Isodaq Technology is now part of Hydro International.

Rainfall intensity alarms

All ISODAQ telemetry loggers support rainfall intensity alarms for channels configured for tipping-bucket logging. The method of alarm triggering was developed for use in fluvial flood warning schemes by the Environment Agency for England and Wales and the Scottish equivalent rivers regulator, SEPA. Up to 4 alarms are supported for each rainfall channel. Each alarm has a set point amount in mm, an integration period and a suppression period. The set point, integration period and suppression period can be individually set for each alarm :-

  • Integration periods - up to 16 periods are supported from 10mins to 7days.
  • Suppression periods – up to 8 periods are supported from 1 hr to 48 hrs The rainfall alarms are checked at a user specified interval.

All four alarms are evaluated at the same interval. In order to evaluate each alarm, the tip record is scanned backwards (most recent tip first) and tips are counted until a tip that is older than the integration period is found. The tip count is converted to an amount of rainfall, then compared with the alarm set point. If the set point is exceeded, a rainfall alarm is generated and the system dials out. After the alarm is generated, the suppression time is set to the time of the alarm plus the requested suppression period. Further alarms (for that setpoint/integration period only) are not generated until after the suppression time. This evaluation procedure is followed for up to 4 alarms per channel.