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Diagnostics & Basic Operations

Some RTU’s may have a file system with support for file downloads. This supports user programs, and configuration files.

The RTU will operate scanning its inputs, normally at a faily fast date. It may do some processing such as change of state processing, time stamping of changes, and storage of the data awaiting polling from the Scada master some RTU’s have the ability to initiate reporting to the SCADA master, although more comman is the situation where the SCADA master polls the RTU;s asking for changes. The RTU may do some alarm processi ng. when polled by the SCADA master, the RTU must respond to the request, which may be as simple as “give me all your data”.to a complex control function to be executed.

Small vs Large

RTU’s are specialty devices manufactured often by small suppliers in batches of as little as one hundred. They are made forniche markets, and at the smaller end can be subject to intense cost pressures.

Therefore not all RTU’s support all functionality. Larger RTU’s may be capable of processing hundreds of inputs, and even controlling smaller “sub RTY’s”. These are obviously more expensive. The processing power of an RTU range from small 8 bit processors with minimal memory to larger sophisticated RTU’s capable of time stamping data to millisecond accuracy.

Some types (sizes) of RTU’s are as follows:

Tiny stand-alone systems That run off batteries for an entire year or more. These systems log data into EPROM or FLASH ROM and download data when physically accessed by an operator. Often these systems use single chip processors with minimal memory and might not be able to handle a sophisticated communications protocol.

Small stand-alone systems that can power up periodically and apply power to sensors (or radios) to measure and/or report. Usually run off batteries that are maintained by solor energy. The batteries are large enough to maintain operation for at least 4 months during the darkness of the winter in the far northern hemisphere. These system generally have enough capability for a much more complex communications scheme.

Medium system: Dedicated single board industrial computers, including IBM-PC or compatible computers either in desk-top enclosures or industrial configurations such as VME, MultiBus, STD bus, PC104 etc.

Large system: Complete Plant control with all the bells and whistles. These are usually in Distributed Control systems in Plants,etc and often communicate over high speed LANS. Timing may be very critical.

Standdards: As indicated RTU’s are specialty devices. There has been a lack of standards, especially in the communication area, and generally RTU’s from one supplier can not be mixed with RTU’s from another supplier.

An industry has grown up developing protocol converters and emulators. Recently some standards have begun to emerge for RTU’s Some Standards are IEC1131-3 For programming RTU’s.