Holly Gates

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About Holly Gates

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  1. Hello, we are using Beckhoff PLCs right now at our company. Two of the biggest challenges with this platform is the lack of local support and lack of consultants who know how to program for the platform. There are a few people here who would like to switch to Allen Bradley. Regardless of the technical merits, local support and consultant is definitely something AB wins at hands down around here. Of course we have our own resources internally, but it would be nice to be able to bring in some extra help from time to time. Does anyone know of engineers familiar with coding structured text for a 61131-3 environment that would be open to consulting? Local would be best (Boston area), but remote might also be an option. Write me privately if you don't want to post here: hgates at 1366tech dot com. thanks, -Holly Gates
  2. C programmable PLC recommendation?

    I'm sure it wouldn't be that hard to learn ladder, and I agree that it is much easier to tackle for people without programming experience. We have a bunch of mechanical engineers around here who probably would rather do stuff in ladder than in C. But I would guess that there are a lot more engineers out there in general who know C rather than ladder. So from my perspective I can get almost any electrical engineer or software engineer in here and they will be able to work on C code, rather than having to search out an engineer with specialized PLC programming skills. I have no experience with ladder, but I have had a few unfortunate encounters with graphical based programming systems that got too complex. For example, labview is great for tasks of low to medium complexity. But when things get quite involved, it becomes totally unwieldy and nearly impossible to debug. Having to debug someone else's C code is annoying, but fundamentally more workable than a huge tangle of interlocking graphical elements in a big blob. The comment about who the customer will be is astute. For internal use, the customer is me or another engineer likely to know C, not an electrician or tech. My ideal solution would support both C and ladder (and maybe other stuff, but if it had those two I think it would serve the two potential user groups here: engineers who can program, and engineers who have not done so before). There is something to the idea that ladder has more symmetry with how a PLC operates (regular scan, compute, output cycles). But there are reasonable ways to do parallel tasks in C too; the basic cycle of a PLC resembles the time slices of a multi-tasking OS like linux. Another thing I like about C is the potential for portability. But if I went with something like CoDeSys, this could also be realized with ladder. Thanks to people in the forum, I now have two very good candidate systems in B&R and Beckhoff. thanks very much! -Holly
  3. C programmable PLC recommendation?

    Ah, nice lead! These are PC based systems it seems; do you know what the pricing is like for a low end CPU? How about expansion modules? I wouldn't be opposed to having ladder as an option, its just that I want C as an option too. thanks, -Holly
  4. Hello all, I was hoping you could offer some thoughts on selecting a PLC. I'm working at a solar cell startup where we are working on new processes for silicon cells to make them more efficient. We are just getting to the point in some of our work where some automation is desired, but we expect to build a fair number of various machines in the future and may even become a machine builder at some point (Our business model is flexible in this difficult funding environment!). I am a skilled electrical engineer and have lots of embedded C and embedded linux programming experience. In the past, I've always used microcontroller boards (mostly ones I designed) along with relays and other external interface hardware. But I do feel there is something to be said for industrially hardened I/O and using hardware that can be purchased easily rather than stuff I build myself. This first application I am looking at right now is very simple and probably could be done even with some of the ultra low end stuff all the PLC vendors offer or a bunch of programmable relays. But ideally I could select and start gaining experience with a PLC platform that could grow with our needs and would allow for code reuse from previous projects. I am a little shocked to find that basically none of the major PLC vendors offer hardware that can be programmed in C. Yes, I know there are structured text, instruction list, and other options available. But I already know C well, and so would most other electrical engineers. I have read a bunch of threads here about the virtues of ladder logic, and I'm sure it makes sense in some cases, but for my needs C would be hugely better. I find it weird that the vendors don't provide for working with the hardware on this level; after all it is a lot more complicated to write the embedded and PC side software that allows graphical ladder programming to work. Just making a C compiler with some support libraries should be nearly trivial since compilers certainly exist already for the microprocessors that the vendors are using inside the PLCs. I don't accept the argument that ladder is inherently better than C for high reliability, industrial, or other places where you don't want the blue screen of death to happen. Automotive computers, flight controls, and health care equipment don't run off ladder logic programmed PLCs. There are well understood tools and techniques for multi-threaded and high reliability programming in C. There is a huge market of PC104 embedded PCs for just such applications. But I like the compact, rail mount nature and low end offerings of the PLC world, which is why I am looking into it. It seems a bit silly to have a PC104 stack in a machine that you could build with a handful of timing relays. Anyway, I was hoping someone would have some leads for reasonably priced hardware from a reputable and somewhat stable vendor that can be programmed in C. There are a number of vendors that sell what are essentially rail mount industrial PCs, but the minimum price points on these are pretty high. If I can't find one line of PLCs that goes from simple and cheap up to complex and expensive that can all be programmed in C, there are two other options I'm considering: - Buy remote I/O blocks from Wago, Beckhoff, Sixnet, Acromag, or others and run them from a microcontroller board or embedded PC over modbus or ethernet - Have two PLC solutions: one for simple applications, which would use a cheap PLC programmed in ladder or whatever the vendor supports, and one for complex applications which I would address with a more pricey IPC style PLC. I've been looking at the Koyo stuff (Click and DirectLogic), which looks great, affordable, and I can buy easily off the web. There are also reasonable low-medium end offerings from Omron, IDEC, Modicon, Mitsubishi. None can be programmed in C though! Anyway, your thoughts are welcome, thanks, -Holly