documentation
Content
CHAPTER 1
DATA ACQUISITION SYSTEMS
1.1 Data Acquisition Data acquisition is the practice of collecting and storing data from sensors or other measurements equipment. Technically, data acquisition techniques could include manual monitoring and recording methods, such as visually inspecting a device or measuring an object, but it generally refers to the use of electronic sensors and data collection equipment. Data acquisition systems abbreviated with the acronym DAS typically convert analog waveforms into digital values for processing. Data acquisition is the process of retrieving control information from the equipment which is out of order or may lead to some problem or when decisions are need to be taken according to the situation in the equipment. So this acquisition is done by continuous monitoring of the equipment to which it is employed. 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 flow meter, ammeter, etc. It can also be data to control equipment such as actuators, relays, valves, motors, etc.
1.2 Evolution of Data Acquisition Equipment
Earlier data was often recorded on paper. Strip chart recorders and plotters would take an input signal and convert that signal to the one or two dimensional motion of a pen on a sheet or roll of paper. It was up to the operator to calibrate the scale of the output recordings on the graphs to accurately reflect the behavior being monitored. The next generation of data acquisition equipment included data loggers, which were electronic systems that could store electronic from connected sensors and then either replay that data later via a paper chart recorder or by connection to a computer, such as a serial cable. Some dataloggers evolved to include floppy drives so data could be recorded to a floppy disk then transferred to a computer.
Fig 1.1: Temperature, humidity, pressure data acquisition system Finally, the advent of computer and controller-based data acquisition allowed users to perform complex measurements and to store and retrieve data electronically. Data acquisition hardware was originally purely analog, requiring an analog-to-digital converter so the data could be stored digitally. Today, many data acquisition systems have the hardware to process signals. However, most sensors still function on a purely analog basis, so analog hardware capabilities are not expected to disappear anytime soon. Today’s real time data acquisition systems are much simpler and are efficient and work throughout the process and also eliminate the need for strip charts etc.
1.3 Components of data acquisition systems
The components of data acquisition systems include:
Sensors that convert physical parameters to electrical signals. Signal conditioning circuitry to convert sensor signals into a form that can be Analog-to-digital converters, which convert conditioned sensor signals to digital
converted to digital values.
values. It begins with the physical phenomenon or physical property to be measured. Examples of this include temperature, light intensity, gas pressure, fluid flow, and force. Regardless of the type of physical property to be measured, the physical state that is to be measured
must first be transformed into a unified form that can be sampled by a data acquisition system. The task of performing such transformations falls on devices called sensors. A sensor, which is a type of transducer, is a device that converts a physical property into a corresponding electrical signal (e.g., a voltage or current) or, in many cases, into a corresponding electrical characteristic (e.g., resistance or capacitance) that can easily be converted to electrical signal. The ability of a data acquisition system to measure differing properties depends on having sensors that are suited to detect the various properties to be measured. There are specific sensors for many different applications. DAQ systems also employ various signal conditioning techniques to adequately modify various different electrical signals into voltage that can then be digitized using an Analog-to-digital converter (ADC). Data acquisition hardware often contains multiple components (multiplexer, ADC, DAC, TTL-IO, high speed timers, RAM). These are accessible via a bus by a microcontroller, which can run small programs. A controller is more flexible than a hard wired logic. Many times reconfigurable logic is used to achieve high speed for specific tasks and are used after the data has been acquired to obtain some results. The fixed connection with the PC allows for comfortable compilation and debugging. Using an external housing a modular design with slots in a bus can grow with the needs of the user. Through the process of data acquisition we are able to monitor the parameters present in an industry, pharmaceutical company or domestic home environment. There are many parameters like temperature, humidity, light intensity etc. the sensors present in the data acquisition systems help in doing so. Since these parameters have to be monitored in a regular basis there arises a need for establishing an automatic controlling system. 1.4 AUTOMATION Automation is the use of control systems and information technologies to reduce the need for human work in the production of goods and services. In the scope of industrialization, automation is a step beyond mechanization. Whereas mechanization provided human operators with machinery to assist them with the muscular requirements of work, automation greatly decreases the need for human sensory and mental
requirements as well. Automation plays an increasingly important role in the world economy and in daily experience. Automation has had a notable impact in a wide range of industries beyond manufacturing (where it began). Once-ubiquitous telephone operators have been replaced largely by automated telephone switchboards and answering machines. Automated teller machines have reduced the need for bank visits to obtain cash and carry out transactions. The main advantages of automation are:
1 2
Replacing human operators in tasks that involve hard physical or monotonous work. Replacing humans in tasks done in dangerous environments (i.e. fire, space, volcanoes, nuclear facilities, underwater, etc.) Performing tasks that are beyond human capabilities of size, weight, speed, endurance, etc. Economy improvement. Automation may improve in economy of enterprises, society or most of humanity. Wireless communication has become an important feature for commercial products and a popular research topic within the last ten years. There are now more mobile phone subscriptions than wired-line subscriptions. Lately, one area of commercial interest has been low-cost, low-power, and short-distance wireless communication used for \personal wireless networks." Technology advancements are providing smaller and more cost effective devices for integrating computational processing, wireless communication, and a host of other functionalities. These embedded communications devices will be integrated into applications ranging from homeland security to industry automation and monitoring. They will also enable custom tailored engineering solutions, creating a revolutionary way of disseminating and processing information. With new technologies and devices come new business activities, and the need for employees in these technological areas. Engineers who have knowledge of embedded systems and wireless communications will be in high demand. Unfortunately, there are few adorable environments available for
3
4
development and classroom use, so students often do not learn about these technologies during hands-on lab exercises. The communication mediums were twisted pair, optical fiber, infrared, and generally wireless radio. The use of wireless automated data acquisition systems help in maintaining a coordinated environment in the industry or at homes. Thus the advent of the data acquisition and control systems are very advantageous and enduring in the long run.
CHAPTER 2
SCADA
SCADA is an acronym that stands for Supervisory Control and Data Acquisition. SCADA refers to a system that collects data from various sensors at a factory, plant or in other remote locations and then sends this data to a central computer which then manages and controls the data. SCADA is a term that is used broadly to portray control and management solutions in a wide range of industries. Some of the industries where SCADA is used are Water Management Systems, Electric Power, Traffic Signals, Mass Transit Systems, Environmental Control Systems, and manufacturing systems. 2.1 SCADA as a System 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.
•
•
•
There are many parts of a working SCADA system. A SCADA system usually includes signal hardware (input and output), controllers, networks, user interface (HMI), communications equipment and software. All together, the term SCADA refers to the entire central system. The central system usually monitors data from various sensors that are either in close proximity or off site (sometimes miles away). For the most part, the brains of a SCADA system are performed by the Remote Terminal Units (sometimes referred to as the RTU). The Remote Terminal Units consists of a programmable logic converter. The RTU are usually set to specific requirements, however, most RTU allow human intervention, for instance, in a factory setting, the RTU might control the setting of a conveyer belt, and the speed can be changed or overridden at any time by human intervention. In addition, any changes or errors are usually automatically logged for and/or displayed. Most often, a SCADA system will monitor and make slight changes to function optimally; SCADA systems are considered closed loop systems and run with relatively little human intervention. One of key processes of SCADA is the ability to monitor an entire system in real time. This is facilitated by data acquisitions including meter reading, checking statuses of sensors, etc that are communicated at regular intervals depending on the system. Besides the data being used by the RTU, it is also displayed to a human that is able to interface with the system to override settings or make changes when necessary. SCADA can be seen as a system with many data elements called points. Usually each point is a monitor or sensor. Usually points can be either hard or soft. A hard data point can be an actual monitor; a soft point can be seen as an application or software calculation. Data elements from hard and soft points are usually always recorded and logged to create a time stamp or history
2.2 User Interface (HMI)
A SCADA system includes a user interface, usually called Human Machine Interface (HMI). The HMI of a SCADA system is where data is processed and presented to be viewed and monitored by a human operator. This interface usually includes controls
where the individual can interface with the SCADA system. HMI's are an easy way to standardize the facilitation of monitoring multiple RTU's or PLC's (programmable logic controllers). Usually RTU's or PLC's will run a pre programmed process, but monitoring each of them individually can be difficult, usually because they are spread out over the system. Because RTU's and PLC's historically had no standardized method to display or present data to an operator, the SCADA system communicates with PLC's throughout the system network and processes information that is easily disseminated by the HMI. HMI's can also be linked to a database, which can use data gathered from PLC's or RTU's to provide graphs on trends, logistic info, schematics for a specific sensor or machine or even make troubleshooting guides accessible. In the last decade, practically all SCADA systems include an integrated HMI and PLC device making it extremely easy to run and monitor a SCADA system.
