Selecting PLC without ladder logic

[graemeian 2]

I am looking for a PLC without the added hit of purchasing some form of ladder logic software. I saw a posting earlier that listed some PLCs that included a reduced version of ladder logic software. I do not want to program in ladder diagram logic. I want to program in line code. Aside from a few counting registers that include timers and encoder counters, a processor (PLC) can only do one function at a time. Is there an industrial PLC that offers the user a choice to use a no (low) cost line code programming language? I do not need something that converts ladders to code. In a high level language, I would need only a few basic commands such as... If...Then Assign a variable Read and write to registers. (including serial port) The AND command Gosub GOTO and some simple math assigns. I could also use an assembly level language: anything but ladders! Is there anything available? I want to thank all for their consideration and responses. Regards, graemeian

[panic mode 246]

not sure if you don't want to pay for programming software or you don't want ladder to be on of the included languages. btw. why not ladder?

[BobLfoot 302]

I too am curious why no ladder logic. I've write in Fortran, Cobol, Basic, Pascal, RPG, C and Assembly Language and worked in Omron, Toshiba and Allen Bradley PLC's. Of all the tasks you list the only one difficult to program in a PLC is the serial comms. And Ladder Logic is simpler for serial comms than Asembly language. So I am curous why no ladder?

[graemeian 2]

Ladder programming can be limiting. I have always been able to program faster using structured line code. When you program in ladder code, it is converted to line code and then converted to machine code.

[TimWilborne 108]

Yes, but can the maintenance guy troubleshoot it faster? Ladder can be limiting, but when you hit these limits you are usually into your high end PLCs which to have such alternatives.

[DanW 41]

My impression is that Codesys is a multivendor development software package that is downloadable at no cost, and it has structured text capability. Each vendor supplies their own libraries of functions compatible with their hardware. This forum has a section dedicated to Codesys. Dan

[BITS N BYTES 66]

Selecting a PLC without ladder logic is YOUR choice. I would normally select a unit for its functionality/stability/ease of programming without a highly skilled person/simplicity of I/O connectivity. There are many more reasons. Most PLC programming packages these days offer more than one way to write code [Ladder, Structured Text, Sequential Function Chart etc. etc.]. If you are dead set on NOT using them then it sounds like you need to look at one of the following. They should do what you want:- http://www.rabbit.com/products/ http://en.wikipedia.org/wiki/PIC16#Instruction_Set Good luck

[ndzied1 1]

You could use the ILC 150 controller from Phoenix Contact. http://www.phoenixcontact.com/global/produ...21718_21734.htm It programs with the free PCWorx Express which gives you Structured Text (sort of like BASIC or Pascal) and Ladder from the IEC 61131 standard. Note that this is not based on CoDeSys. If you want Instruction List (IL - like assembler) or FB then you have to pay for a license. <disclaimer - I work for a Phoenix Contact Distributor>

[paulengr 44]

Again, untrue. Most PLC's support subroutines. Most allow you to place a branch around the "output" instruction so that you can execute several "output" instructions in parallel. Newer PLC's even allow you to daisy-chain the output instructions since they inherited the "enable" input from the function block language. There is a difference though. Algol-like languages (C, Pascal, Java, BASIC, etc.) are optimized towards executing a whole series of commands in a list. On the other hand, ladder logic is optimized towards writing logic which would require very complicated if-then or case/switch statements in Algol languages. It so happens that the complicated if-then statements are much more prevalent in controls systems. For instance it is very common to have anywhere between a half dozen and as many as 2 dozen interlocks, often with various "overrides". This is very ugly to write in an Algol language. In addition, ladder logic is optimized towards writing parallel instructions, and it is extensively optimized towards boolean operations. Again this is an area where Algol-languages are supoptimal. Finally, ladder logic is very easily understood by non-degreed people. At my plant electricians readily read it and even many production folks can muddle their way through a PLC program. But they would struggle with anything I wrote to run on a PC. Ladder logic is also Turing complete. But just as with any Algol-derived language, Turing complete does not mean Turing-convenient. That being said, there are a LOT of Asian and European "off-brand" PLC's that I have found are extremely limiting and/or unpleasant to work with. For instance, a good "name brand" example is most of the smaller Omron PLC's. These are very inexpensive and work wonderfully well as replacements for relay control. The same thing could be said of the "DLxxx" series sold by Automation Direct, and even the "nano PLC's" sold by Allen Bradley (among others). But they are severely lacking in the "advanced" instruction department. Many do not support string or even numerical calculations, or only do so in a very difficult manner. On the other hand, the fully featured Siemens S7 series, the more recent GE Fanuc PACs, and the Allen Bradley PLC's (especially the CLX-series PACs) have very advanced and complete instruction sets. These 3 are using compilers in their programming systems. There is no interpreter in these processors, unlike their older, slower cousins. In practice, I can frequently replace multiple (3-6) smaller or older PLC's with a single PAC system and still have plenty of processor horsepower and memory to spare. BUT, there are cut down versions out there, often even with the "server grade" capabilities. For instance, Allen Bradley sells a complete CompactLogix "starter" system with the programming software for about $2K U.S. They sell a very light version of their Micrologix processor for about $250 U.S., and the programming software itself is free. They also sell "nano PLC's" which are effectively glorified relays which have no programming software (you program it from the LCD panel on the unit) for even less money, but you get a very limited instruction set. I suggest you contact a local Rockwell Automation rep and ask about the "starter kit" for CompactLogix first as a good starting point because with the starter kit, you effectively pay for all the hardware and they throw the software in for free as part of the package. Also, keep this in mind. In comparison to the PC world, in terms of U.S. prices, you can buy a cheap "net book" for about $300 currently. It's effectively a "throw away" PC. You would never keep your accounting database on it but it's OK for web browsing and other "light duty" tasks. For about $1000, you can get a pretty decent laptop, perhaps even a low end Macintosh. You might use it for almost everything but it's not server grade. It has an expected service life of about 3 years. If you buy a good quality server, expect to pay between $2,000 for a low end model (like a DNS server) up to close to $15,000 for a high end model. This time, the hardware is expected to last 5-10 years in an office environment and you can trust that accounting database to run on it. Now consider this. A PLC is intended to operate without failure for 20-30 years including the occasional modification or upgrade. It is intended to operate in an "industrial" temperature range with industrial-grade power (very noisy and full of transients), and with occasional exposure to industrial dust and liquids. It needs to operate without any "blue screens of death", no "Windows Updates", and no reboots once per week "just because". Any PC placed in this environment without extensive modifications to "ruggedize" it such as extra air conditioners, extra power conditioning, shock mounts, replacing Windows with a reliable OS such as Linux or OpenBSD, etc., fails prematurely. A good quality PLC will run about $2,000 and so will the software. So you are getting far better than server-grade hardware for server-grade prices.

[BobLfoot 302]

Case in point to support the above for PLC Ruggedness check out this http://forums.mrplc.com/index.php?showtopic=15702