6
PIN
LED
7.1.2 RS 485
The easiest and cheapest way to connect different measuring devices in a network is the RS485 serial line.
The RS485 standard interface allows a multi-point connection. Between PC and the network, it is required a
Serial RS232 to RS485 Converter. If more than 32 instruments are to be connected, insert a signal repeater.
Each repeater can manage up to 32 instruments. For the connection among the different modules, use a
cable with a twisted pair and a third wire.
The type of connection shown in the following picture uses the third conductor to ensure that all the devices
on the network have the same reference level and improve the reliability of communication.
When there are strong electromagnetic disturbances, which may affect communication, a shielded cable
should be used.
The Rt termination resistance must be installed on the PC and the last instrument connected along the line.
Thanks to these resistances, the reflected signal along the line is reduced.
For a typical telephone pair, Rt can have values from
120 to 150 Ohm.
NOTE. the value of each resistance must not
be lower than 120 Ohm in order to avoid an
overload of line drivers.
The max. recommended distance for a connection is
1200 m at 9600 Baud. For longer distances, lower baud
rates or low-attenuation cables or signal repeaters
are needed.
7.2 FTT-10 LONBUS COMMUNICATION PORT (optional)
The LONBUS interface allows a point to point connection: i.e. instrument to PC or other device. The maximum
recommended node-node length is about 400 m without repeaters. For the connection use a cable UL Level
4, 0.5 mm, 22 AWG twisted pair.
FTT10 LONBUS communication port; connect a single twisted
pair to communicate directly on Lo n Wo r k s
TM
network.
Service Pin LONBUS communication switch; to enable the
Lo n Wo r k s
TM
communication, press Service Pin with a
sharpened object (e.g. a pencil) paying attention not to
damage the overlay layer of the switch.
Comm. Diagnosis LED LED for diagnosis messages on the communication
status;
LED OFF = communication OK
LED is flashing = no communication
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