2.3 Remote Terminal Unit
The RTU connects to physical equipment. Typically, an RTU converts the electrical signals from the equipment to digital values such as the open/closed status from a switch or a valve, or measurements such as pressure, flow, voltage or current. By converting and sending these electrical signals out to equipment the RTU can control equipment, such as opening or closing a switch or a valve, or setting the speed of a pump. The RTU can read digital status data or analogue measurement data, and send out digital commands or analogue set points. The term SCADA usually refers to centralized systems which monitor and control entire sites, or complexes of systems spread out over large areas (anything between an industrial plant and a country). Most control actions are performed automatically by remote terminal units ("RTUs") or by programmable logic controllers ("PLCs"). Host control functions are usually restricted to basic overriding or supervisory level intervention. For example, a PLC may control the flow of cooling water through part of an industrial process, but the SCADA system may allow operators to change the set points for the flow and enable alarm conditions, such as loss of flow and high temperature, to be displayed
and recorded. The feedback control loop passes through the RTU or PLC, while the SCADA system monitors the overall performance of the loop.
A SCADA system could be programmed to:
• • • • • •
monitor high and low levels in the day tanks, fill them when a certain level is reached, calculated and store the volume used, monitor the level in the main feed tank, Alarm when a certain level is reached to notify purchasing (or send an e-mail), Plot the usage of chemicals vs time, process, or any other parameter.
CHAPTER 3
SCADA SYSTEM OPERATION
SCADA stands for Supervisory Control and Data Acquisition. As the name indicates, it is a control system which focuses on the supervisory level. The power supply initiates the functions of data acquisition systems. The power supply consists of a step down transformer which produces a voltage of nearly 9V at its secondary winding. The 9V is presented to a bridge rectifier which produces an unregulated DC voltage and with the help of two linear voltage regulators we obtain voltages 5V and 12V at their outputs respectively. The voltages produced at the regulators are used by the different components like the Microcontroller, Sensors, Relays, Modem and ADC Converter. The relays and GSM modem use 12V where as the microcontroller; sensors and the LCD module utilize 5V. The microcontroller is AT89S52 is used to perform and co-ordinate all the operations in the data acquisition process. The LCD module is used to display the status of the acquisition systems. A pair of relays are used which are used to perform the switching operations during the occurrence of the constraints set. A relay is used to maintain the functions a bulb, representing the heat producing component and the other relay for activating the DC motor for meeting the counter active effect. A ULN2003 IC is used to interface voltages with the relays used by acting as the microcontroller driver for the relays. An ADC0808 is also used so as to provide analog to digital conversion which is mainly useful for the functioning of the sensor modules which understand the analog form of signal. Before discussing the functionality of the GSM modem, the knowledge about MAX232 block would help in understanding. The MAX232 IC is used for voltage conversions between the TTL and the RS232 voltages, which can be best understood by the microcontroller and the GSM modem respectively. There are two sensors which are the LM35 and humidity sensors which are used for detecting the environment of a particular
chamber or a space. So, using these components we are able to acquire data which helps in the controlling of the real time alterations in the environment of a particular enclosure by enabling the counter measures. GSM modem contains a subscriber identification module (SIM), which is present in the supervisor’s handset. The GSM modem is used to intimate the user about the data regarding the temperature and the humidity of the chamber in the industrial plant. The working of SCADA can be understood in two stages. They are: 1. Data Acquisition stage. 2. Data controlling stage.
3.1 Data Acquisition stage In the data acquisition stage the information regarding the temperature and the humidity is obtained on the LCD module. The heat in the chamber is allowed to vary based on its natural course. The sensors help in retrieving the status of the chamber in the plant that is they display the temperature and the humidity When the temperature of a certain area increases over a predefined level, an information via a message is sent continuously till a message is replied back informing a code which activates the counter measure to decrease the temperature of the chamber. Incorporating different sensors help in monitoring different factors whose increase or decrease affects the performance. An additional way of checking is done by giving a missed call to the GSM module which replies the specifications through a message to the inquirer. The SCADA forms the basis of many real time applications in different fields of security, medicine and various other data acquisition fields. Explaining the Data Acquisition in more detail, the outputs of the sensors are linear to variation in input. Hence as temperature increases their outpu also increases. The outputs of the sensors are given to the ADC 0808 for conversion to digital output, which is
understood by microcontroller. The outputs of ADC is given to microcontroller port 0. The port 1 pins help in display in the temperature in LCD module 3.2 Data Controlling Stage When the temperature increases above a certain level the microcontroller activates the MAX 232 block and communicates with the GSM modem. The GSM modem then sends the messages stating the conditions of the temperature rise. The supervisor then sends the message to initiate the counter measure to the GSM modem module. This activates the cooler fan to reduce the temperature of the chamber. The humidity of the chamber is just monitored time to time. This covers the controlling part of SCADA.
CHAPTER 4
HARDWARE REQUIREMENTS
1. AT89S52 MICROCONTROLLER 2. MAX232. 3. RELAYS. 4. LCD DISPLAY.
5. ADC0808. 6. AC DEVICES. 7. ULN2003. 8. GSM MODEM
4.1 AT89S52:
The AT89S52 is a low-power, high-performance CMOS 8-bit microcontroller with 8K bytes of in-system programmable Flash memory. The device is manufactured using Atmel’s high-density nonvolatile memory technology and is compatible with the industry-standard 80C51 instruction set and pinout. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory pro-grammer. By combining a versatile 8-bit CPU with in-system programmable Flash on a monolithic chip, the Atmel AT89S52 is a powerful microcontroller, which provides a highly flexible and cost-effective solution to many, embedded control applications. The AT89S52 provides the following standard features: 8K bytes of Flash, 256 bytes of RAM, 32 I/O lines, Watchdog timer, two data pointers, three 16-bit timer/counters, a six-vector two-level interrupt architecture, a full duplex serial port, onchip oscillator, and clock circuitry. In addition, the AT89S52 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port, and interrupt system to continue functioning. The Power-down mode saves the RAM con-tents but freezes the oscillator, disabling all other chip functions until the next interrupt
4.2 POWER SUPPLY
All digital circuits require regulated power supply. In this article we are going to learn how to get a regulated positive supply from the mains supply.
