power outs

hi. i'm trying to write a program for a class that i'm in. i have it finished apart from the last section. it asks us to ensure that the program will take up where it left off if theres a power out. and i can't find any information on this in the books or in the online tutorial. Can anybody tell me even what commands i need to use to do this?
thanks in advance
Sarahjane

I have done this useing the HMI, set all modes to recover last states before power off.
If you get a reply that it can be done in the program logix please e-mail it to me also.

Thanks
Regards: Doug

Hint #1:

From the manual on this site (http://www.plcs.net/chapters/parts3.htm):

DATA STORAGE-Typically there are registers assigned to simply store data. They are usually used as temporary storage for math or data manipulation. They can also typically be used to store data when power is removed from the PLC. Upon power-up they will still have the same contents as before power was removed. Very convenient and necessary!!

Hint #2: Browse whatever PLC manuals available to you for the word "retentive". "Retentive memory", "retentive coils" etc. All the PLCs have this feature.

Good luck.

In some PLC's the type of coil that you use determines whether it "retains" its last state in memory when the power is shut off (like having the power shut off is something that you want to have happen with a PLC in the first place).

Retentitive coils "remember" their last state when the power is shut off. These are the ones to use when you have a situation where an event has happened and you don't want to "forget" if the power gets shut off.

This is where you need to crack open the manuals, seeing as you intend to keep the make and model of your PLC a state secret.

Read up on retentitive coils.


John

thank you for all your help. we don't actually have a plc, just Gx developer software.

sarahjane,
Probably they want you to use Retentive-type timers, counters and memory locations to save the settings of variables in your program. Retentive devices "retain" their settings even though power is lost or turned off. Most counters in all brands of PLC are "retentive", and the RTO and RTF timers (in the Allen-Bradley PLCs) are also retentive.

In addition to considering how to make the PLC remember where it was before the power failure, it is important for the control logic to know where it should be as soon as power comes on. For example, you may want to put a certain cylinder in the retracted position when power comes back on, regardless of its position on failure. You may not want to turn on a large compressor as soon as power comes back, to allow lubrication and cooling systems to come back on and stabilize.

This is an area where understanding of the physical system and a lot of common sense come into play.

One of the things that you must remember is that you MUST confirm that the system will Fail Safely!!!!! And stay that way on power up.
David

If you are using GX Developer, and selected CPU is not FX,
only L-devices are latched during power los. In FX CPUs some
D-devices are latched as well (read manual) and if you are using
bigger CPUs set the latched areas in the parameters.
For example if you have set D-devices to 12k that means you
have 12*1024=12288 registers. To latch them all, specify
latched range to be 0..12287