I/O networks and E-Stops

When using a Devicenet or ASI network how do you implement E-Stops? You can't inhibit the Common on your output cards because you don't have any. Do you kill power to the network? Shutdown the PLC entirely? I don't see to many other options.

typically you can cut power to devices and leave the network running, here's a product from Turck/InterlinkBT for DeviceNet that might help.
http://www.interlinkbt.com/PRODUCT/dn/dn-pdf/aim-108_109.pdf

E-Stops should be hardwired. You can use ASI or DNET for machine stops or stops for sections of a system.

BTalbot said:

typically you can cut power to devices and leave the network running

Click to expand...

Now that I think about it a little more your right, the output modules need a seperate power supply for the outputs, cut that and your good to go.

E Stop

E Stop means "emergency" stop.
This typically means a hardwire maintain stop button.
The application is to prevent personal injury.
Trip wire saftey stops along conveyors, Mushroom pushbuttons beside crushers and chipping heads etc.
Most people are not comfortable trusting network traffic.

Bruce beerchug

I know companies like Telemecanique (Schnider) make ASi safety relays these work like convetionally safety relays so you can incorporate them into the machines safety circuit. I have not personally used them but have been told they meet the European standards for safety. For those who don't know ASi is a serial but that uses a two wire conductor which is both power ond comms. Each device has it own unique key (40 bits rings a bell) the ASi master polls each device as to its status very fast (ms range) and adjusts its outputs accordingly.

This system would relly come into its own on a facility like a conveyor line where operator stations were regularly moved...

I don't know about Device Net, but there are a range of "ASi Safe" devices that are full safety rated to European standards.
Generally, you use an ASi safety relay, with either ASi E-Stops or an ASi I/O module for your safety functions.
We used IFM brand ASi safe devices and they work well and are quite reliable. As a bonus, they are much easier to trouble shoot than a hard wire system.

Hope this helps,

Doug

PS, before I forget, the ASi web site has a section on this along with a list of products and suppliers.

Also another good point that I liked is that abaility to "zone" the e-stops. You can set up which e-stop relays trip when a e-stop or e-stopS is pushed in. Very nice to have on long assembly lines.

Darren