Rockwell Automation has introduced new BACnet interface options for its PowerFlex 4 and 7 class ac drives, making it even easier for users to employ PowerFlex drive technology in building services applications.
Allen-Bradley PowerFlex drives are increasingly used in applications such as fans, blowers and ventilation systems to improve performance and energy efficiency. Using PowerFlex drives to control fan speed can enable significant energy savings, while at the same time helping to reduce maintenance costs and increase fan motor lifespan. With the addition of the new interface options, PowerFlex drives can now communicate directly with other building systems using the native BACnet protocol.
Developed originally under the auspices of the American Society of Heating, Refrigerating and Air-Conditioning Engineers, BACnet is a data communications protocol designed specifically to meet the communication needs of building services and control systems for applications such as heating, ventilating, air-conditioning control, lighting control, access control and fire detection systems. BACnet became an ISO standard in 2003, and is now widely used by manufacturers of building services or facilities management hardware. The BACnet protocol provides a common mechanism by which computerised equipment of arbitrary function can exchange information, regardless of the particular building service it performs.
PowerFlex BACnet modules are available in two variations - the 20 COMM-B Drive Peripheral Interface (DPI) and 22 COM-B Drive Serial Interface (DSI). The DPI version is compatible with PowerFlex 7-Series drives, including PowerFlex 70 with standard or enhanced control options, PowerFlex 700 with standard or vector control options and PowerFlex 700H. The DSI variant is designed for PowerFlex 40 and PowerFlex 400 drives equipped with the DSI External Communications kits. Both options are designed to be quick and easy to configure, using DIP switches to define the node MAC address, termination and bias settings.
Communication baud rate can be determined automatically or set manually to 9600, 19200, 38400 or 76800 bps. Built-in LED indicators provide a visual indication of drive communications, adapter and network status to assist maintenance and troubleshooting. Both BACnet options are also fully compatible with Allen-Bradley drive configuration tools, including PowerFlex HIMs, DriveExplorer/DriveExecutive v3.01 or higher, which makes commissioning and configuration even easier. The BACnet option card firmware is flash programmable, enabling it to be easily field upgraded if required.
Physical network connection is via an RS-485, two-wire system employing an industry-standard A-, B+, and SHLD terminal convention. Both the DPI and DSI versions employ the BACnet Master/Slave (MS) Token Passing (TP) protocol to handle network access. Using this method, a “token” is passed from device to device on the network. Only when a device has the “token” can it initiate communications with other devices. Master/Slave configuration refers to any device on the BACnet network that has the ability to own the “token”. The Allen-Bradley 20-COMM-B and 22-COMM-B BACnet adapters operate permanently in Master mode, meaning they can initiate network communications at any time - alerting system controllers immediately in the event of a fault or user-defined warning condition.
The energy efficiency and cost of ownership benefits of using ac drives in fan and ventilation applications are well understood. Now, with BACnet capability bringing the sophistication, versatility and flexibility of Allen-Bradley PowerFlex drives to a wide range of building service applications, those benefits are available to more users than ever before.