Research on the Parameter Detection System of Aero-engine Test Based on PC104

The aircraft engine is the core component of the aircraft and the power source of the aircraft. The maintenance quality of the aircraft engine directly affects the use of the aircraft and even affects the flight safety of the aircraft. During the life of the aircraft engine, in order to ensure flight safety, it is required to test the aircraft engine regularly and check the performance of the engine. There are pointer instruments in the cockpit that display the test parameters, but it is inconvenient to observe, the accuracy is not high, and the human error is large. In addition, the maintenance personnel reported that when the engine is tested, a large number of parameters need to be recorded, especially when the engine is tested for failure, the test data needs to be analyzed, which makes the test time long and the data recording and analysis processing very inconvenient. These shortcomings are very incompatible with the requirements of modern high-tech warfare and cannot meet the maintenance requirements of the field. This test parameter detection system is based on PC104 bus technology, which can detect, display, store and print the main technical parameters of the engine test process in real time, so that the maintenance personnel can accurately analyze, judge and eliminate engine failures and improve the reliability of engine use. At the same time, it can greatly shorten the maintenance time, save manpower and material resources, and make the engine maintenance more scientific and targeted.

1 Design foothold

1.1 Ensure reliability

During the development of the system, we always pay attention to its reliability and safety. For outsourced equipment, we ask the supplier to meet the reliability requirements of the GJB standard. The supplier provides complete product certificates, operating and maintenance instructions and other documentation materials, and signs a contract to ensure the reliability of the outsourced equipment. The software and hardware design is carried out strictly in accordance with the design specifications and reliability outline. Electromagnetic isolation sensors are used. The signal input and output ends and power supply of the sensors are isolated. No circuits are added to the instruments on the aircraft, and the original instruments can work normally. When the system and the aircraft are connected, even if the test instrument does not work or does not work properly, the original instruments on the aircraft can work normally.

1.2 Ensure operability

The system was developed with a people-oriented design philosophy, fully taking into account the requirements of maintenance personnel. It has a high degree of intelligence, a good human-machine interface, simple operation, and easy use, and has good operability.

1.3 Ensuring Interchangeability

The interchangeability of components is fully considered in the system design, and standard and versatile components are selected as much as possible. For military products, aviation products are selected as much as possible to ensure that the equipment has good interchangeability and is easy for maintenance personnel to maintain.

1.4 Ensure accuracy

Ensuring accuracy is the design concept that is always adhered to during the development of the system. The following methods are mainly adopted in the development: First, high-precision sensors are selected to ensure that the accuracy of the collected signals can meet the test requirements; second, software filtering methods are used to filter out interference data to ensure the accuracy of the collected data; third, hardware design ensures accuracy, and data collection does not affect the normal operation of on-board sensors and instruments, ensuring that the collected data is true and accurate.

2 Features and functions

The aircraft engine test parameter detection system is a device developed based on the reference of foreign ground detection equipment. It uses PC104 bus industrial computer and EL screen display, which makes the detection system small in size, light in weight, easy to move, simple to operate, high in automation, good in reliability, rich in display information, good in human-machine interface, etc. It can fully detect the engine performance parameters displayed in the cockpit, and its accuracy is higher than that of cockpit pointer instruments.

The system functions include: 1) Real-time detection and display of the engine's high and low pressure rotor speed, engine vibration speed, lubricating oil pressure, lubricating oil temperature, main and auxiliary oil channel fuel pressure and exhaust temperature; 2) Real-time drawing of test curves; 3) Saving test parameter data; 4) After the test, the data and test curves of each parameter during the test can be viewed; 5) The test instrument communicates with the computer data, and the data of each parameter during the test is transmitted to the computer. The maintenance personnel can view the data of each parameter on the computer for analysis and troubleshooting.

3. Structural composition and working principle

The design concept of the test parameter detection system is to use the original sensors of the aircraft without affecting the normal operation of the aircraft instruments and ensuring the safe and reliable operation of the engine. The work of the detection system does not affect the normal operation of the maintenance personnel. When in use, the engine test is carried out according to the ground detection program. This system includes various sensors, controllers, data acquisition cards, detection circuits, keyboards, power supplies and display screens. The detection principle is shown in Figure 1.