Fig 4.1 shows the basic block diagram of a fixed regulated power supply. 4.2.1 Rectifier A rectifier is a device that converts an AC signal into DC signal. For rectification purpose we use a diode, a diode is a device that allows current to pass only in one direction i.e. when the anode of the diode is positive with respect to the cathode also called as forward biased condition & blocks current in the reversed biased condition.A Voltage regulator is a device which converts varying input voltage into a constant regulated output voltage 4.3 GSM Technology GSM Global System for Mobile communications is an open, digital cellular technology used for transmitting mobile voice and data services.GSM supports voice calls and data transfer speeds of up to 9.6 kbit/s, together with the transmission of SMS (Short Message Service). GSM operates in the 900MHz and 1.8GHz Frequency bands. 4.3.1 ARCHITECTURE AND BULDING BLOCKS OF GSM
The GSM specifications define two truly open interfaces within the GSM network. The first one is between the Mobile Station (MS) and the Base Station (BS). This open-air interface is appropriately named the “air interface”
GSM is mainly built on three building blocks: 4.3.1.1 Mobile Station (MS) The MS (mobile station) is a combination of terminal equipment and subscriber data. The terminal equipment such as is called ME (mobile equipment) and the subscriber’s data is stored in a separate module called ME+SIM=MS. Mobile Equipment (ME) Subscriber Identity Module (SIM) The GSM network is divided into three subsystems: network switching subsystem(NSS), Base station subsystem(BSS), and Network Management Subsystem (NMs). The three subsystems, different network elements, and their respective tasks. 4.3.1.2 Network Switching Subsystem (NSS) SIM(subscriber identity module) Therefore
The Network Switching Subsystem (NSS) contains the network elements. Mobile Switching Center (MSC) Home Location Register (HLR) Visitor Location Register (VLR) Authentication Center (AUC) Equipment Identity Register (EIR)
The main functions of NSS are: • • • • •
Call control Charging Mobility management Signalling Subscriber data handling
Mobile services Switching Centre (MSC) The MSC is responsible for controlling calls in the mobile network. It identifies the origin and destination of a call (mobile station or fixed telephone), as well as the type of a call. An MSC acting as a bridge between a mobile network and a fixed network is called a Gateway MSC. The MSC is responsible for several important tasks, such as the following. Call control Initiation of paging Charging data collection
Visitor Location Register (VLR) MSC. VLR is a database which contains information about subscribers currently being in the service area of The MSC/VLR, such as: • • • Identification numbers of the subscribers Security information for authentication of the SIM card and for ciphering Services that the subscriber can use
Home Location Register (HLR) HLR maintains a permanent register of the subscribers, for instance subscriber identity numbers and the subscribed services. In addition to the fixed data, the HLR also keeps track of the current location of its customers. As you will see later, the MSC asks for routing information from the HLR if a call is to be set up to a mobile station (mobile terminated call). In the Nokia implementation, the two network elements, Authentication Centre (AC) and Equipment Identity Register (EIR), are located in the HLR.
Base Station Subsystem (BSS)
The Base station subsystem is responsible for managing the radio network, and it is controlled by an MSC. One MSC contains several BSS’s. A BSS itself may cover a considerably large geographical area consisting of many cells. The BSS consists of the following elements: • • • BSC BTS TC Base Station Controller Base Transceiver Station Transcoder
Base Station Controller ( BSC) The BSC is the central network element of the BSS and it controls the radio network. It has several important tasks. They are • • • • • Connection establishment Mobility management Statistical raw data collection Air and A interface signaling support BTS and TC control
Base Transceiver Station (BTS) The BTS is the network element responsible for maintaining the air interface and minimizing the transmission problems (the air interface is very sensitive for distturbancees).
4.3.1.3 Network Management Subsystem (NMS)
The Network Management Subsystem (NMS) is the third subsystem of the GSM network in addition to the Network Switching Subsystem (NSS) and Base Station Subsystem (BSS). The purpose of the NMS is to monitor various functions and elementsof the network .
4.4 MAX232
The MAX232 is an integrated circuit that converts signals from an RS-232 serial port to signals suitable for use in TTL compatible digital logic circuits. The drivers provide RS-232 voltage level outputs (approx. ± 7.5 V) from a single + 5 V supply via on-chip charge pumps and external capacitors. This makes it useful for implementing RS-232 in devices that otherwise do not need any voltages outside the 0 V to + 5 V range, as power supply design does not need to be made more complicated just for driving the RS-232. The receivers reduce RS-232 inputs (which may be as high as ± 25 V), to standard 5 V TTL levels. These receivers have a typical threshold of 1.3 V, and a typical hysteresis of 0.5 V. The later MAX232A is backwards compatible with the original MAX232 but may operate at higher baud rates and can use smaller external capacitors – 0.1 μF in place of the 1.0 μF capacitors used with the original device. RS-232 Voltage levels • •
•
+3 to +25 volts to signify a "Space" (Logic 0) -3 to -25 volts for a "Mark" (logic 1). Any voltage in between these regions (i.e. between +3 and -3 Volts) is undefined. The data byte is always transmitted least-significant-bit first. The bits are transmitted at specific time intervals determined by the baud rate
of the serial signal. This is the signal present on the RS-232 Port of your computer, shown below.
RS-232 Logic Waveform
4.4.1 RS-232 LEVEL CONVERTER Standard serial interfacing of microcontroller (TTL) with PC or any RS232C Standard device , requires TTL to RS232 Level converter . A MAX232 is used for this purpose. It provides 2-channel RS232C port and requires external 10uF capacitors. The driver requires a single supply of +5V.
MAX-232 includes a Charge Pump, which generates +10V and -10V from a single 5v supply. 4.4.2 Serial communication When a processor communicates with the outside world, it provides data in byte sized chunks. Computers transfer data in two ways: parallel and serial. In parallel data transfers, often more lines are used to transfer data to a device and 8 bit data path is expensive. The serial communication transfer uses only a single data line instead of the 8 bit data line of parallel communication which makes the data transfer not only cheaper but also makes it possible for two computers located in two different cities to communicate over telephone.
Serial data communication uses two methods, asynchronous and synchronous. The synchronous method transfers data at a time while the asynchronous transfers a single byte at a time. There are some special IC chips made by many manufacturers for data communications. These chips are commonly referred to as UART (universal asynchronous receiver-transmitter) and USART (universal synchronous asynchronous receiver transmitter). The AT89C51 chip has a built in UART. In asynchronous method, each character is placed between start and stop bits. This is called framing. In data framing of asynchronous communications, the data, such as ASCII characters, are packed in between a start and stop bit. We have a total of 10 bits for a character: 8 bits for the ASCII code and 1 bit each for the start and stop bits. The rate of serial data transfer communication is stated in bps or it can be called as baud rate. To allow the compatibility among data communication equipment made by various manufacturers, and interfacing standard called RS232 was set by the Electronics industries Association in 1960. Today RS232 is the most widely used I/O interfacing standard. This standard is used in PCs and numerous types of equipment. However, since the standard was set long before the advent of the TTL logic family, its input and output voltage levels are not TTL compatible. In RS232, a 1 bit is represented by -3 to -25V, while a 0 bit is represented +3 to +25 V, making -3 to +3 undefined. For this reason, to connect any RS232 to a microcontroller system we must use voltage converters such as MAX232 to connect the TTL logic levels to RS232 voltage levels and vice versa. MAX232 ICs are commonly referred to as line drivers.
The simplest connection between a PC and microcontroller requires a minimum of three pin, TXD, RXD, and ground. Many of the pins of the RS232 connector are used for handshaking signals. Here four external 10µf capacitors for removing any voltage variations. RXD and TXD pins of microcontroller are connected to Tx and Rx of MAX 232 for serial communication. The nine pin connector RS 232 is used to connect the GSM modem to MAX 232 thereby enabling connection between the two.
4.5 LCD MODULE
To display interactive messages we are using LCD Module. We examine an intelligent LCD display of two lines,16 characters per line that is interfaced to the controllers. The protocol (handshaking) for the display is as shown. Whereas D0 to D7th bit is the Data lines, RS, RW and EN pins are the control pins and remaining pins are +5V, -5V and GND to provide supply. Where RS is the Register Select, RW is the Read Write and EN is the Enable pin. The display contains two internal byte-wide registers, one for commands (RS=0) and the second for characters to be displayed (RS=1). It also contains a user-programmed RAM area (the character RAM) that can be programmed to generate any desired character that can be formed using a dot matrix. To distinguish between these two data areas, the hex command byte 80 will be used to signify that the display RAM address 00h will be chosen.Port1 is used to furnish the command or data type, and ports 3.2 to3.4 furnish register select and read/write levels. The display takes varying amounts of time to accomplish the functions as listed. LCD bit 7 is monitored for logic high (busy) to ensure the display is overwritten. Liquid Crystal Display also called as LCD is very helpful in providing user interface as well as for debugging purpose. The most common type of LCD controller is HITACHI 44780 which provides a simple interface between the controller & an LCD. These LCD's are very simple to interface with the controller as well as are cost effective.
2x16 Line Alphanumeric LCD Display The most commonly used ALPHANUMERIC displays are 1x16 (Single Line & 16 characters), 2x16 (Double Line & 16 character per line) & 4x20 (four lines & Twenty characters per line). The LCD requires 3 control lines (RS, R/W & EN) & 8 (or 4) data lines. The number on data lines depends on the mode of operation. If operated in 8-bit mode then 8 data lines + 3 control lines i.e. total 11 lines are required. And if operated in 4-bit mode then 4 data lines + 3 control lines i.e. 7 lines are required. How do we decide which mode to use? It’s simple if you have sufficient data lines you can go for 8 bit mode & if there is a time constrain i.e. display should be faster then we have to use 8-bit mode because basically 4-bit mode takes twice as more time as compared to 8-bit mode.
