Design and research of automatic test system for a certain type of acoustic self-guided head

O Introduction
The combat performance of contemporary weapon systems not only depends on the high technology and high performance of weapon systems, but also needs to achieve the best combat performance of weapon systems through reliability, maintainability and supportability. With the advancement of science and technology, in the context of the new military revolution with electronic technology and information technology as the main driving force and digital technology as the core, instruments that were originally used as measuring instruments have developed into a relatively complete discipline. And they play an increasingly important role in today's scientific and technological development and national defense construction. The automatic test system includes a computer with computing and processing capabilities. During the test process, various complex analysis, statistics, judgment, and processing results can be output in a variety of ways. The automatic test system avoids errors caused by human factors and can obtain very good testability. By performing a large number of measurements, judgments and analyses, random errors and systematic errors can be greatly weakened, thereby obtaining higher measurement accuracy.
This paper mainly designs an automatic test system for a certain type of anti-submarine self-guided torpedo acoustic guidance head. First, the development status and composition of the automatic test system, as well as the composition and working principle of the acoustic guidance head to be tested are introduced. Then the test method and principle are studied, and the overall design scheme of the test system is proposed based on the purpose and requirements of developing a certain type of acoustic guidance head automatic test system.

1 Introduction to acoustic guidance head
Sonar is a technical device that uses the propagation characteristics of underwater sound to sense and detect underwater targets. It is used to search, measure, identify and track submarines and other underwater targets, conduct underwater acoustic confrontation, underwater tactical communication, navigation and weapon guidance, support ships, tactical maneuvers of anti-submarine aircraft and the use of underwater weapons. The working principle of sonar is echo detection.
A certain type of anti-submarine homing torpedo acoustic guidance head adopts an active/passive combined acoustic homing method, and its homing system adopts an active and passive combined acoustic homing method. Its homing system mainly completes beam formation, transmits detection pulses, receives echo signals and performs signal processing, generates control commands, and memorizes the preset missile signals transmitted from the aircraft. The array consists of: underwater acoustic transducer transmitting array elements, receiving array elements, acoustic fuze array elements shared by the target sensor for receiving/transmitting, water entry sensor, and trigger sensor of the target sensor.

2 Overall design of the test system
2.1 Composition of the test system
The acoustic guidance head test system consists of a test bench, a transducer test device and cables. The connection diagram between the test system and the acoustic guidance head is shown in Figure 1.


(1) Composition of the transducer test device
Array, fixed bracket fixture, simulated water entry circuit, relay board, receiving and transmitting circuit, water entry sensor test circuit.
(2) Composition of the test bench
Cabinet, PXI host box, main control machine, display and interface board, AD board, power board (27V power supply), cable. [page]

2.2 Detection principle and method
2.2.1 Water entry sensor test
The water entry sensor test completes the test of the transmitting transducer and receiving transducer of the homing head. The main control machine is used to control the water entry sensor relay of the transducer test device to conduct, and the two pairs of contacts of the water entry sensor of the acoustic homing head are short-circuited. The change in resistance value can be measured at the plug. The change in resistance value can be used to determine whether the installation position of the homing head test device and the homing head is correct.
2.2.2 Test of the acoustic homing head transceiver array element
(1) Test of the acoustic homing head transmitting array element
The receiving transducer of the transducer test device is connected to the transmitting transducer of the acoustic homing head. When the homing head needs to transmit, the relay card connects the transmission power signal of the specified frequency to each transmitting transducer of the homing head in turn, and transmits sound waves. The transducer test device converts the sound signal of the corresponding receiving channel into an electrical signal in turn, and the A/D board converts the analog quantity into a digital quantity. By processing the collected data, the signal frequency, amplitude and other information are obtained, and the corresponding test results are obtained by comparing with the technical specification data.


(2) Test of the receiving array element of the self-guided head
The transmitting transducer of the transducer test device and the receiving transducer of the acoustic guidance head are connected. The relay card sequentially connects the transmitting power signal of the specified frequency to each transmitting transducer of the transducer test device to transmit sound waves. The acoustic guidance head receiving transducer converts the sound signal of the corresponding receiving channel into an electrical signal in turn, and the A/D board converts the analog quantity into a digital quantity. By processing the collected data, the signal frequency and amplitude information are obtained, and the corresponding test results are obtained by comparing with the technical specification data.
2.2.3 Test objectives of target sensor
(1) Detect whether the target sensor can be powered on normally;
(2) Detect whether each array element of the acoustic fuze can normally transmit the acoustic detection signal;
(3) Detect whether each array element of the acoustic fuze can normally receive the acoustic echo signal;
(4) Detect whether the acoustic fuze can respond correctly to the four working modes.
The target sensor test completes the test of the target sensor power-on and four working modes. After the test device receives the detection pulse emitted by the transmitter, it is triggered to work and imitates the echo to complete the test of the four working modes of the acoustic fuze.

