Minimize CO2 Emissions with Single-Pair Ethernet

The global goal of net-zero carbon dioxide (CO₂) emissions affects all industry segments. In the case of buildings, the goal is challenging because of the large base of environmentally inefficient structures. Many installed control and communications systems have limited monitoring and data handling capacity, and they typically lack advanced data analysis and control to optimize efficiency.

Achieving net-zero CO₂ emissions will require automation systems using artificial intelligence (AI)-based analysis and control. Key to this improvement is the ability to easily deploy sensors throughout a building using long-reach, high-data-rate Single-Pair Ethernet (SPE) based on the 10BASE-T1L standard. The higher data rates will minimize latency and enable real-time control of a building's systems.

This article briefly describes the connectivity requirements of net-zero CO₂ buildings. It then uses 10BASE-T1L devices from Analog Devices Inc. to show how SPE can support improvements in communications and control while improving sustainability.

Limitations in traditional building designs

Traditional building designs employ Building Management Systems (BMSs) to handle overall structure control, with building subsystems generally operating in isolation. Limitations in communications interactivity and available power keep buildings from operating at peak efficiency, resulting in losses that impact the environment. Consider the hierarchical structure of a standard building (Figure 1).

Figure 1: Traditional building systems are hierarchical but may be viewed by function. (Image source: Analog Devices Inc.)

The field/device level at the base of the BMS pyramid in Figure 1 contains local sensors and actuators for the various systems. The building and room controllers level consolidates the field and device data and controls the devices. The enterprise level monitors the entire building and coordinates the controller activity through the BMS.

Traditional building systems, such as heating, ventilation, and air conditioning (HVAC), have a vertical control hierarchy but operate in isolation from systems such as occupancy detection. This means that regardless of occupancy, individual floors still use energy to operate the HVAC system.

The reason for this vertical isolation is the limited performance of existing data interfaces. Lower-level analog and 4 mA to 20 mA current loop and RS485 serial interfaces, along with higher-level interfaces such as Highway Addressable Remote Transducer (HART) and Fieldbus, are relatively slow, with rates of 1200 bits per second (bits/s) to 31.25 kilobits per second (Kbits/s). This limits the amount of data transmitted in a given period.

The 10BASE-T1L (IEEE 802.3cg) Ethernet interface was introduced in 2019 and dramatically increased the data transmission rate, lifting it to 10 megabits per second (Mbits/s) over SPE. It also includes the ability to supply much higher power levels over the same data transmission lines, going from 36 milliwatts (mW) for 4-20 mA current loops with HART to 500 mW (non-isolated) or 60 W max (Table 1).

Table 1: Key features of some common building data interface networks. (Table source: Art Pini, using data from Analog Devices, Inc.)

The slower data interfaces also limit accessibility to field-level sensors and actuators, which means they can only be reconfigured on site. 10BASE-T1L is compatible with all existing Ethernet implementations and can communicate seamlessly with all BASE-T Ethernet network installations, including 10/100/1000/2.5G/5G/10G BASE-T variants, without needing a gateway.

The role of 10BASE-T1L

10BASE-T1L is part of the larger Ethernet 802.3 standard. The name summarizes its characteristics. “10” is the transmission rate of 10 Mbits/s, and “BASE” indicates a baseband signal, meaning only Ethernet signals can be sent over the medium. The “T” signifies the medium as a twisted pair, “1” is the range of 1 kilometer (km), and “L” stands for long range.

The medium specification for 10BASE-T1L does not indicate a particular twisted-pair cable. Instead, it specifies the return and insertion loss of the wiring. This allows the reuse of existing installed wiring, such as Fieldbus Type-A cables.

10BASE-T1L supports full-duplex communication using two amplitude modes: 2.4 volts peak-to-peak (V_P-P) over 1000 m of cable, and 1.0 V_P-P for reduced distances of up to 200 m and in hazardous environments.

The Ethernet standard has a provision to supply power over the same twisted-pair cable used for data communications. In 10BASE-T1L, the power is controlled based on the nature of the environment. The 500 mW is suited to intrinsically safe (meaning hazardous) areas where spark discharge power must be limited. The upper limit of 60 watts is available for safe areas.

The advantages of 10BASE-T1L

The most significant advantage of 10BASE-T1L, after its 1 km range, is its compatibility with the full range of Ethernet BASE-T networks. This eliminates the need for translation gateways between different data network standards. It opens the path from the field level to the enterprise and cloud levels and reduces costs, complexity, and power requirements.

The 10BASE-T1L speed of up to 10 Mbits/s makes it possible to transmit the fundamental measured process values to sensors and actuators along with additional configuration parameters, status data, and even software/firmware updates. Sensors and actuators can be accessed remotely using their IP addresses. Device configuration is more straightforward because 10BASE-T1L-compatible devices eliminate gateways and protocol converters. The extra data-handling capacity can also be used for more complete system diagnostics and troubleshooting routines.

