Application of Single Pair Ethernet in Building Automation

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Ethernet has become the mainstream communication protocol at the top of the control pyramid in building automation. The Institute of Electrical and Electronics Engineers ( IEEE ) recently defined a new Ethernet standard , IEEE 802.3.cg , for 10 Mb/s operation and power transmission over a pair of balanced conductors. Since a single pair of cables can now support both data and power, adopting this standard can save a lot of cost and make it easier to install in building automation applications.

Bringing Ethernet to edge devices requires a lot of effort. Currently , there are multiple communication networks in building automation - such as Modbus for HVAC applications , BACnet for access control , LonWorks for lighting , and Ethernet for fire safety. This network fragmentation requires the use of gateways to perform protocol conversion to unite at the top of the building automation control pyramid . End users must manage complex systems one by one.

The reasons for the existence of various communication networks include the need for longer distances, multi-point connections , power schemes, and support for binding protocols , which can be solved by single-pair Ethernet . Connecting Ethernet to edge devices provides the following benefits : direct access to control systems, status updates, predictive maintenance, standardized hardware, and interoperability between various systems.

SPE Overview

As shown in Figure 1 , standard Ethernet uses single-cable communications with separate cables to send and receive data.

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Figure 1 : 10/100 Mbps standard Ethernet interface

Single Pair Ethernet ( SPE ) is broadly classified into three categories:

• IEEE 802.3.cg (10 Mbps).
• IEEE 802.3.bw (100 Mbps).
• IEEE 802.3.bp (1,000 Mbps).

IEEE 802.3cg is divided into two categories:

• Both long and short cables are longer than a balanced pair of shielded or unshielded wires. 10BASE-T1L : IEEE 802.3 physical layer specification for 10 Mb/s Ethernet local area networks on a single pair of balanced conductors , up to at least 1000 meters ( long distance when using 18 AWG wire for point-to-point connections).
• 10BASE-T1S : IEEE 802.3 physical layer specification for 10 Mb/s Ethernet local area networks on a single pair of balanced conductors for distances of at least 15 meters (shorter distances using 24-26 AWG wire with multidrop connections ).

This article describes the application of 10BASE-T1L , which provides data rates up to 10 Mbps over distances of more than 1000 meters in building automation systems .

The 10BASE-T1L physical layer ( PHY ) uses full-duplex communication over a single pair of balanced conductors with an effective data rate of 10 Mbps in each direction simultaneously . The 10BASE-T1L PHY uses three-level pulse amplitude modulation ( PAM3 ) to transmit at 7.5 megabaud on the link segment . A 33 -bit scrambler helps improve electromagnetic compatibility. The MII transmit data ( TXD<3 : 0> ) is encoded using quad binary ternary ( 4B3T ) encoding to keep the running average ( DC baseline) of the transmitted PAM3 symbols within range. The transmitter output voltage of the 10BASE-T1L PHY is set to 1.0 Vpp or 2.4 Vpp differential using the management data input / output interface , which helps achieve longer communication distances on different cables.

As shown in Figure 2 , SPE uses echo cancellation to achieve full-duplex communication and uses multi-level signaling and equalization to improve signal quality and achieve the required data rate on a single pair of cables . There is no difference in the interface between the processor and the PHY ; however , within the PHY , the transmit and receive sections of the medium-dependent interface need to be modified as described above to achieve single-pair operation.

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Figure 2 : 10/100 Mbps SPE interface

SPE can also send power over the data line ( PoDL ) along the same single pair of cables through a low-pass filter , as shown in Figure 3 .

Figure 3 : PoDL example

Table 1 lists the various power levels supported by the IEEE 802.3.cg standard. The maximum power that can be delivered to the load is 52 W , which is defined under class 15. IEEE 802.3.bu covers power levels below class 10 .

Table 104-1a - Power Classification Requirements Matrix for PSE , PI , and PD for Classes 10 to 15

Classification	10	11	12	15	14	IS
V PSE(max) (V)	30	30	30	58	58	S8
V PSE_OC(min) (V)	20	20	20	50	50	50
V PSE(min) (V)	20	20	20	50	50	50
I PT(max) (mA)	92	240	632	231	600	1579
P class (min) (W)	1.85	4.8	12.63	11.54	30	79
V PD(min) (V)	14	14	14	35	35	35
P PD(max) (W)	1.23	3.2	8.4	7.7	20	S2

Table 1: Power levels supported by the EEE 802.3.cg standard

Advantages of SPE

Transitioning to SPE has several advantages, including installation to manage the entire building using a single communication network. Its benefits reduce the total cost of ownership and increase the return on investment of the building automation system. For example:

• Placing Ethernet connectivity at the edge simplifies the system by eliminating the need for additional gateways and requiring only one communications network.
• PoDL eliminates the need for separate power cables, simplifying the wiring of building automation systems .
• Using only one pair of wires reduces cable cost and weight, making overhead wiring easier.
• Faster, easier installation reduces labor costs.
• The bandwidth improvement compared to existing fieldbus networks provides flexibility for implementing features such as predictive maintenance.
• 10BASE-T1L provides a communication distance of 1000 meters with a data rate of 10Mbps, helping to replace higher-cost optical cables and enable more data transmission.

The following sections explain how SPE is implemented and the associated benefits for various building automation applications.

Fire safety applications

The Fire Alarm Control Panel ( FACP ) is connected to various heat , smoke and gas detectors. In case of an incident, these sensors connected in a signaling loop will sound an alarm and the FACP can communicate with the fire station through the telephone network. FACP usually supports multiple signaling loops to facilitate division into multiple zones or floors for easy identification.