Pin 1 2 3 4 5 6 7-14 15 16 Symbol Vss Vdd Vo RS R/W En DB0-DB7 A/Vee K Function Ground Supply Voltage Contrast Setting Register Select Read/Write Select Chip Enable Signal Data Lines Gnd for the backlight Vcc for backlight
When RS is low (0), the data is to be treated as a command. When RS is high (1), the data being sent is considered as text data which should be displayed on the screen. When R/W is low (0), the information on the data bus is being written to the LCD. When RW is high (1), the program is effectively reading from the LCD. Most of the times there is no need to read from the LCD so this line can directly be connected to Gnd thus saving one controller line. The ENABLE pin is used to latch the data present on the data pins. A HIGH - LOW signal is required to latch the data. The LCD interprets and executes our command at the instant the EN line is brought low. If you never bring EN low, your instruction will never be executed.
4.6 ADC0808
The ADC0808, ADC0809 data acquisition component is a monolithic CMOS device with an 8-bit analog-to-digital converter, 8-channel multiplexer and microprocessor compatible control logic. The 8-bit A/D converter uses successive approximation as the conversion technique. The converter features a high impedance chopper stabilized comparator, a 256R voltage divider with analog switch tree and a successive approximation register. The 8-channel multiplexer can directly access any of 8-single-ended analog signals. The device eliminates the need for external zero and fullscale adjustments. Easy interfacing to microprocessors is provided by the latched and decoded multiplexer address inputs and latched TTL TRI-STATE outputs. The design of the ADC0808, ADC0809 has been optimized by incorporating the most desirable aspects of several A/D conversion techniques. The ADC0808, ADC0809 offers high speed, high accuracy, minimal temperature dependence, excellent long-term accuracy and repeatability, and consumes minimal power. These features make this device ideally suited to applications from process and machine control to consumer and automotive applications. For 16-channel multiplexer with common output (sample/hold port) see ADC0816 data sheet.
4.7 TEMPERATURE SENSOR (LM35)
The LM35 sensor series are precision integrated-circuit temperature sensors, whose output voltage is linearly proportional to the Celsius (Centigrade) temperature.
LM35 Sensor Specification:
The LM35 series are precision integrated-circuit LM35 temperature sensors, whose output voltage is linearly proportional to the Celsius (Centigrade) temperature. The LM35 sensor thus has an advantage over linear temperature sensors calibrated in ° Kelvin, as the user is not required to subtract a large constant voltage from its output to obtain convenient Centigrade scaling. The LM35 sensor does not require any external calibration or trimming to provide typical accuracies of ±¼°C at room temperature and ±¾°C over a full -55 to +150°C temperature range. Low cost is assured by trimming and calibration at the wafer level. The LM35's low output impedance, linear output, and precise inherent calibration make interfacing to readout or control circuitry especially easy. It can be used with single power supplies, or with plus and minus supplies. As it draws only 60 µA from its supply, it has very low self-heating, less than 0.1°C in still air. The LM35 is rated to operate over a -55° to +150°C temperature range, while the LM35C sensor is rated for a -40° to +110°C range (-10° with improved accuracy). The LM35 series is available packaged in hermetic TO-46 transistor packages, while the LM35C, LM35CA, and LM35D are also available in the plastic TO-92 transistor package. The LM35D sensor is also available in an 8-lead surface mount small outline package and a plastic TO-220 package.
LM35 Sensor Circuit Schematic
LM35 Sensor Pinouts and Packaging
LM35 Sensor Sources
There are several manufacturers of this popular part and each has LM35 sensor specs, datasheets and other free LM35 downloads. This amplifier is available from the following manufacturers.
LM35 Sensor Background and Applications
Most commonly-used electrical temperature sensors are difficult to apply. For example, thermocouples have low output levels and require cold junction compensation. Thermistors are nonlinear. In addition, the outputs of these sensors are not linearly proportional to any temperature scale. Early monolithic sensors, such as the LM3911, LM134 and LM135, overcame many of these difficulties, but their outputs are related to the Kelvin temperature scale rather than the more popular Celsius and Fahrenheit scales. Fortunately, in 1983 two I.C.’s, the LM34 Precision Fahrenheit Temperature Sensor and the LM35 Precision Celsius Temperature Sensor, were introduced. This application note will discuss the LM34, but with the proper scaling factors can easily be adapted to the LM35. The LM35/LM34 has an output of 10 mV/°F with a typical nonlinearity of only ±0.35°F over a −50 to +300°F temperature range, and is accurate to within ±0.4°F typically at room temperature (77°F). The LM34’s low output impedance and linear output characteristic make interfacing with readout or control circuitry easy. An inherent strength of the LM34 sensor over other currently available temperature sensors is that it is not as susceptible to large errors in its output from low level leakage currents. For instance, many monolithic temperature sensors have an output of only 1 μA/°K. This leads to a 1°K error for only 1 μ-Ampere of leakage current. On the other hand, the LM34 sensor may be operated as a current mode device providing 20 μA/°F of output current. The same 1 μA of leakage current will cause an error in the LM34’s output of only 0.05°F (or 0.03°K after scaling). Low cost and high accuracy are maintained by performing trimming and calibration procedures at the wafer level. The device may be operated with either single or dual supplies. With less than 70 μA of current drain, the LM34 sensor has very little selfheating (less than 0.2°F in still air), and comes in a TO-46 metal can package, a SO-8 small outline package and a TO-92 plastic package.
The LM35/LM34 is a versatile device which may be used for a wide variety of applications, including oven controllers and remote temperature sensing. The device is easy to use (there are only three terminals) and will be within 0.02°F of a surface to which it is either glued or cemented. The TO-46 package allows the user to solder the sensor to a metal surface, but in doing so, the GND pin will be at the same potential as that metal. For applications where a steady reading is desired despite small changes in temperature, the user can solder the TO-46 package to a thermal mass. Conversely, the thermal time constant may be decreased to speed up response time by soldering the sensor to a small heat fin
4.8 HUMIDITY SENSORS
A humidity sensor, also called a hygrometer, measures and regularly reports the relative humidity in the air. They may be used in homes for people with illnesses affected by humidity; as part of home heating, ventilating, and air conditioning (HVAC) systems; and in humidors or wine cellars. Humidity sensors can also be used in cars, office and industrial HVAC systems, and in meteorology stations to report and predict weather.
A humidity sensor senses relative humidity. This means that it measures both air temperature and moisture. Relative humidity, expressed as a percent, is the ratio of actual moisture in the air to the highest amount of moisture air at that temperature can hold. The warmer the air is, the more moisture it can hold, so relative humidity changes with fluctuations in temperature.
The most common type of humidity sensor uses what is called “capacitive measurement.” This system relies on electrical capacitance, or the ability of two nearby electrical conductors to create an electrical field between them. The sensor itself is composed of two metal plates with a non-conductive polymer film between them. The film collects moisture from the air, and the moisture causes minute changes in the voltage between the two plates. The changes in voltage are converted into digital readings showing the amount of moisture in the air. A person with a respiratory illness or certain allergies might use a home humidity sensor because low humidity can exacerbate breathing problems and cause joint pain, while high humidity encourages bacteria, mold, and fungus growth. Home humidors and wine cellars often have a humidity sensor that helps to maintain a consistent relative humidity optimal to safe long-term storage. Humidity sensors can also be used in homes or museums where valuable antiques or artwork are kept, because these items can be damaged or degraded from constant exposure to too much moisture.
CHAPTER 5
5.1 ADVANTAGES OF SCADA SYSTEM
1. SCADA can continue operating even when telecommunication are temporarily lost. 2. SCADA systems allow a smaller number of operators to control a large number of individual assets. 3. SCADA systems were designed to be used on large scale systems with remote assets over a very large geographical area. 4. SCADA system improves operation, maintenance and customer service and provides rapid response to emergencies. 5. It provides a high level of system reliability and availability. 6. The SCADA system can record and store a very large amount of data. 7. The data can be displayed in any way the user require. 8. Thousands of sensors over a wide area can be connected to the system. 9. The data can be viewed from anywhere, not just on site.
