voltage of the entire circuit Vmax = 1.5V. R51 is the pull-down resistor of the MOS transistor, which raises the drive voltage and prevents electrostatic breakdown of the GS pole of the MOS transistor. The maximum output current of the entire circuit is:

[0090]

[0091] That is, when the measured part is completely short-circuited, the excitation source outputs voltage and current.

[0092] The conduction detection circuit is as shown in Figure 14 as shown. The conduction detection module receives the instruction from the microprocessor, analyzes and executes the conduction detection according to the instruction. A DC low-voltage signal is applied to the input bus of the conduction test loop. This low-voltage signal is switched to different test loops through any MOS transistor on the channel board. After the MOS transistor conducts, the optocoupler is turned on, and the level at SR1 changes from high level to low level. By detecting the level state of SR1 by the microprocessor, it can be indicated whether there is a conduction relationship currently.

[0093] The conduction test loop consists of a 1.5V constant-voltage excitation source, a standard voltage R = 100Ω, and the measured cable. After conditioning the signal circuit, the AD converter measures the resistor R1 and the voltage values U1 and U2 of the measured cable at the same moment. Then, it can be obtained that:

[0094]

[0095] That is

[0096]

[0097] The on-off resistance value R2 of the cable to be measured can be calculated using the known standard resistance value R1. The advantage of this testing method is that it can eliminate the measurement error caused by the fluctuation of the test excitation source. The detector of the present invention further includes a first power supply module and a second power supply module. The first power supply module is integrated on the channel board and is used to provide a constant current source to the driver. The second power supply module is integrated on the test board and is used to provide a constant current source to the microprocessor, the acquisition module, the conduction detection module, the resistance detection module, and the programmed range module.

[0098] In the present invention, the first power supply module and the second power supply module have the same structure and both adopt a linear regulated power supply. This regulated power supply has smaller ripple, better regulation rate, and less external interference compared to a switching power supply, avoiding the influence of the switching power supply on the test and greatly improving the test accuracy and stability. At the same time, for the two power supply modes of mains power supply and lithium battery power supply, a non-disturbing power supply switching circuit is designed using a dual DC power supply fast-switching device, which can be directly powered by the DC power supply converted from the external AC220V mains power, realizing the fast switching of the DC power supply system (the power supply interruption time does not exceed 3 - 5ms), meeting the cable test requirements, and improving the reliability of the DC power supply system. The power supply switching circuit is as Figure 15 shown.

[0099] The tester of the present invention further includes a self-check module disposed on the test board. After the tester has been used for a certain period, the self-check module performs self-check on the test channels and the resistance test function, that is, the inside of the measurement board can simulate the external measurement circuit, that is, there is a self-check circuit that enables the instrument to perform conduction and resistance tests inside, and checks whether the test channels and test functions of the tester are operating normally.

[0100] The tester of the present invention adopts an integrated structure of an internal host computer. Compared with the traditional split-type cable test system structure, this integrated design scheme does not require a separate upper display terminal, has a small volume and light weight, can effectively improve the convenience of using and maintaining the cable tester, and better meets the design requirements of miniaturization, automation, and integration. The present invention selects an EPIC-N80-I5 microcontroller with a wide-temperature military-grade high-definition color liquid crystal display screen to achieve the function requirements of explosion-proof display screen, storage, export, etc. of the host computer.

[0101] The above is only a preferred embodiment of the present invention and does not impose any limitation on the present invention. Any simple modification, change, and equivalent change made to the above embodiments according to the technical essence of the invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A portable intelligent detector for testing multi-core cables with tiny current, characterized in that, It includes a housing, in which a channel board, a test board and a capacitive screen are successively arranged from bottom to top. The inner surface of the capacitive screen is embedded in the test board, and its outer surface is located on the housing. The channel board integrates a 128-channel test point module and a driver; the test board integrates a microprocessor, a communication module, a sampling module, a resistance detection module, a conduction detection module, and a programmed control gear module; The channel board is used to switch 128 test channels and drive each module to work. The sampling module is used to collect the test path voltage and upload it to the microprocessor; the resistance detection module and the conduction detection module perform the conduction and resistance tests on the cable under test through the 128-channel test point module; the programmed control gear module is used to receive the resistance and conduction test results fed back by the cable under test and upload them to the microprocessor. The microprocessor is connected to the capacitive screen through the communication module and realizes human-computer interaction according to the communication protocol; The test circuits of the resistance detection module and the conduction detection module both include a constant current source circuit, a signal conditioning circuit, an AD converter and a single-chip microcomputer. The constant current source circuit collects the voltage signals at both ends of the cable under test and sends them to the signal conditioning circuit. The signal conditioning circuit performs differential amplification processing on the voltage signals to obtain the amplified voltage analog signals and sends them to the AD converter. The AD conversion circuit converts the analog signals into digital signals and sends them to the single-chip microcomputer, and the single-chip microcomputer processes the digital signals to obtain the resistance value of the cable under test; The constant current source circuit adopts a programmed precision constant current source circuit composed of dual operational amplifiers. The programmed precision constant current source circuit includes a first-stage follower (U8), a second-stage operational amplifier (U11), precision resistors (R64), precision resistors (R66), precision resistors (R35) and precision resistors (R67). The first-stage follower (U8), the precision resistor (R64), the positive input terminal of the second-stage operational amplifier (U11) and the precision resistor (R65) are successively connected. The precision resistor (R35) is connected in series with the resistor (R40) and is connected in parallel across the second-stage operational amplifier (U11) and the precision resistor (R65). The precision resistor (R67) is connected to the precision resistor (R66) and is connected in parallel across the second-stage operational amplifier (U11) and the precision resistor (R65). The precision resistor (R66) is coupled to the negative input terminal of the second-stage operational amplifier (U11). The resistor (R40) is connected to the resistance test loop to provide a constant current to the load, and this constant current ≤ 1 mA; The first-stage follower (U8) is used to provide buffering for the reference pin of the second-stage operational amplifier (U11). The output voltage of the second-stage operational amplifier (U11), that is, the programmed voltage DAC1, is the voltage across the resistor (R40). The resistor (R40) converts it into a current. After subtracting the input bias current of the second-stage operational amplifier (U11), it provides a constant current to the resistance test loop; The 128-channel test point module consists of 128 test points. Each test point is composed of four MOS transistors, for a total of 512 MOS transistors. The arrangement method is as follows: The 512 MOS transistors are divided into 8 groups, with each group consisting of 2 MOS transistor boards. Each MOS transistor board has 32 MOS transistors at both the beginning and the end, forming 8 MOS transistor matrix units.

