What is the difference between scada and rtu

A system set up to replace hard wired relays. The were expensive, but not as expensive as DCS systems. They were typically used for discrete. The analog was expensive. They didn't have HMIs integrated with them, so analog controls were hard to monitor. Typically, controls were monitored via lights. Inputs were made through pushbuttons and thumbwheels. These were usually in the form of a panel based display.

This was a huge improvement over Lights and thumbwheels. However, the panels were not well integrated like the DCS. The tags needed to be exported from the PLC, and imported into the panel configuration software. Same thing as an MMI. As time moved on, software became available that allowed personal computers to be used for operator interphases. These were controls put out in remote locations, ie, off site, often hundreds of miles away from the control rooms.

They control the off site equipment. They are set up so that if communications is lost, the process continues on, but is set up to shut the equipment down due to abnormal conditions. The control could be PLCs, but are often a less general controller set up for the specific equipment and industry.

PLCs are preprogrammed based on their application and put into operation. A PLC accepts inputs from the field, process the input based on the programming done and outputs the commands to the field equipment.

It can also accept commands from the plant operators through SCADA and give commands to the field equipment. The features of PLCs vary from one manufacturer to the other but the basic architecture remains the same. RTU stands for a remote terminal unit. Normally RTUs are used at remote stations to control equipment for example, opening and closing of motorized valves in oil pipelines located far away from the control station.

RTUs can support multiple communication protocols at the same time. A limited number of input and output devices can be added to it.

Wikipedia has this covered very well:. The high-end DCS systems have two or more redundant controllers and communication networks usually Ethernet to ensure maximum uptime. DCS are very flexible systems with the ability to handle extremely complicated process control programming. Analog and digital signal processing and conditioning combined with advanced algorithms make DCS systems an extremely valuable tool in any industrial process.

I have been in the wastewater field for 20 years and have also worked on the power and paper industries.