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Safety Relay

03/23/2017 10:56 AM

Does anyone know where i can locate some good documentation on how a safety relay works?

or perhaps a video somewhere?

I have done some preliminary searching but have not really found much except advertisements. Im trying to understand how this thing works in a general sense

Thanks

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Anonymous Poster #1
#1

Re: safety relay

03/23/2017 11:00 AM

Try here.

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#2
In reply to #1

Re: safety relay

03/23/2017 11:08 AM

Thanks, yes i have read that

looking for more technical circuit description

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Anonymous Poster #1
#3
In reply to #2

Re: safety relay

03/23/2017 11:12 AM

One of the documents in the References has 14 authors, all named.

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Anonymous Poster #1
#4

Re: safety relay

03/23/2017 11:26 AM

There are at least 20 videos on this topic in YouTube.

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#6
In reply to #4

Re: safety relay

03/23/2017 12:08 PM

They are all advertisements as i have stated above

They are nothing but sales videos made by the manufacture

I have watched many of them

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#7
In reply to #6

Re: safety relay

03/23/2017 12:23 PM

Have you tried, "HOW THINGS WORK"?

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Anonymous Poster #1
#18
In reply to #6

Re: safety relay

03/23/2017 1:47 PM

No-one knew that until you said so.

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#19
In reply to #18

Re: safety relay

03/23/2017 1:51 PM

yeah yeah very phunny!

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#5

Re: safety relay

03/23/2017 11:35 AM

It really depends on the context of where you are and what you are operating.

Put your searches into the context of your working environment where you will apply these "safety relays".

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#8

Re: safety relay

03/23/2017 12:30 PM

I know this is not a safety relay but can someone tell me what the OL part of this circuit is suppose to represent?

That is a true of off

I was thinking it was an Estop but since Estops are almost always normally closed that makes no sense.

The text says during a fault the current could weld the contact shut

Where is that happening in this picture? No need to explain how the Seal in logic works on the start. That part i get. I just dont understand the OL part

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#9
In reply to #8

Re: safety relay

03/23/2017 12:46 PM
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#10
In reply to #9

Re: safety relay

03/23/2017 12:52 PM

If you have time could you elaborate?

The link you sent me encompasses a lifetime of information

I could spend the next week digging through it. If anyone has time to explain a basic over view that would be helpful

Thanks

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Anonymous Poster #1
#11
In reply to #10

Re: safety relay

03/23/2017 1:12 PM

You've watched all the videos.

You've read all the literature.

You've spoken to all the authors.

What more do you want?

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#14
In reply to #10

Re: safety relay

03/23/2017 1:24 PM

The tutelage you desire requires a mentor that can relate in real time over an extended period of time, you need to find one...Offer to help someone for free, if necessary, to gain the knowledge...most everyone likes a dedicated helper...

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#12
In reply to #8

Re: safety relay

03/23/2017 1:13 PM

The OL relay is normally open, but when temperature goes high (if it is a thermal relay on your 220-240 V 1Ph motor), it switches open, thus disabling current through motor, until it can be reset.

As to welded CR(b) contacts, there should be an estop relay added for just that reason, in series with CR(b). Your stop button is not an estop button.

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#13
In reply to #12

Re: safety relay

03/23/2017 1:22 PM

Thank you james for taking the time

Just what i was looking for.

Thanks very much

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#15
In reply to #12

Re: safety relay

03/23/2017 1:33 PM

Also James

I was just watching a video on Thermal OL relay

The video claimed they were Normally closed.

Is there no standard? and could possibly be either?

Normally closed to me seems like a more desirable idea.

Can you tell me more about the Estop "relay"

we all know an Estop is just a NC switch so what is an estop relay?

Perhaps im looking at a bad picture and should find a better one to exmaine?

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#16
In reply to #15

Re: safety relay

03/23/2017 1:42 PM

If CR(b) fails to open (welded contacts), then normal stop will fail to operate the relay.

IF OLR opens, generally, it is time to wake up and re-think that entire set-up. OL situation when motor output shaft power is far exceeded (along with usually higher ambient temperature), such that the motor in question will overheat, then the NC OL trip opens the source legs to motor, so that one might later start over.

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#17
In reply to #15

Re: safety relay

03/23/2017 1:46 PM

A thermal overload would be closed at ambient temperature, opening on high temperature, which is standard for thermal overload contacts.

