Specifications

Page 2 of 137 Manual Documentation Number: <DocNumber>
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Selecting RS-422 and RS-485 Cabling ....................................................... 43
Number of Conductors .................................................................................... 43
Shielding ....................................................................................................... 44
Cable Characteristics ....................................................................................... 45
Cable Length vs Data Rate ................................................................... 45
Attenuation vs Frequency ..................................................................... 46
Using Cat 5 for RS-422/485 ............................................................................. 47
Transient Protection of RS-422 and RS-485 Systems ................................ 49
What does a surge look like? ............................................................................ 49
Surge Specifications ............................................................................ 50
Common Mode versus Differential Mode ................................................. 52
When Ground is not really Ground .................................................................... 53
Transient Protection using Isolation ................................................................... 55
Isolation Theory ................................................................................. 55
Isolation Devices ................................................................................ 57
Transient Protection using Shunting .................................................................. 58
Shunting Theory ................................................................................. 58
Connecting Signal Grounds ................................................................... 59
Shunting Devices ................................................................................ 60
Combining Isolation and Shunting ..................................................................... 60
Special Consideration for Fault Conditions .......................................................... 62
Choosing the right protection for your system ..................................................... 63
Software ................................................................................................... 65
RS-422 Systems ............................................................................................. 66
RS-485 Driver Control ..................................................................................... 66
RS-485 Receiver Control .................................................................................. 68
Master-Slave Systems ..................................................................................... 68
Four Wire Master-Slave Systems ........................................................... 68
Two Wire Master-Slave Systems ........................................................... 70
Multi-Master RS-485 Systems .......................................................................... 70
Systems with Port Powered Converters .............................................................. 71
RS-485 Devices ......................................................................................... 73
RS-232 to RS-485 Converters .......................................................................... 74
PC Serial Interface Cards ................................................................................. 75
USB to RS-422/485 Converters ........................................................................ 76