Bias Factor/Trigger

Bias Factor

If the measured value of stream is biased with the same factor, you can set the bias factor for this stream on the stream window. The bias factor is defined as the true value/the measured value.

Example of Bias Factor

For example, if the true flow rate of 01FC034 stream is always 20% higher than the measured flow rate, the bias factor will be 1.2.

And this bias factor can be defined on the stream window after checking Use Bias Factor checkbox as shown below.

And then you run reconciliation, the bias measured value (=bias factor * measured value) is used for reconciliation and more accurate reconciled value is achieved.

In this example, the measured value of 01FC034 stream is detected as gross error before setting the bias factor but after setting the bias factor, the bias measured value is not detected as gross error and used in reconciliation.

Trigger (Triggered Constant Setting)

If the measured value of the stream is accurate, the best way to tune the model is to set this accurate stream as constant (tolerance = 0). But if this stream is rundown to tank, imbalance occurs because the inventory of the tank is constant, and receipt and delivery are constant. To avoid this case, the triggering constant flow property can be set at this constant stream.

Example of Trigger

For example, if the rundown streams (FC001 and FC002) are constant and delivery streams (91017/TRUCK_C4 and 91027/TRUCK_C4) are constant, then one of tanks are imbalanced because the all boundary streams are constant.

To avoid the imbalance in the tank, you can set FC001 stream as triggering constant as shown in the below stream window. The check box of Use tolerance value =0 only if not inferred constant is enabled only if zero tolerance, measured, not corrected value.

After setting FC001 stream as triggering constant flow, you run reconciliation and then FC001 stream is automatically set as non-zero tolerance to resolve the imbalance of tank as shown below.

And then the solvability of FC001 is changed into TCR (Triggered Constant Redundant Flow) and the reconciled value shall be adjusted to meet the balance.

If you also set FC002 as triggering constant flow and run reconciliation, FC002 instead of FC001 is changed into TCR since the quantity of FC002 is larger than FC001.

If you set the distribution factor for the stream with triggered constant option, the reconciled value is distributed with the flowrate and distribution factor. The default value of distribution factor is zero and it means no distribution with the same effects as the above explanation.

However, when you set it as one (1) for all triggered constant streams, it will be distributed as the flowrate when they are triggered. In the same example, you define the distribution factor as one (1) for both FC001 and FC002 streams as shown below.

And then run reconciliation. Both FC001 and FC002 streams are changed into TCR (Triggered Constant Redundant Flow) and the reconciled value shall be adjusted by their quantity (both mass and volumetric) distribution factor.

All TCR streams on the active model are shown at the gross error list.

Furthermore, all TCR streams on all models are shown at the Validate Triggered Constant Stream window. (See also Validate Triggered Constant Stream.)

This "triggering constant flow" functionality makes the balancing easier, more reliable and accurate.

AVEVA Production Accounting also allows the trigger option of the stream in running data reconciliation at tracking.

For example, set C_01FC001 stream as a constant in the following tracking model and then run tracking.

The reconciled volume of C_01FC001 stream is fixed as the measured volume of C_01FC001 stream by setting constant stream, and 03004_R tank is detected as Constant Missing Flow Tank since the imbalance is not resolved.

However, C_01FC001 stream is set as triggered constant, then C_01FC001 stream is adjusted as Triggered Constant Flow and 03004_R tank is balanced as shown below.