3 Test system hardware design
3.1 Hardware composition
(1) Cabinet
A standard 31U cabinet is selected, with an overall size of (600 L×600 W×1 600Hmm).
(2) Chassis
The N1 company PXI-1036 6-Slot 3U standard chassis is selected.
(3) Main controller
The NI company 2GB DDR2 RAM for PXI-8101/08/10 andPXIe-8108 Controllers main controller is selected.
(4) AD board The
AD board uses the NI company PXI bus 6259 card, with a conversion accuracy of 14 bits, an input signal voltage range of -5 V to +5 V, and provides 8 I/O ports. According to the detection settings, the 7 receiving channels of the acoustic guidance head, 17 receiving channels of the transducer test device, and 8 receiving channels of the transducer test device acoustic fuse can be selected through the relay card, and the receiving signals of each channel are collected in time. The sampling rate is more than 3 times the frequency of the sampled signal. The input signal voltage range of each channel is -5 V to +5 V. [page]

(5) Power board
The external input power of the entire test system is only: single-phase 220 V/50 Hz. Power supply voltage: +27 V±5%, power supply current not less than 10 A.
3.2 Signal isolation circuit
3.2.1 Digital signal isolation circuit
Among all the digital signals extracted by the tested extension, the digital signal with the highest rate comes from the interface extension, which reaches 250 k/s. Therefore, we use the 6N137 high-speed optocoupler with a maximum rate of 10 M/s to isolate the digital signal required for the test, thereby ensuring the accuracy and reliability of the test system.
The signal is input from pins 2 and 3, the light-emitting diode emits light, and is transmitted to the photosensitive diode through the on-chip channel. The reverse-biased photosensitive tube is illuminated and sent to one input end of the AND gate and the other enable end of the AND gate. When the enable end is high, the AND gate outputs a high level, and after the output transistor is reversed, the optoelectronic isolator outputs a low level. When the input signal current is less than the trigger threshold or the enable end is low, the output is a high level, but this logic high is an open collector, and a pull-up resistor or voltage adjustment circuit can be added to the receiving circuit. TTL level input, when Vcc1 is 5 V, RF can be selected to be about 500 Ω. If no current limiting resistor is added or the resistance is very small, 6N137 can still work, but the light-emitting diode conduction current is very large, which has a great impact on Vcc1, especially when the digital waveform is steep, the spectrum of the rising and falling edges is very wide, which will cause considerable spike pulse noise, and the distributed inductance of the printed circuit board usually makes the ground line unable to absorb this noise, and its peak-to-peak value can reach more than 100 mV, which is enough to make the analog circuit self-excited and the A/D cannot work properly. So if possible, RF should be as large as possible. The output end is powered by the module, Vcc2 = 4.5 ~ 5.5 V, and a 0.11μF capacitor with good high-frequency characteristics must be connected between Vcc2 (pin 8) and ground (pin 5), and it should be placed as close to pins 5 and 8 as possible. This capacitor can absorb the ripple on the power line and reduce the impact on the power supply when the switch of the receiving end of the optoelectronic isolator is working. Pin 7 is the enable terminal. When it is between 0 ~ 0. When the output is 8 V, it forces the output to be high (open circuit); when it is 2.0 V ~ Vcc2, the receiving end is allowed to work. Pin 6 is
the collector open circuit output terminal, and a pull-up resistor RL is usually added. Although the current can reach 13 mA when the output is low, the resistance value should still be selected according to the needs of the subsequent input circuit. Because too small a resistance will increase the power consumption of 6N137, increase the impact on the power supply, and make the bypass capacitor unable to absorb it, thereby interfering with the power supply of the entire module and even bringing spike noise to the ground line. Generally, a few hundred ohms can be selected. If the subsequent stage is a TTL input circuit and there are only 1 to 2 loads, 47 kΩ or 15 kΩ can also be used. Combined with the working principle of the 6N137 optocoupler, we give the digital signal isolation circuit and its peripheral configuration as shown in Figure 3.


