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Old October 21st, 2007, 01:53 PM   #3
PeterW
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Canada

PeterW is offline
 
Join Date: Jun 2006
Location: Edmonton
Posts: 2,522
Quote:
Originally Posted by Doug Hylton
Donít put logic in the I/O wiring
You quite often find hand/manual functions hard-wired, I don't see anything wrong with it as long as the hand/auto switch gives a signal to the PLC to alarm that its not in auto control.

Quote:
Originally Posted by Doug Hylton
What happens when you hit the ESTOP
I'd never kill the PLC, what does that achieve? The fuction of the E-Stop is to lose 'motive' power.


Quote:
Originally Posted by Doug Hylton
If you have big motors running with frequency drives its safer to keep the power on the drive and allow the drive to decelerate the motors. Donít put contactors between the frequency drive and the motors. This is a no no and you can damage the frequency drive. Killing the power to a frequency drive with the motor running can also damage the drive.
That is correct.

Quote:
Originally Posted by Doug Hylton
Remember that the ESTOP is not just for emergencies often the operators will hit the ESTOP just to go to lunch or take a break.
ARE YOU CRAZY?

The E-Stop should only be used in an Emergency, operators who press an e-stop to go for a break should be educated on the purpose of the E-Stop and if they persist send them out of the door.

I realise that safety has not hit the North American continent yet, I'm working on systems where they zone the E-Stops, so you need to know what the E-Stops stop, this is crazy, you see someone in trouble you want the press the NEAREST E-Stop.

The level of the safety system should be determined by a risk assessment.

If operators abuse E-Stop's where does it stop, press an E-Stop then stick you hand in out of site of the E-Stop?

Quote:
Originally Posted by Doug Hylton
The drawing
Or related directly to a drawing and line.

Quote:
Originally Posted by Doug Hylton
Retentive Memory
Pure choice on what you are doing.


Quote:
Originally Posted by Doug Hylton
Safety Circuits
On the whole I agree, although there are machine builders (Krones is one) that certify safety logic and partially put the safety into the PLC code. You cannot change the code.

Also nowadays there are safety PLC's (like PILZ for example) where all the safety is done safely in the PLC.

I don't like what Krones have done and would never sanction safetyu code in a normal PLC but safety PLC's are a different animal made for purpose.

Quote:
Originally Posted by Doug Hylton
Hot backup
horses for courses, very few applications I have worked on would warrant one.


Quote:
Originally Posted by Doug Hylton
Startup
standard commissioning really, athough saying that when using a Siemens I would normally load the full program and place a BEU at the start if there was no interupt blocks switching I/O.

(EDIT: Actually the reason I wouldn't want the program to be running is because I wouldn't want an uncontrolled accident to happen if something wasn't wired correct)


So

Doug Hylton

What prompted you to suddenly enlighten us with your phylosophy










.[/QUOTE]
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