參數(shù)資料
型號(hào)： RS-485
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(yè)數(shù)： 31/44頁(yè)
文件大小： 628K
代理商： RS-485
28
RS-422/485 Application Note
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350
PH (815) 433-5100 -- FAX (815) 434-7094
Isolation Devices
Optical isolation can be implemented in a number of ways. If a conversion
from RS-232 to RS-422 or RS-485 is being made, optically isolated converters
are available. Optically isolated ISA bus serial cards can replace existing ports
in PC systems. For systems with existing RS-422 or RS-485 ports, an optically
isolated repeater can be installed. Examples of each of these type devices can
be found in the B&B Electronics Data Communications catalog.
Transient Protection using Shunting
Shunting Theory
Creating one common ground at the host device provides a safe place to
divert surge energy as well as a voltage reference to attach surge suppression
devices to. Shunting harmful currents to ground before they reach the data port
is the job of components such as TVS (often referred to by the trade name
Tranzorb), MOV or gas discharge tubes. These devices all work by “clamping”
at a set voltage, once the clamp voltage has been exceeded, the devices provide
a low impedance connection between terminals.
Since this type of device diverts a large amount of energy, it cannot tolerate
very long duration or continuous transients. Shunting devices are most often
installed from each data line to the local earth ground, and should be selected to
begin conducting current at a voltage as close as possible above the systems
normal communications levels. For RS-422 and RS-485 systems, the voltage
rating selected is typically 6 - 8 volts. These devices typically add some
capacitive load to the data lines. This should be considered when designing a
system and can be compensated for by derating the total line length to
compensate for the added load. Several hundred feet is usually an adequate
figure.
To apply these type products correctly they should be installed as close to
the port to be protected as possible, and the user must provide an extremely low
impedance connection to the local earth ground of the unit being protected.
This ground connection is crucial to proper operation of the shunting device.
The ground connection should be made with heavy gauge wire and kept as
short as possible. If the cable must be longer than one meter, copper strap or
braided cable intended for grounding purposes must be used for the protection
device to be effective. In addition to the high frequency nature of transients,
there can be an enormous amount of current present. Several thousand amps
typically result from applications of the combination wave test in the ANSI and
IEC specification.
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
RS485-232 制造商:PR 功能描述:
RS485-C1(AS) 制造商:未知廠家 制造商全稱:未知廠家 功能描述:RS232/RS485 CONV (AS)
RS485-C1(EU) 制造商:Equinox Technologies 功能描述:RS232/RS485 CONV (EU)
RS485-C1(UK) 制造商:Equinox Technologies 功能描述:RS232/RS485 CONV (UK)
RS485-C1(US) 制造商:Equinox Technologies 功能描述:RS232/RS485 CONV (US)
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