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Standalone Active Terminator for EIA-485 Networks

The 485-TER is a standalone active terminator that is used on popular EIA-485 networks, such as Modbus RTU and BACnet MS/TP, to provide sufficient termination and biasing to the network to ensure reliable operation. Fail-safe bias ensures that an undriven line assumes a defined state. When a head-end device does not have internal bias and termination, two 485-TER devices should be installed – one at each end of the network. This will provide stability and error free communication.

The 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 485-TER can be installed to stabilize the physical layer of an EIA-485 network by providing the proper voltage bias (greater than 200mV) and termination (120 Ohms) to the network. The 485-TER requires 24VAC +/-10% 1VA or 20-30VDC 0.5W power. Power can be shared with the same power source used by the controller. The 485-TER continues to provide a termination resistance of 120 Ohms to the network even when power is not provided. The 485-TER can be used with either 2-wire non-isolated EIA-485 networks or 3-wire isolated EIA-485 networks.

Shown below is a simplified schematic of the isolated EIA-485 bias and termination circuit:

For more information, visit our BAS-485-TER product page.


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