Update the High-Low state of the tank

High-Low states indicate the fullness of the tank. High-Low states are determined by comparing the current level to the defined bounding levels. State changes are not applied unless the bounding level is exceeded by a configured amount of deadband. There are two sets of High-Low states:

• Levels are defined by the Administrator.

• Levels are defined by the Controller.

The High-Low state determined from Administrator limits has no relationship to that determined by Controller limits. These states also have no relationship to the full or empty condition defined by the Maximum Safe Level and Minimum Safe Level. For more information, see Calculating the Room and the Available Volume.

Each Administrator and Controller-defined level can have alarming enabled. If enabled, an alarm on the state change is issued when the level is crossed.

For Administrator-defined levels, levels are defined that determine a High-Low state in the tank by the height of the product in the tank. The following table details the states from highest to lowest.

Note: From the table, the state is defined by the level that is being exceeded. The definition of any level in the table is optional. If undefined, the state that would occur when the level is exceeded is not used.

For example, if the Low level is not defined, the Low state will not apply. The Normal Empty state will apply from the Normal Empty level to the LowLow level.

For Controller-defined levels, the levels work the same way as the Administrator ones, but there are fewer states. They following table details the states from highest to lowest.