I know NOTHING or very little abt PLC and automation.
But the subject interests me.
Im curious..... why don't ALL plc's talk via ethernet?
Aren't some PLCs based on a proprietary networking
protocol? If yes.... why?
Is ther a primer on PLCs that you can also point me to
that explains the "basics"?
Many PLCs do use Ethernet. If you read introductory
material on Ethernet/IP (a TCP/IP extension with
automation in mind) you'll get answers why plain
Ethernet was not very popular with automation folks.
The main reason Ethernet has not been popular is
the lack of determinism, but there are other reasons.
Really dumb question.....cause I don't really know what
Im talking abt....
but on those PLCs that do NOT use industrial
.. do they use each use a proprietary protocol that
differs from maker to make and thereby making it
impossible to mix and match PLCs?
Very simple. DCSs and PLCs used networks, distributed computing, structured
programming, pre-tested code and a whole host of other recent inventions
long before the names were invented. They still work in existing systems.
The value of upgrading a working system that continues to produce product is
zero. The cost of shutting down these systems to upgrade their systems is
extremely high. Do you see any incentive to change?
The question now is, "Why don't they use it now?" The answer is also
simple. All new products do use it. They were just waiting until feature
creep came up with features that were of value to industrial control
The answer to your last question is that with proprietary systems, the user
does not care *how* they work as long as the *do* work. His objective is
not to design neat new networks. His objective is to make gas, beer,
cookies, hubcaps, etc. Its different now. With 'open' systems you have to
build your own networks. This dumps a lot of extra work onto the end user
and is another reason for their resistance.
PLC's use many types of communication links, including Ethernet
(RS232-RS485-RS422..., different busses). Typically the mid and hi end units
have Ethernet option or com plug-in. Price of Ethernet on protocol? If yes.... why?
It's not all that new, but "yes" and "yes".
The two "main" players are Ethernet/IP and Modbus/TCP and each have their
uses and applications. The industrial world (processing real-time data) is
very different from the IT world (copying files around) and thus requires
completely different protocols - but the hardware mostly remains the same.
Sometimes they do and sometimes they don't - it depends entirely upon the
marketing strategies of the manufacturer in question. But these days it is
most always possible to mix and match PLCs if you really must - no
manufacturer wants to lose a sale just because the next guy can't talk to
That's where System Integrators come in...