Automatic Control and Data Acquisition (scada) for Geothermal Systems

2. DEFINITION OF SCADA SCADA is the technology that enables a user to collect data from one or more distant facilities and / or send control instructions to those facilities. SCADA makes it unnecessary for an operator to be assigned to stay at, or to visit, remote locations in the normal operation of that remote facility. SCADA is an acronym that is formed from the first letters of Supervisory Control And Data Acquisition. A SCADA system allows an operator, in a location central to a widely distributed process such as an oil or gas field, pipeline system, or hydroelectric generating complex, to make set point changes on distant process controllers, to open or close valves or switches, to monitor alarms, and to gather measurement information. When the dimensions of the process become very large – hundreds or even thousands of kilometers from one end to the other – the benefits in terms of reduced cost of routine visits can be appreciated. Typical signals gathered from remote locations include alarms, status indication, analog values, and totaled meter values. However, with this apparently limited menu of available signal types, a vast range of information can be gathered. Similarly, signals sent from the central location to the remote site are usually limited to discrete binary bit changes or analog values addressed to a device at the process. An example of a binary bit change would be an instruction ordering a motor to stop. An analog value example would be an instruction to change a valve controller set point to 70 percent. Given simple signal types like these and some imagination, many control changes can be effected (Boyer, 1993).