Each building can have multiple FACPs , depending on the number of floors and sensors. When facilities such as large residential complexes, offices, schools, or shopping centers expand, it is often necessary to interconnect FACPs between buildings over Ethernet using copper or fiber lines up to 3 to 4 kilometers . Ethernet based on 100BASE-TX/10BASE-T requires multiple repeaters to bridge these distances. In this case, it can be challenging to power them. Another option is to transition to fiber optic cables, which requires the use of media converters on both ends (copper to fiber). Figure 4 depicts an example system.

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Figure 4 : Traditional Architecture – Fiber Optic Connections Between FACPs

Both of these options result in expensive systems. SPE can address challenges up to 1 km ; for longer distances , repeaters powered by PoDL can be used . PoDL eliminates the need for an external power source, further simplifying the system. Figure 5 depicts a fire protection system using SPE .

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Figure 5 : Architecture using SPE between FACPs

Vertical transportation applications

Elevators are complex systems. The primary communication link between the moving car and the machine room controller is via a moving cable. Depending on the building height, this cable can range from 10 to 500 meters or more. Controller Area Network ( CAN ) and LonWorks are commonly used protocols for elevator systems due to their low speed requirements and the required cable distances .

Given the stresses that cables are put under during operation, it is very important that the cables remain reliable over the years . The cables need to bend as the elevator moves up and down, which is not suitable for fiber optic cabling, so most elevator cables are made of copper. Considering the cable length, standard Ethernet is not suitable because it cannot exceed 100 meters .

Now, with SPE offering distances of 1 km and speeds up to 10 Mbps , it is ideal for next-generation elevator designs. There are several main reasons for requiring higher data rates between the car and the elevator controller :

• Stream video content from inside the car back to the machine room.
• Relay advertisements from the machine room to the car.
• Send more data to the elevator controller through various sensors, as well as data from equipment in the car, for predictive maintenance.

An example of predictive maintenance is monitoring the opening and closing motion of elevator doors by measuring the motor current during acceleration, steady state, and deceleration , and analyzing any anomalies. The ability to predict potential failures will avoid elevator downtime and inconvenience for passengers.

Upgrading existing elevators is as important as designing new elevators with more advanced features. One way to solve the retrofit challenge is to install a media converter like CAN to SPE inside the car and SPE to standard Ethernet or CAN in the elevator controller . For the next generation system, the elevator controller may contain a built-in SPE PHY 10BASE-T1L , and the devices in the car will be connected via SPE PHY 10BASE-T1S . The car will also have a built-in 10BASE-T1S-10BASE-T1L Ethernet switch to connect the car with the elevator controller. The emergency lights and communication systems in the car can be powered via PoDL to ensure uninterrupted power supply.

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Figure 6 : Car - machine room communication

HVAC Applications

The unified design HVAC controller can be used to control rooftop units, chiller control units, air handling units, etc. The HVAC controller uses standard Ethernet to connect to higher-level building automation systems such as building management systems, and multiple HVAC controllers can be daisy-chained . To maintain network connectivity when any HVAC controller loses power , electromechanical relays short the Ethernet signals on the input and output ports.

HVAC controllers have multiple analog, digital, or fieldbus interfaces for communicating or controlling multiple sensors that measure parameters such as temperature, humidity, and pressure (Figure 7 ). Sensors can be analog outputs with loop power or support 0 to 10W/4 to 20mA outputs with independent power supplies. HVAC controllers can also connect to actuators such as dampers, fans, and stepper motor drives through communication interfaces or analog connections . SPE interconnection from controller to sensor to actuator simplifies installation with only two wires while providing access to edge devices.

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Figure 7 : HVAC controller interface

Figure 8 illustrates an example of using a humidity sensor where ^{the I2C} interface is connected to a microcontroller (MCU) with built-in media access control ( MAC ) . The SPE PHY ( 10BASE-T1L or 10BASE-T1S ) interfaces with the MCU 's built-in MAC , while the PoDL with a DC/DC converter powers the entire circuit. This architecture has several advantages, including standardization of sensor connectors, reusable hardware, and sensor and hardware diagnostics and calibration.

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Figure 8 : SPE -based sensing

HVAC controllers with multiple SPE ports to connect various sensors and actuators will require application-specific integrated circuits to implement existing Ethernet switch functions.

Video surveillance applications

Outdoor Internet Protocol ( IP ) network cameras are often installed on the perimeter of a building to ensure continuous video capture and to sound an alarm in the event of a serious security breach, giving security personnel ample time to react. These cameras may be 1 km or more from the network video recorder , and bridging that distance over standard Ethernet requires the use of repeaters or fiber optic cables. Using efficient encoding systems such as H.264 and H.265 , data rate requirements drop to less than 10 Mbps , even with a 4-MP sensor at 30 fps .

It is expected that future IP camera products will support SPE , which will simplify installation, and network video recorders will also provide power supply device ports. Class 8 and 9 ( 48V regulated power supply devices) or Class 14 and 15 (maximum 50V to 58V ) can support the power levels required by IP cameras, which may require up to 52 W of power to operate. For most camera systems, even models with built-in heaters, this power is sufficient. For buildings that need to upgrade, an intermediate solution is to use a standard Ethernet to SPE converter.

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Figure 9 : IP Network Camera Connectivity

Summarize

SPE, standalone (data only) or used with power, offers many opportunities for building automation. But until the ecosystem is fully developed, media or protocol converters are still needed to upgrade existing systems, and there are challenges related to the reuse of existing cables (unshielded, untwisted, wire gauge) and connectors, which may not provide the full distance or speed defined in 802.3cg . However, this is not a major obstacle because the future benefits outweigh the limitations. Power supply devices and power supply equipment for SPE are expected to be released in the next few years. Until then, engineered links will power edge devices. You may also see building automation products that support SPE through seamless integration .