A House Divided

Do you live in a house divided by electronics? If you think that religion or politics can be a strain on a marriage, just try living in a house with Mac and Windows devotees. Or two people devoted to Samsung and Apple.

Having multiple brands is just a fact of life and it’s just as true in manufacturing as it is in any other part of life. In our world we have to fight the battle of having Siemens, Rockwell, Omron, GE, and other PLCs in the same plant and often on the same machine. No matter how hard we try to stay with one brand or another to keep maintenance costs under control, we end up somehow, someway, having multiple PLC brands.

In some cases, plants have a not very secret strategy of using multiple PLC brands to keep vendors honest. If you’re a Siemens plant or a Rockwell plant, you often wonder if you’re getting the same service and attention that the plant down the street that has both. In makes sense. Who’s going to get the new product demos, the bigger discounts, and goodies like free training and trips on the corporate airplane? It’s not going to be the customer they’ve had for the last umpteen years. It’s the one they want to woo.

But if you want those vendors to compete for your business, you have to suffer with the additional training and spare parts costs. And you have the problem of integrating devices from the two vendors. In the future, standardization efforts like the PLCopen promise to make that a lot easier, but it’s not going to help us now with the PLCs we’ve deployed over the last ten or twenty years. Just moving a few points of data from one of these PLCs to another can be really difficult.

One way that people attack this is to use a PC with classic OPC (that’s the predecessor to OPC UA). They have OPC drivers, for example, for an Allen-Bradley PLC5 and an Omron PLC. Then they write a Windows application to move the data between them. It’s an ugly solution. You have to write the application, support it, add another PC on the factory floor but in the end, it solves the problem.

A guy asked me about this very problem yesterday. He has GE and Allen-Bradley PLCs. He just needs to move a few points between them. Lucky for him we have the solution in our Modbus to AB PLC gateway. The GE PLC is a Modbus TCP Server device – that means that it is waiting for a Modbus TCP Client device to connect to it and read and write its registers. (Note that the TCP in Modbus TCP means that it’s using Ethernet not serial like Modbus RTU over RS485.) The Allen-Bradley PLC is, well, an Allen-Bradley PLC so it has a plethora of communication options. The one that I suggested we use is their low level, Ethernet application layer allows the gateway to read and write any tag in a Logix PLC or any file element in an old PLC5, SLC, or MicroLogix.

Our 460ETCMC-N34-D, an Allen-Bradley PLC to Modbus TCP gateway, is perfect for him. It will speak to the GE PLC over Modbus and read and write the Modbus registers in the GE PLC. It will speak to the Allen-Bradley PLC over Ethernet to read and write the Tags in the Logix PLC. With a little configuration to match up the tags in the Allen-Bradley side to the registers on the GE side, he’ll have the communications working – quickly and easily.

Much of the time though, it isn’t this easy, but with all the possibilities available in our PLC gateways, making one PLC speak to another sometimes isn’t difficult.

Now if we could do something about those spouses using both Apple and Samsung …