DR Solver options for missing flow detection

The missing flow detection feature is applied only when the Auto Correction for Missing Flow option is selected on the DR Solver tab in the Option dialog.

The following procedure describes how to setup options for missing flow detection:

1. Select the Tools menu.

2. On the Tools menu, in the Tools group, select Option.

   The Option dialog appears.

3. In the Options dialog, select the DR Solver tab.

   

4. In the Missing Flow Detection(MFD) section, select the relevant checkbox.

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

   • Auto Correction for Missing Flows: 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: If selected, only missing flows for tank balance points can be detected. AVEVA Production Accounting will 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 select this option.

   • Forced Balance (alternative): 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, you can select the Forced Balance checkbox. If the Forced Balance option is used, 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 GUI, and passed to the DR Solver engine.

   • Use Reduced Balance (alternative): If selected, the Forced Balance executes on the reduced balance points (balance envelopes) instead of the individual balance points.

   

   • User System Defined Tolerance in MFD: Forces the use of the overall Confidence Level. It is recommended that you select 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.

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 following.

The tolerance used depends on which options you check in the Missing Flow Detection (MFD) frame.

You have two choices:

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

• 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.) The DR Solver dialog box contains a Confidence Level that you can edit..