Emergency Handling of DCS Control System Failures (IV)

Control loop failure, indication malfunction in DCS； If equipped with an on-site control valve, the control valve shall be in a fail-safe state. The process should respond promptly as soon as a failure occurs. If the card supports hot-swappable instruments, they should be replaced promptly to restore normal control as soon as possible.

Abnormalities in the I/O card channels of DCS systems are one of the most common problems. If there are issues with individual channels on the I/O input and output cards, it is possible to transfer the signals from those problematic channels to other redundant channels; however, this requires configuring the signals accordingly. If all the control channels on a card are malfunctioning, the card must be replaced. Currently, DCS systems support hot-swapping for such replacements.

1. Fault in the power supply section of the input card with control points. Phenomenon: The measurement of the control points (the PV value of the regulator) is in an open-circuit state. The corresponding control point does not display properly on the operation station monitor screen. The real-time alarm window on the operation station will display the corresponding alarm message and emit an alarm sound. Action: Immediately switch the automatic regulator to manual mode and control it based on the normal output values, while paying attention to changes in related parameters ； The instrument should be dealt with promptly, and the workshop and relevant departments should be informed. 2. Fault in the non-power supply part of the input card with control points. Phenomenon: The measurement of the control points (the PV value of the regulator) remains in a held state. The corresponding control point does not display properly on the operation station monitor screen. The real-time alarm window on the operation station will display the corresponding alarm message and emit an alarm sound. Action: Immediately switch the automatic regulator to manual mode and control it based on the normal output values, while paying attention to changes in related parameters ； The instrument should be dealt with promptly, and the workshop and relevant departments should be informed. 3. Fault in the power supply section of the card plate with control points. Phenomenon: The positioner of the on-site control valve loses power, which results in a disruption of the air supply and the release of the instrument air acting on the diaphragm of the control valve; as a result, the air-operated valves close completely while the air-shut valves open completely. The control points corresponding to the operation station monitor screen cannot be controlled properly. The real-time alarm window on the operation station will display the corresponding alarm message and emit an alarm sound. 4. Fault in the non-power part of the output cart with control points. Phenomenon: The control valve remains in the position it was in just before the fault occurred, and it cannot be adjusted or controlled using the regulator in the control room. The real-time alarm window on the operation station will display the corresponding alarm message and emit an alarm sound. Treatment: Depending on the actual process conditions, control is carried out on-site using the control valve handwheel or isolation valve; the workshop and relevant departments are notified immediately, and the instrumentation is used to take action promptly.

This post was last edited by jackgao79 on 2009-10-19 at 20:45. Brother, I’d like to share some thoughts. Every system supplier has a random manual. 99% of the causes of failures can be identified. Please read it carefully; the most useful one is that one. All those other experts are nonsense. As for those fatal system failures, it is possible to stop the machine in normal sequence or via an emergency stop; stay calm, and it is best to gather the system’s alarm information and status before restarting it.