The solution includes digital ammeter, digital voltmeter, switch, circuit breakers, control and protection unit, mutual inductor, contactor and other components. Among them digital ammeter, digital voltmeter, switch, circuit breaker are arranged on the front panel of the case. Control and protection unit, mutual inductor, contactor and other components are arranged in case. This equipment should meet the requirements of electromagnetic compatibility indexes, The main measures are taken in the structural design are that shielding the instrument window; shielding the aperture of the case. Each unit reasonable layout and be shielded; cables and power filter, etc.
1. Shielding the aperture of the case
The main factor of influence shielding integrity is the seams of the shielding enclosure. This vehicle electronic equipment is made up of bending butt weld aluminum frame, weld smooth continuous, belongs to the permanent juncture, the radio-frequency resistance of this juncture is similar to the metal plate itself to ensure the electrical continuity at the shields. For the demountable juncture, such as case, locations at the plate, often using screw fastening way, as for the screw spacing should not be too small, the surface not leveling and cover plate material warping deformation and other reasons, make joints place produced inevitably aperture, reduce the chassis shielding effectiveness. We take the two methods to solve the problem: increasing depth pf gap, the chassis curved edge width take 15 mm in order to increase the crack depth, the larger overlapping size, the better shielding effectiveness. Reduce the length of gap, because sheet metal case is hard to do joints in high precision, in order to make up for the defect, the economic and practical method is paste the glue stick back beryllium bronze reed in joints place, because the mechanical spring has certain flexibility, the mechanical spring will deformation, interface will produce some pressure to make joints certain electrical with continuous.
2 Layout and shielding for case internal unit
Reasonable decorate equipment in each unit and the component position can reduce interference degree in economical and practical way. First we must know perfectly about the interference sources and the sensor, in this equipment interference source is control protector, sensitive equipment is digital ammeter and voltmeter, in order to avoid them close, they were placed in the case at the back and front, use the space distance between them to reduce the electromagnetic interference. In order to achieve a more effective shielding effect, put the current, the voltmeter watch into two singled shielded boxes , header of the panel next to shield glass, screws connected glass screen outside the metal, case and shielding box together, thus make table body completely in the electrical continuous metal mask, however the lead of the current, voltmeter lead by the feed through capacitor which is packed in the box of shielding, so make the jamming signal that lead reacted was connected with ground. At the same time the controlling protector also was shielded by shielding box, further reducing the radiation energy to get a better shielded effect.
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