What's the need for a PC-based PLC?

We have a process with a very simple control algorithm and a non-deterministic scan time that doesn’t need to be any faster than once every 15 minutes. I’ve been a proponent of using “real” plc’s my whole career (I’m old), but the pressure here is to switch to a PC-based controller. The more I think about it - and this is today’s question for discussion…
What, if any, is the advantage of using a software-based PLC (e.g. Beckhoff TwinCAT, SoftLogix5800, et al) over a timed script in Ignition? Or even Ignition Edge?
It would seem to me that they are all just programs running as a service under Windows, so, yes, I need a bit of I/O, but I can use anyone’s Ethernet-headed point i/o system for that and Ignition’s Eth/IP or Modbus drivers to read/write to it…

How critical is it that this runs every 15 minutes? What happens if it doesn’t?

Relatively speaking, it’s far more likely that your Ignition gateway is down/offline/crashed/otherwise unavailable than a piece of dedicated hardware would be, even if it’s a soft PLC.

Plus or minus a minute? No problem… And there isn’t a “dedicated” piece of hardware - that’s my point, it would be the same PC the Ignition (or Edge) HMI is running on.

It seems like in this case there is no real reason to use a software-based PLC. It doesn’t seem to me like you have to use Ignition scripting to make it work. You could make it work that way but it sounds like you could just write a simple program to do whatever it is you want to do on a local PC and use that.

The issue you could run into using Ignition over a dedicated PC is the gateway going down or net problems which is more likely than a dedicated comp going down.

Kevin, as an aside, your lack of a crafted sales pitch is astoundingly refreshing and why I appreciate Ignition’s business model so much. I have sat through way too many “IIoT” presentations in the last few years where software companies are promising some magical monolithic data acq/ control system with no hardware. Unfortunately these companies are constantly convincing people who write checks to spend orders of magnitude more, when I could spend orders of magnitude less on a bunch more Ignition gateways and redundant gateways. We will get there, I hope. Anyways, thanks for your candor!

I am 0% sales person and 100% developer, to a fault :laughing:

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These sorts of non-critical applications that might need high-speed I/O were the motivation for my Ethernet/IP module. With its scanner option, Ignition is basically a SoftPLC, with jython called from gateway timer scripts instead of ladder logic. Or SFCs (yuck).

As long as the actuators/drives have suitable “comm loss” configurations for safe stop (which they generally need anyways), there’s not much to worry about.