5.2 DISADVANTAGES
1. SCADA system works only when there is gsm signal coverage that is when there is no signal the system does not work. 2. This system is more complicated because it has controlling unit. 3. With thousands of sensors there is a lot of wire to deal with the system.
5.3 APPLICATIONS
1. Cold storage application. 2. Industry applications (glass industry). 3. Incubator industries. 4. Food processing. 5. Steel manufacturing.
6. Plant machinery maintenance.
CHAPTER 6
CONCLUSION
The project “GSM BASED SCADA” has been successfully designed and tested. Integrating features of all the hardware components used have developed it. Presence of every module has been reasoned out and placed carefully thus contributing to the best working of the unit. Secondly, using highly advanced IC’s and with the help of growing technology the project has been successfully implemented.
REFERENCES
BOOKS
1 2 3
Mohd. Mazidi,PHI, 8051-Microcontroller and Embedded System.2000 David .E. Simon, Embedded Software Primer, Pearson publishers.2005 Shahin farahani, Gsm Wireless Networks.
WEBSITES www.ref.web.cern.ch/ref/CERN/CNL/2002/003/scada/ www.princeton-indiana.com/wastewater/pages/scada/scada-overview.html www.scadanews.com www.sss-mag.com/scada.html www.scada.com
DATA ACQUISITION SYSTEMS
1.1 Data Acquisition Data acquisition is the practice of collecting and storing data from sensors or other measurements equipment. Technically, data acquisition techniques could include manual monitoring and recording methods, such as visually inspecting a device or measuring an object, but it generally refers to the use of electronic sensors and data collection equipment. Data acquisition systems abbreviated with the acronym DAS typically convert analog waveforms into digital values for processing. Data acquisition is the process of retrieving control information from the equipment which is out of order or may lead to some problem or when decisions are need to be taken according to the situation in the equipment. So this acquisition is done by continuous monitoring of the equipment to which it is employed. 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 flow meter, ammeter, etc. It can also be data to control equipment such as actuators, relays, valves, motors, etc.
1.2 Evolution of Data Acquisition Equipment
Earlier data was often recorded on paper. Strip chart recorders and plotters would take an input signal and convert that signal to the one or two dimensional motion of a pen on a sheet or roll of paper. It was up to the operator to calibrate the scale of the output recordings on the graphs to accurately reflect the behavior being monitored. The next generation of data acquisition equipment included data loggers, which were electronic systems that could store electronic from connected sensors and then either replay that data later via a paper chart recorder or by connection to a computer, such as a serial cable. Some dataloggers evolved to include floppy drives so data could be recorded to a floppy disk then transferred to a computer.
Fig 1.1: Temperature, humidity, pressure data acquisition system Finally, the advent of computer and controller-based data acquisition allowed users to perform complex measurements and to store and retrieve data electronically. Data acquisition hardware was originally purely analog, requiring an analog-to-digital converter so the data could be stored digitally. Today, many data acquisition systems have the hardware to process signals. However, most sensors still function on a purely analog basis, so analog hardware capabilities are not expected to disappear anytime soon. Today’s real time data acquisition systems are much simpler and are efficient and work throughout the process and also eliminate the need for strip charts etc.
1.3 Components of data acquisition systems
The components of data acquisition systems include:
Sensors that convert physical parameters to electrical signals. Signal conditioning circuitry to convert sensor signals into a form that can be Analog-to-digital converters, which convert conditioned sensor signals to digital
converted to digital values.
values. It begins with the physical phenomenon or physical property to be measured. Examples of this include temperature, light intensity, gas pressure, fluid flow, and force. Regardless of the type of physical property to be measured, the physical state that is to be measured
must first be transformed into a unified form that can be sampled by a data acquisition system. The task of performing such transformations falls on devices called sensors. A sensor, which is a type of transducer, is a device that converts a physical property into a corresponding electrical signal (e.g., a voltage or current) or, in many cases, into a corresponding electrical characteristic (e.g., resistance or capacitance) that can easily be converted to electrical signal. The ability of a data acquisition system to measure differing properties depends on having sensors that are suited to detect the various properties to be measured. There are specific sensors for many different applications. DAQ systems also employ various signal conditioning techniques to adequately modify various different electrical signals into voltage that can then be digitized using an Analog-to-digital converter (ADC). Data acquisition hardware often contains multiple components (multiplexer, ADC, DAC, TTL-IO, high speed timers, RAM). These are accessible via a bus by a microcontroller, which can run small programs. A controller is more flexible than a hard wired logic. Many times reconfigurable logic is used to achieve high speed for specific tasks and are used after the data has been acquired to obtain some results. The fixed connection with the PC allows for comfortable compilation and debugging. Using an external housing a modular design with slots in a bus can grow with the needs of the user. Through the process of data acquisition we are able to monitor the parameters present in an industry, pharmaceutical company or domestic home environment. There are many parameters like temperature, humidity, light intensity etc. the sensors present in the data acquisition systems help in doing so. Since these parameters have to be monitored in a regular basis there arises a need for establishing an automatic controlling system. 1.4 AUTOMATION Automation is the use of control systems and information technologies to reduce the need for human work in the production of goods and services. In the scope of industrialization, automation is a step beyond mechanization. Whereas mechanization provided human operators with machinery to assist them with the muscular requirements of work, automation greatly decreases the need for human sensory and mental
requirements as well. Automation plays an increasingly important role in the world economy and in daily experience. Automation has had a notable impact in a wide range of industries beyond manufacturing (where it began). Once-ubiquitous telephone operators have been replaced largely by automated telephone switchboards and answering machines. Automated teller machines have reduced the need for bank visits to obtain cash and carry out transactions. The main advantages of automation are:
1 2
Replacing human operators in tasks that involve hard physical or monotonous work. Replacing humans in tasks done in dangerous environments (i.e. fire, space, volcanoes, nuclear facilities, underwater, etc.) Performing tasks that are beyond human capabilities of size, weight, speed, endurance, etc. Economy improvement. Automation may improve in economy of enterprises, society or most of humanity. Wireless communication has become an important feature for commercial products and a popular research topic within the last ten years. There are now more mobile phone subscriptions than wired-line subscriptions. Lately, one area of commercial interest has been low-cost, low-power, and short-distance wireless communication used for \personal wireless networks." Technology advancements are providing smaller and more cost effective devices for integrating computational processing, wireless communication, and a host of other functionalities. These embedded communications devices will be integrated into applications ranging from homeland security to industry automation and monitoring. They will also enable custom tailored engineering solutions, creating a revolutionary way of disseminating and processing information. With new technologies and devices come new business activities, and the need for employees in these technological areas. Engineers who have knowledge of embedded systems and wireless communications will be in high demand. Unfortunately, there are few adorable environments available for
3
4
development and classroom use, so students often do not learn about these technologies during hands-on lab exercises. The communication mediums were twisted pair, optical fiber, infrared, and generally wireless radio. The use of wireless automated data acquisition systems help in maintaining a coordinated environment in the industry or at homes. Thus the advent of the data acquisition and control systems are very advantageous and enduring in the long run.
CHAPTER 2
SCADA
SCADA is an acronym that stands for Supervisory Control and Data Acquisition. SCADA refers to a system that collects data from various sensors at a factory, plant or in other remote locations and then sends this data to a central computer which then manages and controls the data. SCADA is a term that is used broadly to portray control and management solutions in a wide range of industries. Some of the industries where SCADA is used are Water Management Systems, Electric Power, Traffic Signals, Mass Transit Systems, Environmental Control Systems, and manufacturing systems. 2.1 SCADA as a System 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.
