Using North American Standard. I have Light curtains, 2 Palm Buttons and an EStop

tomwhite007_2008 · Mar 8, 2009

I have a machine that has Light Curtains, E-Stop and 2 Palm Buttons. If I wire the Light Curtain’s and E-Stop to safety a Relay(Category 4) do I need to wire the Palm Buttons to a safety relay or can I cheap out and just use the contacts from the Palm Buttons wired to the PLC inputs and create anti-tie down logic?

thanks for you reply

LadderLogic · Mar 8, 2009

I cannot tell you if there is a mandatory standard: your customer is the best authority to check it out with, better in writing.

But I do think that saving $150-200 for a two-hand control (anti-tiedown) relay might potentially lead you and your employer to much heavier damages if, God forbid, someone gets hurt.

And vice versa, of course.

dahnuguy · Mar 8, 2009

all I will say here is , please skimp and save as much as possible on safety features..............it helps the un emplyment rate.

this sort of thing makes my head feel like its going to explode!!!!!!!''

why doesn't anyone ever ask "Is this safe enough with only 2 safety circuits? Maybe I need another redundant safety , it's only another 500 dollars."

glad I don't work at your plant.

and be sure to use the PLC as the safety logic with no hard wiring and no redundant circuit.

LadderLogic · Mar 9, 2009

dahnuguy said:
all I will say here is , please skimp and save as much as possible on safety features..............it helps the un emplyment rate.

That may be true: everyone is trying to cut costs and so on.

But I happened to think that a $150 piece helps unemployment rate better than a multi-million lawsuit against the company.

averellen · Mar 9, 2009

Use the proper devices.
You won't pass your PSHSR, and Canadian Ministry will throw you in jail if something happens.

tomwhite007_2008 · Mar 9, 2009

So maybe what I should ask will it pass PSHSR? Whatever it takes to pass I don't mind implementing. But why spend the extra money. Light curtain already cost enough. Maybe I can do away with the Light Curtains and have a Two Hand Control ties into a Safety Relay. Both hands must be on the Palm Buttons for motion Power. Any feedback is greatly appreciated.

averellen · Mar 9, 2009

I guess the correct question would be what is the machines function. What do you need two hand for anyway.

If you want two hand then use a relay for it.

SR104P's are fairly inexpensive.
http://www.sti.com/relays/SR104P/index.htm

JesperMP · Mar 9, 2009

You have to do a risk analysis.

One difference between a two-hand-controls and a light curtain, is that you must take the time from a hand passing the light curtain to a full stop must not exceed the available distance divided by 2 m/s. ~~With a two-hand-control you dont have to worry about this.~~
Correction: Actually, if there can be some inertial movement even after you release the palm buttons, then you do have to take the distance vs. time into account.

averellen · Mar 9, 2009

In Canada, you still need to worry about other people. It's not enough to have one person in control of the machine. I use Light Curtains. You just need to do a distance calculation.

Giz99 · Mar 9, 2009

It all depends on the function of the machine and the evaluation of the risk assessment for the machine. Does the light curtain protect you from all hazards? Is it wired to a proper safety relay? Have you calculated the appropriate light curtain distance and stopping time? What is the purpose of the two buttons, anti tiedown or only starting the machine? How are your e-stops wired into the safety circuit.

A lot more information is required to properly evaluate a system and ensure that it is "Control reliable" and safe.

Giz.

tomwhite007_2008 · Mar 9, 2009

It is a simple Machine. Few Valves, Cylinders, Cylindicators and Proxies. Valves are 2 Position Open Center. No one else can physically enter the machine if the operator has both hands on the palm buttons. Remember you only get motion power while hands are maintained on the buttons. Do I need Light curtains is my question now. I will wire the Palm buttons into a Jokab JSBR4.

Giz99 · Mar 9, 2009

It all depends on your risk assessment. What prevents a third party or the operator from getting into a hazard area? It has been my experience that most simple machines still require an light curtain.

Check your PM Box.

JesperMP · Mar 9, 2009

tomwhite007_2008 said:
No one else can physically enter the machine if the operator has both hands on the palm buttons.

How does the palm buttons assure that ?
Is the normal operator that uses the palm buttons standing in way of anyone else reaching the machine ? If so, that does not sound safe enough to me.
Correction: It is OK as long as the two-hand-control is sufficient for the safety.
What I meant to say is that someone more or less obstructing the access by others does not in itself add to the safety.

Btw. I stated that you dont have to calculate time with palm buttons. Actually, if there can be some inertial movement even after you release the palm buttons, then you do have to take the distance vs. time into account.

With the distance vs. time OK, then a light-curtain is of course much safer than two-hand-control.
If the distance vs. time is NOT OK, then do NOT install a light-curtain under any circumstances, not even if is used in combination with a two-hand-control.

dahnuguy · Mar 9, 2009

LadderLogic said:
That may be true: everyone is trying to cut costs and so on.

But I happened to think that a $150 piece helps unemployment rate better than a multi-million lawsuit against the company.

You may be the only one who thought I was serious about that.

I was resisting the urge to rant about safety............again. Seems to make everyone uncomfortable, and that's what is most important.

Those multimillion dollar lawsuits you refer to are very very rare.

Most of the time "it was the operators fault" and the comany gets a small fine for some lack of documentation or signage.

Companies actually calculate the risk of a law suit going through. Not if it is likely that someone will be injured. But is it likely that after they are injured, they could prove it was our fault and then if they did that how much would it cost us?

leitmotif · Mar 9, 2009

tomwhite007_2008 said:
So maybe what I should ask will it pass PSHSR? Whatever it takes to pass I don't mind implementing. But why spend the extra money. Light curtain already cost enough. Maybe I can do away with the Light Curtains and have a Two Hand Control ties into a Safety Relay. Both hands must be on the Palm Buttons for motion Power. Any feedback is greatly appreciated.

Do you merely want to pass code?
OR
Do you want to build a safe and reliable machine?
If you cannot afford to do it right the first time how are you going to afford doing it the second
AFTER the added costs of downtime and a possible accident?

Dan Bentler

Using North American Standard. I have Light curtains, 2 Palm Buttons and an EStop

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