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Simplify Industrial Ethernet Networking with Smart PoE Switches

By Bill Giovino

Contributed By Digi-Key's North American Editors

The most widely used wired networking protocol in Industrial Internet of Things (IIoT) applications is Ethernet. As a result, Ethernet cables can be found everywhere in any industrial automation facility. Since electrical power also needs to be available wherever Ethernet is installed, power lines are also found almost everywhere Ethernet cables are located—usually in the same cable bundles.

Power over Ethernet (PoE) has emerged to greatly simplify industrial automation facilities. By transmitting electric power over the same cable as Ethernet connectivity, less cabling needs to be laid out over the facility, making it easier to set up or reconfigure a manufacturing site.

This article discusses how smart industrial Ethernet switches that support PoE can simplify a factory layout while lowering costs. It then introduces two DIN rail Ethernet switches from Henrich Electronics that can supply both network connectivity and power over the same Ethernet cable.

Simplifying industrial automation cable layout

Many industrial automation facilities are designed to be easily reconfigured. For example, an assembly line in a manufacturing facility may need to be taken down and set up to manufacture a different product. Combining Ethernet with PoE increases the modularity of a factory floor by making some equipment almost plug and play—just plugging in the Ethernet cable provides both network connectivity and power. This simplifies the factory setup, making it easier to route cables to equipment.

This also saves time designing the facility while saving the cost of additional cabling and the manpower required to lay the cable. In addition, by providing one central power source for each PoE endpoint —or Powered Device (PD)—on the network, PoE provides a single point of maintenance. A PoE-enabled switch or hub can safely provide up to 90 watts (W) of power for each PD, making PoE appropriate for cameras, compact control panels, and some factory equipment like valves or doors.

PoE also frees up space for additional wiring. Most cable bundles in industrial facilities are limited to about 24 cables total because of heat issues. Cables in the same bundle are usually held together using heavy-duty twist ties that keep the cables tied tightly next to each other. As a result, all the cables in the bundle share and trap heat, which raises the temperature of the entire cable bundle, referred to as “temperature rise.” Because resistance increases with temperature, as the temperature rise increases, power and signal loss due to heat will decrease the power efficiency of each cable in the bundle. PoE eliminates many of the power cables used in industrial automation, which decreases the number of cables in a bundle, reducing heat and preventing signal degradation in Ethernet twisted pairs. This also improves efficiency for carrying power to equipment.

There are presently three standards for supplying PoE over standard Cat5e Ethernet cabling: 802.3af can provide up to 15.4 W of DC power from the power sourcing equipment to each PD; 802.3at (PoE+) provides up to 25.5 W of power; and the latest standard, 802.3bt (PoE++), can provide up to 60 W of power over standard Cat5e Ethernet cabling. 802.3bt can also support up to 90 W of power with Cat6 or Cat6a cabling, which carries power over thicker gauge wire. Each of the standards is backwards compatible.

Adding Ethernet and PoE to a new industrial automation facility

The easiest way to add PoE when building a new network is to incorporate Ethernet switches that support PoE. An easy solution is to use the Henrich Electronics HES5A-4E60-VL DIN rail five-port unmanaged PoE Ethernet switch (Figure 1).

Image of Henrich Electronics HES5A-4E60 Ethernet switchFigure 1: The Henrich Electronics HES5A-4E60 Ethernet switch provides five Ethernet ports, four of which support 802.3bt PoE++. (Image source: Henrich Electronics)

The Henrich Electronics HES5A-4E60 unmanaged Ethernet switch mounts on a standard DIN rail or panel. It is compact at only 92 x 116 x 67.2 millimeters (mm) making it appropriate for space-constrained installations. The HES5A-4E60-VL has five Ethernet ports on the front panel. One is a standard 10/100Base-T port and four are Ethernet PoE++ ports capable of supplying up to 60 W of power to each PD. Using Cat6/a cabling, the HES5A-4E60-VL is capable of providing up to 90 W. It is IP40 rated and can operate over -40°C to +60°C, making it appropriate for most industrial automation facilities.

The HES5A-4E60-VL is also backward compatible with the previous PoE standards of 802.3af, which supports 15.4 W per endpoint, and 802.3at, which supports 25.5 W per endpoint.

When a cable is plugged into one of its four PoE++ Ethernet ports, the HES5A-4E60-VL initiates a short PoE handshaking protocol with the PD. This handshaking determines if the endpoint requires PoE power, and if so, how much power the endpoint is requesting. This allows the PoE switch to safely and efficiently apply the requested power to the Ethernet endpoint, and to safely disconnect power from the PD if the Ethernet cable is disconnected, or if the endpoint stops responding. If a PD is properly powered, an LED indicator for that PoE port on the switch is illuminated to indicate the port is receiving power. This also helps in diagnosing any power issues. For example, if a PD is not operating and the corresponding PoE light is off, it could indicate a damaged or disconnected cable, or possibly that the endpoint is not completing the PoE handshake properly.

