n Active lighting system, which is powered by mains supply.
n Backup lighting system, which is powered by backup power supply (diesel electric generator) of the office.
n Emergency lighting system, which is powered by storage batteries when the mains supply has been interrupted but the backup power supply has not yet started to supply power.
A.11 Protection System
1. ESD protection
The equipment-affecting electrostatic induction comes either from the external electric field such as outdoor high voltage transmission line or lightning, or from the internal system such as indoor environment, floor materials and equipment structure.
Static electricity may damage the chips on integrated circuit boards and cause faults in software and electronic switch. Statistics shows that 60 percent of the damaged circuit boards are caused by static electricity. It is essential to take effective ESD protection measures.
The following measures are recommended:
n Ground the equipment well. While laying the raised floor covered with semiconductive materials, copper foil should be used for grounding at a number of points on the floor (the copper foil should be placed between the cement ground and the semiconductive floor and should be connected with the grounding cable).
n Take dust-proof measure. Dust may do great harm to the optical synchronous transmission equipment. Dusts or other particles getting into the equipment room may cause poor connection between connectors or metal connecting points. When the humidity in the room is high, dust can cause electrical leakage. It is found in maintenance that the equipment failure is often caused by accumulated dusts. Especially when the humidity in the room is very low, electrostatic adherence is likely to occur.
n Keep proper temperature and humidity. Too high a humidity may make the metal components rusty, while too low a humidity may induce static electricity.
n Always wear an ESD-preventive wrist strap and lab coat when touching a circuit board to prevent electrostatic damage to the equipment.
2. Interference prevention
With the development of technologies and social economy, more and more electromagnetic signals are transmitted in the air. They may affect the communication quality by causing cross-talk and stray noise, and even result in communication interruption. The electromagnetic interference (EMI) sources include:
n The corona discharge of the electric transmission line
n The transformer
n Switches
n Waveform distortion of the power supply network caused during the operation of large equipment
n Radio frequency (RF) interference
n Natural interference sources such as terrestrial magnetic field and external radiation.
The interference, from either inside or outside the equipment or the application system, affects the equipment through conductive modes such as capacitance coupling, inductance coupling, electromagnetic wave radiation, common impedance (including grounding system) and cable (power and signal cables). In terms of external relations of the equipment, interference is from the signal cable, power cable, grounding system and spatial electromagnetic wave.
Integrated circuits (ICs) have the interference resistance capability to a degree. However when the external noises go beyond their anti-interference tolerance, corrupted signals and even system malfunction will be caused. It is impossible to eliminate or shield all the interference sources, but the following measures can be taken to suppress the interference signals.
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