Understand tank level alarms

Eight alarm limits are configured for tank level alarms. If the level exceeds either the User High (Hi), Normal Fill, High (Hi), or High/High (HiHi) limits, or falls below the User Low (Lo), Normal Empty, Low (Lo), or Low/Low (LoLo) limits, AVEVA Enterprise SCADA generates an alarm. When the level is once again within normal operating limits, AVEVA Enterprise SCADA generates a Return-to-Normal alarm.

With the exception of the User High and User Low alarms, which do not have to be sequentially-ordered, the level values for the rest of the level tank alarms must be sequentially-ordered. For example, the Low/Low value must be less than the Low value.

• Low/Low: 5

• Low: 6.5

• Normal Empty: 7

• Normal Fill: 8

• High: 8.5

• HighHigh: 9

The alarm limits can be entered via Controller or Advanced Database Editor (ADE) dialogs. There is also a checkbox to enable or disable each of the eight alarms. To avoid tank fluctuations that may set off multiple alarms, a deadband is used (in the same manner as many other AVEVA Enterprise SCADA alarms). For example, once the level reaches a High alarm state, it must drop below the deadband before AVEVA Enterprise SCADA generates the same alarm again.

The two user-configured alarms (User High, User Low) are treated slightly differently from the other six alarms:

• They are not affected by deadband configuration.

• They do not have to have limits in a specific sequence with other alarms. The only requirement is that User Low be less than the User High, if both are enabled.

• They generate an alarm message that functions independently from the message generated by the other 6 limits.

  For example, for a tank, there can only be one alarm active for Low/Low, Low, Normal Empty, Normal Fill, High, or High/High, and one active for User Low or User High. A separate Return-to-Normal message is also generated for the user limits.

• Do not show up in the Current State field of the tank.