Understand tank Deviation (creep) alarms

The idle condition of a tank can be defined by one of two conditions. A tank can be marked idle manually by the Controller through the easy eXtended Operator Station (ezXOS), or, automatically based on up to 12 comparisons corresponding to the tank idle configuration. For automatic operation, if all comparisons succeed, the tank is automatically marked as idle after a configurable time period (to allow for settling).

The tank can be configured with a creep Deviation Type that determines whether creep detection is based on level or volume thresholds. For each type, positive and negative thresholds can be specified. Only one Deviation Type can be enabled for the tank.

When a tank is marked as idle, the current level and volume are saved. If the selected deviation type is Level and the current level in the tank differs from the saved level by more than the configured thresholds, AVEVA Pipeline Operations for Liquids generates a deviation alarm and the new level is saved. This new level now becomes the reference level for future deviation alarms. If the selected deviation type is Volume and the current volume in the tank differs from the saved volume by more than the configured thresholds, AVEVA Pipeline Operations for Liquids generates a deviation alarm and the new volume is saved. This new volume then becomes the reference volume for future deviation alarms.

When a deviation alarm is generated, it does not replace any existing deviation alarm. The current deviation alarm must be acknowledged separately. A flag remains set for a configurable time period so applications can determine if the tank is in a deviation alarm state, even if the alarm has been acknowledged.The time period is configurable via the Timeout (HH:MM:SS) field on the Alarming tab of the Tank Row Edit dialog, as described in Configure the Alarming tab of the Tank record.

The Idle Violation Check Cycle Time (configurable through the Tank Row Edit: Alarming tab) will allow you to configure how often a tank will check for a creep violation. For example, an Idle Violation Check Cycle Time of 00:05:00 means that the tank will check every five minutes for a creep violation.

The configuration of the Tank Idle / Flow Configuration section of the Auto Idle / Ext Flow tab can also be used to determine the expected external direction of the tank flow.

The Creep Alarm Suppression feature allows you to configure how many creep violations are allowed to occur before generating an alarm. The configuration of this feature is enabled on the Tank Row Edit: Alarming tab.

If Enable Creep Alarm Suppression checkbox is selected, then the tank will count the number of creep violations that occur after the tank has gone idle. If the number of violations is greater than the configured Idle Violation Count Limit, then the creep alarm will be generated.