•
•
•
There are many parts of a working SCADA system. A SCADA system usually includes signal hardware (input and output), controllers, networks, user interface (HMI), communications equipment and software. All together, the term SCADA refers to the entire central system. The central system usually monitors data from various sensors that are either in close proximity or off site (sometimes miles away). For the most part, the brains of a SCADA system are performed by the Remote Terminal Units (sometimes referred to as the RTU). The Remote Terminal Units consists of a programmable logic converter. The RTU are usually set to specific requirements, however, most RTU allow human intervention, for instance, in a factory setting, the RTU might control the setting of a conveyer belt, and the speed can be changed or overridden at any time by human intervention. In addition, any changes or errors are usually automatically logged for and/or displayed. Most often, a SCADA system will monitor and make slight changes to function optimally; SCADA systems are considered closed loop systems and run with relatively little human intervention. One of key processes of SCADA is the ability to monitor an entire system in real time. This is facilitated by data acquisitions including meter reading, checking statuses of sensors, etc that are communicated at regular intervals depending on the system. Besides the data being used by the RTU, it is also displayed to a human that is able to interface with the system to override settings or make changes when necessary. SCADA can be seen as a system with many data elements called points. Usually each point is a monitor or sensor. Usually points can be either hard or soft. A hard data point can be an actual monitor; a soft point can be seen as an application or software calculation. Data elements from hard and soft points are usually always recorded and logged to create a time stamp or history
2.2 User Interface (HMI)
A SCADA system includes a user interface, usually called Human Machine Interface (HMI). The HMI of a SCADA system is where data is processed and presented to be viewed and monitored by a human operator. This interface usually includes controls
where the individual can interface with the SCADA system. HMI's are an easy way to standardize the facilitation of monitoring multiple RTU's or PLC's (programmable logic controllers). Usually RTU's or PLC's will run a pre programmed process, but monitoring each of them individually can be difficult, usually because they are spread out over the system. Because RTU's and PLC's historically had no standardized method to display or present data to an operator, the SCADA system communicates with PLC's throughout the system network and processes information that is easily disseminated by the HMI. HMI's can also be linked to a database, which can use data gathered from PLC's or RTU's to provide graphs on trends, logistic info, schematics for a specific sensor or machine or even make troubleshooting guides accessible. In the last decade, practically all SCADA systems include an integrated HMI and PLC device making it extremely easy to run and monitor a SCADA system.
2.3 Remote Terminal Unit
The RTU connects to physical equipment. Typically, an RTU converts the electrical signals from the equipment to digital values such as the open/closed status from a switch or a valve, or measurements such as pressure, flow, voltage or current. By converting and sending these electrical signals out to equipment the RTU can control equipment, such as opening or closing a switch or a valve, or setting the speed of a pump. The RTU can read digital status data or analogue measurement data, and send out digital commands or analogue set points. The term SCADA usually refers to centralized systems which monitor and control entire sites, or complexes of systems spread out over large areas (anything between an industrial plant and a country). Most control actions are performed automatically by remote terminal units ("RTUs") or by programmable logic controllers ("PLCs"). Host control functions are usually restricted to basic overriding or supervisory level intervention. For example, a PLC may control the flow of cooling water through part of an industrial process, but the SCADA system may allow operators to change the set points for the flow and enable alarm conditions, such as loss of flow and high temperature, to be displayed
and recorded. The feedback control loop passes through the RTU or PLC, while the SCADA system monitors the overall performance of the loop.
A SCADA system could be programmed to:
• • • • • •
monitor high and low levels in the day tanks, fill them when a certain level is reached, calculated and store the volume used, monitor the level in the main feed tank, Alarm when a certain level is reached to notify purchasing (or send an e-mail), Plot the usage of chemicals vs time, process, or any other parameter.
CHAPTER 3
SCADA SYSTEM OPERATION
SCADA stands for Supervisory Control and Data Acquisition. As the name indicates, it is a control system which focuses on the supervisory level. The power supply initiates the functions of data acquisition systems. The power supply consists of a step down transformer which produces a voltage of nearly 9V at its secondary winding. The 9V is presented to a bridge rectifier which produces an unregulated DC voltage and with the help of two linear voltage regulators we obtain voltages 5V and 12V at their outputs respectively. The voltages produced at the regulators are used by the different components like the Microcontroller, Sensors, Relays, Modem and ADC Converter. The relays and GSM modem use 12V where as the microcontroller; sensors and the LCD module utilize 5V. The microcontroller is AT89S52 is used to perform and co-ordinate all the operations in the data acquisition process. The LCD module is used to display the status of the acquisition systems. A pair of relays are used which are used to perform the switching operations during the occurrence of the constraints set. A relay is used to maintain the functions a bulb, representing the heat producing component and the other relay for activating the DC motor for meeting the counter active effect. A ULN2003 IC is used to interface voltages with the relays used by acting as the microcontroller driver for the relays. An ADC0808 is also used so as to provide analog to digital conversion which is mainly useful for the functioning of the sensor modules which understand the analog form of signal. Before discussing the functionality of the GSM modem, the knowledge about MAX232 block would help in understanding. The MAX232 IC is used for voltage conversions between the TTL and the RS232 voltages, which can be best understood by the microcontroller and the GSM modem respectively. There are two sensors which are the LM35 and humidity sensors which are used for detecting the environment of a particular
chamber or a space. So, using these components we are able to acquire data which helps in the controlling of the real time alterations in the environment of a particular enclosure by enabling the counter measures. GSM modem contains a subscriber identification module (SIM), which is present in the supervisor’s handset. The GSM modem is used to intimate the user about the data regarding the temperature and the humidity of the chamber in the industrial plant. The working of SCADA can be understood in two stages. They are: 1. Data Acquisition stage. 2. Data controlling stage.
3.1 Data Acquisition stage In the data acquisition stage the information regarding the temperature and the humidity is obtained on the LCD module. The heat in the chamber is allowed to vary based on its natural course. The sensors help in retrieving the status of the chamber in the plant that is they display the temperature and the humidity When the temperature of a certain area increases over a predefined level, an information via a message is sent continuously till a message is replied back informing a code which activates the counter measure to decrease the temperature of the chamber. Incorporating different sensors help in monitoring different factors whose increase or decrease affects the performance. An additional way of checking is done by giving a missed call to the GSM module which replies the specifications through a message to the inquirer. The SCADA forms the basis of many real time applications in different fields of security, medicine and various other data acquisition fields. Explaining the Data Acquisition in more detail, the outputs of the sensors are linear to variation in input. Hence as temperature increases their outpu also increases. The outputs of the sensors are given to the ADC 0808 for conversion to digital output, which is
understood by microcontroller. The outputs of ADC is given to microcontroller port 0. The port 1 pins help in display in the temperature in LCD module 3.2 Data Controlling Stage When the temperature increases above a certain level the microcontroller activates the MAX 232 block and communicates with the GSM modem. The GSM modem then sends the messages stating the conditions of the temperature rise. The supervisor then sends the message to initiate the counter measure to the GSM modem module. This activates the cooler fan to reduce the temperature of the chamber. The humidity of the chamber is just monitored time to time. This covers the controlling part of SCADA.
CHAPTER 4
HARDWARE REQUIREMENTS
1. AT89S52 MICROCONTROLLER 2. MAX232. 3. RELAYS. 4. LCD DISPLAY.
5. ADC0808. 6. AC DEVICES. 7. ULN2003. 8. GSM MODEM
4.1 AT89S52:
The AT89S52 is a low-power, high-performance CMOS 8-bit microcontroller with 8K bytes of in-system programmable Flash memory. The device is manufactured using Atmel’s high-density nonvolatile memory technology and is compatible with the industry-standard 80C51 instruction set and pinout. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory pro-grammer. By combining a versatile 8-bit CPU with in-system programmable Flash on a monolithic chip, the Atmel AT89S52 is a powerful microcontroller, which provides a highly flexible and cost-effective solution to many, embedded control applications. The AT89S52 provides the following standard features: 8K bytes of Flash, 256 bytes of RAM, 32 I/O lines, Watchdog timer, two data pointers, three 16-bit timer/counters, a six-vector two-level interrupt architecture, a full duplex serial port, onchip oscillator, and clock circuitry. In addition, the AT89S52 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port, and interrupt system to continue functioning. The Power-down mode saves the RAM con-tents but freezes the oscillator, disabling all other chip functions until the next interrupt
4.2 POWER SUPPLY
All digital circuits require regulated power supply. In this article we are going to learn how to get a regulated positive supply from the mains supply.
