Remote I/O panel - communication with BRC/NTRL - DO generation without command and DI state changes w/o field i/p
We have been facing problem of digital output status changes from 0 to 1 without any command and digital input status changes from 1 to 0 without actual field input for few minutes and intermittently in a day. This leads to equipment auto start and equipment auto trip anytime in a day.
So, far we have carried out below steps to identify problem.
- Removed prefab cable from affected card . However problem persisted.
- Measured 5volt and 24 volt and found in order. when such phenomena was occurring.
- Change location of affected cards from 3rd from 1st MMU. problem persisted.
- Replaced affected DI and DO cards. Problem persisted.
- Replaced MMU in which affected cards resided . problem persisted.
- Found ICOM and MCOM floating and made grounded with panel earthing. Panel earthpit resistance is 0.5 ohm.
- Formatted controller and reloaded logic. problem persisted.
- Added RS flip flop in DO channel to find out if any command is there in the logic. However, no RS flip flop was found set in the logic and still DO status changes from 0 to 1.
- Confirm all DI and DO cards addressing with configuration and found in order.
Even after taking above steps, we have faced problem of DO status changes and DI status changes without any command or without changes of field input.
As our plant is under operation. we require immediate support for this problem.
Could you check and be sure that you have followed the following recommendation?.
Block Numbering Rules for Remote I/O:
When using RI002 or RIO22 (or a BRC300 as a remote I/O processor) remote I/O block numbering rules are now enforced in the firmware. Failure to properly order the blocks will result in the controller entering Error mode when trying to change mode to Execute:
The function code manual states the following:
NOTE: In order to minimize the possibility of malfunctions, it is essential that the RMP function block (FC146), the RSP function blocks (FC147), and all the slave definition blocks for the remote slaves (FC79, FC83, FC84, FC132, etc.) all reside within the same segment. In addition, these blocks must be sequenced in the following order: FC146 must reside at a lower block number than all FC147s for that link, and the FC147s must reside at lower block addresses than the slave definition blocks and station blocks (FC80) for the remote slaves.