Gross error categories

In the gross error list, there are six categories to notice model imbalance or potential problem for helping easier model tuning.

1. The balance name consisting with only input flows or output flows which have certain values

   For example, if there is no event data in output flow, AVEVA Production Accounting sets input flow to zero even when the measured value is not zero to match the balance. In this case, the balance point turns red and the solvability is set to POS (Problem Out of Service), and lists up this balance point into the gross error list.

   

   

   Double-click on the item of gross error list, to view the selected object on the flowsheet.

2. The balance name with missing flow

   This category lists missing flows which are usually occur in tank movement. The missing flows are of the following four types:

   • Pconst: The constant balance status (Pconst) means that balance point object is not balanced because all connected streams are constant.

   • Missing: If the missing flow detection is on, AVEVA Production Accounting will find out missing flow (Missing) within a certain criteria. The criteria to detect the tank with missing movements is that Abs((end inventory + output flows)–(start inventory + input flows))/(((end inventory + output flow)+(start inventory + input flows))/2) x 100 > (Balance point relative tolerance, %). For details on Balance point relative tolerance, see Initial System Defined Tolerance.

   • CMissing: The constant missing balance status (CMissing) means that balance point object is not balanced because the balance envelope including this balance point consists of constant missing flows.

   • CDensMissing: The constant density missing balance status (CDensMissing) is similar to CMissing but the imbalance is in the second balance type. It means that there is no imbalance in the primary balance type. Since the flows are constant, density must be wrong.

     For more information on the missing flow categories, see Tank object: Balance Results tab.

     

3. Gross error flow

   This category lists gross error flow due faulty measurement and calculates error percentage of the stream. For more information on gross error flow, see Gross error detection.

   You can export the list of detected Gross Error flows/streams to Excel. For more information, see Report.To.Excel.

   

4. Direction Changed Flow

   This category lists reverse flow streams.

   When the tanks are grouped by the unmeasured tank difference stream, the tank difference stream with the negative reconciled value is shown in gross error list since it is calculated from tank inventory change.

   

5. Minimum or Maximum Constrained Flow

   This category lists minimum or maximum constrained streams. For more information, see Gross Error Detection with Min/Max Constraints.

   

6. Triggered Constant Flow

   This category lists triggered constant flow streams. For more information, see the Bias Factor/Trigger function in Stream object: Design Info tab.

   

   When the balance boundary consists of only constant values of stream flow rate or tank inventory, one balance point in the balance boundary should be unbalanced and then other balance points are balanced. If there are tank balance points in the balance boundary, the tank balance point with the largest imbalance is detected. If there are only process (or node) balance points, the process (or node) balance point with the largest imbalance is detected.

   It is reasonable to detect unbalanced point as tank rather than process (or node) since most of the missing flows happen in the tank.

   If it is properly detected as unbalanced tank, the balance status is Constant Missing Flow Tank and then color of the tank is turned into red.

   

   In the below example, depending on the imbalance rule, "TankA" should be detected as unbalanced point.