Hybrid Circuit Fault Diagnosis Based on Current Test

Abstract: in the process of hybrid circuit fault diagnosis using wavelet neural network, the selection of test parameters is very important. A fault diagnosis method based on current test is studied. Through the static and dynamic current information of PSPICE analog circuit and the combination of wavelet neural network, this method proves the feasibility of this method in hybrid circuit fault diagnosis, and provides a new method to improve the fault diagnosis rate of hybrid circuit.

Keywords: wavelet neural network; Hybrid circuit; Current test; fault diagnosis

0 Introduction

With the rapid development of electronic technology and the continuous improvement of manufacturing technology, the complexity of the circuit is increasing and the chip size is decreasing. More and more mixed signal circuits are integrated on the system level chip, not just digital circuits or analog circuits. Because of the different testing methods of two circuits, traditional testing can no longer meet the development needs. This brings hitherto unknown challenges to designers, users and maintainers of the instrument and equipment, and also makes the detection of mixed mode signal circuits more and more seriously. The hybrid circuit fault diagnosis based on current test proposed in this paper is proposed under this background.

1. Theoretical knowledge of current test

Current test is to detect and locate the circuit fault by measuring the power supply current and effectively extracting the circuit fault information. It includes static current test technology IDDQ and dynamic current test technology IDDT.

When the circuit works normally, the quiescent current is very small, but the quiescent current of the defective circuit is very large. Therefore, when the quiescent current in the circuit is detected to be abnormal, it can be determined that the circuit has failed. This is also the principle of IDDQ test. However, some faults in CMOS circuits, such as open circuit fault, do not cause abnormal quiescent current. Therefore, it is necessary to introduce dynamic current test here. Based on this, this paper considers the combination of quiescent current and dynamic current test, rather than simple quiescent current test. IDDT is a short conduction current, that is, during the state transition of CMOS circuit, PMOS transistor and NMOS transistor are turned on at the same time, so that a conduction circuit is formed between power supply and ground, as shown in Figure 1. Since IDDT is the change of current in the process of dynamic conversion, the size of IDDQ does not affect its result. Therefore, it also avoids the influence of the increasing static leakage current of deep submicron circuits on the test. This paper studies the significance of the combination of the two in hybrid circuit fault diagnosis.

2 wavelet neural network for hybrid circuit fault diagnosis

Wavelet neural network is a combination of wavelet analysis theory and artificial neural network ANN theory. At present, there are two ways to combine the two:

(1) Loose combination. That is, wavelet analysis, as a preprocessing means of neural network, provides input eigenvectors for neural network.

(2) Compact combination. Wavelet and neural network are fused directly, that is, wavelet function and scale function form neurons.

This paper adopts the combination of loose wavelet and neural network. Firstly, the modeling and Simulation of normal circuit and fault circuit are carried out through PSpice, and the static current IDDQ and dynamic current IDDT parameters are extracted. The characteristics of the obtained current are extracted by wavelet analysis in MATLAB, and analyzed in combination with neural network. The steps are as follows:

(1) Parameter extraction. The current information of normal circuit and various fault circuits with bridge fault, open circuit fault and so on are extracted in PSPICE.

(2) Wavelet analysis. The current information obtained in (1) is decomposed by wavelet in MATLAB, the wavelet coefficients are extracted, and the RMS is further calculated.

(3) Fault location. Wavelet analysis and BP neural network are combined to analyze and judge the positioning effect. The specific steps are shown in Figure 2.

