SCADA: Remote Terminal Units

Hardware Solutions

Distributed Control System (DCS) components normally constitute a SCADA system. Remote Terminal Units or RTUs are one of the major components of a SCADA System. It can automatically execute a simple logical process without involvement of a master computer and are being increasingly used. IEC61131-3, a functional programming language is commonly used for creating programs to run on these RTUs. IEC61131-3 not being a procedural language like FORTRAN or C Programming requires minimum training. This facilitates performance of both design and implementation of a program to be executed on a RTU by the SCADA system engineers.

Functions Of RTU

The functions of RTU in a SCADA setup is multifarious. RTU is the link or connection to the physical instrument and from a switch or valve, it reads open and close status data. Apart from status data, it also reads pressure, flow, voltage and current measurements. It performs equipment control such as closing and opening of switch and valve or setting the pump speed. Analog measurement data or digital status data can also be read by RTU. After reading it can send analog set points or digital commands.

Alarms

Alarm is one of the most important aspects of a SCADA System. Alarm or the digital status point indicates a value which is either normal or alarm. Alarms are so created that they can be activated only when the condition for their requirement is reached. Fuel tank empty light indicator or alarm in a car is one such example. The alarm draws the attention of the SCADA operator to that part of the system which requires immediate adjustment or even change if necessary. Often in a SCADA system, alarm activation alert managers accompany the sent emails and text messages. The real time alarm and data provide operators with the information needed to respond quickly and adjust or change processes for effective control.