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 .
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.
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.