question regarding Beckhoff PC based control

Okay, so I just showed my customer a demo of his controller. I haven't actually ordered the PLC yet; in fact I haven't totally decided which make and model I will go with. I'm using a trial version of the TwinCat software (which is really slick) and I've written the most of the code already (in ST). I also mocked up a GUI representing the control panel - which I expected to build using discrete components unless he decided to shell out some bucks for a touch screen. Everything went well and he liked the demo.

And then he throws a wrench into the works. He asked why can't we just use the PC and "that software" (meaning TwinCat) to control my machine?

Hmm, why not? It is not a critical application, and my experience with PCs is that if you dedicate them for a specific task and don't mess with them then they are very reliable. The advantage of a PC in this case is that the operator interface is instantly very powerful and flexible.

However, I expect that the cost of the PC plus whatever components support I/O plus software will exceed the cost an appropriate PLC ($500) plus software plus (optional) touchscreen.

Are then any BeckHoff experts out there who can chime in? Are there other PC based systems that are IEC61131 compliant that I should look at? Should I tell my customer to forget the whole idea?

thanks

If you expect your app to fit into a $500 PLC (including I/O), that must be a very small-scale app.

Then a fully functional PC (be that an industrial-grade Beckhoff or a regular one) is an overkill; if you like TwinCAT, look at Beckhoff BC series low-end "bus controllers". They are somewhat limited in capacity comparing to their bigger brothers but basically pretty much the same. No use for a standard PC monitor and TwinCAT Visu for graphcal display though; if you need one, get the Ethernet BC and any touchscreen that can talk Modbus/TCP, for example.

That would be a wash comparing with a PLC-touchscreen solution, but you will still have your fun with TwinCAT.

I did a couple PC based systems using TwinCAT because it seemed logical since most systems needed a PC anyway for things such as Operator Interface and database interaction.

A couple years ago, I decided it was better to use a CX10xx series controller based in Windows CE as the controller. One big factor in that decision was the fact that a TwinCAT software license for a PC is about $1500. A complete CX system with IO hardware and a TwinCAT runtime typically comes in at less that $1000. You do the math!

I have even written VB apps that run directly on the CX controller that retreives data from TwinCAT and transfers it to a SQL server eliminating the need for a PC in some applications. Add a touch screen monitor and run a VB app on the CX controller and I then have a PLC and HMI. This all turns the question around and makes me ask... why would I use PC based control?

Freindlyfire,

You could also use the BL20 or BL67 IO from TURCK and run CoDeSys which I believe is the platform for TwinCat, minus the software costs as TURCK has it for free. The code would run in the BL platform as it is the PLC and you could use the Visualization in CoDeSys to be your HMI on the PC. This is just an idea. Here are some photos of the BL67 in use.

TURCK BL67 Machine

Joe_WaZoo

Hi guys, thanks for all the thoughtful replies.

Yes, this is a small application. The PLC accepts about ten inputs and drives about ten outputs. Inside the black box is a fairly simple state machine (8 steps). consists of a state machine (8 states). Oh yeah, it also controls a stepper motor (spits out pulse and direction signals). The $500 PLC I refer to is the Omron CP1L/H exact model TBD. Their IEC61131 capable software is not terribly expensive (<$500), but I haven't tried it out yet. I'm not expecting it to be as capable as TwinCat actually but hopefully it will surprise me.
I was planning to build a control panel using discrete components but I will take some time to look at off the shelf interfaces (touch screens and stuff).

Archie, thanks for the heads up about the license cost for TwinCat. This is a definite roadblock towards adopting a Beckhoff solution.

Joe, thanks for the neat idea. I looked over the Turck web site but their product line is not easy to understand. I'll get in touch with them about it. I'm a bit worried about local support for these products. It is not a good sign when there is only one Canadian representative and they are based 3000km from my office!

friendlyfire said:

The $500 PLC I refer to is the Omron CP1L/H exact model TBD. Their IEC61131 capable software is not terribly expensive (<$500), but I haven't tried it out yet.

Click to expand...

Hello friendlyfire,
If you are planning to use CP1L or CP1H, then be aware that while these PLCs support Function Blocks (that can be programmed in Ladder or ST), they do not support ST or SFC at Task (Program) level as their bigger brothers (CJ / CS series) do.
There is only Ladder for this PLC type.
If you must have ST at program level, then may I suggest the CJ1M range (maybe CPU11 or 21), the price difference may not be too great!

The Omron's implementation of IEC STL is somewhat limited and not as powerful as TwinCAT's.

