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    Introduction To SCADA and Telemetry

    Talib Al_Munawri

    Posts : 337
    Join date : 2009-07-03
    Age : 30
    Location : Sultanate of Oman

    Introduction To SCADA and Telemetry

    Post by Talib Al_Munawri on Thu Sep 30, 2010 7:20 am

    Introduction To SCADA and Telemetry

    Definition – SCADA

    What is SCADA?

    SCADA (Supervisory Control And Data Acquisition) system refers to the combination of telemetry and data acquisition.

    It consists of:

    • Collecting information
    • Transferring it back to a central site
    • Carrying out necessary analysis and control
    • Displaying this data on a number of operator screens

    * The SCADA system is used to monitor and control a plant or equipment.
    * Control may be automatic or can be initiated by operator commands.

    Definition - Telemetry

    What is telemetry?

    Telemetry is usually associated with SCADA systems. It is a technique used in transmitting and receiving information or data over a medium.

    • The information can be measurements, such as voltage, speed or flow.

    • These data are transmitted to another location through a medium such as cable, telephone or radio. Information may come from multiple locations. A way of addressing these different sites is incorporated in the system.

    Definition – Data Acquisition

    What is data acquisition?

    • Data acquisition refers to the method used to access and control information or data from the equipment being controlled and monitored.

    • The data accessed are then forwarded onto a telemetry system ready for transfer to the different sites.

    • They can be analog and digital information gathered by sensors, such as flowmeter, ammeter, etc.

    • It can also be data to control equipment such as actuators, relays, valves, motors, etc.

    Components of SCADA System

    • Remote Station
    • Communication Network
    • Central Monitoring Station (CMS)
    • Field Instrumentation

    Remote Station

    • Field instrumentation connected to the plant or equipment being monitored and controlled are interfaced to the remote station to allow process manipulation at a remote site.

    • It is also used to gather data from the equipment and transfer them to the central SCADA system. The remote station may either be an RTU (Remote Terminal Unit) or a PLC (Programmable Logic Controller).

    Communication Network

    • The Communication Network refers to the communication equipment needed to transfer data to and from different sites.

    • The medium used can either be cable, telephone or radio.

    • Remote sites are usually not accessible by telephone lines. The use ofradio offers an economical solution.

    • Radio modems are used to connect the remote sites to the host. An on-line operation can also be implemented on the radio system. For locations wherein a direct radio link cannot be established, a radio repeater is used to link these sites.

    Central Monitoring Station (CMS)

    • The Central Monitoring Station (CMS) is the master unit of the SCADA system

    • It is in charge of collecting information gathered by the remote stations and of generating necessary action for any event detected.

    • The CMS can have a single computer configuration or it can be networked to workstations to allow sharing o information from the SCADA system

    Field Instrumentation

    • Field Instrumentation refers to the devices that are connected to the equipment or machines being controlled and monitored by the SCADA system

    • These are sensors for monitoring certain parameters; and actuators for controlling certain modules of the system

    • Field instruments are usually either discrete or analog

    Field Instrumentation (Analog Devices)

    - These instruments convert physical parameters (i.e., fluid flow, velocity, fluid level, etc.) to electrical signals (i.e., voltage or current)

    - Signals using current (mA) are more common because they can be used for longer distances with less error due to signal loss

    Field Instrumentation (Discrete Devices)

    • Digital inputs and outputs are used to differentiate the discrete status of the equipment

    • Usually, <1> is used to mean EQUIPMENT ON and <0> for EQUIPMENT OFF status. This may also mean <1> for FULL or <0> for EMPTY

    Field Instrumentation (Digital or Smart Devices )

    • Instruments that provide more than one variable on one pair of wires (turbidity, temp,pH, etc.)

    • Usually wired on a bus network

    • Saves installation cost in wiring

    • Provides diagnostic information of instruments

    Typical System Configurations

    Three Basic Types

    • Point-to-Point
    • Point-to-Multipoint
    • Peer-to-Peer

    System Configurations Point-to-Point

    • Most simple type of communications
    • One station talks directly to the other (ie: water tank to well pump)

    System Configurations Point-to-Multipoint

    • Usually has one master polling location
    • Sometimes CMS
    • Most common type

    System Configurations Peer-to-Peer

    • All sites talk directly with each other
    • Communications protocol has to be able to support this type of communication
    • Manufacturing facilities and treatment plants are good examples that use this type of communications

    SCADA HMI Examples Remote Stations

    SCADA HMI Examples Central Monitoring Station

    Human Machine Interface (HMI)

    • Graphical representation of a process

    • Usually a software application on a PC at CMS to let the operator interface with control system

    • Has control functionality

    • Alarm capabilities

    • Data Historian and trending

    • Typical software packages: Tetragenics MC3000, Wonderware, Intelution and RSView32

    Tips in Planning SCADA System

    Get involved with your engineer for vendor and equipment selection
    Check references of integrators’ past installations
    Select vendor that can respond quickly if needed
    Select systems that can be serviced by another
    integrator in the event of having to change integrators
    Hire integrator that has background with your process requirement
    If using radios, a path study is highly recommended
    Bury fiber optic cable when possible (this is fairly inexpensive during new construction)
    Enter a yearly maintenance contract with the vendor


    Check antenna connections and other communications equipment yearly
    Calibrate instruments regularly, as per manufactures recommendations (at least quarterly)
    Backup your data at least once a month
    Have backups of HMI and other software applications
    Have a spare hard drive formatted and ready to go
    Keep spare parts for field instruments in inventory

    Posts : 20
    Join date : 2009-09-13
    Age : 30
    Location : *OMAN*

    Re: Introduction To SCADA and Telemetry

    Post by LoRdBOy on Thu Sep 30, 2010 5:13 pm

    Thanks BROVESOR

      Current date/time is Tue Aug 22, 2017 9:47 pm