DCIS, SMART, HART

Please could anyone forward me the architectures , communications used in DCIS.( dstributed control and informstion systems.) what are the detials involved in it, WHAT IS I/O system,, What are controllers and for what purpose,mmi, hmi, console, historian, their functions, data buses, hardware of dcis,control concept etc.. etc.. i mean to say in detial.

please could anyone explain me in detail about the differences in

1) smart, hart (what are all these) protocols, differences,when are the used? for what purpose 2), why 4-20 ma signals used.what is 4-20 ma? 3) Please can any one forward me the details at this address

email address is snipped-for-privacy@yahoo.com

You are asking for one of us to provide you a personal, two year course in industrial control. I am willing to discuss your questions in this newsgroup, but for private lessons I would charge about the same as my present rate of pay. If you are interested in a NG discussion, please check here regularly. You will get the benefit of various opinions and you will learn they are not always the same. If you wait for private e-mail you get nothing.

In industry a detailed presentation of a complete process control system would cost about $500,000.

In the process industries, the great majority of all analog signals use the

4-20 mA format where 4 mA represents 0% of scale and 20 mA represents 100% of scale. This format is used for a number of reasons:

1 - Current is superior to voltage for long distance signalling because insulators are a better quality than conductors. That is, voltage drop in a voltage signal can cause error while current loss through insulators is negligible.

2 - An 'elevated zero' is used so that the transmitters gets operating power even when the signal is zero. In this way a single pair of wires carries both power and information. Telephones work the same way. There is a DC carrier with AC signal superimposed on it.

There is a second reason for the elevated zero: Slight errors in calibration can be accommodated by going slightly below 4 mA. Modern control systems allow a bit of under range. This is impossible if there were a true zero since it is rare for electronics to be able to handle negative going signals without a DC bias.

3 - The mA signal is passed through a 250 Ohm resistor to produce a 1-5 V signal for the op amps. Thus there is a minimum of 1 watt power consumption. This is sufficient to exceed most sources of interference.

Walter.