memory

[aakash]

hi 

i have question the device memory in plc ,is that automatic erased as plc is off ,i wana ask as taking the back up i havent check the device memory .Can it effect the program or not

[Theuns]

Hi aakash device memory is used when there is a power failure etc set by the developer for the program or lets say process  etc. to continue when power is restored if u made a backup of the program for reasons unknown like plc failure etc that would be fine. If however u want to reload the program lets say while halfway trough process or such situation u will have to set the relevant bits etc manually

[Ron_S]

It depends on how the program is set up in parameters (and which plc)

Normally you don't upload the device memory when saving the program from a plc.

If the memory area is set to retentive it will not alter after a power off

Programmers know this and put important data in retentive memory and temporary data in none retentive.

Just a word of warning: I did it a long time ago so I know

If you do upload the memory,  you are saving the program in the state it was when you uploaded it.

If you down load the whole program and the memory the machine will be put back in the state you uploaded it at

This can have disastrous consequences.

My example:  I did this on a brick stacking machine. (it took bricks from one conveyor and built them up into a cube on another conveyor)

I uploaded the memory on layer 1 and put it back while it was on layer 10; Result - the brick layer grabber tried to put its load on layer 2

crashing into the cube of bricks and smashing the grab and bricks and everything............Red face..... lesson learned.