Hybrid Circuit Fault Diagnosis Based on Current Test 1

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Main Features of Cable Fault Tester
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Cable Fault Detector_ Medical Devices Will Maintain High Growth in the Coming Years
Cable Fault Detector_ Medical Devices Will Maintain High Growth in the Coming Years
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Detection Method of Power Cable Fault
Detection Method of Power Cable Fault
1. Rough measurement of power cable fault (1) bridge method bridge method is a classical method of power cable fault location, which has a long history. Including DC resistance bridge method, DC high voltage resistance bridge method and capacitance bridge method. The resistance bridge method can only test some cable faults with low insulation resistance between single phase and ground or between two phases; High voltage bridge method is mainly used to test single-phase grounding fault or phase to phase and ground fault of main insulation with resistance greater than 10k Ω but less than megohm; The capacitance bridge method is mainly used to test the open circuit and broken wire fault of cables. The bridge method is relatively simple and convenient to operate, but it needs to know the original data such as the accurate length of the cable in advance. At the same time, it is not suitable for detecting high resistance faults. Most of the actual power cable faults are high resistance faults. Because the bridge current is very small when the fault resistance is very high, it is difficult for general sensitive instruments to detect. (2) Traveling wave method 1) low voltage pulse method low voltage pulse method is mainly used to measure the fault distance of open circuit, short circuit and low resistance faults of cables; At the same time, it can also be used to measure the cable length, wave velocity and identify and locate the middle head, T-joint and terminal head of the cable. Test principle: input a low-voltage pulse signal from the test end to the cable, and the pulse signal propagates along the cable. When encountering the impedance mismatch point in the cable, such as open circuit point, short circuit point, low resistance fault point, etc., a reflected pulse will be generated. The position of the fault point is calculated according to the round-trip time difference DT between the reflected pulse and the transmitted pulse and the pulse propagation speed v. 2) High voltage pulse method high voltage pulse method uses high voltage signal to turn cable fault into short circuit or low resistance fault instantly, so that the reflection coefficient of fault point is close to - 1, and the fault point almost produces total reflection. There are usually two basic flashover methods, namely direct flashover method and impulse flashover method. When testing cable fault by flashover method, the reflected wave formed at the cable fault point is high-voltage pulse wave, which cannot be displayed directly through the instrument. Generally, a sampler is needed to convert the high-voltage pulse formed at the fault point under the action of high voltage into the low-voltage pulse signal required by the instrument. According to different sampling methods, it is divided into voltage method, current method and voltage induction method. Wherein, R1 is the voltage dividing resistance, R2 is the sampling resistance, LP is the current sampler, C is the energy storage capacitor and B is the transformer. DC high voltage flashover method (direct flashover method): apply DC voltage to the fault cable to make the fault click through the room for discharge and flashover. Then, the fault distance can be calculated according to the transmission speed V of the traveling wave in the cable. The direct flash method is mainly used to test the flashover high resistance fault of power cable, and can also be used to test the leakage high resistance fault with particularly high resistance but lower resistance compared with the intact phase. Figure 6 shows the principle circuit of direct flash test. Impulse high voltage flashover method (impulse flashover method): due to the large equivalent internal resistance of DC high voltage power supply used in direct flashover method, the power output power is limited to a certain extent. For most leakage high resistance faults, direct flashover method cannot be tested. The impulse flashover method uses the high-capacity charging capacitor as the DC high-voltage power supply, which is connected to the fault cable to cause the flashover and discharge at the fault point to form an instantaneous short circuit. It is mainly used to test the leakage high resistance fault of power cable, and can also be used to test the low resistance, open circuit and flashover high resistance fault of power cable. The test principle circuit is basically the same as that of the direct flash method, except that a spherical gap is inserted between the energy storage capacitor and the cable, as shown in Figure 7. 2. Precise measurement of power cable fault point (1) acoustic measurement method uses the sound wave generated when the fault point is discharged for fixed point. The sound sensor detects the sound signal above the power cable. The place with loud sound is the location of the fault point. The farther away from the fault point, the smaller the vibration sound. (2) When the fault point flashover discharges under the action of impulse voltage, the acoustic magnetic synchronization method receives the electromagnetic wave and vibration sound wave generated by the discharge of the fault point at the same time, and judges whether the measured signal is generated by the discharge of the fault point to accurately judge the location of the fault point. (3) The audio induction method adds a certain power low-voltage audio signal to the fault of the cable at one end of the tested circuit. When the tested signal is transmitted to the short-circuit or disconnection point, it cannot continue to transmit along the cable, so there will be obvious signal size changes on both sides of the cable fault point. If the signal changes are detected through the receiver above the cable path, The location of the fault point can be determined. At the same time, the accuracy and integrity of various basic data of cables are also very important to improve the efficiency of fault point finding, such as cable laying direction, total cable length, distribution of cable intermediate joints, etc.
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