Enhanced Device Control function block execution

Select the Permissive device option to require a permissive before the state changes to an active state. When the Permissive device option is True, the PERMISSIVE_D input must be True for an Active state setpoint to change the PV_STATE to that Active state. PERMISSIVE_D does not have to be True before SP_D can be changed to an Active state.

However, when there is an interlock to an active state active , the output is changed according to the interlock, even if PERMISSIVE_D is False.

Select the Permissive to Any State device option to require a permissive before the state changes to any other state.

When the Permissive to Any State device option is True, the PERMISSIVE_D input must be True for any state setpoint to change the PV_STATE to that state. When the block is in an active state, even a setpoint to a passive state does not change the PV_STATE if PERMISSIVE_D is False, unless there is a shutdown, a trip, or an interlock condition to the passive state active.

It is sometimes acceptable for the device to lose a confirm feedback for a short period of time without generating a failure. This can happen for vibrating devices. Specify the maximum amount of time for the confirm state to be lost before declaring the loss of feedback signal a failure by configuring the TRIP_TIME parameter.

When the Trip device option is not selected, if the confirm signal is lost for longer than TRIP_TIME (whether active or passive), the device fails (FAILURE_STATE = State n confirm lost ) and OUT_D does not change.

When the Trip device option is selected, if an active confirm signal is lost for more than TRIP_TIME, the device trips (OPERATION_STATE = Tripped, FAILURE_STATE = State n confirm lost, and OUT_D is set to the Passive State.

In a confirmed passive state, a loss of confirmation longer than TRIP_TIME results in FAILURE_STATE = State n confirm lost and OUT_D does not change (same as if the Trip option was not selected).

The block determines PV_STATE from the PV_D value. PV_D is normally a copy of FV_D. However, sometimes the hardware that confirms the device state fails. In this case, the operator can confirm the state of the field device visually. When the field device is in the correct state, the operator can turn on the ignore PV switch (IGNORE_PV = True).

The ignore PV switch is generally used when the hardware fails and the value of FV_D is not relevant until the device is repaired.

When IGNORE_PV is True, the value of process variable (PV_D) is forced to accept the requested output state (OUT_D) as confirmed without using (ignoring) an actual feedback as soon as PV_D is different than OUT_D, independently of SP_D. Select IGNORE_PV in the Block Alarms dialog (right click on block and select Assign Alarms) to generate an alarm and event in the log.

INTERLOCK_STATE is a Named Set where the Named States correspond to the six states of the EDC block.

The default value of INTERLOCK_STATE is 255 (Named State = Passive State). When INTERLOCK_STATE is at default, the block uses the state number defined by the PASSIVE_STATE parameter as the state to interlock the block.

When INTERLOCK_D becomes True again (and when there is no shutdown), and device option Reset Required is False, the OPERATION_STATE becomes Normal, PV_STATE might return to its former state if the SP Track on Shutdown/Interlock device option is False. There is no delay on the return.

When SHUTDOWN_D becomes True or a trip occurs (Trip device option is selected, and FAILURE_STATE = State n confirm lost, where n is the active state), the same thing happens as described above for loss of the interlock input (INTERLOCK_D transitions to False), except that OPERATION_STATE is changed to Shutdown or Tripped and OUT_D is set to the Passive State and not to the state defined by INTERLOCK_STATE.

The OPERATION_STATE Shutdown always has priority over Interlocked and Trip. Interlocked has higher priority than Trip.

The block SP Track to Passive on Active Confirm Timeout device option works with the Passive on Active Timeout device option as described in the previous sections.

The STATE_MASKS parameter defines the output and input combinations of IO_OUT_n and IO_IN_n for each of the six different states that can be contained in the parameters SP_D, OUT_D, FV_D and PV_D.

If all STATE_MASKS Inputs of the SP_D or OUT_D from Shutdown/Interlock/Trip are marked as not used (a grayed out check box) while other states have inputs that are used, the state is confirmed and the inputs determine the PV_D from the other state patterns does not cause the EDC block to fail because the PV_D does not match the SP_D. For example, a Motorized Operated Valve where STOP, OPEN and CLOSE are the setpoints but in STOP, the Inputs are not used for that state (when SP_D is STOP, PV_STATE is set to Confirmed STOP) but if the inputs match OPEN, the PV_D is set to OPEN and no failure is generated.

The requested state (stored in OUT_D) is decoded to the individual IO_OUT_n channel outputs according to the corresponding output state mask. The outputs IO_OUT_n can be either sustained or pulsed, depending on the associated value of IO_OUT_DURATIONn.

When IO_OUT_DURATIONn is non zero, the associated IO_OUT_n is pulsed and the duration of the pulse is defined by this parameter. Otherwise, IO_OUT_n is sustained.

When IO_OUT_DURATION1 = 0, there is no pulse at all, the IO_OUT_1 is the output.

When DISABLE_IO_OUT is False, the EDC block works in the same way as DC block: the IO_OUT_n discrete output channel values are determined from the output mask that corresponds to the current state stored in OUT_D.

When DISABLE_IO_OUT is True, IO_OUT_n are forced to zero, independently of OUT_D.