You are not registered yet. Please click here to register!


 
 
plc storereviewsdownloads
This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
 
Try our online PLC Simulator- FREE.  Click here now to try it.

---------->>>>>Get FREE PLC Programming Tips

New Here? Please read this important info!!!


Go Back   PLCS.net - Interactive Q & A > PLCS.net - Interactive Q & A > LIVE PLC Questions And Answers

PLC training tools sale

Reply
 
Thread Tools Display Modes
Old February 1st, 2018, 03:27 PM   #1
aand74
Member
Belgium

aand74 is offline
 
Join Date: Dec 2005
Location: Deinze
Posts: 72
Safety : two hand operation

I have an application where I should do two hand monitoring for safety.
However, I have several standard inputs, and only one failsafe digital input.
For an operation the button on the failsafe input must be pushed together with one of the buttons on the standard digital inputs.
I should think I need to activate two digital inputs for real safety standard.
Has in my case : combination safety input and digital input, any safety relevance?
  Reply With Quote
Old February 1st, 2018, 04:05 PM   #2
the_msp
Lifetime Supporting Member
United Kingdom

the_msp is offline
 
the_msp's Avatar
 
Join Date: May 2008
Location: Northern Ireland
Posts: 568
Do it right and use a two hand control relay. I did one recently, ironically in Belgium, can share part numbers etc.
__________________
Regards,

Patrick

https://www.youtube.com/user/MrMatrixEngineering
  Reply With Quote
Old February 1st, 2018, 04:30 PM   #3
jaden
Member
United States

jaden is offline
 
Join Date: Sep 2009
Location: Pleasant Dale, Nebraska
Posts: 89
Bear in mind that a standard PLC is not safety rated. Outputs can short On.
  Reply With Quote
Old February 1st, 2018, 05:11 PM   #4
keithkyll
Member
United States

keithkyll is online now
 
Join Date: Jul 2005
Location: Heath, TX
Posts: 1,912
As mentioned previously, use a safety relay built for that exact function. See these from Automation Direct.
  Reply With Quote
Old February 2nd, 2018, 03:10 AM   #5
cardosocea
Member
United Kingdom

cardosocea is offline
 
Join Date: Nov 2016
Location: Duxford
Posts: 554
Wouldn't connecting both buttons in series into that digital input do what you need?

I'm not familiar to the standard on this, but seeing as every or nearly every emergency stop button on Earth is wired in series with a couple more, perhaps the same logic can be applied here?
  Reply With Quote
Old February 2nd, 2018, 04:07 AM   #6
Ronnie Sullivan
Member
United Kingdom

Ronnie Sullivan is offline
 
Join Date: May 2010
Location: London
Posts: 414
It's against the regulations cardosocea.

The two buttons have to be pressed within a short time to each other (stops somebody wedging one of them on)
  Reply With Quote
Old February 2nd, 2018, 04:08 AM   #7
nightline
Member
Netherlands

nightline is offline
 
Join Date: Feb 2010
Location: Prinsenbeek
Posts: 354
Quote:
Originally Posted by cardosocea View Post
Wouldn't connecting both buttons in series into that digital input do what you need?

I'm not familiar to the standard on this, but seeing as every or nearly every emergency stop button on Earth is wired in series with a couple more, perhaps the same logic can be applied here?
This is absolute not the way!!! An operator can easily stick one button with tape ore something, and use the other button in "one-hand" mode.
A safety relay mentioned for this function checks for the timing between both rising flanks of both inputs.

Funny thing is that there are also pneumatic types...
  Reply With Quote
Old February 2nd, 2018, 04:36 AM   #8
the_msp
Lifetime Supporting Member
United Kingdom

the_msp is offline
 
the_msp's Avatar
 
Join Date: May 2008
Location: Northern Ireland
Posts: 568
This is not e-stop this is THC which requires the operator to have both hands placed on a separate button for the entire duration of the dangerous movement. The buttons must be spaced a certain distance apart, the height of this station must be a certain height from the floor to prevent button pressing from the hip etc, the buttons must be shielded. The station must be a certain distance from the danger zone. The THC relay has logic that both buttons must be pressed within 0.5s of each other - releasing either button during the operation requires that both buttons must be released and then set again within 0.5s - this prevents an object being placed on one.

http://www2.schneider-electric.com/r...201A55_05).pdf
Attached Files
File Type: pdf two hand control relay.pdf (85.7 KB, 5 views)
__________________
Regards,

Patrick

https://www.youtube.com/user/MrMatrixEngineering
  Reply With Quote
Old February 2nd, 2018, 05:12 AM   #9
lfe
Member
France

lfe is offline
 
Join Date: Jun 2007
Location: France
Posts: 59
The right reference : https://www.iso.org/obp/ui/#iso:std:...851:ed-1:v1:en


About 15 years ago I passed a safety inspection by a risk control company and the use of two normal PLC inputs for the two-hand pushbuttons was accepted, but provided they were pressed within 0.5 sec ... but a lot of time has passed and maybe the norm has changed.
  Reply With Quote
Old February 2nd, 2018, 05:49 AM   #10
Ronnie Sullivan
Member
United Kingdom

Ronnie Sullivan is offline
 
Join Date: May 2010
Location: London
Posts: 414
And here's ya belt and braces circuit diagram
Attached Images
File Type: jpg 2hands.jpg (32.6 KB, 76 views)
  Reply With Quote
Old February 2nd, 2018, 06:51 AM   #11
cardosocea
Member
United Kingdom

cardosocea is offline
 
Join Date: Nov 2016
Location: Duxford
Posts: 554
Quote:
Originally Posted by Ronnie Sullivan View Post
The two buttons have to be pressed within a short time to each other (stops somebody wedging one of them on)
Hadn't thought of that. Thanks.
  Reply With Quote
Reply
Jump to Live PLC Question and Answer Forum

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Topics
Thread Thread Starter Forum Replies Last Post
Safety Lock Status in Safety Program Kalagaraz LIVE PLC Questions And Answers 0 May 11th, 2017 09:15 AM
Contrologix "I/O Not Responding" oxlacey LIVE PLC Questions And Answers 15 April 11th, 2016 08:58 AM
Trying to understand safety PLC's (specifically Siemens) Jieve LIVE PLC Questions And Answers 3 June 24th, 2014 08:27 AM
Estop relay question g.mccormick LIVE PLC Questions And Answers 6 December 6th, 2013 07:54 AM
Review of Banner SC22-3 safety controller kolyur LIVE PLC Questions And Answers 1 June 15th, 2008 07:42 PM


All times are GMT -5. The time now is 06:51 AM.


.