S7300 CPU upgrade advice

STL???

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Join Date
Sep 2005
Location
UK
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Happy new year everyone,
Yes i havent been back at work a day and i'm in trouble...

I have an inherited machine which basically hasnt worked well since an upgrade (additional crane) prior to its transfer to us.

The manufacturer has gone bust, so no assistance there.

Basically OB35 is called every 10mS to execute positioning code for 2 transporters, this morning i had the following fault in the diagnostic buffer:

ErrOB35.JPG


If i understand the Fault correctly, the code in OB35 doesnt execute completely before the next call is triggered 10mS???? then OB80(loaded in the PLC)is called.


I spoke to a guy who was involved with the project from the start, and he said that a CPU Upgrade was suggested when the second crane was installed(request declined) so the OB35 code was toggled for each encoder per interrupt.

The CPU currently installed is a CPU 316-2 DP
6ES7 316-2AG00-0AB0 /1.1

The program is large and riddled with Any/DB pointer code, the scan time is also 130mS+

I'm looking at upgrading the CPU and seeing if this helps, although a blank OB121 PROG_ERR is loaded - so i expect mistakes in the code.

despite this the machine still runs although it under/overshoots alot.

What would you guys do?

Thanks for your help
Steve
 
I would definitely look into exchanging the 316-2DP with a 317-2DP. You can expect the new CPU to be approx 5 times faster than the old one.

Another option could be to try and optimise the code in OB35.
If it contains calls to subroutines, then maybe moving all the code from the subroutines into OB35 and changing the parameter passing to direct adressing can give a boost.

Code optimizing can be fun (!), maybe you can post the content of OB35.
 
Hi Jesper & Simon,

I was looking at the spec's for the 317 and although its not a straight exchange in the hardware config, the speed is significantly faster (hopefully not that fast - it screws something else up :D).

With regard to the code, OB35 is made up from various smaller FC's so ill post them individually as i run into issues.

Thanks again - Steve
 
I have a couple of ideas.

Maybe the overshooting is caused more by the 130ms cycle time than (directly) by the timeouts of OB35. Maybe the startsignal to contactors or VFDs are handled outside OB35.
If this is the case, try to reset the startsignal directly in OB35. I also think you have to access the outputs directly (PQx.y).

Calls to error OBs in itself increases the cycle time, so some kind of improvement can be achieved by avoiding the timeout OB80. Try to increase the set time for OB35 from 10 ms to 15 or 20 ms.
 
And the blank OB121 is VERY suspicious.

Program a counter in OB121, only to see if it is called frequently.
If that is the case, then that also increases the cycle time.
 
If the single axis crane did not overshoot, the double axis crane overshoots most likely due to the fact that the position loop is now running every 20ms instead of 10ms.
 
Hi

correct me if I am wrong but the error sits in OB35 ... whatever it does is longer than 10msec.Can't you reduce the software that's called up in OB35 or optimise it .

looking at ( a very old) instruction set a simple
O I x.x takes 0.2us on a 313
O M x.x takes 0.6us
O Dbxx.DBXyy.y takes 2.7us
if a lot of DBX operations are used it may save time to convert to MW

Just an idea

Eric
 
Hi Eric,
Thanks for your input, everything is DB format even instance DB variables(Stats) are referenced/wrote to outside of the Calling FB.

I have a lot of questions with regard to the methods used in this program but ill start a new thread for them.

Regards Steve
 

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