机载测控计算机的电磁兼容设计

以某机栽测控计算机为例,介绍了电磁兼容设计过程及主要的电磁干扰源和耦合途径;分析、预测了机载测控计算机工作的电磁环境及电磁兼容性;找出了干扰源,并针对不同干扰源提出了相应的电磁兼容设计方法;给出了某电路电磁兼容设计前后性能指标测试曲线。比较结果说明：机载测控计算机电磁兼容性设计合理,工作稳定可靠。该方法适用多种电子设备的电磁兼容设计。

Implementable Design of Electromagnetic Compatibility in Airborne Computer for Measurement and Control in UAV

In order to ensure proper functioning of airborne computer for measurement and control, the heart of UAV (Unmanned Aerial Vehicle), the design of its electromagnetic compatibility (EMC) in complicated electromagnetic environment is very difficult but must be tackled. We aim to provide such design through theoretical analysis and reanalysis coupled with much laboratory testing and several hundred hours of flight tests. Our design must meet the stringent requirements of U.S.MIL-STD-461. Northwestern Polytechnical University has designed, built, and operated many UAVs, ranging from 15kg to 185kg. In this paper we concentrate on the 85kg UAV. First we analyze the electromagnetic environment. There are many interference sources around the airborne computer for measurement and control, such as high power radio transmitter, receiver, engine, power, all kinds of relays and crystal oscillators in other electronic equipment, etc. The radio transmitter is the biggest interferer in them. Then, complying with the requirement that immunity margin (IM) be above zero, we explain how to work out an implementtable plan to suppress electromagnetic interference (EMI). Our explanation is divided into five parts: (1) choice of CPLD (complex programmable logic device), whose working frequency range is 50~70MHz, and SMD (surface mount device) as active and passive device respectively; (2) design of multilayer printed wiring board according to the "grounding, bonding and decoupling" rule; (3)filtering and photocurrent isolation of interfering signals of different frequencies; (4) screening, which includes RF(radio frequency) cable shield and partial screens for parts;(5)programs in ROM of airborne computer for measurement and control to deal with unexpected faults caused by interference, thus making the computer more robust against interference. Our EMC design of computer was tested in laboratory and then in hundreds of hours of flight test. Without EMC design, the computer was badly affected by EMI. With EMC design the airborne computer could satisfy the five requirements of U.S.MIT-STD-461: CE03 (15 kHz~50 MHz); CS01~02(25 kHz~400 MHz); RS03(14 kHz~1 GHz); CS06(25~50 kHz); RE02 (14 kHz~10 GHz).