The end of PLCs?

LearnTillYouDie said:

PLC are stable and do not require updates, that makes them secure and isolated from malware. Can PC based do the same? Not for the price.

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Sweeping statement of the year alert !

PLC firmware is constantly being updated for both new functionality, security and bugfix, admittedly nothing like Windows 10 but it still happens on a regular basis.

The big difference between PCs and PLCs is the scope of work. Both have limitations in their scope, but PCs have a much wider scope. For the purpose of this discussion, I will use the term PC to represent non-PLC based computers and their operating systems, so don’t get hung up on that term.
A PC is designed for the masses, allowing functions that the masses want: web surfing, communications, gaming, multimedia, and office software to name just a few. Each of those functions are wide-ranged and because of that wide range of needs, creates a situation where the PC becomes the ‘jack of all trades’, or good at most things, but an expert at nothing. The wide range of applications and speed to market of PCs create a situation where the hardware, firmware and software that make them run is constantly updated. A person who installs only office software and minimal other software will not necessarily see the “bugs” of someone who is doing 3D modeling, gaming, communications and multimedia. Open communications and networking alone create huge variables and potential for updates in a PC. In addition to the broad range of software that can be installed, many different manufacturers and models of hardware can be installed in a PC (memory, storage media, graphics and comm cards).
A PLC is designed for specific purposes. Yes, the purposes are broad, but nowhere near the scope of a PC. This allows the hardware and firmware to be fine-tuned for the limited software (application) that will be loaded to it. The hardware that can be installed in a PLC is limited. If the hardware is not made by the manufacturer of the PLC, then it has to be vetted by the manufacturer to ensure it works properly in that environment. Because of this tighter scope, the firmware and software updates are less frequent than that of a PC.
I like to compare a PLC vs PC in terms of using the right tool for the job. I carry a multitool on my belt and use it regularly. I use the screwdrivers, file, saw, scissors and pliers regularly, but only for quick, non-critical jobs. If I were installing a deck, I would not use the screwdriver on my multitool. I would use a screwdriver (powered, if possible). I could use my pliers to remove the nuts holding a subplate in, but a better choice would be a ratchet and socket. If I use my multitool beyond the scope it was developed for, I will need to repair it or buy a new one more frequently than a dedicated tool.
I have heard the death knell of the PLC since I got into this business. That was many years ago. I don’t see that happening any time soon unless the computers become more stable, are guaranteed to work for every hardware option and do not require frequent updates.
Sorry for the long post.

drforsythe said:

...
I have heard the death knell of the PLC since I got into this business. That was many years ago. I don’t see that happening any time soon unless the computers become more stable, are guaranteed to work for every hardware option and do not require frequent updates.
Sorry for the long post.

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+1, no need for an apology.


Another issue is liability: PLCs are often involved in processes where significant monetary damage, injury or death could occur; cf. the many repeated warnings in PLC programming manuals. This puts very different, and much more stringent, requirements on hardware and operating system software for PLCs running a potentially dangerous process, compared to concern for someone losing their latest edits to a BSOD. The costs of extra design work for those requirements, and of an OEM's liability insurance, have to be recovered in the prices of the PLCs.



I might use a PC-based or RPi "PLC" to randomly cycle my lights while away on vacation; it may not be wise to do the same with my garage door, at least not without a physical safety override.

drbitboy made me think of something to ponder:


Windows10-SIL3 Edition


Don't be anywhere near that nuclear power plant.

Another old joke ca. 2005 ...


Four system managers meet for lunch in Manhattan.


The first says, "My MVS TSO system has been up for 18 days."


The next says, "That's nothing, my VAX/OpenVMS system has been up for 198 days."


The next says, "That's noting, my Debian Linux system has been up for 1,998 days.


The last says, "My Windows NT Server has been up for 18 hours."


And the first three say "Wow. You win!"

drbitboy said:

Another old joke ca. 2005 ...


Four system managers meet for lunch in Manhattan.


The first says, "My MVS TSO system has been up for 18 days."


The next says, "That's nothing, my VAX/OpenVMS system has been up for 198 days."


The next says, "That's noting, my Debian Linux system has been up for 1,998 days.


The last says, "My Windows NT Server has been up for 18 hours."


And the first three say "Wow. You win!"

Click to expand...

My PLC-5 has been running since 1998. lol.