Industrial Ethernet has very rapidly become the reliable technology Infrastructure for Automation Communication within production plants, Utility Substations and ITS environments. Some of the reasons for this rapid change is based on flexibility, expandability, reliability, resilience, open world standard protocols, ability to adopt legacy protocols, ease of troubleshooting and maintenance and minimized cabling requirements.
Most Programmable Logic Controllers (PLC) and Remote Terminal Units (RTU) vendors are now making their equipment with Ethernet interfaces forcing the migration to Ethernet based systems. It is now possible to activate a PLC/RTU in the field and have visual confirmation (for safety purposes) over existing infrastructure such as : fiber, Satellite, GSM , Wifi or WiMAX options- remotely!
Ethernet typically uses a standard Unshielded Twisted Pair Cable (UTP) with a category rating based on the performance required. The cable is fairly inexpensive but has a distance limitation to 100m (This is without any interfering factors). When a connection is required further than 100m then you would look at the following options to extend the connection required:
- Switch to repeat the signal and propagate it a further 100m (This is a limited option)
- Convert the UTP Cable to a Fiber Cable through the use of a media converter
- Fiber to be used is Multimode or Singlemode
- The selection of fiber is based on the distance and the speeds you require from your system
- Wireless
- This is typically used in applications that don’t have a high data throughput and is prone to be less reliable than UTP or Fiber
- Wireless can be used from a few meters to a few Km’s, this is based on if you are using un/licensed frequencies which in turn will dictate if you should have line of site communication or not.
When most plants started with Ethernet, correct planning for future vision was not always kept in mind with regards to considerations of expansions of the plant/site, future implementation of additional PLC’s, RTU’s, IP Camera’s, VoIP, Fire Detection and many more peripherals. Such expansion would have an impact on the original design for IP Structures and design layouts. Thus your initial design and choice of equipment will be a large factor in how the expansions would be dealt with.
The equipment to use for the communication backbone in Automation Systems is critical since majority of the automation process is reliant on reliable communication. It is critical since failure of equipment or design will impact production and potentially be a safety hazard!
Logical Network Separation:
Before we separate the logical portions of the network we need o understand how a network initiates and completes its required communication.
Once you have your physical network topology layout with your planned systems of infrastructure redundancy, we then need to look at the types of traffic to be used, along with how many different types of communications will be taking place over the network.
An IP Address and Subnet mask are used on the end devices in order specify the network they are logically connected to.
192.168.0.0/24 Would represent an IP Address range from 192.168.0.1-254. So any device assigned with a 192.168.1.0 range would not be able to communicate to 192.168.0.0 range without routing the traffic through.
In order to understand a portion of how this takes place we need to understand the different types of addressing structures such as:
Unicast : This is a standard message from one device to another device
Broadcast : This is a message that is sent from 1 device to EVERY device on the network (subnet)
Multicast : This is a message block that is sent from one device to one device or to many devices but not necessary to all devices
When device “A” wishes to send data to device “B”. Device “A” will send a broadcast message requesting for information on the location of Device “B”. This Broadcast message is very intense on the network and will travel to ALL devices on the same subnet. With too many Broadcasts the network will suffer with communications and without any Broadcasts the network would not work at all.
So if an Intelligent Ethernet Device (IED) in a 192.168.0.X range wishes to communicate to a PLC in the same range, a Broadcast will be sent to the 192.168.0.0 range and no other subnet range!
From this we can see the importance to logically separate the network if running multiple purpose systems over the same existing Ethernet Infrastructure. Such examples would include PLC, Scada, VoIP, IP Video and Seismic networks.
Virtual Local Area Networks (VLAN’s) can be use to separate theses different types of traffic. There are 3 main types of VLAN’s namely:
- Port Based VLAN’s
- MAC Address Based VLAN’s
- IP Based VLAN’s
These different options are based on the different layers referred to by the 7 Layer Open System Interconnection (OSI) which were developed by International Standardization Organization (ISO).
Bringing the past equipment forward to Ethernet with a simple converter:
The reality is if you have an existing plant it is not a financially feasible option to replace all older PLC’s/RTU’s to the new age style with Ethernet Ports embedded.
In such a case, use of a Serial Device Server would be required in order to convert existing RS232/422/485 Serial communication to Ethernet.
There are two methods for making use of these converters:
Method 1)
This method is the picture on the left and describes how we could extend the Serial over Ethernet using two hardware devices, one on each end.
Method 2)
This method required a Virtual Port Software Package on the PC end, this will create a virtual Com Port and communicate directly with the Serial Device Server in the field as if directly connected with Serial
Both these methods are very good examples on how to extend your serial communication via Ethernet as well as integrate the Serial Communication into your Scada/HMI.
Typical Serial Conversion to Ethernet would require the device to understand the Serial Protocol being used (WIN, TIN, DNP3). Ruggedcom are able to convert these known protocols and even legacy Serial Protocols as a RAW Serial Data Encapsulation. If you are using a legacy Serial Protocol then this method would be a good choice for you since no further development would be required, in effect, you would be simply extending your Serial Network through your Ethernet Infrastructure.
How to manage your Ethernet Network:
In order to manage an Ethernet Network effectively, you would require to have all your Ethernet Switches/Routers enabled for Simple Network Management Protocol (SNMP) and if possible to have the end devices also configured with this standard protocol.
A network management station is an intelligent piece of software that communicates via SNMP to all managed devices on the network to gain information regarding their state of operation and their health status thus assisting to be proactive rather than reactive to any potential maintenance required on the network.
If a problem occurs, the system will automatically notify the relevant person on shift with an email or sms regarding the state of the network and condition of the notification.
Training on such a system is an essential part to a successful deployment and reliable communication with maximizing safety!