PLC-5 program downloaded from EEPROM by-self.

[AB2005]

We have a PLC-5 in a printing machine. Few weeks ago, I made some online change in the running program of PLC but did not burn in to EEPROM. So EEPROM had the original program. Today I found that the change which I made was not present in PLC. I suspected that the program in PLC was corrupted and it downloaded the program from EEPROM but such thing happen when battery is low and we cycle the PLC power but I found no battery error and the key was on RUN position. I failed to understand the possible reason that why that problem happened. Any idea?

[HJTRBO]

Power cycle by someone?

[hagos]

Dear Folks,

Long time since I worked in AB PLC's, but I recall that there is a DIP switch at the rack back plane which controls the EEPROM.

Please refer to the manual & let's know what will come up with you.

Cheers
Hagso

[Malcolmt]

It sounds like you have an issue with the setting of the dip switch on the backplane behind PLC.
If 6&7 are off then the memory module transfers each time at power up
If 6&7 are on then the memory module only transfers at powerup if the PLC memory is not valid.
If 6 = on and 7 = off then the memory module never transfers to the PLC. This is the preferred setting if you don't use a module in your system.

[AB2005]

Hello Malcolmt

Sorry for replying late as I was busy for another project. Both 6&7 switches are ON but i did not understand that why PLC memory failed and it loaded the program from EEPROM as there is no error message received about low battery. I have checked the battery voltage and found 3.1V at no load. However I have replaced the battery. Lets see what happen.
Is there any way to check how many times PLC loaded the program from EEPROM?

[yasirkhi]

You must assure that you have original program saved, just in case you. Refer to manual and see what Malcolmt is asking about dip-switches settings.

[OkiePC]

Originally Posted by AB2005

Hello Malcolmt

Sorry for replying late as I was busy for another project. Both 6&7 switches are ON but i did not understand that why PLC memory failed and it loaded the program from EEPROM as there is no error message received about low battery.

The memory corruption that caused the load from EEPROM would have wiped away any error messages, and there are two main causes aside from low battery:

1) Incoming power problem. Electrical noise from high frequency devices, voltage fluctuations, poor grounding and lightning are common sources.
2) Early sign of power supply failure.

There are probably other possible explanations, but those are two that I have experienced.

The use of EEPROM backup can hamper your ability to perform run time edits...Any time there is a mismatch and you have the settings enabled to Load On Memory Error, you run the risk of this happening. So, either defeat the EEPROM, and rely on a PC with RSLogix5 to recover if the fault returns, or plan scheduled burning of the EEPROM.

I have seen voltage level disturbances cause this to happen, if there is a brownout for just a few cycles. We used an expensive constant voltage transformer to supply a steady 120vac to all the PLC-5s I supported and I only saw one power supply failure among some 2 dozen of them. It was ten years old and it wiped itself twice about 30 days between occurrences, and then another month later, no sign of life from the PS.

As for managing EEPROMs and maintaining online editing power: I have the same issue with a bunch of SLCs, and what I do, is put in the rung comment for LAD2 rung 0:"2012-MM-DD: PC : NOT BURNED TO EEPROM!" followed by a list of descriptions of the un-burned edits and save it to our share drive.

When the weekend rolls around or whenever there's an opportunity, I store to EEPROM and then delete that section of the rung comment.

Paul

[AB2005]

Hi OkiePC;

Thanks for replying. I have already installed a true sine wave ONLINE type UPS at PLC power supply some months before. So your second point could be valid that "early sign of power supply failure".
As i already requested "Is there any way to check how many times PLC loaded the program from EEPROM?" Please answer.
This time I am getting this information from HMI. The designed in "emBase" software which have this option that if PLC loads the program from EEPROM, HMI saves date and time. Obviously, HMI collects this info from PLC. I am assuming that may be HMI providing wrong info which needs to be verify by another way.

[OkiePC]

Originally Posted by AB2005

As i already requested "Is there any way to check how many times PLC loaded the program from EEPROM?" Please answer.
This time I am getting this information from HMI. The designed in "emBase" software which have this option that if PLC loads the program from EEPROM, HMI saves date and time. Obviously, HMI collects this info from PLC. I am assuming that may be HMI providing wrong info which needs to be verify by another way.

There is a bit which gets set after a load from EPROM occurs. Your HMI can watch for a rising transition of that bit address and then reset it in order to be able to detect the next occurrence.

The bit is address in an enhanced PLC-5:
S:10/03 "memory module transferred at power-up"