Scada?

I have read in several forums about SCADA. Having been limited to PLC's and their HMI. I was wondering if someone would care to fill me in on what is SCADA? Thanks.

SCADA is a term for Supervisory control and data acquisiton.

Look at this site (its covered with ads but does have a decent tutorial).
http://members.iinet.net.au/~ianw/primer.html

SCADA

Supersory
Control
---------- You supervise the controls

You give Set Points, limits, recipe,math results...

Mainly a slow process, every n seconds or so. You could do faster things but the speed is the domain where the PLC rules. You could even turn off the SCADA once the data has been sent to the PLC ...

Data
Aquisition
---------- You collect Data

To make nice trend, graphic, SPC evaluations. Even to send to other gizzmos like ERPs and various accounting Database. They are often used to interface between the shop and the office.

All this comes with nice display (HMI) to help the operators set some variables, like Set points or Starts and Stops of processes or single loops like a motor.

Some people use HMI and SCADA interchangably, so you may know more than you think.

I prefer to differentiate the two. If it's got historical trending, the ability to log data to an external database, and/or some powerful scripting capabilities, it's a SCADA.

If it just a visualization package for the PLC, then it's an HMI.

By that definition, these days, most software packages (Wonderware, et al) are SCADA. If it's part of some hardware (Panelview, et al), it's an HMI (or OIT to us old-timers)

SCADA, PLCS, and HMI are not mutually exclusive, and often reside on the same system. SCADA (usually PC based) needs some kind of I/O to get data into the PC, usually over a serial or ethernet network. This can be done by remote I/O, RTUs (Remote Terminal Units) or PLCs. In this case local controland protection logic is incorporaed into the PLC. Often a PLC has a local HMI for local operator control. The SCADA system generally is used for major trends and process data logging, and alarm notification.