During the test run, the high and low pressure rotor speed analog signals, vibration speed analog signals, lubricating oil pressure analog signals, lubricating oil temperature analog signals and exhaust temperature analog signals output by the engine are led out from the aircraft connection plug, and the analog signals of each parameter are isolated and converted into DC voltage signals through the detection circuit. The fuel pressure transmitters of the main and auxiliary oil channels are connected to the measuring joints on the main and auxiliary oil transfer rings of the fuel. The pressure transmitter senses the oil pressure changes and outputs a DC voltage signal proportional to the fuel pressure of the main and auxiliary oil channels. These DC voltage signals are converted into digital quantities through the data acquisition card and sent to the controller. The values ​​of each parameter are calculated by the program in the controller. The controller stores the detected data in the data storage device through program control, and displays the test data and test curves of each parameter on the EL display screen.

The controller is the core part. Its main function is to read the data corresponding to each parameter from the data acquisition card according to the user program, calculate the actual value of each parameter and store it in the data storage device; control the EL flat panel display to display the human-computer interaction interface, the test data of each parameter, the test curve, etc. It uses the embedded industrial computer with PC104 bus produced by Shengbo Technology Co., Ltd., the model is SysCentreModule/SDXpn. Its main technical data are: 1) Embedded 486 processor, operating frequency 50MHz; 2) 16M bytes of RAM; 3) 1M video memory; 4) Standard DMA, interrupt timing controller; 5) Industrial standard BIOS with extension; 6) VGA supports monochrome LCD, EL display, and analog CkT; 7) Support DOC electronic disk; 8) Power supply requirements: +5V ±5%, 0.8A; 10) Working environment temperature: -40～+80℃.

The data acquisition card completes the acquisition of analog signals of various parameters. It uses the multifunctional data acquisition card PM511P with PC104 bus produced by Beijing Zhongtai Yanchuang Computing Technology Co., Ltd. It has 16 A/D conversion channels, 4 D/A channels, 24 programmable switch input and output, 3 counting channels, and can work under the environmental conditions of -40～+80℃. In addition, the acquisition card also completes the acquisition of keyboard signals.

The power supply is used to convert the 27V DC power of the airport into +5V, ±12V, +24V DC power required by the system's internal circuits. Two DC-DC converters are used to convert the 27V DC power into +12V, -12V, +24V and +5V DC power required by PC104 and other electrical components. It has high conversion accuracy and can work stably in an environment of -40 to 55°C.

The EL display screen is used to display prompt characters during human-computer interaction, data of various parameters detected, test curves, etc. The model used is EL640.480-AGI-ET. Its main technical parameters are: 1) Resolution: 640×480; 2) Size: 8.1 inches; 3) Power supply: 12V; 4) Operating temperature: -40～+85℃.

The DOC electronic disk is used to store the parameter data detected during the test run, and is also used to store the operating system files of the controller, the control program files of the instrument, etc. The capacity of the DOC electronic disk is 128M. The keyboard uses a simple switch-type keyboard, and the keyboard signal is sent to the industrial computer of the PC104 bus through the data acquisition card.

The keyboard on the panel is used for human-computer interaction and inputting commands and data into the controller. It has 6 keys and uses a simple switch-type keyboard. The keyboard signal enters the controller through the data acquisition card. The interface is simple, convenient and applicable.

4. Detection circuit design

The function of the detection circuit is to convert the current, voltage and frequency signals that can reflect the size of each parameter into a 0-5V DC voltage signal that can be picked up by the data acquisition card.