Fig 4.1 shows the basic block diagram of a fixed regulated power supply. 4.2.1 Rectifier A rectifier is a device that converts an AC signal into DC signal. For rectification purpose we use a diode, a diode is a device that allows current to pass only in one direction i.e. when the anode of the diode is positive with respect to the cathode also called as forward biased condition & blocks current in the reversed biased condition.A Voltage regulator is a device which converts varying input voltage into a constant regulated output voltage 4.3 GSM Technology GSM Global System for Mobile communications is an open, digital cellular technology used for transmitting mobile voice and data services.GSM supports voice calls and data transfer speeds of up to 9.6 kbit/s, together with the transmission of SMS (Short Message Service). GSM operates in the 900MHz and 1.8GHz Frequency bands. 4.3.1 ARCHITECTURE AND BULDING BLOCKS OF GSM
The GSM specifications define two truly open interfaces within the GSM network. The first one is between the Mobile Station (MS) and the Base Station (BS). This open-air interface is appropriately named the “air interface”
GSM is mainly built on three building blocks: 4.3.1.1 Mobile Station (MS) The MS (mobile station) is a combination of terminal equipment and subscriber data. The terminal equipment such as is called ME (mobile equipment) and the subscriber’s data is stored in a separate module called ME+SIM=MS. Mobile Equipment (ME) Subscriber Identity Module (SIM) The GSM network is divided into three subsystems: network switching subsystem(NSS), Base station subsystem(BSS), and Network Management Subsystem (NMs). The three subsystems, different network elements, and their respective tasks. 4.3.1.2 Network Switching Subsystem (NSS) SIM(subscriber identity module) Therefore
The Network Switching Subsystem (NSS) contains the network elements. Mobile Switching Center (MSC) Home Location Register (HLR) Visitor Location Register (VLR) Authentication Center (AUC) Equipment Identity Register (EIR)
The main functions of NSS are: • • • • •
Call control Charging Mobility management Signalling Subscriber data handling
Mobile services Switching Centre (MSC) The MSC is responsible for controlling calls in the mobile network. It identifies the origin and destination of a call (mobile station or fixed telephone), as well as the type of a call. An MSC acting as a bridge between a mobile network and a fixed network is called a Gateway MSC. The MSC is responsible for several important tasks, such as the following. Call control Initiation of paging Charging data collection
Visitor Location Register (VLR) MSC. VLR is a database which contains information about subscribers currently being in the service area of The MSC/VLR, such as: • • • Identification numbers of the subscribers Security information for authentication of the SIM card and for ciphering Services that the subscriber can use
Home Location Register (HLR) HLR maintains a permanent register of the subscribers, for instance subscriber identity numbers and the subscribed services. In addition to the fixed data, the HLR also keeps track of the current location of its customers. As you will see later, the MSC asks for routing information from the HLR if a call is to be set up to a mobile station (mobile terminated call). In the Nokia implementation, the two network elements, Authentication Centre (AC) and Equipment Identity Register (EIR), are located in the HLR.
Base Station Subsystem (BSS)
The Base station subsystem is responsible for managing the radio network, and it is controlled by an MSC. One MSC contains several BSS’s. A BSS itself may cover a considerably large geographical area consisting of many cells. The BSS consists of the following elements: • • • BSC BTS TC Base Station Controller Base Transceiver Station Transcoder
Base Station Controller ( BSC) The BSC is the central network element of the BSS and it controls the radio network. It has several important tasks. They are • • • • • Connection establishment Mobility management Statistical raw data collection Air and A interface signaling support BTS and TC control
Base Transceiver Station (BTS) The BTS is the network element responsible for maintaining the air interface and minimizing the transmission problems (the air interface is very sensitive for distturbancees).
4.3.1.3 Network Management Subsystem (NMS)
The Network Management Subsystem (NMS) is the third subsystem of the GSM network in addition to the Network Switching Subsystem (NSS) and Base Station Subsystem (BSS). The purpose of the NMS is to monitor various functions and elementsof the network .
4.4 MAX232
The MAX232 is an integrated circuit that converts signals from an RS-232 serial port to signals suitable for use in TTL compatible digital logic circuits. The drivers provide RS-232 voltage level outputs (approx. ± 7.5 V) from a single + 5 V supply via on-chip charge pumps and external capacitors. This makes it useful for implementing RS-232 in devices that otherwise do not need any voltages outside the 0 V to + 5 V range, as power supply design does not need to be made more complicated just for driving the RS-232. The receivers reduce RS-232 inputs (which may be as high as ± 25 V), to standard 5 V TTL levels. These receivers have a typical threshold of 1.3 V, and a typical hysteresis of 0.5 V. The later MAX232A is backwards compatible with the original MAX232 but may operate at higher baud rates and can use smaller external capacitors – 0.1 μF in place of the 1.0 μF capacitors used with the original device. RS-232 Voltage levels • •
•
+3 to +25 volts to signify a "Space" (Logic 0) -3 to -25 volts for a "Mark" (logic 1). Any voltage in between these regions (i.e. between +3 and -3 Volts) is undefined. The data byte is always transmitted least-significant-bit first. The bits are transmitted at specific time intervals determined by the baud rate
of the serial signal. This is the signal present on the RS-232 Port of your computer, shown below.
RS-232 Logic Waveform
4.4.1 RS-232 LEVEL CONVERTER Standard serial interfacing of microcontroller (TTL) with PC or any RS232C Standard device , requires TTL to RS232 Level converter . A MAX232 is used for this purpose. It provides 2-channel RS232C port and requires external 10uF capacitors. The driver requires a single supply of +5V.
MAX-232 includes a Charge Pump, which generates +10V and -10V from a single 5v supply. 4.4.2 Serial communication When a processor communicates with the outside world, it provides data in byte sized chunks. Computers transfer data in two ways: parallel and serial. In parallel data transfers, often more lines are used to transfer data to a device and 8 bit data path is expensive. The serial communication transfer uses only a single data line instead of the 8 bit data line of parallel communication which makes the data transfer not only cheaper but also makes it possible for two computers located in two different cities to communicate over telephone.
Serial data communication uses two methods, asynchronous and synchronous. The synchronous method transfers data at a time while the asynchronous transfers a single byte at a time. There are some special IC chips made by many manufacturers for data communications. These chips are commonly referred to as UART (universal asynchronous receiver-transmitter) and USART (universal synchronous asynchronous receiver transmitter). The AT89C51 chip has a built in UART. In asynchronous method, each character is placed between start and stop bits. This is called framing. In data framing of asynchronous communications, the data, such as ASCII characters, are packed in between a start and stop bit. We have a total of 10 bits for a character: 8 bits for the ASCII code and 1 bit each for the start and stop bits. The rate of serial data transfer communication is stated in bps or it can be called as baud rate. To allow the compatibility among data communication equipment made by various manufacturers, and interfacing standard called RS232 was set by the Electronics industries Association in 1960. Today RS232 is the most widely used I/O interfacing standard. This standard is used in PCs and numerous types of equipment. However, since the standard was set long before the advent of the TTL logic family, its input and output voltage levels are not TTL compatible. In RS232, a 1 bit is represented by -3 to -25V, while a 0 bit is represented +3 to +25 V, making -3 to +3 undefined. For this reason, to connect any RS232 to a microcontroller system we must use voltage converters such as MAX232 to connect the TTL logic levels to RS232 voltage levels and vice versa. MAX232 ICs are commonly referred to as line drivers.
The simplest connection between a PC and microcontroller requires a minimum of three pin, TXD, RXD, and ground. Many of the pins of the RS232 connector are used for handshaking signals. Here four external 10µf capacitors for removing any voltage variations. RXD and TXD pins of microcontroller are connected to Tx and Rx of MAX 232 for serial communication. The nine pin connector RS 232 is used to connect the GSM modem to MAX 232 thereby enabling connection between the two.
