Sending and receiving data over a given distance has grown from a passion in humans to a necessity. In 1810, a German man created a system for sending encoded messages via air bubbles. He crafted a device that attached wires to the bottom of an aquarium, one per letter of the alphabet, and when a specific wire was energized bubbles would form and rise to the top of the aquarium. This allowed for a slow and cumbersome transmission of human readable information. This device kicked off a race that eventually gave us the telegraph and transmission of data over long distances via Morse code.
Sending data over long distances progressed, and as the need for computers to transfer data arose, the need to transfer data on the factory floor became paramount to all control and supervisory control and data acquisition (SCADA) platforms. One of the most popular of these protocols being the Serial RS232 Communication protocol. Serial Communication is a method for transferring human readable code to computer readable code utilizing the ASCII format and serial ports.
The RS232 Serial protocol is an asynchronous communication method. This allows transmission of data intermittently with varying bit rates without the use of an external clocking mechanism for timing because the timing is encoded within the symbols. Serial RS232 ports on programmable logic controllers (PLCs) are connected to external devices with nine or 25 pin cables that are used to transfer data by turning certain pins on and off. This leads to a communication method where the devices talk to each other to establish they are there, powered on, and ready to receive data. Once this handshake happens, data is transferred until the receiving device can’t process it anymore, wherein the sending device signals a pause to let the receiving device catch-up before it starts sending data again. Once all the data is sent, the sending device turns off its Request to Send (RTS) pin and the external device sits around waiting for more data.
All of this was pretty great at one point, but now several communication protocols and methods have been developed since the Serial Communication revolution, which are able to transfer more data, longer distances, at a higher rate. There are VERY few instances where Serial Communication would be preferred over something like Ethernet/IP, EtherCAT, or Profinet. It is time to stop buying devices that use Serial Communications as their primary communication method.
As recent as last week, we’ve had projects where Serial devices were specified and purchased for greenfield installations. In some cases, this is done because the purchasing lead was unaware technology had moved on, and in other cases it was done because they went to an older section of the plant and ordered what was already installed.
Supporting Serial devices is cumbersome and difficult, not to mention it only allows for 1:1 communication between devices which is extremely limiting. Almost all modern PLCs and programmable automation controllers (PACs) do not have a Serial Port provided natively, and external cards are becoming more expensive and sparsely documented. As a System Integrator it is our duty to provide the best technology as efficiently as possible, and integrating serial devices is a surefire way to increase project costs. The time it takes to unravel the bit structure, create code for communication, and troubleshoot errors greatly outweighs equivalent efforts with modern communication protocols. Modern Comms also allow for a greater amount of data including diagnostics, errors, and critical process parameters to be transferred. In this age of Big Data, that is becoming supremely important.
Equipment vendors will likely go where the money is, and if orders keep coming in for new Serial RS232 devices, they will keep producing new product lines with RS232 options. Right now, on a major Automation vendor’s website you can find a recent article on why Serial Communication is reliable, robust, and great for deployment followed by their line of Serial communication cards and PLCs. On the same website you can find an article on the need to migrate away from Serial for all the reasons listed above as well as in depth analysis on why Serial Communication needs to go away.
Just as you don’t see an overwhelming amount of US households rushing to buy the latest model of telegraph this Holiday season, you don’t see anyone communicating with each other via aquarium bubbles. Stop buying Serial RS232 Comms devices, and look towards more cost effective, modern, and more supportable options. Your budgets, staff, and project schedules will thank you.
Will Aja is the vice president of customer operations at Panacea Technologies, a certified member of the Control System Integrators Association (CSIA). For more information about Panacea, visit its profile on the CSIA Industrial Automation Exchange.
