Digi HygroClip DI digital interface - Manual (Page 23)

IN-E-HyClip DI-V1_10
Rotronic AG
Bassersdorf, Switzerland
Document code Unit
Instruction Manual
Document Type
HygroClip DI digital interface: instruction
manual
Document title
Page 23 of 24
© 2007; Rotronic AG IN-E-HyClip DI-V1_10.doc
Lightning protection
Cabling in areas with a risk of lightning requires a lightning protection. For cabling underground in
between buildings, we recommend the use of special fiber optic cables. If this is not possible, use
copper cables that are suitable for underground installation.
Additional guidelines for RS-485 wiring (products with a serial interface)
RS-485 Cable
Using a symmetrical transmission method in combination with low capacity/ low attenuation
twisted pair cables, allows extremely reliable long distance connections. The use of a high grade
shielded cable avoids cross talk between the transmitted signals and also reduces the potential of
external interference. For the RS-485 cable, we recommend using a cable Cat. 5e ANSI/ TIA
/EIA-568-A-5.
In general the RS-485 cable should be shielded and comply with the following specifications:
-
Cable capacitance <=300pF/m or 90 pF/ft
- Line impedance 100 Ω ±15 Ω
- Line resistance 140 Ω/km or 225 Ω
- Signal lines Twisted pair
In addition, we recommend terminating each end of the RS-485 cable with a 240 Ohm resistor.
RS485 Network
Addr. 1 Addr. n RS485 device connectors
240 Ω 240 Ω
Note: all instruments connected to the network should use the same baud rate
Voltage potential issues
The existence of a voltage-potential between instruments that are interconnected can be a source
on concern in large installations, installations with different mains power supply and in inter-
building networking.
As a first measure, the shield of a signal cable should be connected at both ends. In the case of a
data cable, a low-resistance potential equalization cable may also have to be used. This cable
should be run parallel and as near as possible to the data cable, preferably in the same conduit.
The shield of the data cable should under no circumstances be used as equalization cable! The
conductors of the potential equalization cable should ideally be stranded in order to be effective
also in case of high- frequency interference.