4.1 Speed ​​detection circuit design

The principle of engine speed detection is shown in Figure 2. The isolated voltage sensor isolates the output signal of the speed sensor and outputs a -5v~+5V voltage signal proportional to the voltage of the output frequency signal of the speed sensor. The output signal is filtered by the filter circuit to filter out the high-frequency interference signal, and then the output signal is converted into a standard 5V square wave signal by the shaping circuit and the frequency is kept unchanged. The frequency of the 5V square wave signal is measured by the single-chip microcomputer and the engine speed is obtained by calculation, and the digital quantity proportional to the speed is output to the D/A converter. The D/A converter converts the digital quantity proportional to the speed into a 0~5V DC voltage proportional to the speed, and then sends it to the data acquisition card. After A/D conversion in the data acquisition card, it becomes a digital quantity and is then sent to the controller. The actual value of the speed can be obtained by calculation in the controller. [page]

4.2 Vibration velocity detection circuit design

The dotted box above in Figure 3 shows the working principle of the original vibration speed detection device on the engine. The electronic combination in the figure is used to sense the weak AC voltage signal output by the two vibration speed sensors of the engine, and then convert it into a DC voltage signal, and then send it to the vibration indicator for indication.

The dashed box below in Figure 3 represents the engine vibration speed detection circuit. The DC voltage signal corresponding to the vibration speed sent to the vibration indicator is led out to the vibration speed detection circuit. The isolation voltage sensor isolates the DC voltage signal corresponding to the vibration speed, outputs a proportional DC voltage signal, and then filters out the high-frequency interference signal through a filter, and finally sends it to the data acquisition card. After A/D conversion in the data card, it is converted into a digital quantity and then sent to the controller. The actual value of the vibration speed can be obtained through calculation in the controller.

4.3 Design of lubricating oil pressure detection circuit

In Figure 4, the left dotted box indicates an oil pressure sensor, and the right dotted box indicates an oil pressure gauge, which constitute the original oil pressure detection device on the aircraft. The oil pressure determines the displacement of the movable armature in the oil pressure sensor, and the displacement of the movable armature determines the inductive reactance of the two coils. The change of the inductive reactance of the two coils changes the current change of the two wire frames of the flow ratio meter of the oil pressure gauge, and the current ratio i1/i2 of the two wire frames corresponds to the oil pressure one by one. The oil pressure gauge is a current ratio meter. Its pointer deflection angle corresponds to the current ratio i1/i2 one by one, that is, a certain oil pressure corresponds to a certain oil pressure indication value.

If the oil pressure is determined by detecting the current ratio of the two wires, the original oil pressure gauge on the aircraft will be destroyed, which is obviously not allowed. Through theoretical analysis, it is found that the current ratio I1/I2 of the two wires connecting the oil pressure sensor and the oil pressure gauge corresponds to the current ratio i1/i2 of the two wires of the oil pressure gauge flow ratio meter. Therefore, the oil pressure is determined by measuring the current ratio I1/I2 of the two wires connecting the oil pressure sensor and the oil pressure gauge.

The middle dotted box in Figure 4 represents the oil pressure detection circuit. The isolated current sensor converts the current signal of the two connecting lines of the oil pressure sensor and the oil pressure gauge into a DC voltage signal, and then adjusts the voltage signal output by the isolated current sensor to a 0-5V DC voltage signal that can be recognized by the controller through the proportional amplifier circuit and sends it to the data acquisition card. After being converted into a digital quantity by D/A in the data acquisition card, it is sent to the controller, and the actual value of the oil pressure can be obtained through calculation in the controller.

The relationship between the pulsating DC current I1 and I2 on the two wires connecting the lubricating oil pressure sensor and the lubricating oil pressure gauge and the output voltage of the corresponding isolation current sensor is u1=0.1×l1, u2=0.1×l2. The range of I1 and I2 is 0~50mA, and the output voltage of the isolation current sensor is 0~5V. The relationship between I1/I2 and lubricating oil pressure is shown in Table 1.

5 Conclusion

The aircraft engine test parameter detection system is an important equipment for field engine maintenance and has been delivered for use. According to the feedback, the system has the characteristics of small size, light weight, easy to move, high degree of automation, easy operation and convenient field use. The application of this system avoids repeated disassembly and replacement of parts and repeated test runs during the troubleshooting process, saving time, manpower and material resources, reducing engine wear, and increasing the service life of the engine. It greatly improves the efficiency of maintenance work, saves maintenance costs, and will bring great economic benefits to users.