Rockwell Automation 1757-FFLD Linking Device Configuration Manual - Manual (Page 92)

Publication 1757-PM002A-EN-E - June 2006
4-38 Applications
17. Right-click Pressure_Loop and select Verify to verify the routine.
To add robustness into the strategy, add logic to handle bad quality
inputs or loss of input. You must force the PID into manual when the
input is determined to be faulty so that you are not attempting to
control with questionable field data as a reference.
18. Select the PID block properties button and edit it to expose the PVFault
and ManualAfterInit input pins.
The PVFault pin will force the PID function block into manual when
the input is true and the ManualAfterInit pin will force the PID function
block into manual when the CVInitReq is true.
19. Wire the existing FFLD:0:I.In[1].InitPrimary input reference to the
ManualAfterInit input pin.
This signal will force the PIDE fucntion block into manual when the
initialization signal is received.
20. From the Move/Logical category of function blocks, select the BOR
function block.
21. Wire the “Out” output of the BOR function to the PVFault of the
PIDE function block.
22. Wire FFLD:0:I.In0Fault using an input reference connector to the In2
input pin of the BOR function block.
23. Finally, wire FFLD:0:I.In[0].InitiateFaultState using an input reference
connector to the In3 input pin of the BOR function block.
These inputs will cause a PVFault condition based on input quality of
condition.
24. From the Select/Limit category of function blocks, select the HLL
function block.
25. Wire the “LowAlarm” output of the HLL function to the In1 of the
BOR function block.
26. Wire “FFLD:0:I.In[0].Quality” using an input reference connector to
the In input parameter of the HLL function block.
27. Edit the HLL function block so that the HighLimit is 4.
This function block will evaluate the quality signal of the fieldbus data
and send a true signal if the quality association is BAD; 0.