Analogue input question. s7-224

Hi all this is my first post on this forum.I am new to programing PLCs although i have worked with them for many years. I have recently been asked to write a short program for a simple punch and die. I have the program running and it works ok .BUT. now they want to be able to speed the host machine up and down and they want my punch to auto-adapt. This means that i have to set a delay on the outputs as the machine slows down. Conveniently the main drive motor is controlled via a lenze utit which gives out a 0-10v supply proportional to its speed. now, how do i use this analogue input to affest the delay time of a TON timer?
ie at 10 volts no delay
at 3 volts 1 second delay
I am using microwin and although i have only had it a week i am becoming quite conversant in it. but this really has thrown me.
Any help would be gratefully appreciated.

Gareth

Gareth

How many delay steps are you looking at here? Is it just a case of 10v - 3v no delay, 3v to 0v 1sec delay?

To get you started, the analogue input value in the PLC will be between 0 and 32,000 (0v and 10v), you will probably need to do some conversion on this to 'engineering' units. Then using these units you can either use a compare to write a specific value to a memory word area or write your engineering units directly to a memory area. Then on the PT pin of your chosen TON timer, instead of writing a constant (eg +10), use the memory area where you are writing your engineering units/specific values to (eg MW10).

You then have your variable timer, using just the one.

This will need some refining to your specific needs, but hopefully you get the idea.

Paul

Be very careful with this one - can things bump into each other if things go wrong ? if the answer is no , then OK , if yes , is there also a way of hardware interlocking this to prevent equipment damage ? ( assuming that this is not already in place )

Thanks for the quick reply guys. What i need is a delay of 0 seconds at 10v and a delay of 1 second at 3v. And i need the delay to scale at all values in between. 10BASET ..In answer to your question about things bumping in to each other the answer is no its all interlocked. How do i use the analogue input to reference a TP of a timer? Is there a function block which i can use to scale the input? with gain and offset and such? My microwin course starts in january but i need this to work now. (such are the joys of production engineering).

Thanks again
Gareth

Gareth, There isn't a specific function block included for this purpose, it's really down to how YOU want it work. There are several ways to achieve this, using several different functions. Basically, what you will be doing is taking the value from your analogue input and scaling it to something more useful to you (as previously suggested) eg - 0 to 10V will give 0 to 32000 in AIW0 (if it's the first channel you're using),then you can scale or move that into area's of memory to manipulate as you need to. The value (0-32000) comes in as an integer value, so initially you need to use the 'Integer Maths' blocks, then you can do all sorts of things to get the value you need at the timer preset (PT).

If you took the value in AIW0 then divided by 1000 for example, you could then move the result to say VW100, then create a timer and instead of a constant as the preset, you could assign VW100. This would give you a value of 0 at 0V and 32 at 10V (not what you needed, but you get the idea! )


Hope this helps......



Rob.