Conversion of the electrical signals used
by SCADA master and remote terminals to present serial binary data to the
signalling format used by the associated communication channel(s) is performed
by Data Circuit Terminating Equipment (DCE).
The DCE for operation of voice-grade analog
channels is commonly referred to as a “modem.” Additional DCE functions should
include
1) Electric isolation or neutralization
between the remote or master terminal and the communication channel [10].
2) Detection of channel busy and idle
states.
3) Detection of degraded signal quality.
SCADA terminals may be arranged either with
integral or external DCE. The interface between the terminal equipment and the
DCE should meet certain requirements, and the DCE to channel interface.
Data Rates
Master and remote terminals should include
a provision for the selection of an operation at any of the following standard
data rates:
1) 600 b/s
2) 1200 b/s
3) 2400 b/s
4) 4800 b/s
Data rates of 75 b/s, 150 b/s, or 300 b/s
may also be used if required for special applications, such as the use of
frequency division-multiplex or power-line carrier channels. These lower data
rates necessarily limit the SCADA system response times and throughput; their
use should be minimized.
Operation at 9600 b/s may be used to
support large-capacity remote terminals in point-to-point channel
configurations. If dedicated fiber optic channels are used, extremely high data
rates can be accommodated.
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