參數(shù)資料
型號: RS-422
廠商: Electronic Theatre Controls, Inc.
英文描述: RS-422 AND RS-485 APPLICATION NOTE
中文描述: RS - 422和RS - 485接口應(yīng)用筆記
文件頁數(shù): 30/44頁
文件大?。?/td> 628K
代理商: RS-422
RS-422/485 Application Note
27
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350
PH (815) 433-5100 -- FAX (815) 434-7094
Vcc
Port
Device
Data Lines
Local Chassis Ground Connection
Ground line
Figure 4.5 RS-485 Device with Signal Ground
Connected to Chassis Ground
Transient protection using Isolation
Isolation Theory
The most universal approach to protecting against transients is to
galvanically isolate the data port from the host device circuitry. This method
separates the signal reference from any fixed ground. Optical isolators,
transformers and fiber optics are all methods commonly used in many types of
data networks to isolate I/O circuitry from its host device. In RS-422 and RS-
485 applications, optical isolators are most common. An optical isolator is an
integrated circuit that converts the electrical signal to light and back,
eliminating electrical continuity. With an isolated port, the entire isolated
circuitry floats to the level of the transient without disrupting data
communications. As long as the floating level of the circuitry does not exceed
the breakdown rating of the isolators (typically 1000 - 2500 volts) the port will
not be damaged. This type of protection does not attempt to absorb or shunt
excess energy so it is not sensitive to the length of the transient. Even
continuous potential differences will not harm isolated devices. It is important
to note that isolators work on common mode transients, they cannot protect
against large voltage differences between conductors of a data cable such as
those caused by short circuits between data and power circuits.
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