Basics Modbus - Siemens SITRANS LG270 Operating Instructions Manual

Ʋ Aluminium housing, stainless steel
housing - investment casting, stain-
less steel housing - electro-polished
Overvoltage category
Protection class
Approvals
Instruments with approvals can have deviating technical data (depending on the version). For such
instruments, the corresponding approval documents must be noted.

10.2 Basics Modbus

Bus description
The Modbus protocol is a communication protocol for the communication between instruments. It is
based on a Master/Slave or Client/Server architecture. By means of Modbus, a Master and several
Slaves can be connected. Each bus participant has an unambiguous address and can send mes-
sages to the bus. This is initiated by the Master, the addessed Slave answers. For data transfer, the
versions serial (EIA-485) as well as the mode RTU are available. In the RTU and ASCII mode inter-
esting here, data will be transmitted in binary form. The telegram consists generally of the address,
the function, the data as well as the transmission check.
Bus architecture
In the version Modbus RTU, up to 32 participants can be connected to the bus. The length of the
twisted two-wire cable can be up to 1200 m. The bus must be terminated on both sides at the last
bus participant with a terminating resistor of 120 Ohm. The resistor is already integrated in the
SITRANS LG270 and is activated/deactivated via a slide switch.
The prerequisites for maintaining the protection rating are a suitable cable as well as correct mounting.
5)
IEC 61010-1
6)
IEC 61010-1
7)
84
IP 66/IP 68 (0.2 bar), NEMA 6P
III
6)
III
7)
SITRANS LG270 - Operating Instructions
5)
PBD-51041066