6 ms·

For modern industrial applications, the safety circuit is often (edit- see child comment's note on safety PLCs) managed by discrete safety relay hardware such a

For modern industrial applications, the safety circuit is often (edit- see child comment's note on safety PLCs) managed by discrete safety relay hardware such as the AB GuardMaster or Pilz PNOZ. There's a good chance these weren't even available at the time of OP's application! A common configuration involves emergency stops, guard doors, light curtains, etc. being wired in a pair of loops with the relay. The relay continuously monitors both loops (usually with a phased pulse train), and any interruption or crossover will trip the unit. Only when the loop states return to nominal will the relay permit a reset to re-enable the outputs. The safety relay's outputs are generally connected to dumb hardware interlocks on the various dangerous bits of the machine.

_trampeltier 9y ago
No, most even small machines arrive with a kind of "Safety Integeated" right in the PLC. Even the smallest PLCs like a Siemens S7 1200 are now aviable with Safety Integrated. So Profi-Safe and ASi-Safe are very common. It does reduce A LOT of wiring. But of course brings new problems, for example RJ45 jack and plugs sometimes break the connection for a very short time if you touch it and you lose a safety packet over Profi-Net and .. boom .. emergency stop. Special if you use a lot of drives in a machine, any kind of Safety Integrated reduce the wiring a lot and makes cabinets much much smaller. But on the other side, for just once, yes I like Pilz PNOZ. Easy to use .. and I'm pretty sure you can buy a PNOZ even in 100 years.
- snerbles 9y ago
  It needs a little extra to meet PLd/e, no? I usually work with Allen-Bradley, my Siemens experience is rather lacking. Most of our customers would run away screaming from anything that's not hardwired safety, and are too cheap to shell out for a fully-blown safety PLC like the GuardLogix.
  - _trampeltier 9y ago
    Yes of course it needs a bit of extra. But for a pretty "low" price these days. Special if you build the same machine many times, you can safe much wiring time. Most maintenance people like hardware solutions because they are more easy to bridge ... With a software solution you can show easy for each safety button/switch a message on a display. Do it with a wired safety.
MarkSweep 9y ago
As a programmer, I like this approach to human safety for robots. By putting electrical interlocks on the doors that expose humans to the robot you can make it impossible for a software error to hurt a human. For some applications where you need to have humans working in the same area with the robot things get a lot hard. You probably need some software involved in enforcing speed limits for robots. The compliance engineers I've talked to say getting safety certification for software is quite arduous. In this case the off-the-shelf solutions the parent child comments mention become valuable.
- _trampeltier 9y ago
  Just slow down machines is not enought. I'm still stunning how much the operators trust on things like E-Stop and Safety-Doors. They open the doors, don't even look and go into the machine with there hands. Most people have no idea what's behind a E-Stop and Safety-Doors these days. Also how much paper work each time .. sadly the paper part grows very fast .. and does not really help at all. Just worthless paper.
  - bsder 9y ago
    > I'm still stunning how much the operators trust on things like E-Stop and Safety-Doors. They open the doors, don't even look and go into the machine with there hands. Wow. Where I am we sometimes do this, but never without real thought. And, generally, we revisit that part of the process again and again over time. One example: initial setup of a CNC machine part. If you don't have $50K-$100K, you are setting this up by hand. You are moving the cutting head while your hand is in the same space. If you screw up, it probably won't rip your hand off, but you will likely wind up with a solid, painful gash and it might break a small bone if you get really unlucky. People don't respect servos enough. They're remarkably powerful and probably moreso than you expect.
    - froindt 9y ago
      > initial setup of a CNC machine part. If you don't have $50K-$100K, you are setting this up by hand. Curious what specifically you need your hand inside for? Do you simply mean the machine is on (though entirely inactive) while putting the part in, touching off the part slipping the business card in and out, or something else entirely?

_trampeltier 9y ago

No, most even small machines arrive with a kind of "Safety Integeated" right in the PLC. Even the smallest PLCs like a Siemens S7 1200 are now aviable with Safety Integrated. So Profi-Safe and ASi-Safe are very common. It does reduce A LOT of wiring. But of course brings new problems, for example RJ45 jack and plugs sometimes break the connection for a very short time if you touch it and you lose a safety packet over Profi-Net and .. boom .. emergency stop. Special if you use a lot of drives in a machine, any kind of Safety Integrated reduce the wiring a lot and makes cabinets much much smaller. But on the other side, for just once, yes I like Pilz PNOZ. Easy to use .. and I'm pretty sure you can buy a PNOZ even in 100 years.

snerbles 9y ago
It needs a little extra to meet PLd/e, no? I usually work with Allen-Bradley, my Siemens experience is rather lacking. Most of our customers would run away screaming from anything that's not hardwired safety, and are too cheap to shell out for a fully-blown safety PLC like the GuardLogix.
- _trampeltier 9y ago
  Yes of course it needs a bit of extra. But for a pretty "low" price these days. Special if you build the same machine many times, you can safe much wiring time. Most maintenance people like hardware solutions because they are more easy to bridge ... With a software solution you can show easy for each safety button/switch a message on a display. Do it with a wired safety.

MarkSweep 9y ago

As a programmer, I like this approach to human safety for robots. By putting electrical interlocks on the doors that expose humans to the robot you can make it impossible for a software error to hurt a human. For some applications where you need to have humans working in the same area with the robot things get a lot hard. You probably need some software involved in enforcing speed limits for robots. The compliance engineers I've talked to say getting safety certification for software is quite arduous. In this case the off-the-shelf solutions the parent child comments mention become valuable.

_trampeltier 9y ago
Just slow down machines is not enought. I'm still stunning how much the operators trust on things like E-Stop and Safety-Doors. They open the doors, don't even look and go into the machine with there hands. Most people have no idea what's behind a E-Stop and Safety-Doors these days. Also how much paper work each time .. sadly the paper part grows very fast .. and does not really help at all. Just worthless paper.
- bsder 9y ago
  > I'm still stunning how much the operators trust on things like E-Stop and Safety-Doors. They open the doors, don't even look and go into the machine with there hands. Wow. Where I am we sometimes do this, but never without real thought. And, generally, we revisit that part of the process again and again over time. One example: initial setup of a CNC machine part. If you don't have $50K-$100K, you are setting this up by hand. You are moving the cutting head while your hand is in the same space. If you screw up, it probably won't rip your hand off, but you will likely wind up with a solid, painful gash and it might break a small bone if you get really unlucky. People don't respect servos enough. They're remarkably powerful and probably moreso than you expect.
  - froindt 9y ago
    > initial setup of a CNC machine part. If you don't have $50K-$100K, you are setting this up by hand. Curious what specifically you need your hand inside for? Do you simply mean the machine is on (though entirely inactive) while putting the part in, touching off the part slipping the business card in and out, or something else entirely?