An emergency stop relay is merely an electrically-operated switch that does the same as an emergency stop button.

<...Is there no standard?...> In the limit, it is for the Client to determine the appropriate <...standard...> to use, often recommended by the Contractor(s), and the Commissioning Engineer to determine whether what is about to be shipped or has been installed is designed, installed, operates and performs according to the selected <...standard...> upon detailed inspection of the equipment. Such activities are commonly known as "Factory Acceptance Testing" and "Site Acceptance Testing".

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#20
In reply to #12

Re: safety relay

03/24/2017 7:08 AM

"The OL relay is normally open..." - think this was a typo/senior moment .

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#23
In reply to #8

Re: safety relay

03/24/2017 2:27 PM

Dear wannabecontroller, I hope part of your trouble understanding this diagram is language. OL stands for "Over Load". It is usually a current sensing device but can also be temperature sensing. I do not want to discourage any one from learning, but your questions are so basic that it makes it look like you are into an area where small mistakes or misunderstandings can have drastic consequences. While it is great that you are asking these questions, if you are working on something that could result in someone getting hurt if there is a fault in the control, please have your work reviewed by a competent person before releasing it. Thank you, and even though some make harsh comments, keep asking questions until you fully understand things. Someday you will be looking at such questions and thinking "Doesn't every one know this?".

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#24
In reply to #23

Re: safety relay

03/24/2017 2:38 PM

We can only add that if your skin is particularly thin, you, as an engineer will bleed a lot.

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#27
In reply to #23

Re: safety relay

04/01/2017 3:27 PM

You probably missed the part where he is fresh out of school and just started his first job where he works under a senior engineer..

Your post is not exactly what I would call encouraging for the future engineer

I also find it interesting James because I have heard you say that several times

I don't know what field you work in or what country but your view of the workforce appears to be very outdated. The professional engineering environment I work in everyone is interested in helping one another including electricians and technicians. We don't pick at each other like you and others here on the forums do.

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#21

Re: Safety Relay

03/24/2017 9:00 AM

We started years ago with just a normally closed emergency stop switch that would open when pushed and shut down a relay/contactor, for, let's say, a motor. Worked fine for years. Well then some safety folks got involved and said what if the single contact fails - better add a second set and a second circuit to relays so if one fails, the other will still shut the motor down. Then they said, what if that overload on that other motor opens, shouldn't we know that and shut the primary motor down as well if the system is not being attended by an operator who could push the e-stop button? So began the development of the safety relay. We have a relay that has multiple contact sets, often three NO and one NC with the NO sets wired in series and the NC set wired in parallel, because back up is necessary. It also monitors not just the 2 circuits from the E-Stop button, but overloads on other less essential motors, or light curtains on machines as well. One of those open and the E-Stop is activated without a button being pushed. Then they complained that there is associated machinery elsewhere that probably should stop the primary system if there is a failure there. So now we have remote capabilities as well. Then they wanted a reset capability, so things wouldn't start as soon as the e-stop switch was reset and a way to alert folks that this was tripped. That's the NC section and the the additional input terminals, often noted as S31 and S33 or whatever. They reset the relay after triggered by a momentary make NO pushbutton if and only if all the other faults are reset. (e-stop button, overloads, light curtains, whatever) No need for an operator to check - the relay checks for him. The NC section will be wired to an indicator light so it turns on when the relay is tripped and announces that we have a problem.

Basically, it is the outcome of the "can't be too safe" mentality of todays safety environment. Cover you buttox on all possible outcomes.

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#22
In reply to #21

Re: Safety Relay

03/24/2017 9:45 AM

And hence the 10 X cost factor.

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#26
In reply to #21

Re: Safety Relay

03/28/2017 5:38 AM

Control units I used to design and build 25 years ago, which fitted in a 19" rack-mount box 3U (5¼") high, now take up a 1000mm x 800mm (39" x 31½") wall-mounted steel case, like this:

- and the old units also contained the PSU, which now requires a separate case!

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#25

Re: Safety Relay

03/27/2017 2:10 PM

I believe this is what you are looking for. You can download the manuals for each version.

http://ab.rockwellautomation.com/Relays-and-Timers/Safety-Relays/Specialty

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