Safety Controllers - Safety Scanners

[Karinrinkashi]

Hello everyone,

I have never worked with safety controllers before but i have an idea of how they work, not too complicated to figure that out.
Can someone direct me to a resource that i can use to understand safety controllers and how to use them to cut power to a system in more detail?

An explanation would be helpful too.

Also, most safety scanners nowadays use 24V and we have machines that are still 120V. How can one use a 24V circuit to control safety in a 120V system. I have heard relays are not allowed in safety circuits, is that correct?

Thank you for any and all help

 

[Timbert]

Relays are absolutely allowed in safety circuits otherwise it would be darn near impossible to control.

The big difference is that the relays need to be safety-rated and implemented so they can be monitored by the safety controller. The actual implementation various on the required level of safety.

To be honest, yes the concepts of a safety system are "not too complicated to figure that out." But the details, the devil is in the details. It's easy to think you understand the concept of the safety system but not understand all the factors that involved in ensuring safety. One small variation from proper implementation can completely negate the entire safety system.

I would start with Allen-Bradley's Safebook.

P.S. and when it comes to safety the enemy is "I have heard...". If it is not in a recognized international safety standard or the like ignore what you've heard, it's probably wrong. When people (including me) claim you got to do x or you can't do y, demand to see written proof, chapter and verse.

 

[Mray]

Relays are absolutely allowed in safety circuits otherwise it would be darn near impossible to control.

The big difference is that the relays need to be safety-rated and implemented so they can be monitored by the safety controller. The actual implementation various on the required level of safety.

To be honest, yes the concepts of a safety system are "not too complicated to figure that out." But the details, the devil is in the details. It's easy to think you understand the concept of the safety system but not understand all the factors that involved in ensuring safety. One small variation from proper implementation can completely negate the entire safety system.

I would start with Allen-Bradley's Safebook.

P.S. and when it comes to safety the enemy is "I have heard...". If it is not in a recognized international safety standard or the like ignore what you've heard, it's probably wrong. When people (including me) claim you got to do x or you can't do y, demand to see written proof, chapter and verse.

Tnx Timbert for introducing that nice PDF.

 

[mk42]

It's easy to think you understand the concept of the safety system but not understand all the factors that involved in ensuring safety. One small variation from proper implementation can completely negate the entire safety system.

As an example of this, those small variations could be things as simple as how the wires are routed between a sensor and the safety controller, whether the PLC supply is used or a common supply, etc.


The actual programming in a safety PLC is relatively straightforward, but there are a lot of concepts around it that are very very detail oriented.

 

[Karinrinkashi]

Thank you for that PDF Timbert, i just logged in today since Friday. Let me go over and see how it works.