I’ve come to realize that my world is pretty different from the world experienced by many others. For example, I have the freedom to set my schedule. I pretty much come and go as I please and lately I’ve decided to stay out of the office until 10 or 11 each day.
Pretty nice, huh? The other half of that is that I still work 12 hours a day. There are always blogs like this to, plans to make, books to ready and study and a myriad of other things that go into running a business.
My world is different in how I look at the automation industry. In one of the ways I look at it there are only two classes of devices; messaging devices and I/O devices.
I/O devices, of course, are the work horse devices of EtherNet/IP. EtherNet/IP I/O devices, officially called EtherNet/IP I/O Adapters, are the sensors and actuators of the factory floor. They gather inputs from the field, condition them and send them to a Scanner device. If you have an I/O device and need to get your I/O device on EtherNet/IP, we’ve been successfully donning that now for about 12 years. It can take as little as a few hours but that’s not what I want to talk about today.
Today, I’d like to talk about those Messaging Devices. So, what are Messaging Devices and why would you want Messaging Devices on EtherNet/IP.
In my terminology Messaging Devices are any device that produces data at an intermittent rate greater than 3, 4 or 500 ms. In that definition, barcode devices, scales, RFID devices are all messaging devices.
Now scales are interesting. You could have a scale in continuous mode where you want it to deliver it’s current value continuously. In that scenario, you have a EtherNet/IP Scale that is just like an I/O Adapter. In fact, I would configure it as an I/O Adapter on EtherNet/IP.
But if your scale delivered it’s current weight every 2 seconds when the conveyor places a product on it, then it’s a messaging device. In fact, when we do scale applications we make them into dual EtherNet/IP devices able to act either as a messaging device or as an I/O device.
So what’s a messaging device on EtherNet/IP?
Well, the RTA approach is a little different than what many other EtherNet/IP implementers do. We make messaging devices as EtherNet/IP Client devices that are able to open connections to PLCs and other controllers and initiate messages.
Because they can open the connection and issues messages, our EtherNet/IP devices don’t monopolize the Ethernet bus. They only send messages when data is available.
An EtherNet/IP Barcode reader sends its barcode only when a barcode is available. An EtherNet/IP RFID device sends tag data to the controller only after reading a tag. And an EtherNet/IP Scale sends its scale data either when it is read or continuously.