SCADA, which stands for Supervisory Control and Data Acquisition, is a common process control application that collects data from remote locations for processing by a central computer

Data acquisition software is designed to collect, record, store, analyze and present data collected from digital devices such as sensors or gauges. Data acquisition (DAQ) is the digitizing and processing of multiple sensor or signal inputs, usually with signal conditioning

Data acquisition systems make various types of physical measurements, such as temperature, pressure, flow, strain, position, and speed, using electronic equipment. The data collected is  sent to a computer for analysis and display. Data acquisition and control (DAC) systems also take action (control) based on the data they receive. Turning on or off lights, motors, valves, heaters, and fans are common functions of control. Sending out voltage, current, digital words, pulses, and waveforms are also forms of control from the DAC system. DAC software running in the computer coordinates and executes these functions.

 There are many parts of a working SCADA system. A SCADA system  includes signal hardware (input and output), controllers, networks, user interface (HMI), communications equipment and software. All together, the term SCADA refers to the entire central system. The central system  monitors data from various sensors that are either in close proximity or off site (sometimes miles away).

For the most part, the brains of a SCADA system are performed by the Remote Terminal Units (sometimes referred to as the RTU). The Remote Terminal Units consists of a programmable logic controller.The RTU are set to specific requirements, however, most RTU allow human intervention, for instance, in a factory setting, the RTU might control the setting of a conveyer belt, and the speed can be changed or overridden at any time by human intervention. In addition, any changes or errors are  automatically logged for and/or displayed. Most often, a SCADA system will monitor and make slight changes to function optimally; SCADA systems are considered closed loop systems and run with relatively little human intervention.

One of key processes of SCADA is the ability to monitor an entire system in real time. This is facilitated by data acquisitions including meter reading, checking statuses of sensors, etc that are communicated at regular intervals depending on the system. Besides the data being used by the RTU, it is also displayed to a human that is able to interface with the system to override settings or make changes when necessary.

SCADA can be seen as a system with many data elements called points.  Each point is a monitor or sensor. Points can be either hard or soft. A hard data point can be an actual monitor; a soft point can be seen as an application or software calculation. Data elements from hard and soft points are  always recorded and logged to create a time stamp or history

 SCADA system includes a user interface,  called Human Machine Interface (HMI). The HMI of a SCADA system is where data is processed and presented to be viewed and monitored by a human operator. This interface  controls where the individual can interface with the SCADA system.

HMI's are an easy way to standardize the facilitation of monitoring multiple RTU's or PLC's (programmable logic controllers).  RTU's or PLC's will run a pre programmed process, but monitoring each of them individually can be difficult,  because they are spread out over the system. Because RTU's and PLC's historically had no standardized method to display or present data to an operator, the SCADA system communicates with PLC's throughout the system network and processes information that is easily disseminated by the HMI.

HMI's can also be linked to a database, which can use data gathered from PLC's or RTU's to provide graphs on trends, logistic info, schematics for a specific sensor or machine or even make troubleshooting guides accessible. In the last decade, practically all SCADA systems include an integrated HMI and PLC device making it extremely easy to run and monitor a SCADA system