Understand Virtual Flow Computer (VFC) Catch-Up state

The Max Reasonable Reverse Flow Rate (vol/h) value configured for the accumulator reflects the maximum possible flow rate going in the opposite direction on a unidirectional pipeline.

If the delta reported at the accumulator indicates a negative flow rate greater than the Max Reasonable Reverse Flow Rate (vol/h), the delta will be regarded as an anomalous condition and the volume of the accumulator will stay the same. However, if the delta indicates a negative flow rate that is less than or equal to the Max Reasonable Reverse Flow Rate (vol/h), it may affect the accumulator volume depending on the configuration being used.

If the Volume Accumulation Mode is Positive Only, the Virtual Flow Computer (VFC) will enter a Catch-Up state. In this state, there will be no volume change (though the change is tracked internally). The volume will not go up until the rate providing the volume has re-accumulated the volume it "lost" due to the negative flow. When the previously read accumulation value is reached again, the VFC will automatically exit the Catch-Up state. The following diagram provides an example:

Note: In rare situations, it may be desirable to manually exit the Catch-Up state to account for a legitimate backward jump.

To manually exit the Catch-Up state, perform the following steps:

1. Inhibit the VFC until it displays the Current Status as INHIBITED. For more information on how to perform this action, see Inhibit a Virtual Flow Computer (VFC) record.

2. Set the VFC back to uninhibited again.
As a result, the VFC will move from the CATCHUP state to the NORMAL state, and the volume accumulation will continue.

If the volume's Accumulation Mode is Positive and Negative, the volume will be decremented by the amount indicated by the delta.