E-stop & Light Curtain

HI
which one is the primary control E-STOP or LIGHT CURTAIN circuit.
Thanks

Hi

From my point of view, E-Stop must have the highest prioriti since, as indicated by its name, is an emergency device.

Ligth curtain is to protect the operator ans is used during normal operatiom mode to avoid machine movements when the operator is inside the machine.

If you need to know how to connected, first you need to define how dangerous is your machine and in each way you need to protect people.

Both must deprive actuators of energy if an unsafe condition exists.

So, If they will take same result you can connect both to one safety relay, if your system is not in category IV.

One safety relay have at least two safe contacts that you must use to cut power.

Different locations have different rules, however a common theme is that:
- E-Stops shut down everything in the area
- Light curtains generally only shut down the equipment that can be accessed through the light curtain.
- Light curtains can also be muted under specific conditions.

Fox, Safety Relays have two contacts for a purpose other than connecting two different devices. The idea behind Sil III is that there is redundancy in the wiring of the devices. So, 1 e-stop, two sets of wires traveling two different paths back to the safety relay. If one shorts, the other will still stop the machine.

Yes Maverik, I know that, but to help our friend we need to know better the aplication in order to suggest how to connect and which relays should be used

I always have they e-stops kill the master control relay.


Depending on the applications, my light curtains may kill the MCR, and sometimes it disables the inputs to a secton of a machine, or just specific outputs, in other words, an inhibit of sorts. ALL DEPENDING on application. If the light curtain is for a major safety function, then ib WILL kill the MCR!

regards.....kc

CaseyK said:

I always have they e-stops kill the master control relay.


Depending on the applications, my light curtains may kill the MCR, and sometimes it disables the inputs to a secton of a machine, or just specific outputs, in other words, an inhibit of sorts. ALL DEPENDING on application. If the light curtain is for a major safety function, then ib WILL kill the MCR!

regards.....kc

Click to expand...

I'm just curious here (verses being critical) but in what kind of application would a light curtain drop the MCR? What I mean is that, a light curtain allows the operator to access hazardous areas, disabling outputs that control actuators in and around the access area, so that the operator doesn't have to drop the MCR every time. ie, It acts as a "temporary" switch.

Unless you mean in combination with a muting module which would make sense. But, if is only tied into the MCR, it would seem the light curtain could be replaced with a door and safety gate switch, a less expensive solution.

The E-Stop is not the primary Control. The light curtain is the primary safety device because it is used to avoid injury. The E-Stop is used after damage has already occured. An E-Stop is not a preventative device, which makes it secondary.

a door with gate switch is less expencive but if this is something that requires frequent access, cost advantage will definitelly be on light curtain side because it saves time and boosts productivity. muting is bypassing of light curtain and as such is never 100% safe (it's more of a last resort). i've seen plenty of cases where muting was done be simple relay powered by plc output. this is not correct. muting should be automatic, independant of plc program (unless it's a safety plc, safety plc outputs and logic behind it is done using safety functions and not user program) and it should meet same category level as the circuit that is muted.
one of frequent mistakes is to use one safety controller for e-stop for example, other for light curtain (or light curtain with built in monitoring function), then have light curtain outputs go through e-stop controller to pair of contactors but monitor contactor only by e-stop controller.
if the contactors are switched by or powered through outputs of more than one controller, each of controllers should monitor them. this is why safety relays/contactors sometimes have so many NC contacts.
there is a lot of gothas and dos and donts so it can take a long time to find out what is good and what not. i suggest taking safety circuit design seminar or workshop.

jstolaruk said:

I'm just curious here (verses being critical) but in what kind of application would a light curtain drop the MCR? What I mean is that, a light curtain allows the operator to access hazardous areas, disabling outputs that control actuators in and around the access area, so that the operator doesn't have to drop the MCR every time. ie, It acts as a "temporary" switch.

Unless you mean in combination with a muting module which would make sense. But, if is only tied into the MCR, it would seem the light curtain could be replaced with a door and safety gate switch, a less expensive solution.

Click to expand...

Many types of equipment! One example, a balancing machine for a golf cart tire. Everything is open. Machine rotates about 3-4 turns with a hefty drive. After the "hihg spot is located, it will turn 5/8 of a turn to mark the "spot". Hook your hand, hit the stop button, it will rotate 1/2-3/4 turn. Light curtain shuts it off in less then 1/8 turn. Cannot have guards on machine.

Lots out drill presses and multiple drills, cap tighteners, etc must be shut down quickly to keep osha and local fire dept inspectors happy. Yes, they do inspect safety in some areas.

regards.....kc

In our plant, we have a palletizer that was manufactured by a company that is no longer in business. It uses safety cages, and doors with switches that drop out the MCR only. This machine also lacks a "home run function", thus if a door is opened durring operation it is hell to get back into sequence. I'm in the process now of doing a complete up grade of the PLC and the controls. The PLC is a very early S5. Needless to say, on my new plc the E Stops will drop out the MCR on this unit and the door switches will drop out functions related to the areas of entry. There will also be a home run or go home function. Our company origianlly saved a total of 3,000 dollars on purchase price by not buying these options from the manufacturer. I would imagine that over the last 15 years this 3,000 in savings has cost us millions in lost production.

Makes sense to me Maverick!

I have some machines that throw in an interupt and kills the MCR. When the light curtain clears, the reset button can be hit, and everything goes back to normal.. Sometimes the logic can be hairy.

regards.....kc

jstolaruk said:

I'm just curious here (verses being critical) but in what kind of application would a light curtain drop the MCR? What I mean is that, a light curtain allows the operator to access hazardous areas, disabling outputs that control actuators in and around the access area, so that the operator doesn't have to drop the MCR every time. ie, It acts as a "temporary" switch.

Unless you mean in combination with a muting module which would make sense. But, if is only tied into the MCR, it would seem the light curtain could be replaced with a door and safety gate switch, a less expensive solution.

Click to expand...

A perfect exaple would be a Palletizer..The one i am working on now has all the Estops you could think of..each one of them drops the MCR..However some bonehead still tried to clear the machine without hitting the estop..(A stack had fallen over..the machine shouldnt move becouse of other switches a fallen stack trips..however...) An eye was cleared and the pusher stared to push...(Thank god for the Other 4 estops i put in!!) No one was hurt but they then asked for me to do something..a curtain was the only viable solution..There is an area of 8' that someone could walk thru..If they walk thru at the wrong time they will end up stuck between two 3000lb pallets..Not nice!!..so we put the curtain in..if the curatin is broken then the MCR drop out..machine stops..There should be NO reson why anyone goes into the curatin zone during normal operation..