The pull-up resistor at the output end of the isolation circuit is generally from a few hundred ohms to a few thousand ohms. In general, the higher the signal rate, the lower the resistance value. This design takes 350 Ω. After experiments, it is confirmed that the design can meet the test requirements.
3.2.2 Analog signal isolation circuit
In the analog signal isolation circuit, we use the precision linear light FIL300 of Texas Instruments. TIL300 is composed of an isolated feedback photodiode and an output photodiode. The device uses special manufacturing technology to compensate for the nonlinearity of the LED time and temperature characteristics, so that the output signal is linearly proportional to the servo light flux emitted by the LED. It has a peak isolation of 3500 V and high transmission gain stability (0.05%/℃). Figure 4 shows the analog isolation circuit diagram.


The main problem of TIL300 application is to select a suitable preamplifier and calculate the resistance values ​​of R1, R2, and R3 in the circuit within the linear range of work.
Establish the working state of TIL300
TIL300 works in current mode. According to the parameter table given by the device, the working current of its light-emitting tube LED should work in the range of 1 to 10 mA. Within this range, the servo current gain K1, that is, the servo current transmission ratio is 0.7% to 1.25%, and the forward current gain K2, that is, the positive current transmission ratio is 0. 7%～1.25%, so the transmission gain of TIL300 is 1.

4 Test system software design
As an important part of the entire test system, the software has a good human-computer interface, which can easily set test conditions, select test items and other information. If the test result items and other information are available, it can provide accurate fault diagnosis strategies and record, display and print test results.
4.1 Functions of the test system software
(1) Provide a human-computer interaction interface.
(2) It has the functions of hardware startup, initialization self-test, test instruction issuance and hardware control instruction issuance.
(3) It has the function of monitoring various states returned by the product under test.
(4) It has the function of performing statistical calculations on the test data read.
(5) It has the function of converting test data into visual images and drawing them into curves.
(6) It has the function of providing intuitive data result display for the user interaction layer.
(7) It has the functions of storage, query, report, printing and backup of test data. [page]

4.2 Software overall process



5 Electromagnetic compatibility
Electromagnetic compatibility is one of the important performances of the test system. The electromagnetic compatibility design of the test system is an important guarantee for realizing the specified functions of the test system and giving full play to the effectiveness of the test system. Electromagnetic compatibility design is carried out while the test system function design is being carried out. The purpose of electromagnetic compatibility design is to enable the designed test system to achieve electromagnetic compatibility in the expected electromagnetic compatibility environment.
5.1 Electromagnetic interference sources of the test system
The electromagnetic interference sources of the test system come from two aspects: electromagnetic interference outside the test system; electromagnetic interference inside the test system.
(1) Coexistence of strong and weak signals;
(2) Interference from components such as transformers, relays, and switches;
(3) Common source and common ground interference between components;
(4) Other interference.
5.2 Analysis of electromagnetic coupling paths
Through analysis, the following paths can be determined as electromagnetic coupling paths of the test system:
(1) Conducted interference caused by the power supply;
(2) Common impedance interference generated by the grounding system;
(3) Signal crosstalk caused by distributed parameters between interconnects;
(4) Common mode emission interference caused by improper termination of interconnects and housings.
5.3 Electromagnetic interference suppression measures taken in the test system design
(1) Use different power supplies for sensitive circuits and interference circuits, and filter the switching power supply;
(2) When laying cables, separate the power line and signal line as much as possible, and separate the input and output ends.
(3) Install sensitive cables away from power supplies, transformers and other high-power devices.
(4) Use compatibility measures such as shielding, filtering and overlapping to reduce the interference of inductive coupling and capacitive coupling to an allowable level.
(5) Set up digital ground and analog ground according to circuit characteristics, and adopt a single-point grounding scheme.
(6) Take appropriate shielding measures for the shell of electrical circuit connectors.

6 Summary
Through the performance analysis of a certain type of anti-submarine self-guided torpedo acoustic guidance head, the overall design plan of the test equipment is proposed. The test principles and methods of each part of the acoustic guidance head are introduced, and the signal isolation circuit is introduced. The software part uses the object-oriented, visual design rapid application development software platform Labview to complete editing, compilation, connection and debugging. Finally, the electromagnetic compatibility design is proposed.