# Tag Words and Channel States

In addition to channel status messages, the RTU has available a small set of globally applicable Tag Words.

Tag Words are automatically appended to the end of each channel status message, in order to reflect the state of the channel, not to be confused with its current value reading from the last scan. The channel status message plus the appended Tag Word(s) constitute the channel status report.

Tag Words appended to Channel Status Messages include the following:

- NORMAL — Any channel with no input violation will have the Tag Word "Normal" appended to the channel status messages.
- ALERT — Any channel with an input violation which has not been present longer than the Alarm Trip Delay for that channel will have the Tag Word "Alert" appended to the channel status messages.
- ALARM — When the input violation has persisted continuously for the Alarm Trip Delay period, the channel goes into Unacknowledged Alarm State, and the Tag Word Alarm will be appended to the channel status messages.
- NOW NORMAL — If the violation that originally caused the alarm has returned to normal, the Tag Words "Now Normal" will be appended to the channel status messages.
- ACKNOWLEDGED —- Any channel that was in an unacknowledged alarm state, and was acknowledged by an operator, will have the Tag Word "Acknowledged" appended to the channel status messages.
- NOW NORMAL, ACKNOWLEDGED —- any channel which is both acknowledged and whose input violation has returned to normal, will have the Tag Words "Now Normal, Acknowledged" appended to the channel status messages.

For a channel to be able to initiate an alarm report it must be pre-configured with "Alarm Violation Criteria" to specifically define what reading value(s) will constitute an alarm violation.

With this in mind, the following describes how the RTU reflects both the current reading value and the state in reports, as events progress:

Event or Period Progression | Channel State
No Violation: | NORMAL
Violation Occurs: | ALERT
Alarm Trip Delay Period: | ALERT
Unacknowledged Alarm: | ALARM
Dials until Acknowledged: | ALARM
Alarm Acknowledged: | ALARM, ACKNOWLEDGED
Alarm Reset Time, Channel Violation Returns to Normal: | ALARM, NOW NORMAL, ACKNOWLEDGED
Alarm Reset Timed-out, Channel Ready for New Alarm: | NORMAL

Initially with no violation, the channel's state is NORMAL. If the channel were queried for a report at this time, the report would consist of the channel status message as described above, followed by the Tag Word "Normal".

Whenever the current value reading changes so that it constitutes a violation, the channel first begins timing out its configured Alarm Trip Delay period. During this timeout period, the state is ALERT. If the channel were queried for a report at this time, the report's message would change to reflect the changed value, and the tag word would change from "Normal" to "Alert".

If the violation persists continuously long enough to satisfy the Alarm Trip Delay, the state changes from Alert to Unacknowledged Alarm. This in turn causes the RTU to initiate attempts to deliver alarm reports to the various destinations available to it, typically personnel's phone numbers. The RTU continues notification efforts until the alarm is acknowledged. During this time, the report for this channel will be the same, except that the Tag Word is changed from "Alert" to "Alarm".

Note: While the state is Unacknowledged Alarm, the default Tag Word for reporting this state is just "Alarm."

After having tripped into this Unacknowledged Alarm state, if the current reading value happened to return to a non-violation value, the additional Tag Words "Now Normal" would be added to the tag word "Alarm" in the report.

Similarly, after the alarm is acknowledged, the Tag Words "Alarm, Acknowledged" would be appended to the message, along with "Now Normal" added if there were no immediately current violation.

The fact that Tag Words are automatically added to messages should be considered when determining the exact content of each message element.

See Also

Customizing Tag Words

Tag Words for Discrete Channels

Tag Words for Analog Channels

Remaining Tag Words