The accumulator point keeps a running total of changes in the source point values. The accumulator can be either a signed integer, an unsigned integer or a floating point data type and can have one of two forms of operation:
Delta Accumulator Points
A Delta Accumulator point keeps a running total of the delta between the previous value of the results an arithmetic expression (the point_expression field in derived_point.dat) and the current value. The delta accumulator point may be a signed or unsigned integer or a floating point data type.
The value for a delta accumulator is initialized to zero, or if a Startup Condition is specified it is initialized according to the Startup Condition. The first update of the accumulator occurs after the second update of the point_expression value. Updates continue until a Reset Condition occurs.
A Reset Condition occurs when the value in the reset_point_id changes. At that point, the value of the Delta Accumulator is reset to the init_value or if the init_value is not present, it is reset to zero(0). The value in the reset_point_id can be changed by an operator or automatically by software.
You must set a variance_value for a Delta Accumulator. This is the maximum acceptable delta value that can be added to the accumulator. In the event of a variance condition, the system logs a message to the Status Log. Counting continues from the new value, but the delta is not added to the accumulator.
You may set a rollover_val for a Delta Accumulator. This is the maximum acceptable value for the point. If you do not specify a rollover value, the data type for the source point in the Equation is used as the default Rollover value.
When a Rollover condition occurs, the accumulator point is set to an adjusted value which accounts for the data overflow and a message is logged in the Status Log.
Value Accumulator Points
A Value Accumulator point keeps a running total of the changes in an expression by adding the current value of the expression to the Value Accumulator. The Value Accumulator may be a signed or unsigned integer or a floating point data type.
The value for a Value Accumulator is initialized to zero, or if a Startup Condition is specified, it is initialized according to the Startup Condition. Updates continue until a Reset Condition occurs.
A Reset Condition occurs when the value in the reset_point_id changes. At that point, the value of the Value Accumulator is reset to the init_value or if the init_value is not present, it is reset to zero(0). The value in the reset_point_id can be changed by an operator or automatically by software.
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Derived point file (DERIVED_POINT). |
