SIEMENS
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Siemens IK PI · 2015
Industrial Remote Communication
Remote Networks
Modems for the conventional telephone network
MD2 dedicated line modem
7
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Overview
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Frequency-modulated (FSK) dedicated line modem;
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Half-duplex data transfer over 2-wire dedicated line,
duplex data transfer over 4-wire dedicated line
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Thanks to the modem's relaying ability, lines with several
connected stations can also be implemented. The MD2 can
also be used as repeater on 2-wire and 4-wire dedicated lines.
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Private or leased telephone lines can be used as dedicated
lines. The MD2 is also suitable for connection to a radio device
with modem input.
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Benefits
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RS 232 and RS 485 interface
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Isolation between voltage supply and RS 232/RS 485 interface
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4 different transmission rates to select
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Supports tandem stations
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Integrated double transformer for the connection of two 2-wire
lines
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Integrated repeater function for multiplication of range
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Suitable for connection to a wireless device with modem input
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Application
The MD2 modem can be used as a dedicated-line modem
independently of the SINAUT ST7 system. Due to its design and
the electrical properties, the MD2 is especially suited for use in
the industrial sector.
Examples of use outside the SINAUT ST7 system:
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Extension of Profibus and MPI links;
see FAQ 23671172 (for PB) or 23671640 (for MPI)
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As leased line modem for S7-200;
see Micro Automation Set MAS 17
The MD2 enables distances of up to 33 km (at 1 200 bit/s),
27 km (at 2 400 bit/s) and up to 11 km (at 9 600 and 19 200 bit/s)
to be spanned without amplifiers/repeaters (guide values for
uncoiled communication cable of type 2 x 2 x 0.8 J-Y(St)Y).
By interconnecting two MD2 modems to a repeater, the specified
distances can be extended several times.
The MD2 modem permits the construction of network structures
in the "point-to-point", "star" or "linear" configurations, as well
as combinations of these basic structures. If the modem is used
in the control center, a small star network comprising two 2-wire
cables can be connected at the modem output. By connecting
several MD2s (max. 32) by means of their RS 485 interfaces, the
star network can be expanded to a multiple of 2 x 2-wire.
For the arrangement of an MD2 along a line, the modem output
can be switched to high impedance. This reduces the insertion
loss to a minimum and thus only marginally reduces the maximal
bridgeable distance. The very short transmitter make-times
ensure a prompt execution of the data traffic with the "polling"
used in the dedicated line network.
Apart from private dedicated lines, the MD2 can also be con-
nected to Telekom leased lines. Corresponding approval exists.
In the case of exclusively analog leased lines, the transmission
rates 1 200 and 2 400 bit/s are possible, whereas for analog/
digital-converted leased lines the speed is usually limited to
1 200 bit/s for technical reasons.
The MD2 is also ideal for data transmission via a walkie-talkie
with modem input. In order to switch the walkie-talkie on and off
via its PTT input, a floating optical relay is integrated in the MD2
modem that is linked with the RTS signal of the RS 232 interface.
The two connections of the optical relay are available on the
RJ12 socket.
As walkie-talkies usually only transmit voice signals in the 300 to
3 000 Hz frequency range, the transmission rate with the MD2
modem is limited here to 1 200 bit/s. For 2 400 bit/s, the fre-
quency range would have to exceed 3 300 Hz.
© Siemens AG 2014