RFL SMX3/40 Page 3 of 24 Issue 2.02
User Manual
07 May 2009
1. Introduction
Power utilities have historically used RFL9850 voice frequency modems for
teleprotection and SCADA communications. Separate frequency bands within the
available spectrum provide two channels over single private circuits rented from BT
or other telcos. Historically these rented circuits have been analogue circuits from
end to end, but BT, for example, are now in the process of converting the central
sections of some of these circuits to digital.
It has been found that where digital elements have been introduced into these
circuits, although there is no significant degradation in the character format of the
serial data conveyed, the introduction by BT of analogue to digital converters has
introduced additional end-to-end delays. This may affect performance; for example,
some types of circuit protection relay (e.g. the MPR - LZPK102 relay) time their
transmissions from the zero crossing of the protected circuit. The receiving relay
expects the start of the received message to be within a certain period of its own
measured zero crossing. Thus the introduction of additional transmission delays
associated with analogue to digital converters causes errors to be recorded.
The RFL digital Sub-MUX SMX3/40 enables up to four V24 (typically RS232) data
channels to share a single X21 digital communications link, (e.g. BT Kilostream,
microwave), eliminating the delays introduced by analogue to digital converters. User
interfaces are compatible with standard industrial formats enabling the SMX3/40 to
be used in many applications that require legacy equipment to operate over current
X21 communication links.
2. Features
The RFL SMX3/40 Sub-MUX is a hardened (EATS 48-5) sub-rate multiplexer. The
equipment is 19” rack mountable, 1U high, with reversible mounting brackets
permitting either the connectors or the LEDs to face the front of the rack.
BT
KiloStream
Port assignment &
sharing
X21
Channel C
Channel B
Channel D
Concatenation
SMX3 / 40 Block Diagram
V24
port 1
Concat
Channel A
V24
port 2
V24
port 3
V24
port 4
Manymanuals.com
Manymanuals.de
Manymanuals.fr
Manymanuals.it
Manymanuals.pl
Manymanuals.cz
Manymanuals.es
Manymanuals-pt.com
Komentáře k této Příručce