V
Dear Sir,
On 23.06.2010, at 16:41 hrs., one of our Ammonia Plants got tripped due to PLC-1 (H51-HS) problem. The sequence of events and observations made are as follows:
1). Initially, the following diagnostic displays were noticed on the CUs of the PLC:
1308, 1309, 1310
1407, 1408, 1409, 1410
1501, 1502, 1503, 1509, 1510, 1511, 1512 (non-redundant)
2101
2201, 2205, 2206, 2207, 2208
2301, 2305, 2306, 2307, 2308
All these are connected with Digital Inputs only.
2). Checked the detailed error indication menu in ELOP and found NO ERROR connected with this incident.
3). Checked HZ-PA1-1 building block in ELOP and following was observed:
Fault Mask: 4 (Hardware Watchdog)
I/O Fault: H (Multiple errors)
Faulty position 1 I/O bus: 1308
4). Acknowledged the errors on CU-2. Errors got reset on both the CUs and RUN indication appeared.
5). However, within few minutes, CU-2 has gone to STOP mode. CU-1 was in MONO mode.
6). Within a minute or two, CU-1 also gone to STOP mode. Checked the detailed error indication menu in ELOP and found some of the messages like 187 in CU-2.
7). Tried to RUN the PLC from ELOP with 'Alt+F1' command but in vain. Hence reloaded the latest backup in both the CUs. Subsequent attempt to RUN the PLC has failed and both the CUs have continued to be in STOP mode.
8). Then loaded the program in CU-1 and succeeded in taking it into RUN mode. Display on CU-1 was MONO.
9). Suspecting that CU-2 (F8620/11 Module) to have gone defective, replaced it with spare one. Reloaded the program and is found to be normal.
10). Since this PLC is for a critical service (Shutdown System of Ammonia Plant), replaced the CU-1 as well with another spare one. Loaded the program and redundancy checks were carried out successfully between these CUs.
11)After that plant was running normal with new CUs
You are requested to kindly go through these details and analyze so that the root cause of the problem could be identified at the earliest.
We are available for providing any other information required to facilitate a thorough analysis and taking up all control measures to avoid recurrence of such problems. It may please be noted that NFCL has another four such PLCs (H51-HS) and two numbers H41 PLCs.
I WOULD BE VERY HAPPY IF ANYONE CAN THROW SOME LIGHT ON THIS ISSUE AND HELP ME OUT
G VIRENDRA KIRAN
Manager - Instrumentation
Nagarjuna Fertilizers and Chemicals Limited, Kakinada INDIA 533 003
On 23.06.2010, at 16:41 hrs., one of our Ammonia Plants got tripped due to PLC-1 (H51-HS) problem. The sequence of events and observations made are as follows:
1). Initially, the following diagnostic displays were noticed on the CUs of the PLC:
1308, 1309, 1310
1407, 1408, 1409, 1410
1501, 1502, 1503, 1509, 1510, 1511, 1512 (non-redundant)
2101
2201, 2205, 2206, 2207, 2208
2301, 2305, 2306, 2307, 2308
All these are connected with Digital Inputs only.
2). Checked the detailed error indication menu in ELOP and found NO ERROR connected with this incident.
3). Checked HZ-PA1-1 building block in ELOP and following was observed:
Fault Mask: 4 (Hardware Watchdog)
I/O Fault: H (Multiple errors)
Faulty position 1 I/O bus: 1308
4). Acknowledged the errors on CU-2. Errors got reset on both the CUs and RUN indication appeared.
5). However, within few minutes, CU-2 has gone to STOP mode. CU-1 was in MONO mode.
6). Within a minute or two, CU-1 also gone to STOP mode. Checked the detailed error indication menu in ELOP and found some of the messages like 187 in CU-2.
7). Tried to RUN the PLC from ELOP with 'Alt+F1' command but in vain. Hence reloaded the latest backup in both the CUs. Subsequent attempt to RUN the PLC has failed and both the CUs have continued to be in STOP mode.
8). Then loaded the program in CU-1 and succeeded in taking it into RUN mode. Display on CU-1 was MONO.
9). Suspecting that CU-2 (F8620/11 Module) to have gone defective, replaced it with spare one. Reloaded the program and is found to be normal.
10). Since this PLC is for a critical service (Shutdown System of Ammonia Plant), replaced the CU-1 as well with another spare one. Loaded the program and redundancy checks were carried out successfully between these CUs.
11)After that plant was running normal with new CUs
You are requested to kindly go through these details and analyze so that the root cause of the problem could be identified at the earliest.
We are available for providing any other information required to facilitate a thorough analysis and taking up all control measures to avoid recurrence of such problems. It may please be noted that NFCL has another four such PLCs (H51-HS) and two numbers H41 PLCs.
I WOULD BE VERY HAPPY IF ANYONE CAN THROW SOME LIGHT ON THIS ISSUE AND HELP ME OUT
G VIRENDRA KIRAN
Manager - Instrumentation
Nagarjuna Fertilizers and Chemicals Limited, Kakinada INDIA 533 003
