1. Benefits of Industrial over Commercial Switches
Industrial Ethernet Switches are designed to operate in plant floor environments. The specifications of Industrial Ethernet switches (temperature, shock, vibration, etc.) meet or exceed the equipment being connected (PLC’s, Ethernet I/O, HMI’s, etc.). Most commercial Ethernet switches have commercial temperature ratings (0-40C) and do not publish shock and vibration specs. Most Industrial Ethernet Switches are rated for a minimum of 0-70C operation and have excellent shock & vibration specs.
In addition, Industrial Ethernet switches are housed in rugged industrial style steel enclosures using Din-Rail or panel mounting. Most commercial switches and media converters cannot mount conveniently inside equipment enclosures.
Another added benefit derived from using Industrial Ethernet switches is redundant power inputs. Commercial switches rely on a single power supply to power the switch, while Industrial switches typically run off DC power, and have redundant power inputs. This allows the weakest link (the power supply) to have a hot standby back up, ensuring maximum uptime.
Industrial Ethernet switches carry a Class I Div 2, group ABCD rating while the commercial counterparts do not. This allows the Industrial Ethernet switches to operate where explosive gases are being used (very typical for industrial applications).
Because Ethernet has been available in the office environment long before industrial Ethernet equipment existed, the equipment is well known for its performance and reliability and low cost. Quite often, when companies evaluate the technology, they do not examine the alternatives of purchasing Industrial Ethernet Switches versus commercial switches and routers. However, In this instance, the evaluation is simple. Fortunately, Industrial Ethernet switches provide advantages over the 4 primary alternatives being used. All of these alternatives utilize commercial Ethernet switches and are listed below:
· Wire all connections to a climate-controlled environment
In this scenario, the customer will place commercial network equipment in a climate controlled environment and run a cable to every industrial Ethernet node. This is costly and decreases reliability. Industrial Ethernet switches offer the opportunity to eliminate significant, expensive wiring efforts when compared to this approach.
· Build climate-controlled environments in harsh areas.
In this scenario and in order to reduce wiring costs, customers will build a climate-controlled environmental enclosure to house commercial equipment in a harsh environment (i.e. NEMA 4 enclosures with Peltier coolers and bulkhead-mounted connectors). This is often very costly and increases the number of components that can fail. Industrial Ethernet Switches can be installed directly in harsh locations, thus eliminating the need for expensive climate controlled enclosures.
· Simply use commercial equipment without regard to environmental mismatches.
This is an alternative, but not a very good one. In this scenario, the customer utilizes commercial equipment in the harsh environment. This equipment is not rated for these environments and will probably fail and/or decrease the reliability of the system. In our discussions with customers utilizing this alternative, it was only implemented because they were not aware that industrial grade equipment was available. They are very open to utilizing Industrial Ethernet Switches.
In addition, many commercial switches use cut-through techniques and can propagate bad packets on the network. However, today's Industrial switches use "store and forward" technology that
performs CRC (cyclic redundancy checks) and ensures the data Integrity of any packets being forwarded.
· Utilize Hubs instead of Switches
While hubs are cheaper than switches they do not eliminate collisions and are obsolete by today's standards. Hubs create determinism issues associated with Ethernet Networks due tot he collision domain they created. The following discussion illustrates the basic difference between switches and the now obsolete hubs.
Difference between Ethernet Switches and Hubs
A hub, also known as a repeater, is a simple device that connects Ethernet nodes. Hubs forward data packets they receive from a single port to ALL ports. All devices connected to a single hub or interconnected hubs share the same bandwidth. As nodes are added to the network, they compete for available bandwidth (typically 10 or 100 Mbs). Therefore, data collisions are guaranteed when a hub is used and network determinism (the ability to guarantee a packet is sent/received in a finite amount of time) is impossible. This is the primary reason Ethernet has historically not been accepted in control applications. Most control systems have a time requirement for packet transmission (< 100ms). This cannot be guaranteed with a hub and is especially if the network is busy. You can imagine the problems this can cause in a mission-critical control application.
This is analogous to a single lane road. You cannot get onto the road until traffic is clear. With a hub, you cannot send a packet until network traffic is clear.
Another dated analogy is a party-line phone system. If you shared a party line phone with 8 users, anytime any of the users received a call; your phone would ring. All users would have to answer to determine if the call was for them. In addition, no other user can use the phone while someone else is using it. An Industrial Ethernet Switch is a more complex device with built-in intelligence to connect Ethernet nodes. The switch eliminates the problem of network determinism by providing full bandwidth with storage to a node or group of nodes. The switch eliminates all collisions domain that typically make Ethernet nondeterministic. A switch efficiently sends data only to the appropriate network port or segment, not the entire network as a hub does. The switch forwards data based on learned MAC addresses (unique for each hardware device on the network) contained in the data packet. The switch must store the source MAC addresses of devices it receives frames from, requiring high-speed dual ported SRAM (hubs have no memory requirements). The switch determines the location of each node and establishes a temporary connection between itself and the node and terminates once the packet is transferred.
Using our highway analogy, we have turned the single lane road into an 8-lane divided (RX and TX) highway. A lane can be dedicated to mission-critical nodes ensuring traffic can always get through in a pre-determined time. Using the phone analogy, your phone rings only when the call is for you and you can use the phone when other people are using it.
In summary, an Industrial Ethernet Switch increases network bandwidth and provides network determinism for Industrial control applications, and provides the most cost-effective solution for industrial environments.
It is the customer's responsibility to review the advice provided herein and its applicability to the system. Red Lion makes no representation about specific knowledge of the customer's system or the specific performance of the system. Red Lion is not responsible for any damage to equipment or connected systems. The use of this document is at your own risk. Red Lion standard product warranty applies.
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