2. The portable intelligent detector for testing multi-core cables with tiny current according to claim 1, characterized in that, The microprocessor is connected to the communication module, the sampling module, the resistance detection module, the conduction detection module, and the program-controlled gear module. The microprocessor is used to receive the control instructions input through the capacitive screen, send the gear selection control signal to the program-controlled gear module, send the resistance detection control signal to the resistance detection module, and send the conduction test control signal to the conduction test module. The sampling module is used to collect the voltages of the resistance of the cable under test and the standard resistance, and upload them to the microprocessor. The microprocessor calculates and outputs the resistance value and the conduction result according to the test circuit, and displays them through the capacitive screen.

3. The portable intelligent detector for testing multi-core cables with tiny current according to claim 1, wherein The program-controlled gear module is also connected to the resistance detection module and the conduction detection module. The program-controlled gear module receives the gear selection control signal from the microprocessor and the test results feedback from the cable under test, and uploads them to the microprocessor. The program-controlled gear module has a total of 4 gears. Each gear includes a relay (K15), a relay (K23), a precision resistor (R35), a resistor (R27), and an LED lamp (D20). The relay (K15) and the relay (K23) each lead 2 pins to be connected to the precision resistor (R35), the resistor (R27), and the LED lamp (D20) to form a four-wire test circuit. The precision resistor (R35) and the resistor (R27) are used to calculate the resistance value of the cable under test, and the LED lamp is used for test debugging. Each gear represents a different order of magnitude of resistance, and the microprocessor controls it to shift gears. The relays in the program-controlled gear module use AGQ200A4H model relays.

4. The portable intelligent detector for testing multi-core cables with tiny current according to claim 1, characterized in that, The sampling module includes an AD8421 chip and three-way relays. The AD8421 chip cooperates with the three-way relays to switch the precision resistor. The AD8421 chip is connected to pins 2 and 3 of the second-stage operational amplifier (U11) to achieve the gain control of the collected voltage.

5. The portable intelligent detector for testing multi-core cables with tiny current according to claim 1, characterized in that, Heat dissipation holes and channel output interfaces are provided on the side wall of the housing. There are at least two channel output interfaces. The 128-channel test point module is connected to the cable under test through the channel output interface.

6. The portable intelligent detector for testing multi-core cables with tiny current according to claim 1, characterized in that It also includes a first power supply module and a second power supply module. The first power supply module is integrated on the channel board and is used to provide a constant current source for the driver. The second power supply module is integrated on the test board and is used to provide a constant current source for the microprocessor, the sampling module, the conduction detection module, the resistance detection module, and the program-controlled gear module.

7. The detection method of a portable intelligent detector for testing multi-core cables with tiny current according to any one of claims 1-6, characterized in that, This detection method includes resistance detection and conduction detection. Conduction detection process: The conduction detection module receives the instructions from the microprocessor, analyzes and executes the conduction detection according to the instructions. A DC low-voltage signal is applied to the input bus of the conduction test loop. This low-voltage signal is switched to different test loops through any MOS transistor on the channel board to achieve the conduction test of the internal lines of the cable under test. The conduction test circuit consists of a 1.5V constant voltage excitation source, a standard resistor R with a value of 100Ω, and the cable under test. After passing through the signal conditioning circuit, the AD converter measures the resistor R1 and the voltage values U1 and U2 on the cable under test at the same moment. Among them, U1 is the voltage on the standard resistor, and U2 is the voltage on the resistor under test. Then, we can get: That is Use the known standard resistor value R1 to calculate the on-off resistance value R2 of the cable to be measured, send it to the microprocessor, compare the actual resistance of the cable under test with the standard resistor value to determine whether the cable under test is conducting; Resistance detection process: (1) Single-core cable The resistance detection module receives the instruction from the microprocessor, analyzes and executes the resistance detection according to the instruction. Before detection, the microprocessor controls the program-controlled gear module to select the middle gear. During detection, the driver drives the test point one d1_1 terminal and the test point two d2_2 terminal. The constant current source flows through the program-controlled gear module from the L1 of the test point one, through the cable under test, and out from the L3 of the test point two to the ground. The signal conditioning circuit collects the voltage signal of the cable under test, sends the voltage signal to the AD converter to be converted into a digital signal and then sends it to the single-chip microcomputer. The single-chip microcomputer calculates the resistance value, sends it to the program-controlled gear module, compares it with the resistance of the program-controlled gear module, and sends the comparison result and the resistance value to the microprocessor. The microprocessor controls whether to shift gears according to the comparison result; repeat the above process 10 times, send the measured resistance value of the cable under test to the microprocessor, calculate its average value, and display the result through the capacitive screen; (2) Multi-core cable Since the conductivity of each core has been measured in the conduction test, when detecting the resistance of a certain core, only need to close the test points measured in the conduction test at one end - the other end to obtain the resistance value of this core.

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