Missing Flow Detection (MFD)

The missing flow detection feature is applied only when the Auto Correction for Missing Flows option is selected.

There are five checkboxes that control missing flow detection and correction.

• Auto Correction for Missing Flows

  It determines whether DR Solver performs missing flow detection. This means AVEVA Production Accounting will find the balance points with missing flows and alters the results of reconciliation to assume that the detected missing flows were real and of the predicted size.

• Limit MFD to Tanks Only

  When enabled, only missing flows for tank balance points can be detected. AVEVA Production Accounting does not, in this case, assign a missing flow to a node or process. If, in your plant, missing flows most often happen around tanks because the oil movement data on the tanks are missing, it is recommended to check this option.

• Forced Balance

  If you want to simply detect the missing flow with the user defined tolerance assigned to the balance point to which the suspected missing flow belongs, select the Forced Balance checkbox.

  When the Forced Balance option is enabled, DR Solver detects a missing flow whenever the balance point in question has a measured imbalance larger than the tolerance of the balance point. The measured imbalance of any balance point is the sum of the measured values of input flows minus the sum of the measured values of output flows. The tolerance of each balance point is assigned using the AVEVA Production Accounting GUI, and passed to the DR Solver engine.

  

If the Use Reduced Balance checkbox is checked, the Forced Balance executes on the reduced balance points (balance envelopes) instead of the individual balance points.

The criteria to show 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 (3%).

Balance Point Relative Tolerance (3%) is defined at the Initial System Defined Tolerance (see Initial System Defined Tolerance).

To detect missing flows, AVEVA Production Accounting uses a proprietary and complex method that considers the imbalance and tolerance of the balance points around the suspected missing flow. The tolerance of the balance point is defined as:

• The tolerance of the balance point = Sqr(S(tolerance of each flow connected to the balance point)2)

The tolerance used depends on which options you check in the Missing Flow Detection (MFD) frame. You have two choices:

1. Use the tolerance assigned to the stream that the missing flow would belong to. This is the default.

2. Use the overall Confidence Level to calculate the tolerance as 100%-Confidence Level. This derived tolerance is then applied to each balance point. (For example - A Confidence Level of 95% would result in 100-95=5% being used as the tolerance for each flow.) To force the use of the overall Confidence Level, check the Use System Defined Tolerance in MFD checkbox. We recommend that you check this checkbox since the missing flow on a given balance point is not highly related to the tolerance of input and output flows on that balance point.

   The DR Solver dialog box contains a Confidence Level(%) property that you can edit.