PLC comm problem/ PLC Inoperative

[raan]

I have been working on a pwm motor control project for an electric  vehicle for the physically limited and have been disconnecting power to the plc since the plc normally runs on batteries which  also power the drive motors.  The PLC has been retaining the program and works fine after reconnecting the batteries. However the last time I reconnected the plc would not communicate nor would it execute the program. The red led below the rtc led is on. I believe it is the pause light. Any ideas on to restore the plc back to health?
raan

[support]

Your program seems to have been corrupted and that may be the reason why it doesn't work. Please follow instruction in your installation guide on the use of DIP switch #4 to reset the PLC program. The following are the steps:

1) Turn ON DIP switch #4.
2) Reset PLC by turning OFF power and then ON again
3) Open "Serial Communcation Setup" in TLServer and change the baud rate to 9600. Then type in the command "IR*". You should get a "IR01*" in return.
4) Now, transfer a blank program into the PLC to clear out the corrupted EEPROM.
5) Turn OFF DIP Switch #4
6) Reset PLC as in 2)
7) Change the baud rate to 38400.
8) Now the PLC should be workable as per normal.

[Will Steed]

This is exactly what happened to one of my systems using an MD2424, with the same problem showing up that Alan described on his post on the 28 Nov 03.  I also had a pause indication on the PLC and I was getting a "Transfer Protected By Passord" dialoge box prompting me for a password when I have never enabled the password protection on any of my PLC's.

I tried the reset instructions described below to no avail.  I repeatedly tried to upload a blank and new program and couldn't get it to work.  When I ran the online monitoring it said that the program had encountered a fatal error and was halted.  The system had been working well for a week prior to this.  

Today I went to the site and found the program running properly with no pause indication on the PLC.  The only thing that happened overnight was that the system was shut down.  I don't understand what happened and I also hope that this doesnt happen often as the the PLC is on a remote system running a screening plant.

The power for the PLC is drawn from the battery/alternator system on the Cat engine.  Originally I wasn't using a capacitor filter on the wires for the PLC, when the program halted I had thought that the cranking amps when starting the engine may be causing a voltage spike to the PLC and corrupting the program.  I have since added the capacitor.  Please advise if there is anything else that can be done to prevent the above problems.

Thank you

Will Steed

[support]

Will, I am a little confused. You mentioned that you tried the reset instruction described in this post to no avail. Yet you mentioned that when you went to the site later you found that the PLC is running properly. Does it mean that initially you tried the instruction remotely? How were you able to turn ON DIP Switch and perform the reset if you were not at the site?

If your PLC gets back to running properly after a overnight shutdown without your manual intervention or transfering the program to the PLC, then it is likely that it RAM copies of the PLC CPU has been corrupted by the electrical noise in the system but the EEPROM copy is still intact. So after a power down and reset, the PLC runs the program properly again.

Protecting the supply to the PLC is important. Power to the microprocessor electronics is like life blood to human being. The PLC I/O circuit already filtered most of the noise coming from the  I/O but the power supply noise goes directly to CPU.  

Diesel/gas power generator are pretty noisy fellow. However, most power surge filter on the market are for AC circuit. You may want to try to search for a DC power filter to improve the reliability of your system.

[Will Steed]

Thanks for the quick reply, that is why I enjoy working with your product.  The great support.

Let me clarify a bit, I went out to the site earlier in the week when the customer detected the problem, I was unable to get the system to load a new program at that time, I tried the reset procedures at that time when I was on site.  What was really perplexing was the fact that whenever I tried to upload the program I got the Password Dialoge box.  Like I said I have never enabled the password protection.
When I went out to the site later in the week and found the PLC running properly, I did not have my laptop with me and therefore was unable to see if it would let me reload the program.
Do you have any ideas about the Password problem, or is there a back door around this function when it pops up.  I am using version 5.1 of the software.

Thanks

Will

[support]

If the PLC seems to be working properly and you are able to perform online monitoring, yet unable to transfer new program to the PLC, then you type in the following command at the serial command prompt in the TLServer:
 
@01$cKILL00*
 
(notice small letter "c" and capital "KILL")
 
That would delete the corrupted program and password which must have been there because of the corruption.  You will need to re-transfer your program to the PLC because the original program in your PLC will be deleted.