All I/O cards in the DeltaV I/O subsystem support failure action operation. The failure action depends upon the card type. After the controller downloads a configuration to an I/O card, it enables a 2 second RailTimeOut Period in the I/O cards. After the timeout period is enabled, if communications to the controller are lost for more than 2 seconds, the I/O cards will enter the failure action mode. Once a card is in the failure action mode, it requires an exit failure action mode from the controller to resume normal operations. This 2 second timeout period is not configurable by the user, nor can it be disabled.
A card enters its failure mode when communications with the controller are lost for more than 2 seconds. Among the conditions that cause configured I/O cards to enter the failure action mode are:
A simplex controller is removed.
A simplex controller is upgraded.
A hardware or software failure in the controller that interrupts communications for more than 2 seconds.
I/O cards must be receiving DeltaV power and field power to enter the configured failure action mode.
While all DeltaV I/O cards support failure action, a card's failure action operation depends upon its type. All configured I/O cards turn on the red Error LED, but only output cards take any further failure action. The following failure action configuration options are available for configured OUTPUT channels:
Failure Action Mode – Designates if the channel should HOLD LAST VALUE or OUTPUT FAILURE ACTION VALUE.
Failure Action Value – Specifies the value used if the channel is configured to OUTPUT FAILURE ACTION VALUE.
| Card | Failure Action Mode options |
|---|---|
|
Analog Output |
Hold Last Value: The output is held at the last value received from the controller before the failure action condition occurred. Go to Configured Failure Action: The output is driven to the configured failure action value when the failure action condition is entered. Note All outputs values below 1 mA (including failure action values) are clamped to 1mA to ensure that the open loop detection mechanism of the D/A converter is always operable. |
|
Discrete Output |
Hold Last Value: The outputs continue with the latest configuration and output values. This applies to all channel types. If the channel is configured to be continuous pulse output type, it continues with the latest period and duty cycle. If the channel is configured to be a momentary pulse output type, it continues to process the current pulse. No additional pulses can be generated. Go to Configured Failure Action: In this mode, failure action forces the outputs to go to predefined levels. If the channel is configured as momentary or continuous pulse output type, the pulse is aborted for the failure action value. |
Redundant Cards
For redundant Series 2 cards, loss of controller communication with both cards causes both cards to take their failure action, but with slight differences. Both cards illuminate their red Error LEDs, but only the active card drives the field outputs. Removing the active card will NOT cause failure action output values to remain, since a switchover cannot occur when a card is removed.