Pete explains: B&B converters for the industrial bus world

The industrial bus traditionally was used to allow a central computer to communicate with field devices. As the cost of computing went down, the industrial bus allowed computers to communicate with each other to coordinate industrial production.

Industrial buses cover a large area. Often different areas of the network are supplied by different power sources. Even though all of the sources are grounded, a voltage difference can exist between the grounds of these voltage sources. This voltage difference can upset the data line in an RS-422/485 bus by pushing the signal voltage out of range and, in some cases, excess voltage can damage equipment.

Another source of excess voltage potential can be caused by intermittent sources. Power line surges and lightning are causes of this type of disturbance, but other causes, such as large electric motors starting and stopping, can temporarily affect the ground reference voltage. The solution to this problem is to use RS-422/485 devices that provide isolation between different parts of the network.

Two popular industrial buses that use the RS-232 and RS-422/485 standards are Modbus and Data Highway/DH-485. Modbus can be configured for either RS-232 or RS-485 in a 4-wire mode. (Note: Modbus Plus is not RS-232 or RS-485 compatible). DH-485 is the name of the industrial bus produced by Allen-Bradley and is used on some SLC 500 controllers.

RS-485 is also available on some PLC-2, 3 and 5 controllers. The industrial buses that adhere to the RS-232 and RS-422/485 standards are listed below along with products compatible with them. Our products support these buses at the physical layer and are often used as repeaters, line extenders and isolators. We also offer a custom design service to solve particular problems that arise from industrial buses.

What’s so hot about Send Data Control (SDC)?

As operating systems become more complex, it is increasingly difficult to control an RS-485 driver with standard software and the RTS line. This is especially true in Windows and multi-tasking operating systems.

With B&B’s Automatic Send Data Control circuit, driver control is in the converter hardware, so you don’t have to work with software at all. The circuit monitors data flow and enables the driver during transmission and automatically disables it when no data is being sent. There is no need to rework software or install new drivers.

Most B&B Electronics RS-232 to RS-485 converters and RS-485 serial cards include Automatic Send Data Control.