When I first became involved in Programmable Controllers, one of the common questions was how to define when a PLC was needed. From a control standpoint, the common answer was that if you had 4 or more relays in the design of the control circuit, the PLC was likely a better choice. This is based on raw cost or projected cost of future improvements which programmable devices are well suited to and hard wire is not.
In those early days of programmable control the most important metric was the speed. How many instructions the unit could process in period of time. Early PLCs were not very fast, typically running hundreds of instructions in 10 to 20 milliseconds. At the time, this speed would have been in stark contrast to the more common DCS or Batch Controller technology that processed PID loops that might take hours. Process controls for refining chemicals from crude oil or brewing beer require hours to complete and control system update rates are not a great concern.
In the modern age a similar paradigm becomes useful. How fast is fast? When a company is engaged in manufacturing speed is relative. If the factory has to make 1.2 million cans of beer a day control system update rates are critical. This production rate is roughly 14 cans per second 24 hours a day 365 days a year. And that is precisely what many breweries are up against. It is a horrendous pace to keep up with and maintenance is extremely difficult.
Downtime is scheduled once a year and outages are expensive. At the rate of $1. per can retail, a one hour outage is over $50,000 an hour. Of course, the brewery produces products on multiple lines so a single line shutdown does not stop production, but you get the idea. Each process in the plant has to be coordinated with the others to end up with the final production capacity. If the “bodymaker” machine is producing 150 can bodies a minute, its going to require at least 6 bodymakers to keep up with production demand.
That also means that 4725 gallons an hour of beer have to be available for filling the cans. So if brewing takes a certain number of days for the beer to mature, 113,400 gallons have to be in process at all times. And this is just for one plant.
So in the same manufacturing environment we have processes than run in days and processes that run in the milliseconds. They all require automation to some degree. In the past the hardware requirements were unique. Today, any cellphone can run the software needed.
So where is the differentiation? Now its all in software.