A
Problem description:
During download changes a have got a message that area for Hot Standby is too small and download was not possible. After this I made Optimize Project, downloaded all program to PLC and copied program from primary PLC to Standby PLC. Few hours after this I had situation that this PLC lose all inputs from field and all running device stopped with fault status. This fault status is generated when PLC have not signal from digital inputs that drive is electrically ready.
I have checked historical alarms on HMI applications and there is a lot of alarms and events generated exactly in this same time when problem with PLC occurred. There are alarms that devices are electrically not ready (logic zero on input), valves are closed (logic zero on inputs) but physically were opened continuously, circuit breakers were off (logic zero on inputs) but were still on (Circuit breakers can be switch on only manually, in the alarms all circuit breakers were switch off and on in these same time what physically is not possible), that means power supply was always available. This problem repeats few times and we decide switch off Hot Standby PLC. Without Standby PLC one PLC was working properly without this problem.
To solve this problem my first idea was to try optimizing using memory in PLC. I remove all not used functions, remove not used tags, change all equal literals to constants and I made once more optimize project. Also I move to None Transfer Area 1400 registers 4x for reduce cycle time. I also installed on the rack new CPU. After download program and start system this same problem cam after about one hour.
The last time I make few times complete download to this unlucky PLC. After download I switched power on Standby PLC cleared memory and started copy program from Primary PLC. After finished download I sow on Standby module that Primary PLC switched automatically to Standby mode and Standby PLC switched to Primary then after one second both PLC switched back to previous status. In this time I saw that all indications on inputs modules blinked and heard snap from output relays when there were de energize and then energize. Effect of this was these same like described before.
In Project->Special in my project I have set for watchdog timeout 25 (250ms). My cycle time with Hot Standby is about 230-240 ms. Is it possible that this parameter is too small for my PLC? Can I increase this parameter to the maximum value 2550 ms without any bad influence to the stable work PLC.
Please give me any comments for this problem, maybe you know already this situation and you can give me some solution for this.
A have also few questions regarding this problem:
1. How find out the correct length of IEC Heap Size for exchange information between Primary and Standby PLC?
2. How much Global Data should by free for correct work?
3. How much IEC Hot Standby Data should by free for correct work PLC with Hot Standby function?
4. If small area for Hot Standby means that PLC will work not properly or only that I will not be able in the future make any new change in the software but PLC will work still properly.
5. If only free area in IEC Memory is necessary for properly work of PLC.
6. What is the maximum of Cycle Time for correct work PLC with Standby function (In my PLC Cycle Time without Hot Standby is about 85ms, with Hot Standby about 230ms.)?
7. It is possible that me problem can be related with bad communications between both PLC Primary and Standby? For example bad connection via fiber optic cables. How to check the cable?
8. What is the influence for stable work PLC and Hot Standby function to make Optimize Project?
9. How to check a CPU?
Informations below are from program where I made only optimize project and with this project described problem exist. In the brackets I put for compare settings from another PLC, which is working properly with Hot Standby function.
For information: I’m not using LL984 standard.
Project Settings:
PLC Family: Quantum
CPU: 140 CPU 534 14
Memory Size: 64K logic
IEC Runtime: Enable
IEC Heap Size: 948 (1020)
Global Data (KB): 32 (18)
Memory Partition
Maximum state memory: 65024 (65024)
State Memory Used: 64476 (63200)
State Memory Usage: 99% (97%)
Discrete
Coils(0x) 1664 (1200)
Input(1x) 1696 (1200)
Registers
Input(3x) 154 (144)
Houl(4x) 4600 (10300)
IEC Hot Standby Data
Reg(3x): 58500 (51000)
Specials:
Watchdog Timeout: 25 (25)
Online editing: 20 (20)
Memory Statistic (online)
IEC
Total memory: 930,796 Bytes 100%(1,018,104)
Free memory: 395,232 Bytes 42.5% (500,692 Bytes 49.2%)
Used memory
User Program: 398,576 Bytes 42.8% (392,300 Bytes 38.5%)
EFB Library: 16,016 Bytes 1.7% (16,032 Bytes 1.6%)
User Data: 120,972 Bytes 13.0% (109,080 Bytes 10.7%)
Global Data
Configured: 32,768 Bytes 100% (18,432 Bytes 100%)
Used: 31,312 Bytes 95.6% (11,890 Bytes 64.5%)
PLC Scan Time 230 ms/scan (233)
During download changes a have got a message that area for Hot Standby is too small and download was not possible. After this I made Optimize Project, downloaded all program to PLC and copied program from primary PLC to Standby PLC. Few hours after this I had situation that this PLC lose all inputs from field and all running device stopped with fault status. This fault status is generated when PLC have not signal from digital inputs that drive is electrically ready.
