SCADA
Abstract
SCADA stands for Supervisory Control And Data Acquisition. SCADA refers to a system that collects data from various sensors at a factory, plant or in other remote locations and then sends this data to a central computer which then manages and controls the data. SCADA focuses on gathering and circulating the right amount of system information to the right person or computer within the right amount of time so that creative solutions are made possible.
Description of SCADA
The keyword supervisory indicates that decisions are not directly made by the system. Instead, the system executes control decisions based on control parameters entered by the agency staff. The system monitors the health of the process and generates alarm notifications when conditions are out of tolerance. It is also tasked with placing the process in a safe mode. It waits for user inputs to correct problems. The supervisory mode is designed to operate the system in a manner that avoids out of tolerance conditions. In a water / wastewater process, pumps are started and stopped by the system according to limits assigned by operations. As long as the system responds correctly to the control commands, the system remains in control. It includes three processes.
. Industrial processes include those of manufacturing, production, power generation, fabrication, and refining, and may run in continuous, batch, repetitive, or discrete modes.
. Infrastructure processes may be public or private, and include water treatment and distribution, wastewater collection and treatment, oil and gas pipelines, electrical power transmission and distribution, civil defense siren systems, and large communication systems.
. Facility processes occur both in public facilities and private ones, including buildings, airports, ships, and space stations. They monitor and control energy consumption.
SCADA can be used to monitor and control plant or equipment. The control may be automatic, or initiated by operator commands. The data acquisition is accomplished firstly by the RTU's (remote Terminal Units) scanning the field inputs connected to the RTU (RTU's may also be called a PLC - programmable logic controller). This is usually at a fast rate. The central host will scan the RTU's (usually at a slower rate.) The data is processed to detect alarm conditions, and if an alarm is present, it will be displayed on special alarm lists. Data can be of three main types. Analogue data (i.e. real numbers) will be trended (i.e. placed in graphs). Digital data (on/off) may have alarms attached to one state or the other. Pulse data (e.g. counting revolutions of a meter) is normally accumulated or counted.
These systems are used not only in industrial processes. For example, Manufacturing, steel making, power generation both in conventional, nuclear and its distribution, chemistry, but also in some experimental facilities such as laboratories research, testing and evaluation centers, nuclear fusion. The size of such plants can range from as few as 10 to several 10 thousands input/output (I/O) channels. However, SCADA systems evolve rapidly and are now penetrating the market of plants with a number of I/O channels of several 100K.
