View Full Version : A Level PLC; Alternitives

March 18th, 2004, 04:39 PM
Can anyone help?

I'm an A level student studying PLCs as a unit.

I need to find out what the alternitives to PLCs are i.e. mitsibishi basic...etc

can anyone help? lots of info please

March 18th, 2004, 04:43 PM
I fear to watch - yet I cannot look away.

Allen Nelson
March 18th, 2004, 05:27 PM
One alternative to PLCs:

Cheap, unskilled labor.

Steve Bailey
March 18th, 2004, 06:04 PM
There is the LLC (Limited Liability Corporation) and the LLP (Limited Liability Partnership). There is Sole Proprietorship, but that offers no legal shield of your personal assets. Of course there is the tried and true Subchapter S Corporation.

Tom Jenkins
March 18th, 2004, 06:50 PM

(Actually true. The first industrial automation I'm aware of was when a young boy, hired to open and close a valve on Newcomen's steam engine, figured out that if he tied a string to the piston rod it would operate the valve itself, freeing him to go play.)

Steve Bailey
March 18th, 2004, 07:13 PM
Imagine a water buffalo harnessed to drive a set of millstones. A carrot is attached to a stick in such a manner that the carrot hangs in front of the water buffalo, but just out of reach. The stick is attached to the water buffalo's harness, so as the water buffalo walks forward to try to get the carrot, the carrot also moves forward. This example of feedforward in motion control predates Tom's example by several centuries.

March 19th, 2004, 07:55 AM
Well, in the early 1970's we had the mini-computers. Next we built hardware driver boards that read the mini's address buss and data buss. We also had the STD buss conrol cards. The STD cards were coupled to the I/O with hundreds of Opto22 modules. However, the mini was much more compact. Of course we also had the mini-skirt........
Those we the daze......

March 19th, 2004, 11:58 AM

STD = Simple To Design... What a contradiction in terms...:shock:

It was a good idea gone bad.

March 19th, 2004, 12:20 PM
JIT - Just in Time. Company trades it's ability to deliver product in a crunch in return for some tax savings.

I wonder just what tax percentage a corporation's reputation is worth? Five percent? Ten?


March 19th, 2004, 02:29 PM
Just in Time offers much more than tax savings. In large production cycles JIT cuts many overhead costs including logistics, warehousing, production of undused parts, etc..

However JIT requires a well oiled and maintained orginization. The great pitfall is that if one single thing does not goes as planed, then EVERYTYHING stops dead.

JIT often does not work well in small, or highly specialized production runs.

March 19th, 2004, 11:55 PM

I suppose it is clear by now that your question is not very specific! Did you want to know what are the alternatives for NOT using PLC's, or did you want to know some alternative PLC brands?

Some popular brands in the U.S. are Allen-Bradley, Siemens, and Automation Direct.

The alternatives for not using PLC's have already been discussed by others, but probably the LAST common method used before PLC use was wide-spread was the electro-mechanical relay control box. I remember that in 1979 I helped build a relay control cabinet that had 110 relays. It controlled a lock hopper for a gasifier. In fact there was a problem with the system, but the logic had became so convoluted that none of the engineers could figure out the problem. Finally in desperation, I attempted to simulate the logic on an early desktop computer, the Apple II. I wrote a BASIC program that simulated exactly the relay schematic diagram, and finally did uncover the bug.