Gross error detection

AVEVA Production Accounting can detect gross errors in mass or volume balance and help the user to confirm where they are located. Using only raw measurements, AVEVA Production Accounting finds the imbalance of each balance point which consists of only redundant flows and then pinpoints the most probable gross errors. AVEVA Production Accounting automatically detects and excludes gross error measurements until the remaining redundant flows satisfy a given confidence level. However, AVEVA Production Accounting does not exclude the gross errors silently. It is important that you have the opportunity to check and confirm the gross errors, although they were already excluded from the reconciliation.

The following types of gross errors are excluded and presented to you:

• Balance points with a configuration problem: Such points consist of only input flows or output flows.

• Nonsolvable flows: You may choose to use the ability to apportion nonsolvable flows by ratio in order to distribute flow to otherwise nonsolvable streams.

• Balance points with missing flows: AVEVA Production Accounting recognizes a missing flow by noting that one particular balance point cannot be balanced, yet the upstream and downstream balance points do balance, and the total amount of flow is either reduced or increased when traced from the upstream side to the downstream side of the configuration. The option to identify missing flows can be disabled after commissioning to force AVEVA Production Accounting to assume that the model has no missing flows, which will cause this error to appear as a larger imbalance.

• Faulty measurement flows: Faulty measurements cause the imbalance on neighboring nodes to be similar in magnitude but opposite in sign, which is a condition than AVEVA Production Accounting can automatically recognize.

It is clear how you must deal with the first two types of gross errors. For configuration problems you must correct the configuration. Nonsolvable flows, assuming that your model was correctly made, must be handled by using distribution logic to apportion fixed ratios of known flow.

For the last two types of gross error listed above, the AVEVA Production Accounting DR algorithm has special logic to enable the overall balance to proceed.

AVEVA Production Accounting has to ignore the problem on a local basis, while still drawing attention to it.

• In the case of missing flows, the balance point that is affected by the missing flows is not balanced by the algorithm. It will, however, be highlighted on the flowsheet using color.

• In the case of faulty measurements, the faulty measurement flow is treated by AVEVA Production Accounting as an unmeasured flow to allow the balance to complete, and highlighted in color.

This ability to proceed with the reconciliation algorithm execution despite encountering certain kinds of errors is a significant advantage of AVEVA Production Accounting, because it allows you to identify more problems in a single run of the algorithm, which saves you time. Without the ability to ignore missing flows and faulty measurements, you would have to perform many more iterations of the algorithm by hand, after fixing each problem as it was detected.

Gross error detection flow diagram

The following figure shows the overall flow diagram for gross error detection in AVEVA Production Accounting.

Figure: Overall Gross Error Detection Steps

Note that the objective is to feed into the reconciliation algorithm only measurements which are valid, and redundant. Any other values must be filtered out as they are not candidates for reconciliation.