Explore the history of communication systems.
Digital communication is of the utmost importance to industrial facilities - all safety and production systems rely on access to reliable, real life data. Read on for an overview of how digital protocols have evolved over the last few decades!
In the early days, control systems used simple switches to activate motors, relays and other devices. As processing and production systems became increasingly complex, the need for advanced communication became clear.
What is a digital communication system?
Wires and connectors between devices are the primary components of a communication system - think of an Ethernet cable with an 8-pin Jack. A communications system also includes a protocol that determines rules such as speeds, nodes, voltage levels, etc.
Packet data must also be considered, as the more complicated the communication is, the more information the more transmitted, which translates to longer packets. There are two main types of digital communication: device level and control level. At the device level, input sensors and output coils send data to a central processor. At the control level, processors need to be able to share information with one another.
Digital Systems Timeline: 1940s-Today
Bell Labs invents first transistor (1947)
This innovation allowed for faster signal switching at significantly lower voltages.
It wasn’t until the late 1950s that it became necessary for multiple devices to communicate over distance. By this time, software, cables and wires advanced to solve the problems associated with standard stranded wires.
RS 232 (1960)
The RS 232, one of the earliest communication standards, is still used today. In 1960, the accepted maximum was around 50 ft at 20 kilobits per second (kbps) - using this standard, a 2-GB file would take 222 hours to transfer!
Referred to as “point to point,” this method involves two devices communicating at either end of a wire. While most newer models use USB, point to point is still used today to program PLCs.
The development of RS 232 was also contemporaneous with several significant advancements in computing, including:
- Modicon 048, the first PLC (1968)
- Intel 4004, the first microprocessor (1971)
- First Apple computer, the Apple 1 (1976)
While the RS-232 offered an important standard for many devices, it was not technically designed for use with industrial signals.
Modicon, one of the earliest PLC companies, created Modbus, a hugely popular platform that is still used in many systems today - albeit with modern adaptations.
Rather than defining the physical limits like RS 232, Modbus describes the arrangement of transmitted data - referred to as a “frame.” This design allowed packets of data to be sent over a variety of cables that used varying protocols, including Ethernet. Soon after the publication of Modbus, MS-DOS was released in 1981, ushering in a new computing era.
Today, Ethernet is universally recognizable as the most common standard for internet access via hardwired cable. While this is usually true, the Ethernet Internet Protocol (IP) is less about the physical cables, and more about how the streams of bits and machine connections are structured.
Other standards, including Modbus, are often wrapped into an Ethernet frame, allowing older equipment to send data to machines in any modern system.
While the name is similar to RS 232, the RS 485 is an entirely different type of communication system. With a few wires used in twisted pairs to increase length and speed, devices with unique addresses connect along the wire. This system allows a large number of devices to communicate with each other at higher speeds.
Only two years later in 1985, the original Windows 1.0 graphical OS was released.
CAN bus (1986)
The CAN system, or Controller Area Network, uses RS485 to connect simple controllers or low level I/O devices across a broad area at higher speeds, accomplishing this while using a simpler structure than Ethernet. Because of these features, CAN bus has been the adopted standard for vehicle engine control systems for many years.
After the development of CAN, several spurs were developed in turn, but needed to be standardized. In 1988, Fieldbus implementation stepped into the scene, providing installation guidance and general rules while pointing to other systems like PROFIBUS and ControlNet for exact packet size and structure rules.
PROFIBUS, a subset of Fieldbus, offers rules for packet structures applicable to a variety of equipment manufacturers. It’s important to note that PROFIBUS differs from ProfiNet, which is a modified form of Ethernet specific to industrial use.
DeviceNet (Early 1990s)
Another spur of CANBus, DeviceNet allows low-level I/O devices to communicate with controllers using somewhat small data packets. In comparison to many other connection methods, DeviceNet is somewhat slow, but quite resilient to interference.
In the mid 1990s, Universal serial bus (USB) was introduced, evolving over time in speed and abilities. Today, USB is used to program many modern PLCs, thanks to its near universal computer and manufacturer support.
An additional subset of Fieldbus, ControlNet is most often used to connect controller networks. Using ControlNet, PLCs may connect with VFDs, PCs and HMIs - though rarely to devices.
Wi-Fi and the 802.11 Standard (1997)
In the late 1990s, the first 802.11 standard was released, allowing data to be sent wirelessly. While it’s rarely used in industrial facilities thanks to its unreliability in noisy settings, technological innovation may eventually remedy this weakness.
Another widely used wireless standard, Bluetooth’s application in industrial settings is uncommon, as it shared the same downside as Wi-Fi. Despite this weakness, Bluetooth is used by millions of consumers across the globe.