Category: Industrial Control Systems (ICS)

There are several versions of the Modbus protocol because the protocol was originally developed for serial connections but has been adapted for the networking world. These include:

Modbus is one of the oldest and most popular ICS protocols in use today, largely because of it’s openness and simplicity. Modbus is a digital communication protocol for two or more devices to talk to one another. Modbus is related to the application-level protocols of the Open System Interconnection (OSI) network model. The physical layer […]

There are dozens of protocols used in the ICS domain. Many of these protocols were developed to support a specific technology, and as such, are uncommon or only applicable to a single vendor. Some ICS devices are old—they can be in use 25 or 30 years—and use proprietary protocols developed by vendors that are no […]

Some field controllers are assigned a higher priority where they are polled more frequently than other field controllers. For example, critical field controllers may be polled twice a second, while lower priority devices are polled once per minute. Polling rates also depend on the information being reported. The status of regional high voltage transmission lines […]

The star topology is constructed from a central device, either a switch, router, or hub, which every other node in the network connects to. In this design, each distinct cable only connects two physical devices, with one end hooking up to a node on the network and the other hooking up the central device. If […]

The ring topology is constructed from a closed loop cable, known as a ring, that each node on the network connects to. In this topology, the network forms a circular shape and data is transmitted clockwise via a token that each node in the network actively listens for. If a node does not want to […]

The bus topology is constructed on a single cable, referred to as the bus, that each node on the network connects to. Each of these nodes passively listens for data being transmitted along the bus. If one node wants to transmit data to another node along the bus, it sends out a signal to the […]

Now that we are more familiar with common elements and architectures of ICS, let’s look at how information moves within a control system, starting with network topologies and methods. ICS or network topology refers to how the network is built from the ground up, where things connect, and how the information flows through this foundation. […]

This diagram is a simplified representation of an ICS communication network. The process is controlled by an application running inside the field controllers, which communicates with a series of field inputs and outputs devices. The field controllers consolidate the data and transmits it to the HMI stations where it is presented on displays. The data […]

Sometimes these control loops are nested and/or cascading – whereby when multiple sensors are available from measuring conditions in a controlled process, a cascade control system can often perform better than a traditional single-loop. For example, the steam-supplied water heater shown heats water using cascade control. The second controller has taken over responsibility of manipulating […]