Instruction manual

Glossary
70 025-9209
Radio modem
See radio interface module.
Relay Output Module
The module that connects a device to equipment to be
controlled by the SCADA system. The equipment must
have on/off controls.
Report by exception
See exception reporting.
Retry
For autopolling and exception reporting, an additional
attempt to communicate with a device that fails to respond.
Retry Timeout
For autopolling, the timeout period begins at the end of the
polling transmission from the Controller and determines
when an RTU is considered to have failed to respond.
Rings to Answer
The number of rings to wait before letting the modem
answer incoming calls.
RS-232
Standard for asynchronous serial data communications
defining connectors and signal levels.
RS-232 Watchdog
Function in a Controller that looks for messages from the
PC.
RS-232 Watchdog
Timeout
A Controller monitors its RS-232 communications with the
PC running the SCADA program. If the Controller does not
see any messages in the set period, the SCADA program
has failed.
RTU
Remote Terminal Unit. — Usually a small stand-alone data
acquisition and control device in the field that allows the
central SCADA master to communicate with field
instruments. It provides the interface between a radio
transceiver, or other communications link, and the
equipment being monitored and controlled. Its function is
to control process equipment at the remote site, acquire
data from the equipment, and transfer the data back to the
central SCADA master. The Models 1708 and 1716 are
RTUs.
RTU Address
Device address of an RTU.
RTU Poll Interval
For autopolling, this represents the interval between
receiving a response from the last RTU polled, and sending
a poll to the next RTU in the sequence.