S7-300 and speed control

dimigav · Dec 13, 2013

I wrote a program for a machine and now I must add new features.
I must follow the speed of another machine using load-cells and potentiometer for micro-adjustment. I need to know a technique for this.

Thanks!!!

JRW · Dec 13, 2013

Post a sketch
You following the lead machine by an analog signal?
Give us more detail

dimigav · Dec 14, 2013

I try to read the speed from main motor M with tacho that gives 0-10V analog signal. But, because the type of the fabric I don't want tension, so I use a loadcell that also gives 0-10V calibratided from 0-10Kgrams. And with a potentiometer I select the tension (Kgrams) that I need. The analog signal from that goes to a frequency converter driving the M1 motor.

Thanks

JRW · Dec 14, 2013

Very nice sketch
Looks like a tenter frame with a folder (load cell trim)
I've worked on a few of those- I hope this logic helps
Retrieve this sample and run it on PLCSim. I tried to comment it to your motor names etc..
This block also does a "draw percent" if you need it for motor M2

dimigav · Dec 14, 2013

Yes is a stenter with folder, but M1 and M2 is a squeezer unit.
For the M2 I need only a pot to increase little bit the speed if needed.

JRW · Dec 14, 2013

so you will have a pot for M2? (that wasn't mentioned in post 3)
Then use the same FB again (with different instance data block) but only give the draw values HI and LOW a small trim value
Set the bit for Mode Ratio to false
The out put "follower speed" will go to M2's drive
I hope that makes sense

dimigav · Dec 15, 2013

I thing is OK. Thanks JRW!!!

If I want to give the number of the tension from an OPERATOR PANEL in kg and not in percent I must scale the tension_kg number in percentage and then put it into FB100?

JRW · Dec 15, 2013

Your welcome.
Just remember the internal PID is 0-100. So scale your 0-10kg to 0-100 and send to "OperatorSettings".TensionSetpoint.
So replace network 1 with your own scale instruction

dimigav · Jan 3, 2014

how critical is to use OB35? The program is very large (I mean the other program). So, can I use OB1 (in my CPU not supported OB35, or any cyclic interrupt) to run the speed control?

JRW · Jan 3, 2014

What s7 CPU doesn't have an ob35?
Remember , just because it's not in the blocks folder doesn't mean it can't be inserted
I recommend you call this code from ob35
Just create an fc, then put this code in the fc you just created.
In your timed cyclic ob , call your fc

You can try from ob1 but you probably will have trouble tuning it

dimigav · Jan 3, 2014

Cpu 312ifm (6es7 312-5ac02-0ab0)

JRW · Jan 3, 2014

Interesting!
I stand corrected, I don't see 312's very often.

Try a 100ms timer bit to the call for an FC with this FB in it

Some of the folks here might have better ideas but this should work

KalleOlsen · Jan 4, 2014

JRW said:
I stand corrected, I don't see 312's very often.

I have never touched one my self.
But from the docu it looks like the newer model chews code quite fast. And it has got OB32, 33, 34 and 35.

Kalle

dimigav · Jan 25, 2014

Dear JRW,

I started to test the machine and I found a problem.
FB100 never gives speed lower than the lead_drive_speed, even if the feedback from the loadcell is zero (and of course the setpoint is positive).
Why??

JRW · Jan 25, 2014

Make sure inside the PID settings (instance data block)
Low out is -100
High output is 100
This will give a +10 to -10 % output as long as your input to FB is .9 and 1.1 default values

S7-300 and speed control

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