Exam related...

not sure how to answer this one,exam is tomorrow so plz help! lol...Question is: PLC's are simliar to 'conventional' computers in terms of hardware technology,but have a number of features,which make them suitable for industrial control. List four of these....

1: They don't crash. (without good reason).
2: You can stick big wires in them.
3: They can be screwed to a panel.
4: They don't receive spam.
will this do?

I think it has to do with why they are used to program control systems....

Mmmm... That's a tough one.

1. PLCs can't be used to play Solitaire.
2. You can't download images from internet **** sites to PLCs.
3. PLCs are less susceptiple to adware and viruses than conventional PCs.
4. PLCs run at slower clock speeds than conventional PCs. As a result they generate less intermolecular friction and run cooler.

Good luck on your exam and welcome to the world of industrial automation. I'm confident that the technique of seeking the answers on the internet will be equally useful when you're troubleshooting a balky production line at 2AM.

You don't have useless features (at least not so many)
You don't need several GBmemory for your programs
You can shake them and they still work
Try to find an application for an old PC (Win95)...good luck. With the plc it will be easier

thnx a lot...u've all been very helpful

Just a comment.

The question has a wrong starting point:
"PLC's are simliar to 'conventional' computers in terms of hardware technology ... "
Absolutely not.

PCs more or less configures themselves through advanced methods in close cooperation with the operating system. This is great when it works, and equally aggrevating when it doesnt work.

PLCs have either a fixed hardware configuration, or must be specified by the programmer in detail.

I have no idea what the answers are but this is my thoughts.

1. Programmed with dedicated software specific to automation.
2. I/O built in and expandable.
3. Multiple network or communication options
4. Device interface options..ie AS-i, Devicenet, Profibus etc etc

When you find out what the answers should be let me know.

well I'm not gonna be covering the message boards with my college queries but if the thread is still here after I get the answer from the lecturer then I will certainly let u know

Jesper I am not sure I agree with that assessment. A PC and PLC both use a CPU and memory. A PC has bios which tells it how to work on startup and allows installation of an OS. A PLC has firmware, kind of a bios and OS combo, that tells it how to work on startup and allows communication/programming.

The basic hardware components are similar but after that point there are a multitude of differences depending on certain aspects.

Technically since the advent of PACs (programmable automation controllers) the differences are slowly becoming a gray area.

I have never doubted that plcs (or now pacs) will not be a standard in industrial applications. I have my thoughts that the plcs/pacs will become more like PCs in the future. I have never meant at any point that a PC had to be a MAC, DELL, use Linux, or Windows. I was refering to hardware...ie 3ghz CPU, 2gig ram, flash drives or hard drives...the physical components that a PC uses.

I have no idea when or who but eventually I think someone will design and build a system that is "fully standalone"..ie you can hook a keyboard or connect to it by Ethernet and program it...all the hardware and software will be within the unit.

Right now I think the market is more favorable to the smaller units that is why so many are extending and developing their micro automation line.

The future always brings changes tho.

How about a PLC used a risc chip rather than a cisc chip. does not use the 8085 instruction set. does not handle higher mathematics as well as a PC. and has a differnet standard on communications. I'm not positive if those are the answers your looking for however they are considerations

mordred said:

... does not handle higher mathematics as well as a PC.

Click to expand...

This is entirely dependent upon the PLC you are using. Some handle higher mathematics exceptionally well.

But I admit that those PLCS that use only BCD math, or can't count higher than 9999, or require you to manage both sixteen bit registers when doing floating point math are vexing at best.

true enough my question is do they perform their mathematics as per the older PC's that of adding for multiplication. Or do the CPU's perform as per the math coprocessor on the 386 ds and later CPU's where the coprocessor was moved onto the CPU itself?

Mordred,

The Modicon Quantum range of PLCs use the Intel 80XXX range of microprocessors (80186, 80486, and pentium).
So you get cisc instruction sets, and sometimes a maths coprocessor. The software cannot always handle having a maths coprocessor, so for ladder and FDB your maths is handled the old "add for multiplication" method. IL and ST can access the co-processor, so you get faster floating point maths. I don't know if it can access the co-processor in 984 LL.

My info is 3 years old, but it shows that some PLCs are closer to PCs than many people think.

Also I have seen that some brands have HDD storage available, and can even host web pages.

Doug