KROHNE CORIMASS MFC 85 Interface EN - Manual (Page 24)

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1. General
The Mass flow Converter, MFC 081/085 with Modbus/RS 485 interface fitted, is able to
communicate with an external device (PC or other suitable computer system) using the
Modbus protocol. This option allows data exchange between PC or computer and single or
multiple devices.
The Bus configuration consists of one external device as a master and one or more converters
(MFC 081 or MFC 085) as slaves. For Bus operation the device address and baud rate must
be programmed in the menu 3.11.0 of the MFC 081/085. Devices connected to the Bus must
have different unique addresses and the same baud rate and settings.
The transmission uses 8 (eight) data bits, even or odd parity and 1(one) or 2 (two) stop bits at
a selectable baud rate of 1200 to 19200.
2. Technical Specifications
Interface RS 485, galvanically isolated
Baud rate 1200, 2400, 4800, 9600, 19200 baud
Protocol Modbus RTU
(Available as a separate document on
request)
Maximum participants on Bus 32 per line, master included (may be
extended by repeaters)
Coding NRZ bit coding
Address range Modbus: 1 – 247
Transmission procedure half duplex, asynchronous
Bus access master/slave
Cable screened twisted pair cable
Distances maximum 1.2 km without repeater.
(Dependant on baud rate and cable
specifications)
Technical data of the Modbus interface (according to EIA standards)
Kind of signal transmission: Differential
Maximum number of transmitter/receivers: 32
Maximum voltage on driver output: –7 V to +12 V
Minimum voltage on driver output, max.load: U diff > 1,5 V
Maximum input current (off state) –20 µA to +20 µA
Receiver input voltage –7 V to +12 V
Sensitivity of the receiver –200 mV to +200 mV
Receiver input resistance > 12 k ohm
Short circuit current of transmission < 250 mA