In this paper, the problem of electromagnetic interference in windshield heating controller of a certain type of aircraft is analyzed, and a simple and effective solution to electromagnetic interference is proposed. Aircraft uses a large number of electronic and electrical equipment. Electromagnetic compatibility directly affects the function and performance of the aircraft and its systems. When testing the function of the windshield heating system, the main windshield heating channel on the left side can not work properly.
After investigation, it is found that the design of the windshield heating controller (WHC) is unreasonable and sensitive to the magnetic field on the aircraft. By analyzing the electromagnetic environment to determine the interference source and the interference equipment to determine the sensitive components, the problem was solved smoothly. The problem windshield heating system consists of windshield heating controller, windshield heating film, windshield temperature sensor, circuit and control switch. The heating film and temperature sensor are embedded in the glass.
Each machine is equipped with two windshield heating controllers.
Each windshield heating controller has two independent channels. Channel 1 controls the heating of the main windshield and channel 2 controls the heating of the ventilation window. The heating power supply is 3-phase 115V AC, the heating film of the main windshield is connected by_type, and the ventilation window is connected by Y type. As shown in Figure 1 below.
When the windshield heating system is tested on the ground, it is found that all the windshield heating controllers can work normally when installed on the right side; after the windshield heating controllers are installed on the left side, the main windshield heating accident is reported, and the heating passage of the ventilation window is not reported. The fault of windshield heating system is closely related to the installation position of windshield heating controller.
Preliminary judgment, the windshield heating controller installed to the left side, in its installation position was subject to electromagnetic interference. The purpose of electromagnetic environment analysis is to find possible sources of interference. When the aircraft is electrified, the electromagnetic field near the installation position of the left and right windshield heating controller is measured. The results (fig. 2) show that there are differences between the left and right sides of the electromagnetic field. Especially in the frequency band of 400 Hz (note: AC on the machine is 400 Hz), the field intensity on the left side is obviously higher than that on the right side. On-the-spot inspection found that the installation position of the left windshield heating controller is less than 1 meter away from the power supply cable in the power supply center, which inevitably produces interference magnetic field. In addition, the direction of AC cable of windshield heating system itself is unreasonable. The cable is almost attached to the left windshield heating controller.
When the windshield heating system works normally, the heating current can reach 24A, and the interference caused by it can not be ignored. One of the functions of the windshield heating controller is to monitor the heating current. The main component of the heating current monitoring circuit in the windshield heating controller is Hall sensor. Hall sensor is integrated by Hall element (sensitive to magnetic field) with amplifier circuit, temperature compensation circuit and regulated power supply circuit. As shown in Fig. 1, in the main windshield heating channel, the heating current monitoring circuit monitors the line current of the_-type load. If an undercurrent or overcurrent is detected in the system, the windshield heating controller will cut off the heating circuit and output the system fault warning signal. Because the warning threshold is too narrow, after the external magnetic field is superimposed on the Hall sensor, the magnetic flux detected by the Hall sensor reaches the warning threshold, thermostatic element resulting in the windshield heating system can not continue to work properly. In view of the above analysis, three aspects can be considered to solve the interference problems: (1) shielding the interference magnetic field, that is, reducing the magnetic field intensity of the installation location of the interfered equipment; (2) improving the anti-interference ability of the interfered equipment; (3) keeping the interfered equipment away from the interfering source. Magnetic shielding is a complex matter.
It is usually shielded by high permeability materials (mainly nickel alloys) around interference sources. The main purpose of this method is to change the direction of the magnetic field.
Shielding measures may have adverse effects on other onboard equipment and increase the weight of the aircraft significantly. If we consider installing the windshield heating controller in a magnetic shielding container, it is not conducive to the heat dissipation of the windshield heating controller. The measures of shielding magnetic field are not suitable for aircraft. Improve the anti-interference ability of windshield heating controller of magnetic interference sensitive equipment.
Adjust the parameters of Hall sensor, relax the alarm threshold of undercurrent and overcurrent appropriately within the allowable range, and adjust the position of sensor in the windshield heating controller, or select the current monitoring element insensitive to external disturbance magnetic field to replace Hall sensor. Keep the interfered equipment away from the interfering source. The windshield heating controller is arranged in the area where the magnetic field is weak in the magnetic field environment, and the direction of the windshield heating system cable is reasonably arranged. The internal design of the windshield heating controller was improved, and the installation position of the windshield heating controller was adjusted. The fault was eliminated. By solving the electromagnetic interference problem of windshield heating controller, a set of simple and effective solutions to the electromagnetic interference problem are found, that is, to analyze the electromagnetic environment to determine the interference source, to analyze the interference equipment to determine the sensitive components, and to determine the solutions around the interference source and sensitive components.