Which Platform Should I Use?
When I worked for automation distributors I was required to promote and recommend only the products that the distributor sold. This sometimes caused a conflict of interest: is this the most appropriate solution for this application? The first distributor I worked for sold Omron and Eagle-Signal PLCs. If I was in a plant that was full of Allen-Bradley controls this could be a tough sell… the customer usually had a significant investment in both hardware and training particular to A-B. Once a facilities engineer in a smaller plant said “If you guys can figure out a cost effective way to replace our PLCs I’ll put all Omron in here”. In his case he was tired of paying for the yearly software licenses that Allen-Bradley charges hundreds of dollars for. Of course there was no economical way for either of us to do this, so the plant remained A-B.
The next company I worked for was an Allen-Bradley distributor. As a product specialist I learned that A-B required all of their distributors to staff several technical specialists and of course this costs money. In return Allen-Bradley distributors get protected territories and the customers get support and training on their products.
When I started my own automation company I generally had to use whatever the plant specified. This required having a lot of different software packages and of course paying the dreaded support fees to both Allen-Bradley and Siemens. There were occasions however where I was able to choose a controls platform myself. There were a variety of factors I would consider when evaluating a new system:
- Existing hardware, software and training. Is there already a majority of one type of controller in the plant? Do the maintenance and engineering departments like it and are they trained? How much support will they need?
- Cost. How much is the customer willing to spend to implement the solution?
- Spare parts. Are replacement components readily available in the local area?
- Suitability. Will a micro PLC do the job? Will there be a large amount of data that will need to be recorded and analyzed? Will the processor be fast enough/have enough memory? Are special purpose cards such as high resolution analog, servo or math/basic required?
- Ease of programming. Is the software user-friendly? Are there special purpose instructions or functions to make programming easier?
All of these things would have an impact on the platform I would choose.
My general impression of the platforms I have used in the past in no particular order:
- Allen-Bradley: Maybe the most user friendly software. A wide range of PLC products and special purpose cards including 3rd party vendors. Probably the largest installed base in the US. Great support, both locally and on the phone. Also one of the most expensive, especially when taking into account software and support fees.
- Siemens: If you’re not used to the programming techniques and configuration the software can be complex. Ladder, STL and SFC can be used somewhat interchangeably. Probably the largest installed base worldwide, especially in Europe. A wide range of PLC products and accessories, good phone support, though you will be asked to give a callback number. Local support can be spotty, vendors may overlap territories and local support expertise can vary widely. Also one of the most expensive hardware and software options.
- Automation Direct/Koyo: Fairly inexpensive and easy to use software and hardware. Not as wide a selection of special purpose modules and not as large of an installed base. No local support, but phone support is excellent. The Automation Direct catalog is a must have for controls geeks.
- Omron: Midrange priced hardware and software. A wide variety of special purpose modules and several hundred programming functions. Used widely by OEMs, installed base is mostly in Japan. Phone support is not bad but has deteriorated over the past few years. Local support varys widely as vendors/distributors may be small or large.
- Mitsubishi: Software pretty bad, hardware very good. Some of the fastest processors on the market. Local support almost nonexistent in most areas, phone support not much better. Installed base is mostly in Japan, though OEM machines are common in the US.
- GE: Midrange cost for both hardware and software, not as wide a variety of products as A-B and Siemens. Software easy to use and quite flexible. Installed base is mostly in the US. Local support varys, phone support and documentation is pretty good.
- Modicon, ABB: I don’t have a lot of experience with Modicon or ABB PLCs so I can’t say much. The installed base in the US is not very large, I understand there is much wider usage in Europe. Modicon is part of GroupeSchneider.
- Bosch, Toyoda, Panasonic, Fuji, Eptak: I have some experience with all of these but they are small players in the US, very difficult to find vendors (except for Bosch…)
- Labview/National Instruments, Opto-22, PC control: Good support, many local vendors, somewhat expensive especially for smaller applications.
Since this is a topic that comes up often I appreciate any input to this post, especially on the platforms I didn’t have much information on or that weren’t mentioned.
If you’re doing a lot of data handling, go the PC or PC plus motion controller &/or PLC route. Doing the kind of data manipulation I’ve done on a PC would be painful or impossible on a PLC.
Opto-22 and PC based controls aren’t expensive compared to a comparable PLC. (OK, LabView might be…)
I don’t like any company that uses dongles or (especially) software “tokens”, since they always got lost or reformatted. That’s a strike against Omron (at least when we last used their PLCs) and Allen Bradley (yep, our laptop that had the AB software installed is no longer working).
A-B support has its limits: last time we did a A-B project, they weren’t very familiar with Structured Text (that was a few years ago; hopefully it’s better now).
I’ve used Panasonic PLC’s extensively (usually combined with a PC), and am quite happy with them. I’ve had to cram a PLC and a bunch of valves into a small space, and most other PLC’s would be way too big.
Another interesting I/O system is the Beckhoff/Wago K-bus “slice” system (e.g. Wago 750-xxx). There are modules for almost every need (including ADC, DAC, 4-20mA, quadrature encoder input, PWM output, stepper drive), and a variety of available fieldbus interfaces (DeviceNet, CANOpen, Profinet, Interbus, Modbus/TCP, etc), including controllers with PLC functionality (e.g. Wago 750-8xx). Kontron makes an embedded PC (ThinkIO-P Duo, probably re-sold by Wago) with a K-bus interface and typical PC specs (>=1G RAM, dual 1G Ethernet, Linux/WinXP/soft-PLC software). I’m playing with these now, but haven’t used them in production.
There’s a balance between sticking with the tried-and-true and trying out new approaches that could yield improvements.
I concur on the Opto-22 and Beckhoff, good stuff. The PC platform hasn’t been adopted widely in industrial facilities though, maintenance depts. have some training to do before they can typically support anything but ladder. Personally I like the Automation Direct stuff, price can’t be beat, but as you said, A-B and Siemens seem to be most of what I see.