Replacing existing programs

I had a small program running on my PLC trainer (ab ML1K), 3 inputs (toggle switches) and 6 outputs (small pilot lights). I wasn’t sure if I could upload (or download ) the new program (zombie box) on the PLC with the devices intact and add 1 more input for the “start switch” and 1 output for the solenoid. Would it be safe to proceed… Because of my uncertainty I disconnected everything and just wired the required devices to run under the new program, was I right to do that or was there an alternate solution, comments?

You could have left the other inputs and outputs intact. if the new program doesn't refer to them then they will affect nothing and not turn on. Your new logic will jsut use what it references.

Be aware that (in your new program) any data values left in the output image will still be there...If there is a "1" in 0:0/7, and it is not referenced in the program, then that 1 will happily stay there and that output point would stay on as long as the PLC is in run mode.

It is simple enough to open up the data table and over write it with a 0 to turn it off, if something like that were to happen. And, since it's a trainer, no harm should be done if one of the outputs were left on inadvertently in such a manner.

If the new program doesn't refer to them then they will affect nothing and not turn on.

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Even if your new program DOES use the same input or output addresses, it can still work. For example, your Zombie Box needs a start switch. If one of your old trainer inputs is a maintained-contact selector switch, then use that input address in the Zombie program for your start switch.

As for the output lights, don't worry about them. Your Zombie box only had 1 solenoid outupt, and you can use any of the lights to simulate that solenoid. It will not matter whether the others are on or off, but they should stay off.

Any inputs or outputs not used by a new program can be left wired up to the old devices, as long as this does not create some type of human safety problem - for zombies, you don't have to worry because they are already dead.

For future reference, here is the thread about the Zombie Box and Casket Knocker:
http://www.plctalk.net/qanda/showthread.php?t=75191
I see that there is an error in the Casket Knocker program. I somehow duplicated Rung 001, so delete the duplicate Rung 002.

I did what you asked

Lancie1 said:

I see that there is an error in the Casket Knocker program. I somehow duplicated Rung 001, so delete the duplicate Rung 002.

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downloaded to the PLC and it pounds three times in a row and that's it! It looks like the zombies gave up very sad..
I watched as the program unfolded and it seems to stop functioning at either rung 6,7 or 8, what do you think..btw your derby soap box is realy cool, it reminds of me of grandpa Munster's dragula http://www.munsterkoach.com/Dragula1.htm

I will check it using the LogixPro Simulator and let you know if I find an error.

I forgot to add the reset instruction for the counter, to allow it to recycle. Add a new Rung 003: XIC C5:0/DN triggers a RES for the C5:0 Counter.

 

    |     C5:0/DN          C5:0   |

003 |-------| |-----------(RES)---|

    |                             |

Kapooski, I am sorry that I messed up your program. I seem to forget important things a lot lately. I once could focus on a program for hours at a time. Now I am lucky to get 15 minutes. That is why I had to quit working in the field - no longer reliable. Guys, it may happen to you, so store up some nuts for those days when you will have survive on what you did in the past to put food on the table.

Well my friend Mr. Lancie1 (I hope I may call you that) I wish I knew everything that you've forgoten about PLC! And I would not worry about the "knocker", I got an entire year until next Halloween. Right now I have the box rigged that somebody is trying to close the lid so "it" can be left alone...(tested it without PLC,video is next..)

I added the rung which would be rung 004, (I think because some of the instructions move up one rung because of removing the duplicated instructions as instructed, so rung 003 would be the T4:1 DN with CTU C5:0. Please tell me if I'm right...
My next question on rung 0002 what does I:0/0 do?

I used I:0/0 for your Start/Stop switch. That is an external input that controls whether or not the program is "active" or operating. With this switch ON, it will run. With it off, it will stop running. On Rung 002, the I:0/0 input is enables or disables Output O:0/0. Because the outputs are the part that creates actions, I usually make sure I have those disabled when my Start switch is off. That way, if someone accidently deletes the switch, say on Rung 000, then the output will still go OFF when the On/Off switch is turned off (using the belt and suspenders method for beginners).

Thank you for the explanation, after looking at the program again rung by rung it makes perfect sense.