The additional data capacity available due to the higher data rate is also usable in linking building systems for data exchange. AI-based analysis and control permit complimentary regulation to obtain the most efficient joint operations. Consider what this looks like in a 10BASE-T1L-equipped building (Figure 2).

Figure 2: Shown is the addition of 10BASE-T1L interoperability from the edge transducers to the cloud. (Image source: Analog Devices Inc.)

SPE for 10BASE-T1L allows the connection of multiple transducers and actuators on the edge level to room controllers. Existing devices linked by legacy interfaces can still be used or converted to Ethernet compatibility. Systems are linked together at multiple levels using the appropriate version of Ethernet, allowing the possibility of real-time control.

10BASE-T1L building network topologies

Multiple devices can connect to the SPE network in a ring or in-line network topology (Figure 3).

Figure 3: 10BASE-T1L, like other Ethernet variants, supports ring and in-line topologies to connect multiple devices. (Image source: Analog Devices Inc.)

Each topology offers reduced cable length compared to the alternative star network topology. The ring topology additionally provides a redundant path in case of device failure. Each device requires two Ethernet ports to pass data down the network in either topology.

To implement this, designers can use Analog Devices’ ADIN2111CCPZ-R7, a low-power, dual-port 10BASE-T1L transceiver that integrates a switch, two Ethernet physical layer (PHY) cores with a media access control (MAC) interface, and all the associated circuits, including internal buffer queues. It is directly controlled via a serial peripheral interface (SPI). The SPI is compatible with many controllers, permitting easy selection that maximizes performance, power usage, and price. The switch supports numerous routing configurations using the dual Ethernet and SPI ports, enabling in-line or ring network topologies. The fact that the 10BASE-T1L switch contains a MAC interface means the controller need not include one, which increases the number of potential controllers that can be chosen. Figure 3 shows ring and in-line topologies using the ADIN2111CCPZ-R7 as the two-port switch.

The ring configuration uses a dual switch for all the devices. The in-line configuration does not need a dual switch, as the last device only requires a single MAC-PHY transceiver like the ADIN1110CCPZ. Like the switch, this Ethernet transceiver includes a MAC and therefore supports a broader range of mating controllers. This opens long-range Ethernet connectivity to many low-power and less expensive controllers. A built-in MAC may also allow existing controllers to be used if 10BASE-T1L is being retrofitted into an existing BMS. Each transducer or actuator will have its controller and access to Ethernet through the transceivers, giving it an IP address.

Looking at the controller side of the ring and in-line network arms in Figure 3, the ADIN1100CCPZ-R7 Ethernet transceiver is a good choice. This transceiver does not include a MAC, just an Ethernet PHY. The ADIN1100CCPZ-R7 is intended to operate with controllers that incorporate MAC functionality like those used in the control panel shown. It interfaces with the remote control processor via a Management Data Input/Output (MDIO) interface. The MDIO interface is a two-wire serial interface for communication between the MAC in a host processor and the ADIN1100CCPZ-R7.

All the ADIN1100 series devices are rated to operate over a cable length of up to 1700 m, more than the 10BASE-T1L specification. They are also rated to operate over a nominal temperature range of -40°C to +85°C. The models listed (CCPZ) have an extended temperature range of -40°C to +105°C.

Power over SPE

Powering remote field-level devices can be problematic, especially when retrofitting existing systems. The 10BASE-T1L specification supports single-pair power over Ethernet (SPoE), which supplies standardized power and Ethernet data over a single twisted-pair cable. For this function, designers can use the LTC4296AUK-1-PBF, a five-port power-sourcing equipment (PSE) controller (Figure 4). It is designed for interoperability with 802.3cg-powered devices (PDs) using 24 volt or 54 volt systems that can be easily integrated into the ADIN series 10BASE-T1L products.

Figure 4: Shown is the LTC4296AUK-1 used as a five-port PSE controller. (Image source: Analog Devices, Inc.)

This application example of the LTC4296AUK-1 supplies power to five instances of the ADIN1100 Ethernet transceiver via the transformer/capacitor power coupling networks. The ADIN1100s are each driven by a MAC media-independent interface (MII). Each PSE is protected by a high-side automatic current limiter (ACL) for controlled inrush and short-circuit protection. The LTC4296AUK-1 has an operating temperature range of -40°C. to +125°C.

Conclusion

Greater digitalization of buildings will enable management systems to access all the sensor data and control capabilities, and the cross-linking of building systems will provide the foundation for operational automation. To enable this, 10BASE-T1L over SPE brings 10 Mbit/s data transmission rates, a long reach of up to 1 km, and standard Ethernet IP connectivity to every corner of a building. Building controllers can now achieve longer reach from the cloud to a virtually unlimited number of edge devices. This enables the optimization of a building’s overall operations to reduce CO₂ while best serving its occupants.