Edit: Note that I have posted an updated TwinCAT 3 Review in 2014.

So back in 2010 I wrote about my first impression of TwinCAT 2 and later that same year I wondered if automation programmers would accept TwinCAT 3. I was lucky enough to be involved in the TwinCAT 3 beta, and now that the 32-bit version of TwinCAT 3 is available for general release we’ve deployed 2 production systems based on TwinCAT 3, and will likely deploy more in the future. What follows are my impressions of the current state of TwinCAT 3 based on our experiences with those 2 systems.

I think the best way I can describe TwinCAT 3 to the non-initiated is by comparing it with Allen-Bradley’s ControlLogix platform with their RSLogix 5000 programming environment. I say that because I’m familiar with that platform, and so are most of my North American readers (I assume). It speaks well of Allen-Bradley that they are the de-facto default control system platform around here.

We often fall back on car analogies, and I don’t want to break with tradition. If ControlLogix is the Ford Taurus of control systems (common, reliable, with lots of performance for most tasks, lots of room, and fairly maintenance free) then TwinCAT 3 is something like the Rally Fighter. That is, it’s road legal, fairly rare, requires lots of TLC and understanding and may not be as reliable, but will take you places you’ll never get to go in a Ford Taurus.

When it comes to speed, TwinCAT 3 with Beckhoff’s EtherCAT I/O is a beast. I can’t stress this enough. We’re running both production systems of TwinCAT 3 with both a 0.5 millisecond logic scan time and a 0.5 millisecond I/O bus scan time and we’re only using about 10% to 15% of the available horsepower of each system. You can see and react to things in the TwinCAT 3 system that you’ll just miss in a ControlLogix processor. For instance in one case we’re driving an output off of an absolute encoder and the repeatability of turning on that output is much better than anything we’ve seen with any other controller.

Furthermore, data accessibility is light years beyond any traditional PLC. In one test I moved a 400 kB block of data from the real-time (ladder logic program) to a .NET program running under windows on the same PC and all I can say is that it’s nearly instantaneous. That’s an advantage of having the HMI and real-time executing on the same physical hardware.

That’s not even getting into the new C++ integration (which I haven’t used).

Any TwinCAT 3 vs. ControlLogix system comparison will also certainly favor the Beckhoff solution when it comes to price. At least I can’t seen any case yet where that’s not true by a significant margin. I can’t say exact prices, obviously, but I’m confident that’s generally a true statement.

Does that mean I think the competition is a hands-down blow-out in favor of TwinCAT 3? No. In fact if you’re considering trying TwinCAT 3 I can’t even go so far as to give you my blessing right now. It has problems.

TwinCAT 3 crashes with a blue screen. Regularly. There, I said it. That’s the dirty secret. Everyone’s fears about PC-based control on the factory floor were around stability and in our experience TwinCAT 3 isn’t stable yet. This is odd to me because we have another system with TwinCAT 2 and it’s solid as a rock. Unfortunately our TwinCAT 3 system crashes with a blue screen regularly, and the crash report always shows that it’s some kind of memory violation in their Tc*.sys files, which are the system files responsible for running their real-time system under ring 0 of the OS (as far as I understand). I’ve never even seen blue screens with Windows 7 until trying out TwinCAT 3. There are actually two different times that it crashes: (1) randomly, and (2) when I try to do an online change.

Beckhoff’s response was that we were running it on 3rd party hardware. They loaned us a Beckhoff industrial PC to try. We tried it for a week and we didn’t see any random crashes, but it still crashed the real-time when I tried to do an online change, and it also crashed the IDE almost every time I recompiled the program. In fact that’s the reason we had to stop the test with Beckhoff’s hardware after only one week. I needed to compile a change and couldn’t get it to compile. It did work on our 3rd party PC (an HP desktop PC).

Now, I don’t think these are insurmountable problems. Beckhoff is still coming out with new versions on a regular basis. Their new support for 64-bit windows operating systems is on the horizon. TwinCAT 2 seems stable and I’m sure TwinCAT 3 will get there eventually. However, for the moment, if you’re considering the plunge, I suggest waiting about a year before bothering to check it out. If you just need the speed, consider TwinCAT 2, as even though it doesn’t take advantage of multiple cores it will likely do what you need and is a much more mature product at this point.