What are the most common communication protocols used in Critical Power Communications?

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Transfer switches provide an ideal location to monitor power sources and loads. To do so, transfer switches must communicate with other power and network devices. The most common protocols used in critical power communications include digital input-output (digital IO); serial communications, including RS485; and IP-based communications over Ethernet.

Digital IO

The simplest inputs to power management systems are digital signals, which have two states: off and on. Remote indication of an alarm signal is an example of digital communication – when a condition triggers an alarm, a switch closes contacts to complete a circuit and voltage becomes present. This voltage could be used to light an indicator lamp or operate a relay to initiate subsequent actions. Devices can use dry or Form C contacts to communicate with other devices such as signal lights, relays, and annunciators.

Analog Signal

Analog devices send measured values by varying signal circuit voltage or current levels. For instance, a 4-20 milliamp (mA) circuit might be used to signal a measured value to another device. A signal for indicating the level of an engine-generator fuel tank is an example of this type of communication, where a 4mA current indicates the minimum sensible value (empty) and a 20mA current indicates the maximum value (full). In operation, the current would continuously scale with the parameter measured by the originating sensor.

Serial/RS-485

Serial/RS485 Serial protocols transmit data sequentially along a single circuit, a process known as serial communication. Serial communication is often used in industrial settings because it is less affected by electrical noise and because it can span relatively long distances. Serial communication can be deployed in half-duplex and full- configurations by using one or two pairs, respectively, of twisted copper wires. The type of data transmission requires electronic ports that can code and decode the serial data sent between originating and receiving devices.

Internet Protocol-Based Data over Ethernet

Ethernet denotes Local or Wide Area Networks that use Transmission Control Protocol/Internet Protocol (TCP/IP) to send addressable data over copper wire or optical fiber. Multiple, uniquely addressed devices can be connected to one circuit and devices decode only the packets that contain their address. Ethernet can support the simultaneous use of multiple data protocols. Modbus TCP/IP, SNMP, and BACnet IP are examples of IP-based communication protocols used on Ethernet networks. These are the types of protocols needed to transmit data for feature-rich power systems and IoT applications. This requires electronic processors to convert and buffer data for transmission over Ethernet pathways.

Supporting Document:

Communication Modules for Critical Power Equipment