Specifications

Chapter 4 - Transient Protection of RS-422 and RS-485 Systems RS-422 And RS-485 Applications Ebook
Page 60 of 137 Manual Documentation Number: <DocNumber>
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Shunting Devices
There are two types of shunting devices to choose from. The least
expensive type is single stage, which usually consists of a single TVS
device on each line. Three stage devices are also available. The first
stage of a three-stage device is a gas discharge tube, which can handle
extremely high currents, but has a high threshold voltage and is too
slow to protect solid state circuits. The second stage is a small series
impedance which limits current and creates a voltage drop between the
first and third stage. The final stage is a TVS device that is fast enough
to protect solid state devices and brings the clamping voltage down to
a safe level for data circuits.
Combining Isolation and Shunting
Installing a combination of both isolation and shunting protection can
offer the highest reliability in a system.