S7 Pulse Train ?

Hi,

I want to start a device every 20 min for aproxm.. 20 sec.. then wait 20min until next start.. S7 timers are driving me mad.. is there a simple way to program this ??

//_ Jim

You can use a counter to accomplish this.
Use a 1 sec pules on the input to the counter.
Use an integer compare block to turn on the output for the device if the counter value is less than 20.

When the counter value is >= 1220 ((20minutes*60sec)+20 seconds) then reset the counter value.

Jemac

okey.. so there is no standard function for this..

I do not think that there is a standard function for this.
It would not be difficult to make your own FC for this.
Once you have written it, you can use it over and over in the
future.

For the 1sec pulse you can use go to the Hardware Config and select the CPU properties. Go to the "Cycle/Clock Memory" tab and check the "Clock Memory" box and enter a memory byte number in the place for it.
Example "5"
Save and download the hardware config and then you can use M5.5 as the 1 second pulse.

ha det god
Jemac

I do not think that there is a standard function for this.

Click to expand...

It depends on what you call a standard function. The simplest way to accomplish this is to use a cyclic interrupt OB (OB30..OB38). Strictly speaking, it's not a function, but it's pretty standard.

Kind regards,

Here´s one proposal that have the functionality.

Anyway, if you are to reuse the code many times it´s better to make a FC/FB and do it like earlier poster suggested.

jvdcande said:

It depends on what you call a standard function. The simplest way to accomplish this is to use a cyclic interrupt OB (OB30..OB38). Strictly speaking, it's not a function, but it's pretty standard.

Kind regards,

Click to expand...

I thought of suggesting the cyclic interrupts, but personally, I like to reserve them for higher level functions (safety, PID, etc)

Plus there are a limited number of interrupts to use. I think 4 on the S7-300 and 8 on the S7-400. I do not know about the S7-200.

Jemac

Okey.. some good suggestions here.. I like to hear ppl that se this in diffrent angles.. Gives me a better picture how the PLC works..

The one suggestion with the FC sounds good, then i can re use this over and over again... And the one with timers is also a way to make it quick..

If i make an FC i suspect that i need the sulution with a memory bit and a counter built in to the FC..

One thing that crossed my mind here is... What if I use, for example counter C10 in my FC.. and say for example thtat i want to use this FC in another S7 program in future.. can there be a conflict with the Counters i C10 is already in use by this program ? Does S7 warn me about this ?


//Jim

Use an FB, STAT variables for memory and IEC counters/timers (SFB4 etc.) - no conflicts.

okey.. But if I use the IEC timers and counter... what shall i put where the ??? of the block is, might sound stupid asking this.. but with the standard timers i only use ex.. T20.. T3 etc.. ?

never mind.. I found out.. But im getting sick of all these DB´s now hehe

Are you aware of the implications of using multiple instance FB's

If you want to make a FC for your ON/OFF timer, I would not use the counter function built in to the S7 software. What I would do is make a FC and store the accumulated time value (the count) in a Memory Word.
You can do this by defining the accumulated value in the IN/OUT section of the header. Then assign a MW to it when you call the FC. I tried it yesterday and it worked pretty good.

I used the following header assingnments:
IN:
TIME_ON INT
TIME_OFF INT

IN/OUT:
ACC_TIME INT

OUT:
TIMER_OUT BOOL

TEMP:
TOTAL_TIME INT

LAD1
TOTAL_TIME = TIME_ON + TIME_OFF

LAD2
IF ACC_TIME < TIME_ON THEN TIMER_OUT = TRUE

LAD3
IF ACC_TIME >= TOTAL_TIME THEN ACC_TIME = 0

LAD4


----------||--------------[P]----------ACC_TIME=ACC_TIME+1
1Sec Pulse ONE_SHOT








OB1

LAD1
______________
| FC1 |
-----------|EN | Q0.0
| TIMER_OUT|------------( )-----
20---|TIME_ON |
| |
1200---|TIME_OFF |
| |
MW 300---|ACC_TIME |
| |
--------------


Please excuse the pseudo-code and the poor ASCII art, but you should be able to understand what I was talking about.

Jemac

jemac25 - when you create an FC like this and want to post it, create the source code (in absolute addressing format) and post that - we can then copy/paste the source code into Step 7 and compile it to produce the block with no typos.

Thanks,
I was in a hurry and I wanted to get the information to Jim before he went home for the day.

Jemac