Problems with timers on S7-224

I am having problems with the timers on the S7-224 PLC.
Basically the operation goes like this:
1) A pack is pushed through the sealing jaw of a sleeve sealer.
2) When the pusher has returned home the sealing jaw closes.
3) With the sealing jaw closed a current is passed through a resistance wire cutting and sealing the film around the pack.
4) When a set time is reached the current is turned off and the sealing jaw opens allowing the next pack to be pushed through.

The problem I have is the time the cutting wire is switched on has to be automatically varied to allow for the fact that there is already heat stored in the wire after the first seal. ie to stop the wire being over stretched and eventually breaking.

In other words the seal timer has to constantly change up and down dependant on the number of packs the line is running at at any particular moment.

I have written and tested the part of the program to change these values automatically but the timer just won't seem to accept anything other than the first value that is pushed into it. I have tried VD, AC and MW but nothing seems to work.

Any suggestions?

Thank You.

Dear Anonymous,

I would suggest that using a timer to adjust the heat in the wire would be unreliable. Heat in a conductor = resistance. As the conductor gets hotter, the resistance will rise. This natural phenomena should allow you to detect the heat of the wire by measuring the voltage drop from one end to the other, or the current passing through it.

Or you could use a simple adjustable DC motor control to regulate the current & voltage in your wire, preventing it from becoming too hot and or allowing you to set a constant fixed heat setting when turned on. I would suggest you check out IPC Automation.. They make a small 1/4 hp DC motor control that my help.

I have one suggestion: why don't you use a variable to determine the time instead of a constant?

After all, variables can be adjusted, that's why we call them variable and not constant .

Regards,

Check back here in the next day or two. I'm sure Ron (rsdoran) will offer his suggestions. He recently did a very similar project. Try searching for "sealer" in this forum for a few starting points. Here, I'll automate it for you. Click the search button below...


beerchug

-Eric

Thanks for the comments, even if some were slightly sarcastic. I have played with the program a little more and have found where I was going wrong. I had forgot to convert the real number into an integer. Everything works now.
Thanks again

Rocco,

My wife says I'm sarcastic too.. I don't get it? Wadi say?

Like they say, if you want a friend.. Get a dog.

I'm glad you found your problem. and appreciate your last post saying so. Were always courious to see the outcome.

Have Fun!

I didnt mean you elevmike. sorry for any misunderstanding.
Rocco