ROTRONIC HygroLab - Manual (Page 13)

IN-E-HyLab-V4_11
Rotronic AG
Bassersdorf, Switzerland
Document code Unit
Instruction Manual
Document Type
HygroLab bench top indicator version 4:
instruction manual
Document title
Page 13 of 51
© 2006; Rotronic AG IN-E-HyLab-V4_11
- All devices within a multi-drop should use the same Baud rate. See Baud rate compatibility
requirements.
- Models with Ethernet (TCP/IP) interface: please note that the Baud rate of the HygroLab and
the Baud rate of the internal Ethernet module should be set to the same value.
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.