Building management system protocols such as Modbus RTU and BACnet MS/TP utilize EIA-485 networks. This robust and popular technology for interconnecting devices on a network uses differential signaling over a twisted pair cable. Significant data rates (up to 115.2 kbps) and long cable lengths (> 1000 meters) can be supported. However, reliable back-and-forth data transmission requires attention to some key issues.
The BAS-485-TER is a standalone active terminator. It addresses two aspects of EIA-485 networks that must be considered in order to obtain reliable operation:
The BAS-485-TER is a compact device that can be applied in the field quickly and easily. It comes with an isolated cover, allowing it to be installed almost anywhere. The BAS-485-TER requires 24VAC 1VA or 20-30VDC 0.5W power. Because it has an internally isolated DC to DC converter, power can be shared with the same power source used by the other devices on the network. The BAS-485-TER continues to provide a termination resistance to the network even when power is not available. The BAS-485-TER can be used with either 2-wire non-isolated EIA-485 networks or 3-wire isolated EIA-485 networks. When a head-end device does not have internal termination and bias then two BAS-485-TER should be installed—one at each end of the network.
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