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Author
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Topic: PLC Instead of Dedicated Automation
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John Walsh
Film God
Posts: 2490
From: Connecticut, USA, Earth, Milky Way
Registered: Oct 1999
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posted 04-15-2006 08:30 AM
Depends on how the design is done. For example if you buy a 'complete' PLC system, like the SLC500 or Micrologix, it can get expensive. This is because you are paying for the 'already designed' PC boards with IO, and the ease of working with relatively simple ladder logic. By the time you purchase all the modules for a system of this type, (to get the amount of IO you need) the price easily could be over $1500.
OTOH, if you just bought the controller IC itself (like the ones from Microchip) you must design your own PC board. Not really hard to do, but it can take a little longer then you'd think, because the design must be 'hardened' to withstand all of the noise form motors, xenon ignition, etc. Complete PLC systems cost more, beacuse this has been done for you.
For projector automations, it seems many people have kind of rolled their own, by using a standard microcontroller IC, like the INTEL 8051, dsigned their own PC board, and programed using something that generated regular machine code.
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Will Kutler
Phenomenal Film Handler
Posts: 1506
From: Tucson, AZ, USA
Registered: Feb 2001
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posted 04-19-2006 09:06 PM
Interesting thread. One of my current ASU classes is PLC programming.
"PLCs are normally used in industries where real-time control is necessary.
"In the late 1960s the automotive industry controlled many of its processes and machines with relay-based control systems. This was inefficient and costly to industry due to the following reasons:
Relays could only control on/off type operations, while manufacturing and process equipment was becomming more sophisticated.
Every time a new car model was introduced or a line change was made, it took days or weeks to change the wiring.
Relays were bulky and took up a lot of space.
In 1968, the Hydromatic Division of General Motors addressed these issues by drafting a set of specifications for a new type of solid state control system and presenting it to the control industry. In 1969 MODICON (MOdular Digital CONtroller) delivered the first PLC to GM.
PLC are able to withstand rugged industrial enviornments, are easily installed and maintained, modular, control flexibility (change program rather than wiring), easy transition for people who worked with relays"
Quotes curtesy of Jerry Gintz classroom Power Point lecture/presentation.
Allen-Bradley is the industry standard for PLCs, and this is what we are learning on.
Cheers
Kutler
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