Understand How the Pressure / Flow Monitoring (Pressmon) application detects leaks

The following sections describe how the Pressure / Flow Monitoring (Pressmon) application detects leaks.

Pressure Checks

Administrative staff set the deadbands for pressure and flow for use in comparing the actual telemetered data with the expected data.

The figure below illustrates an example of actual and predicted pressure. The solid curved line represents pressure samples, and the dashed line represents the predicted pressure values plot. In this example, the predicted pressure happens to have no slope.

Slope of the Line

The number of data samples used for calculating the slope of the pressure plot is configurable. A minimum of two and a maximum of 15 data points may be used. Running averages are maintained for the samples over a preset time interval. The system then extrapolates the next value (y) by applying the slope (m) and time-base period (x). If the resultant value falls outside of the deadband DB1, a second check is performed when the next sample is obtained. The second check is performed against the second deadband value, DB2. If this limit is also violated, a Pressure Deviation alarm and event are generated.

Flow Rate Checks

If both pressure limits are violated, flow rate deviation processing begins using the record's configured list of flow rate points. The checking process continues for a configured period of time.

Flow rate deviation calculations use the same technique employed for pressure deviation, with each flow rate having its own set of samples and calculations.

The record can be set to stop processing flow rate violations when there are no pressure violations. This ensures that flow rate processing only takes place when there is an active pressure violation. Controllers can inhibit or enable processing for each flow rate point.

Telemetry Failures

In the case where communications are lost between AVEVA Enterprise SCADA and the device supplying telemetry data, all pressure and flow monitoring affected by the lost data is automatically suspended, and the affected Pressure / Flow Monitoring (Pressmon) records are marked as stale in easy eXtended Operator Station (ezXOS).

As mentioned previously, running averages are stored for each slope being calculated. The Pressmon application can be configured to reset its stored values automatically when communications are restored. The Pressmon application can also be manually reset by administrative staff, or by anyone with the required authorization level.