Help with Idec PLC FC4A-D40K3 - safety stuff
Help with Idec PLC FC4A-D40K3 - safety stuff
(OP)
I work for Keystone Resort in Colorado. We are using Idec PLCs (FC4A-D40K3) to control our ski lifts. I was curious about some safety features that are associated with PLCs. I have searched on the internet and have found some general information about watchdog timers and power failure checks. My two main concerns would be the watchdog timer and a low voltage dropout. I would like to have the ability to implement a watchdog timer fault and a low voltage fault.
Any suggestions appreciated. :)
Any suggestions appreciated. :)





RE: Help with Idec PLC FC4A-D40K3 - safety stuff
You cannot rely on the PLC internal logic or PLC inputs/outputs for life safety functions.
For better PLC reliability, you can get into parallel PLC processors, redundant I/O, voting logic, fail-safe configurations, UPS power, etc.
RE: Help with Idec PLC FC4A-D40K3 - safety stuff
Thanks for your concern but you are assuming. We have safeties in place that are wired in the fashion you mentioned. My question was directed at the PLC level. Say the program craps out on a divide by zero or gets caught in some "loop", that is what the watchdog timer is for. Say our batteries start to crap out, then can this particular PLC throw a fault and shut down?
The PLC monitors detachable chairs in the couture of the terminal. How can one "hard wire" in a safety monitoring system? It would not be feasible or maybe even possible to do.
RE: Help with Idec PLC FC4A-D40K3 - safety stuff
RE: Help with Idec PLC FC4A-D40K3 - safety stuff
RE: Help with Idec PLC FC4A-D40K3 - safety stuff
That's an interesting attitude.
Best of luck.
RE: Help with Idec PLC FC4A-D40K3 - safety stuff
Of course you could always pay a consultant who will charge enough to make it worth his while putting up with your attitude problem. None of us get paid for doing this: we just have a chance to help like-minded individuals and get some help ourselves now and then. A little bit of friendly courtesy goes a long way.
As for your questions:
Low voltage alarm -
Could implement it either through an analogue input on the PLC with a compare function to set a digital flag, or use an external sensing relay and wire it in through the digital I/O. The latter will almost certainly be cheaper unless you have a spare analogue input. Use the input to drive the PLC to a safe state.
Watchdog -
Are you trying to detect that the processor is 'alive' or that the program is executing? What do you intend to do with the watchdog if it detects a fault condition?
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One day my ship will come in.
But with my luck, I'll be at the airport!
RE: Help with Idec PLC FC4A-D40K3 - safety stuff
ScottyUK,
No analog inputs used with our application. And with the watchdog in the event of a timeout, I would have it shut down the lift. If the PLC can't cycle thru its "ladder", then it is not monitoring properly.
An email I got today from Idec. My questions to Idea were the same that I posted to this forum. Guess my "bad attitude" really got to him.
RE: Help with Idec PLC FC4A-D40K3 - safety stuff
The Idec MircoSmart does have two analog inputs. One is connected to a pot and the other is two open pins that measure 0-10 volts. It is located on second to left "column" and above the programming port.
As
RE: Help with Idec PLC FC4A-D40K3 - safety stuff
RE: Help with Idec PLC FC4A-D40K3 - safety stuff
Good info - thanks. I've not met this brand of PLCs before. Sorry about earlier post - I shouldn't post when I'm in a cranky mood. Can I give myself a black star?
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One day my ship will come in.
But with my luck, I'll be at the airport!