SCADA stands for supervisory control and data acquisition. It generally refers to industrial control systems: computer systems that monitor and control industrial, infrastructure, or facility-based processes, as described below:
• Industrial processes include those of manufacturing, production, power generation, fabrication, and refining, and may run in continuous, batch, repetitive, or discrete modes.
• Infrastructure processes may be public or private, and include water treatment and distribution, wastewater collection and treatment, oil and gas pipelines, electrical power transmission and distribution, Wind farms, civil defense siren systems, and large communication systems.
• Facility processes occur both in public facilities and private ones, including buildings, airports, ships, and space stations. They monitor and control HVAC, access, and energy consumption.
A SCADA System usually consists of the following subsystems:
• A Human-Machine Interface or HMI is the apparatus which presents process data to a human operator, and through this, the human operator monitors and controls the process.
• A supervisory (computer) system, gathering (acquiring) data on the process and sending commands (control) to the process.
• Remote Terminal Units (RTUs) connecting to sensors in the process, converting sensor signals to digital data and sending digital data to the supervisory system.
• Programmable Logic Controller (PLCs) used as field devices because they are more economical, versatile, flexible, and configurable than special-purpose RTUs.
• Communication infrastructure connecting the supervisory system to the Remote Terminal Units.
Industrial Use of SCADA System
This article describes the function of SCADA, its application in oil and gas flowing, waste water management, power and electricity surges.
WHAT DOES SCADA DO?
From a central reading location a SCADA system can track a number of remote sites equipped with Remote Terminal Units (RTUs) or Programmable Logic Controllers (PLCs). The RTUs can measure an array of conditions and a wider variety of parameters, including temperature, current, voltage flow, and tank levels.. The following types of sensors can be included in RTUs:
BLOCK DIAGRAM ::
Fig 1 :: Basic Block Diagram Of SCADA
The components we are using in PC based SCADA ie Sensors, Analog to Digital convertors, MAX 232, Desktop,crystal oscillator, ULN driver, relays.
In this PC based SCADA we are controlling temperature automatically of respective machine and monitoring voltage and current of that machine by using temperature,voltage and current sensors which are connected to respective machines.The temperature sensor we are using is LM35 whose specifications is -55ºc to 135ºc.where as thermistor can withstand low temperature and monitoring the readings of voltage and current for that we are using variable resistance pots.and the output of voltage,current and temperature sensors are analog but the micro controller supports only digital data.so this analog data is converted to digital data using ADC.and in this project we are using AD0809 IC,in which the technique involved is successive approximation to convert analog to digital.and sensors are communicated to micro controller in this we are using is AT89S52 micro controller which is advanced version of 8051 which has xtra feature i.e.,it supports serial communication UART.and it has watch dog timer which is used to set when the program is stuck.and this micro controller send the data serially from ADC to desktop through MAX232.here max 232 is used to provide communication between micro controller and th pc,because directly micro controller and pc cannot communicate each other,the reason behind this is the language used in micro controller is TTL.
The specification of TTL is for logic’1’=5.v and for logic’0’=0.v.where as RS232 language is used in desktop,the specification of reserved standarad 232 logic is for logic’1’= -3 to -25.v and for logic’0’ = -3 to 25.v. so to convert TTL logic RS232 logic or from RS232 logic to TTL logic.,we have to use MAX232 which consists of inverting amplifiers.The clock frequency given to the micro controller is through crystal oscillator in that we are using quartz oscillator to provide very constant frequency,the clock frequency given ADC is from IC555 TIMER is astable multi-vibrator
To drive the loads we are using ULN drivers,which amplifies the current to 500m,amp and the supply given to this ULN drive is +12.v and the IC we are using is ULN2003A , which consists of darlington pair arrays acts as inverters.and this ULN driver has 7 i/p pins of that we are using only 1 pin to drive only one relay.
The power supply provided to all sections are given through circuit which includes step down transformer,rectifier,filter and regulator.The available power supply is 230.v AC.But the required voltage is 5.v and 12.v Dc.To step the voltage we use step down transformer.and it is 12v AC.This 12vAc is given to bridge rectifier which gives 11v pulsated DC and this is given to capacitive filter circuits.To get 11v Dc which is given to ULN driver and also to regulator 7805 to get 5.v DC with 500m amp current.