I have checked historical alarms on HMI applications and there is a lot of alarms and events generated exactly in this same time when problem with PLC occurred. There are alarms that devices are electrically not ready (logic zero on input), valves are closed (logic zero on inputs) but physically were opened continuously, circuit breakers were off (logic zero on inputs) but were still on (Circuit breakers can be switch on only manually, in the alarms all circuit breakers were switch off and on in these same time what physically is not possible), that means power supply was always available. This problem repeats few times and we decide switch off Hot Standby PLC. Without Standby PLC one PLC was working properly without this problem.
To solve this problem my first idea was to try optimizing using memory in PLC. I remove all not used functions, remove not used tags, change all equal literals to constants and I made once more optimize project. Also I move to None Transfer Area 1400 registers 4x for reduce cycle time. I also installed on the rack new CPU. After download program and start system this same problem cam after about one hour.
The last time I make few times complete download to this unlucky PLC. After download I switched power on Standby PLC cleared memory and started copy program from Primary PLC. After finished download I sow on Standby module that Primary PLC switched automatically to Standby mode and Standby PLC switched to Primary then after one second both PLC switched back to previous status. In this time I saw that all indications on inputs modules blinked and heard snap from output relays when there were de energize and then energize. Effect of this was these same like described before.
In Project->Special in my project I have set for watchdog timeout 25 (250ms). My cycle time with Hot Standby is about 230-240 ms. Is it possible that this parameter is too small for my PLC? Can I increase this parameter to the maximum value 2550 ms without any bad influence to the stable work PLC.
Please give me any comments for this problem, maybe you know already this situation and you can give me some solution for this.
A have also few questions regarding this problem:
1. How find out the correct length of IEC Heap Size for exchange information between Primary and Standby PLC?
2. How much Global Data should by free for correct work?
3. How much IEC Hot Standby Data should by free for correct work PLC with Hot Standby function?
4. If small area for Hot Standby means that PLC will work not properly or only that I will not be able in the future make any new change in the software but PLC will work still properly.
5. If only free area in IEC Memory is necessary for properly work of PLC.
6. What is the maximum of Cycle Time for correct work PLC with Standby function (In my PLC Cycle Time without Hot Standby is about 85ms, with Hot Standby about 230ms.)?
7. It is possible that me problem can be related with bad communications between both PLC Primary and Standby? For example bad connection via fiber optic cables. How to check the cable?
8. What is the influence for stable work PLC and Hot Standby function to make Optimize Project?
9. How to check a CPU?
Informations below are from program where I made only optimize project and with this project described problem exist. In the brackets I put for compare settings from another PLC, which is working properly with Hot Standby function.
For information: I’m not using LL984 standard.
Project Settings:
PLC Family: Quantum
CPU: 140 CPU 534 14
Memory Size: 64K logic
IEC Runtime: Enable
IEC Heap Size: 948 (1020)
Global Data (KB): 32 (18)
Memory Partition
Maximum state memory: 65024 (65024)
State Memory Used: 64476 (63200)
State Memory Usage: 99% (97%)
Discrete
Coils(0x) 1664 (1200)
Input(1x) 1696 (1200)
Registers
Input(3x) 154 (144)
Houl(4x) 4600 (10300)
IEC Hot Standby Data
Reg(3x): 58500 (51000)
Specials:
Watchdog Timeout: 25 (25)
Online editing: 20 (20)
Memory Statistic (online)
IEC
Total memory: 930,796 Bytes 100%(1,018,104)
Free memory: 395,232 Bytes 42.5% (500,692 Bytes 49.2%)
Used memory
User Program: 398,576 Bytes 42.8% (392,300 Bytes 38.5%)
EFB Library: 16,016 Bytes 1.7% (16,032 Bytes 1.6%)
User Data: 120,972 Bytes 13.0% (109,080 Bytes 10.7%)
Global Data
Configured: 32,768 Bytes 100% (18,432 Bytes 100%)
Used: 31,312 Bytes 95.6% (11,890 Bytes 64.5%)
PLC Scan Time 230 ms/scan (233)
