Modicon Premium operation initialization

Hi every body,

I'm using a Modicon (Schneider) Premium Hot Standby PLC (2 redundant CPU's).
My problem is that after the PLC power failure recovery, it continues the operation cycle at the point it had left when the power failure occurred. That means all the connected equipment which were working will continue to work after power recovery. I think that was due to the fact that a warm start has been done in the PLC. That situation is not acceptable in my application because safety is required and the system should be stopped after power failure happens. I've gone through the documentation and found that Cold Start will help to initialize the memory area. I tried to set the system bit %S0 at the first scan cycle (using %S21), but it was unsuccessful, the PLC continued also the operation. Also I tried to check "Initialize %MWi on cold start" option from the CPU configuration but also doesn't work and the "Cold Start Only" option is missing. Any ideas?

How about using an external connection to tell if power has been removed. This way your initialization programs will then be called.

Just a thought.
Regards,

Thanks Garry, But I'm trying to find out a standard solution, I believe that Cold Start will do the job but I need to know how to force cold start after power recovery.

Ahmed Sami
Senior Automation Engineer

Euler this can be due to a lot of factors. not only how the cpu starts. If for instance you have grafcet it will not reset unless it is told to do so or if the cpu is reset (not a power cycle). First inspect the software then let us know

euler13 said:

Thanks Garry, But I'm trying to find out a standard solution, I believe that Cold Start will do the job but I need to know how to force cold start after power recovery.

Ahmed Sami
Senior Automation Engineer

Click to expand...

You can't force a cold start after a power recovery, a power recovery is a cold start, also you cant write to system bits, they are generally read only.

You need to detect a warm or cold start happening and initialise your code accordingly.

We use these bits to detect a restart and hold off certain things happening like comms to wait for networks to come back up etc.

If you enable %MW initialisation on start you will loose any set points or data you have in the registers.

As Chud says, its got a lot to do with your application an what you code looks like.

Thank you guys for help.

chud,
My program contains several programming languages but not grafcet, my question is can I have a PROGRAMMED CPU reset rather than using the physical reset switch?

tragically1969,
As I understood from the manuals a power recovery will not cause a cold start unless a "Loss of context" is detected (which is not the case). So I believe the CPU is always performing a warm start at restoral after power supply outage. Also I thought that I can not write system bits but the manuals state that "Initialization from Unity Pro ,Forcing the system bit %S0" is one of the cold start causes which made me confused. I know I can program my shutdown procedure at the first scan cycle of the program. But what I need to know if there was any standard way to have a programmed (conditional) cold start or memory initialization (which will reset all the memory area except the variables have declared initial values).