FriendlyFire,

I can simpathize about your support location being so far away. If you are interested, I will be teaching a FREE TURCK Intro CoDeSys and IO class on Wedneday March 12th at our Dallas training facility. And this will follow with a Red Lion HMI class on Thursday March 13th. Both classes are completely Hands-On, no PowerPoints allowed in my training sessions. Though this is not much closer to you, it might be a nice trip to get out of the cold up. Here is the link to registration if interested.

Class Sign Up

Thanks,
Joe_WaZoo

I have just checked my Beckhoff components price information. A BC series "bus controller" (i.e. a mini-PLC) goes between $200 to $300 a piece, depending on the type of communications; 2 8-pt input terminals and 2 8-pt output terminals will cost about $200 together. Add a "bus end" terminal for $15.

A pulse train output module is close to $200. However, Beckhoff has two terminals to drive a stepper motor directly, without an amplifier: a 1.5 Amp costs about $200 and a 5 Amp one - about $320.

Do your math. It seems to me it is not that much more expensive comparing to your Omron solution. And you could always try to negotiate discounts with Beckhoff.

lots more great info, thanks.

"LadderLogic", the Omron solution looks to be about $900 including software, which is a bit less that the Beckhoff parts you mention... BUT what about the cost of a TwinCat License? I don't have an answer yet from my Beckhoff rep but Archie points out in this thread that this runs about $1500! If true then I can't go in that direction.
I plan to use an integrated stepper driver combo by the way ($110) and this Omron PLC provides a pair of pulse outputs, so the combo is pretty cheap.

Joe, thanks for the invite. No budget for this, besides still waiting for my passport renewal... I will look into Turck products in detail. I have registered for the "demo" version of CoDeSys although it appears to be a working version, is that correct? It looks like the HMI component is not free (and I would need this to use a PC as an interface), do I understand correctly?

Paulus, thanks for the tip. I suspected as much actually. I'll check with my Omron rep about upgrading to the CJ1M range, but I'll probably end up just making my code fit the PLC rather than spending any more $$. I've asked my Omron rep for a trial of the s/w so I'll check it out soon.

I'm not clear if this presents a problem... If I can squeeze my state machine code into a FB then I don't think this will bother me (the state machine is about 40 lines of code - mostly a big CASE statement actually.

A bit of background: I'm new to PLC coding but I have lots of experience programming very sophisticated FPGAs and EPLDs, and ST is sort of like the VHDL language I used to use. I think I am missing a bit of basic understanding about PLC architecture, and specifically how function blocks work.

thanks all,
FF

LadderLogic said:

The Omron's implementation of IEC STL is somewhat limited and not as powerful as TwinCAT's.

Click to expand...

Limited to cover probably 99% of what you will ever really need!

friendlyfire said:

which is a bit less that the Beckhoff parts you mention... BUT what about the cost of a TwinCat License? I don't have an answer yet from my Beckhoff rep but Archie points out in this thread that this runs about $1500! If true then I can't go in that direction.
I plan to use an integrated stepper driver combo by the way ($110) and this Omron PLC provides a pair of pulse outputs, so the combo is pretty cheap.

Click to expand...

Just for clarity, the $1500 is for a runtime license if you are going to use it as PC based control. If you use a BC, BX, or CX control then you can use the trial software to program them even after the 30 day run-time expires. The only part that expires is the PC based control runtime.

If you are using stepper motors, Beckhoff has a stepper motor card/driver that goes on the IO just like any other IO. The stepper motor wires directly into the terminal eliminating the need for an external driver. Pretty good card and I used a few of them on some projects.

http://www.beckhoff.com/english.asp?busterm/kl2541.htm

ok, thanks for the clarification on that. I have a meeting set up with my Beckhoff rep later this week. The driver card you pointed me to is quite perfect for my application, but I did notice this little gem: KS2541: estimated market release 2nd quarter 2008. You say that you have used them - was that an older version or something?

Today was a big day - The email with the link to CoDeSys arrived as did a courier package with the Omron CX One trial version CD. Play time!

friendlyfire said:

The driver card you pointed me to is quite perfect for my application, but I did notice this little gem: KS2541: estimated market release 2nd quarter 2008. You say that you have used them - was that an older version or something?

Click to expand...

I used the KL2541 which has been out for a couple years. The only difference between the KL2541 and the KS2541 is the latter has a removable terminals block. Beckhoff has been gradually making a removable terminal block version of all their terminals.

On that Omron software, one quirk that I did not like was that you could write FB's in structured text, but it would not let you online monitor the code which made it more difficult to troubleshoot the code. That was back in version 5 on a CS1, so maybe they fixed that in the later versions.