EMC problems are often a reason for restricting the export of Chinese electronic products. This article mainly discusses the sources of EMI and some very specific methods of suppression.
Electromagnetic compatibility (EMC) is the performance of a device, device, or system that allows it to function properly in its own environment without simultaneously causing strong electromagnetic interference to any other device in the environment (IEEE C63.12- 1987) "For wireless transceivers, the use of non-continuous spectrum can partially achieve EMC performance, but many related examples also show that EMC is not always able to do so. For example, high-frequency interference occurs between laptops and test equipment, between printers and desktop computers, and between cellular phones and medical instruments. We call this interference electromagnetic interference (EMI).
EMC problem source
All electrical and electronic equipment will have intermittent or continuous voltage and current changes, sometimes at a relatively fast rate, which will result in electromagnetic energy being generated at different frequencies or between one frequency band, and the corresponding circuit will emit this energy. Go to the surrounding environment.
EMI has two ways to leave or enter a circuit: radiation and conduction. Signal radiation is leaked through the slots, slots, openings, or other indentations in the housing; signal conduction is free to radiate in the open space by coupling to the power, signal, and control lines, causing interference.
Many EMI suppressions are achieved by a combination of shielded and gap-shielded shields. Most of the following simple principles can help achieve EMI shielding: reduce interference from the source; isolate and isolate the interference by shielding, filtering or grounding. Anti-interference ability of sensitive circuits, etc. EMI suppression, isolation, and low sensitivity should be the goal of all circuit designers, and these should be done early in the design phase.
For design engineers, the use of shielding materials is a way to effectively reduce EMI. A wide variety of housing shielding materials are now available, ranging from metal cans, sheet metal and foil strips to spray coatings and coatings on conductive fabrics or tapes (such as conductive paints and zinc wire coating). Whether it is metal or a plastic coated with a conductive layer, once the designer has determined that it is the outer casing material, it is time to start selecting the liner.
Metal shielding efficiency
The suitability of the shield can be evaluated using the shielding efficiency (SE). The unit is decibel and the formula is:
SEdB=A+R+B
Where A: absorption loss (dB) R: reflection loss (dB) B: correction factor (dB) (for multiple reflections in a thin shield)
A simple shield reduces the intensity of the generated electromagnetic field to one tenth of the original, ie SE equals 20 dB; in some cases it may be required to reduce the field strength to one of the original one hundred thousandth, ie SE is equal to 100dB.
Absorption loss refers to the amount of energy loss when electromagnetic waves pass through the shield. The absorption loss is calculated as:
AdB=1.314(f&TImes;σ&TImes;μ)1/2&TImes;t
Where f: frequency (MHz) μ: magnetic permeability of copper σ: conductivity of copper t: thickness of the shield
The magnitude of the reflection loss (near field) depends on the nature of the electromagnetic wave generation source and the distance from the wave source. For a rod-shaped or linear transmitting antenna, the closer the wave source is to the wave resistance, the higher the distance, and then the distance from the wave source decreases, but the plane wave resistance does not change (constantly 377).
Conversely, if the source is a small coil, then the magnetic field will be dominant, and the closer the wave source is, the lower the wave resistance will be. The wave resistance increases as the distance from the wave source increases, but when the distance exceeds one-sixth of the wavelength, the wave resistance no longer changes and is constant at 377.
The reflection loss varies with the ratio of the wave resistance to the shielding impedance, so it depends not only on the type of wave but also on the distance between the shield and the source. This applies to small shielded devices.
Near field reflection loss can be calculated as follows:
R (electric) dB = 321.8 - (20 & TImes; lg r) - (30 × lg f) - [10 × lg (μ / σ)]
R (magnetic) dB = 14.6 + (20 × lg r) + (10 × lg f) + [10 × lg (μ / σ)]
Where r: the distance between the source and the shield.
The last term of the SE formula is the correction factor B, which is calculated as:
B=20lg[-exp(-2t/σ)]
This formula is only suitable for near-field environments and where the absorption loss is less than 10 dB. Since the absorption efficiency of the shield is not high, the internal re-reflection increases the energy passing through the other side of the shield layer, so the correction factor is a negative number, indicating a decrease in the shielding efficiency.
A Battery Charger supplies current to the base plate. Once the AGV is in charging position and the collector has made contact with the base plate, the AGV computer turns on the current.
The base plate has chamfered entry/exit ramps to facilitate smooth drive-on/drive-off of the spring loaded collector.
Battery charging stations may be installed anywhere within the system where the production process allows the AGV to stop (staging areas, turn arounds, loading stops etc.).
2 Phase Battery Charging Contacts,2 Phase 200A Charging Contacts,200A Battery Charging Contact,2 Phase Charging Contacts
Xinxiang Taihang Jiaxin Electric Tech Co., Ltd , https://www.chargers.be