A stand-alone data acquisition and control unit

8/7/2019 A stand-alone data acquisition and control unit

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SCADA RTU

A stand-alone data acquisition and control unit.

A small computer that provides intelligence in the

field, and allows the central SCADA master to

communicate with the field instruments.


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SCADA

RTU

Process

Central

SCADASystem

Main functions:Control process equipment at the

remote site

Acquire data from the process

Transfer the data back to the

central SCADA system Communicationlink


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There are two basic types of RTU

Single board RTU: The "single board RTU"

which is compact, and contains all I/O on a single

board. A typical single board RTU normally hasfixed I/O

e. g. 16 digital inputs, 8 digital outputs, 8 analogue

inputs, and say 4 analogue outputs.

It is normally not possible to expand its capability.


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Modular RTU : The "Modular RTU" has a

separate CPU module, and can have othermodules added, normally by plugging into a

common "backplane" (a bit like a PC motherboard

and plug in peripheral cards).

The modular RTU is designed to be expanded by

adding additional modules. Typical modules may

be a 8 analog in module, a 8 digital out module.Some specialized modules such as a GPS time

stamp module may be available.


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RTU Hardware features:

CPU and volatile memory.

Non volatile memory for storing programs and data.

Communications capability either through serial port(s)

or sometimes with an on board modem.

Secure Power supply (with battery backup).

Watchdog timer (to ensure the RTU restarts if something fails).

Electrical protection against "spikes".

I/O interfaces to DI/DO/AI/AO's.

Real time clock.


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RTU Software Features:

Real time operating system. This may be a

specific RTOS, or it may be code that started out

life as one big loop scanning the inputs, and

monitoring the communications ports.

Driver for the communications system i.e. the

link to the SCADA Master.

Device drivers for the I/O system i.e. to the

field devices.


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RTU Software Features:

SCADA application e. g. scanning of inputs, processing

and storing of data, responding to requests from the SCADA

master over the communications network.

Some method to allow the user applications to be

configured in the RTU. This may be simple parameter setting,enabling or disabling specific I/O's or it may represent a

complete user-programming environment.

Diagnostics.

Some RTU's may have a file system with support for file

downloads. This supports user programs, and configuration

files.


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Types 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 withminimal 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 solar energy. The batteries are large enough to maintain operation forat least 4 months during the darkness of the winter in the far northern hemisphere.

These systems generally have enough capability for a much more complex

communications scheme.

Medium systems. Dedicated single board industrial computers, including IBM-PC

or compatible computers either in desk-top enclosures or industrial configurationssuch as VME, MultiBus, STD bus, PC104 etc.

Large systems. 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.


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Standards

DNPs and IEC870 for communications

IEC1131-3 for programming RTU's.


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PLC's vs RTU's

A PLC (programmable logic controller) originally

had less communications capability and more

programmability

RTU's have ability to handle difficult

communications. RTU's originally had poor

programmability in comparison to PLC's.

At present we are seeing the merging of

RTU's and PLC's.


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Document By

SANTOSH BHARADWAJ REDDY

Email: [email protected]

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A stand-alone data acquisition and control unit

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