I have a lot of customers that want EtherNet/IP. But just like buying anything else, it’s just not that easy.
Just last week I did something that almost no one does anymore. I bought a camera. That’s right: I bought a device designed specifically to take pictures. Still pictures and movie pictures.
And like any other complex buy, it wasn’t as simple as it seemed at first. There are lots of different types of cameras for lots of different purposes. There are cameras for photographing wildlife, cameras for underwater shots, and cameras that you can strap to your head for who knows what reason (the last thing I want is a camera strapped to my head).
EtherNet/IP is something complex, possibly even more complex than a camera. There are a few different kinds of EtherNet/IP and you have to decide what is going to work best in your application.
The EtherNet/IP Scanner is our software that opens connections, send outputs to devices, and gets inputs from devices. It is the “PLC side” of an EtherNet/IP network. The Scanner is usually the controller in the system and there is usually just one controller, but there could be more.
The most difficult part of implementing a Scanner is that the Scanner must be configured. It must know what devices to open, what each IP address is, how many bytes of data are being transferred from each device, and how much to send to each device. How you get that data to it is an application decision. You can read the EDS file for the devices, you can use some custom application program, or, in a lot of cases, you can make the device list fixed. A fixed device list is one where the devices are always going to be there and never change. The tools of a Robot, for example, would be an application where the device list would be fixed. Those tools are going to always be there, day in and day out, and never change.
You want to buy an EtherNet/IP Scanner when you need to control a set of devices on an EtherNet/IP network. Typically, your device is going to be the controller, getting inputs, processing logic against those inputs, and setting outputs. If that’s what you want, then you need an EtherNet/IP Scanner.
An EtherNet/IP Scanner opens EtherNet/IP devices. Those devices, on that end of the network, are called Adapters. Adapters are end devices like valves, I/O blocks, drives, scales, meters and everything else you might find in an automation system. An Adapter has one job: connect the virtual I/O that gets transferred back and forth from the Scanner with the real world I/O. An Adapter takes the Outputs from the Scanner and manipulates real world, physical outputs. An Adapter takes real world inputs, digitizes them and sends them back to the Scanner. If no Scanner talks to it, an Adapter just sits there idling away its time (like some folks I know at big companies).
You want an EtherNet/IP Adapter if your device translates physical, real world inputs and outputs to digital signals that have to be sent someplace. Most devices are EtherNet/IP Adapters.
But the fun doesn’t stop there: there is a third kind of EtherNet/IP device that RTA invented (Ok, it’s really PCCC but we invented a fancy name). We call it the EtherNet/IP Tag Client. An EtherNet/IP Tag Client is software that simply allows an application program to read or write any Tag or File-Register in a ControlLogix, CompactLogix, PLC5E, MicroLogix or any other Allen-Bradley PLC.
The Tag Client is perfect for devices like a barcode scanner. A scanner doesn’t need to send the last scan it received every 1 msec, every 10 msec or even every second. It really only needs to send data when it has data, so the EtherNet/IP Adapter software is really overkill. You could use it. You could send the same value to the Scanner 10,000 times, then read the next value and send that data 10,000 or 100,000 times, but why waste all that bandwidth? Instead, with the Tag Client software, your barcode scanner or or RF Reader can just send data to the PLC when it arrives. That’s much simpler. The Tag Client offers a much more efficient way to do things. It’s also a really simple way to monitor data in the PLC.
These three types of EtherNet/IP application software don’t mean that you just have to pick between the EtherNet/IP Scanner, Adapter or Tag Client. After that, there is a choice of platforms. And that’s what the next blog will discuss.