S7 PID Controller

shaju stephen · Apr 6, 2008

Dear All,

[font=&quot] We have a Siemens 315 2DP PLC used on Sheet Extruder to control the Barrel & Die zone temperatures (250 to 300 deg C) Total of 18 zones are controlled with FB41 Function Block in the user program.

[/font] During the process, all the Temperature Control loops in the PLC stops updating both the Inputs & Outputs and the CPU seems like "hanging".

Actual Temperature reading (PV) will be same as at the time of "hanging" without any change.

Outputs like "Heater On" and "Cooling Blower On" will maintain continously ON, if it was ON at the start of 'hanging".

After may be 10 minutes, CPU will start updating the Inputs and Outputs.

By the time the for those zones whose heaters were ON, will have high temperature (+ 30C).

For those zones whose blowers were ON will have less temperature.

CPU not showing any error indication.

Thanks & regards to all

S Stephen

cjd1965 · Apr 6, 2008

Hi

Has this ever worked OK before? Usually with a large # of loops it is customary to only process a few per scan to prevent the interrupts from slowing the PLC scan.

It sounds to me your loops are all solving on the same scan

Cheers

rohan tandon · Apr 7, 2008

Was this system working earlier and this 'hanging' problem appeared recently or is it a new setup?

Can you post the program here so we can have a look at it?

shaju stephen · Apr 7, 2008

CPU RAM capacity

thank u all for the support.
our doubt is that 315 CPU RAM (128KB) not enough to handle 16 PID loops?
whether we should go for 317 CPU with RAM 256KB?

Manglemender · Apr 7, 2008

Using a 317 will be better only because it is a faster processor. If the memory were insufficient in the 315 you, wouldn't get the program into it.

As others have said: Did this ever work? Are all the PID loops running on the same scan or are they split into groups running on different time slices?

Nick

rohan tandon · Apr 7, 2008

I dont think anybody can help you if you aren't going to respond to questions...

You are going to waste a lot of money and time if you just upgrade the CPU without finding out the real problem. This isnt a windows PC which hangs and need more memory.

Has this system been working before?

shaju stephen · Apr 7, 2008

this is a new installation.
we face this problem from the begining.

cjd1965 · Apr 8, 2008

Have you paid for machine / software

Sounds like the PLC program does not fulfill its purpose. Get the machine supplier or the PLC programmer to complete the task of getting it to work.

After all, what else is not working...... is it a safe machine?

rohan tandon · Apr 9, 2008

It is most likely a programming error as cjd1965 said. If the machine supplier / manufacturer is not supporting you then you can contact Siemens support in Dubai, there is plenty of local support for Siemens PLC's in dubai.

S7 PID Controller

shaju stephen

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cjd1965

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rohan tandon

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shaju stephen

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Manglemender

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rohan tandon

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shaju stephen

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cjd1965

Lifetime Supporting Member

rohan tandon

Lifetime Supporting Member

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