The HES5A-4E60-VL is an unmanaged switch, which means it is plug and play. Once an Ethernet cable is plugged into any of its five ports, the switch requests the endpoint’s Ethernet MAC address. The HES5A-4E60-VL has a 1,024 entry MAC table for storing known MAC entries to IP addresses. If the MAC is not in the MAC table it is assigned a new IP address. If the MAC address is found in the table, the IP address is read from the MAC table entry and assigned to the endpoint. The switch does not need to be configured or managed in any way.

For more sophisticated industrial automation networks, Henrich Electronics offers the HES6GM-4E-2SFP-VLW DIN rail six-port managed PoE+ Ethernet switch (Figure 2). This IP30 rated Ethernet switch has an operating temperature rated for a wide -40°C to +75°C range, making it suitable for dry, dust-free industrial environments that may experience temperature extremes too inhospitable for long-term human exposure.

It has a 4,096 entry MAC table and supports 10/100/1000Base-T, making it compatible with the latest gigabit Ethernet standard. It supports up to 30 W of power for each PD.

Image of Henrich Electronics HES6GM-4E-2SFP-VLW DIN rail Ethernet switchFigure 2: The Henrich Electronics HES6GM-4E-2SFP-VLW DIN rail Ethernet switch has six Ethernet ports, four of which support PoE+. The switch can be configured by a web browser to set alarms and alerts for various operations. (Image source: Henrich Electronics)

The HES6GM-4E series can be DIN rail or panel mounted. It is a managed switch, which means it can be completely plug and play like the HES5A-4E60, or it can also be configured using a web browser from a PC connected to any of its Ethernet ports. Security allows up to ten IP addresses to be granted permission to access the web browser interface. Other features of the web browser configuration interface include automatic email alerts for security issues, setting Dynamic Host Configuration Protocol (DHCP) parameters, port-based traffic control, and limiting, port forwarding, and access to the system log. The browser interface can also access the 4,096 entry MAC table to review, edit, or delete entries.

Cabling for harsh industrial environments

Industrial environments can see temperature extremes as well as be exposed to liquids ranging from salt water to oil to gasoline that can corrode unprotected surfaces. For cabling, constant physical abuse such as being stretched around sharp corners or run over by trucks can degrade or damage cable shielding, or in extreme cases, break the electrical conductors carrying data and power. This requires a heavy-duty industrial strength cable built to withstand industrial abuse. Also, to handle both signal and power delivery, PoE requires high quality cables. Four twisted pairs are required to provide data and power. Wire gauge must be no smaller than 24 AWG to minimize heat rise with enough efficiency to provide 60 W of power per cable.

For the harshest environments, Samtec Inc. has introduced the RCE-01-G-13.00-D Cat5e Ethernet cable assembly (Figure 3). This 13 meter cable contains four twisted pairs—two pairs for data and two pairs for PoE power.

Image of Samtec Inc. RCE-01-G-13.00-D is a Cat5e cable assemblyFigure 3: The Samtec Inc. RCE-01-G-13.00-D is a Cat5e cable assembly rated at IP68. Both the cable and the RJ45 connectors can withstand the harshest industrial environments. (Image source: Samtec Inc.)

Each RJ45 male connector has a space-saving rectangular design and is sealed against dust and liquids. The connectors use a push-to-seal latching mechanism that creates a distinct audible click when properly inserted. The latches are designed to be easily removed with a minimal of effort.

The RCE-01-G-13.00-D Cat5e cable uses 24 AWG conductors making it appropriate for 802.3af and 802.3at power delivery.

Conclusion

PoE has become easier to use with the introduction of Ethernet switches that can handle the power. Selecting the proper PoE Ethernet switch for an industrial automation application can save time and cost, while providing safe and efficient power delivery as well as reliable network connectivity on the same cable.

Disclaimer: The opinions, beliefs, and viewpoints expressed by the various authors and/or forum participants on this website do not necessarily reflect the opinions, beliefs, and viewpoints of Digi-Key Electronics or official policies of Digi-Key Electronics.

About this author

Bill Giovino

Bill Giovino is an Electronics Engineer with a BSEE from Syracuse University, and is one of the few people to successfully jump from design engineer, to field applications engineer, to technology marketing.

For over 25 years Bill has enjoyed promoting new technologies in front of technical and non-technical audiences alike for many companies including STMicroelectronics, Intel, and Maxim Integrated. While at STMicroelectronics, Bill helped spearhead the company’s early successes in the microcontroller industry. At Infineon Bill orchestrated the company’s first microcontroller design wins in U.S. automotive. As a marketing consultant for his company CPU Technologies, Bill has helped many companies turn underperforming products into success stories.

Bill was an early adopter of the Internet of Things, including putting the first full TCP/IP stack on a microcontroller. Bill is devoted to the message of “Sales Through Education” and the increasing importance of clear, well written communications in promoting products online. He is moderator of the popular LinkedIn Semiconductor Sales & Marketing Group and speaks B2E fluently.

About this publisher

Digi-Key's North American Editors