4.5 LCD MODULE
To display interactive messages we are using LCD Module. We examine an intelligent LCD display of two lines,16 characters per line that is interfaced to the controllers. The protocol (handshaking) for the display is as shown. Whereas D0 to D7th bit is the Data lines, RS, RW and EN pins are the control pins and remaining pins are +5V, -5V and GND to provide supply. Where RS is the Register Select, RW is the Read Write and EN is the Enable pin. The display contains two internal byte-wide registers, one for commands (RS=0) and the second for characters to be displayed (RS=1). It also contains a user-programmed RAM area (the character RAM) that can be programmed to generate any desired character that can be formed using a dot matrix. To distinguish between these two data areas, the hex command byte 80 will be used to signify that the display RAM address 00h will be chosen.Port1 is used to furnish the command or data type, and ports 3.2 to3.4 furnish register select and read/write levels. The display takes varying amounts of time to accomplish the functions as listed. LCD bit 7 is monitored for logic high (busy) to ensure the display is overwritten. Liquid Crystal Display also called as LCD is very helpful in providing user interface as well as for debugging purpose. The most common type of LCD controller is HITACHI 44780 which provides a simple interface between the controller & an LCD. These LCD's are very simple to interface with the controller as well as are cost effective.
2x16 Line Alphanumeric LCD Display The most commonly used ALPHANUMERIC displays are 1x16 (Single Line & 16 characters), 2x16 (Double Line & 16 character per line) & 4x20 (four lines & Twenty characters per line). The LCD requires 3 control lines (RS, R/W & EN) & 8 (or 4) data lines. The number on data lines depends on the mode of operation. If operated in 8-bit mode then 8 data lines + 3 control lines i.e. total 11 lines are required. And if operated in 4-bit mode then 4 data lines + 3 control lines i.e. 7 lines are required. How do we decide which mode to use? It’s simple if you have sufficient data lines you can go for 8 bit mode & if there is a time constrain i.e. display should be faster then we have to use 8-bit mode because basically 4-bit mode takes twice as more time as compared to 8-bit mode.
Pin 1 2 3 4 5 6 7-14 15 16 Symbol Vss Vdd Vo RS R/W En DB0-DB7 A/Vee K Function Ground Supply Voltage Contrast Setting Register Select Read/Write Select Chip Enable Signal Data Lines Gnd for the backlight Vcc for backlight
When RS is low (0), the data is to be treated as a command. When RS is high (1), the data being sent is considered as text data which should be displayed on the screen. When R/W is low (0), the information on the data bus is being written to the LCD. When RW is high (1), the program is effectively reading from the LCD. Most of the times there is no need to read from the LCD so this line can directly be connected to Gnd thus saving one controller line. The ENABLE pin is used to latch the data present on the data pins. A HIGH - LOW signal is required to latch the data. The LCD interprets and executes our command at the instant the EN line is brought low. If you never bring EN low, your instruction will never be executed.
4.6 ADC0808
The ADC0808, ADC0809 data acquisition component is a monolithic CMOS device with an 8-bit analog-to-digital converter, 8-channel multiplexer and microprocessor compatible control logic. The 8-bit A/D converter uses successive approximation as the conversion technique. The converter features a high impedance chopper stabilized comparator, a 256R voltage divider with analog switch tree and a successive approximation register. The 8-channel multiplexer can directly access any of 8-single-ended analog signals. The device eliminates the need for external zero and fullscale adjustments. Easy interfacing to microprocessors is provided by the latched and decoded multiplexer address inputs and latched TTL TRI-STATE outputs. The design of the ADC0808, ADC0809 has been optimized by incorporating the most desirable aspects of several A/D conversion techniques. The ADC0808, ADC0809 offers high speed, high accuracy, minimal temperature dependence, excellent long-term accuracy and repeatability, and consumes minimal power. These features make this device ideally suited to applications from process and machine control to consumer and automotive applications. For 16-channel multiplexer with common output (sample/hold port) see ADC0816 data sheet.
4.7 TEMPERATURE SENSOR (LM35)
The LM35 sensor series are precision integrated-circuit temperature sensors, whose output voltage is linearly proportional to the Celsius (Centigrade) temperature.
LM35 Sensor Specification:
The LM35 series are precision integrated-circuit LM35 temperature sensors, whose output voltage is linearly proportional to the Celsius (Centigrade) temperature. The LM35 sensor thus has an advantage over linear temperature sensors calibrated in ° Kelvin, as the user is not required to subtract a large constant voltage from its output to obtain convenient Centigrade scaling. The LM35 sensor does not require any external calibration or trimming to provide typical accuracies of ±¼°C at room temperature and ±¾°C over a full -55 to +150°C temperature range. Low cost is assured by trimming and calibration at the wafer level. The LM35's low output impedance, linear output, and precise inherent calibration make interfacing to readout or control circuitry especially easy. It can be used with single power supplies, or with plus and minus supplies. As it draws only 60 µA from its supply, it has very low self-heating, less than 0.1°C in still air. The LM35 is rated to operate over a -55° to +150°C temperature range, while the LM35C sensor is rated for a -40° to +110°C range (-10° with improved accuracy). The LM35 series is available packaged in hermetic TO-46 transistor packages, while the LM35C, LM35CA, and LM35D are also available in the plastic TO-92 transistor package. The LM35D sensor is also available in an 8-lead surface mount small outline package and a plastic TO-220 package.
LM35 Sensor Circuit Schematic
LM35 Sensor Pinouts and Packaging
LM35 Sensor Sources
There are several manufacturers of this popular part and each has LM35 sensor specs, datasheets and other free LM35 downloads. This amplifier is available from the following manufacturers.
LM35 Sensor Background and Applications
Most commonly-used electrical temperature sensors are difficult to apply. For example, thermocouples have low output levels and require cold junction compensation. Thermistors are nonlinear. In addition, the outputs of these sensors are not linearly proportional to any temperature scale. Early monolithic sensors, such as the LM3911, LM134 and LM135, overcame many of these difficulties, but their outputs are related to the Kelvin temperature scale rather than the more popular Celsius and Fahrenheit scales. Fortunately, in 1983 two I.C.’s, the LM34 Precision Fahrenheit Temperature Sensor and the LM35 Precision Celsius Temperature Sensor, were introduced. This application note will discuss the LM34, but with the proper scaling factors can easily be adapted to the LM35. The LM35/LM34 has an output of 10 mV/°F with a typical nonlinearity of only ±0.35°F over a −50 to +300°F temperature range, and is accurate to within ±0.4°F typically at room temperature (77°F). The LM34’s low output impedance and linear output characteristic make interfacing with readout or control circuitry easy. An inherent strength of the LM34 sensor over other currently available temperature sensors is that it is not as susceptible to large errors in its output from low level leakage currents. For instance, many monolithic temperature sensors have an output of only 1 μA/°K. This leads to a 1°K error for only 1 μ-Ampere of leakage current. On the other hand, the LM34 sensor may be operated as a current mode device providing 20 μA/°F of output current. The same 1 μA of leakage current will cause an error in the LM34’s output of only 0.05°F (or 0.03°K after scaling). Low cost and high accuracy are maintained by performing trimming and calibration procedures at the wafer level. The device may be operated with either single or dual supplies. With less than 70 μA of current drain, the LM34 sensor has very little selfheating (less than 0.2°F in still air), and comes in a TO-46 metal can package, a SO-8 small outline package and a TO-92 plastic package.
The LM35/LM34 is a versatile device which may be used for a wide variety of applications, including oven controllers and remote temperature sensing. The device is easy to use (there are only three terminals) and will be within 0.02°F of a surface to which it is either glued or cemented. The TO-46 package allows the user to solder the sensor to a metal surface, but in doing so, the GND pin will be at the same potential as that metal. For applications where a steady reading is desired despite small changes in temperature, the user can solder the TO-46 package to a thermal mass. Conversely, the thermal time constant may be decreased to speed up response time by soldering the sensor to a small heat fin
4.8 HUMIDITY SENSORS
A humidity sensor, also called a hygrometer, measures and regularly reports the relative humidity in the air. They may be used in homes for people with illnesses affected by humidity; as part of home heating, ventilating, and air conditioning (HVAC) systems; and in humidors or wine cellars. Humidity sensors can also be used in cars, office and industrial HVAC systems, and in meteorology stations to report and predict weather.
A humidity sensor senses relative humidity. This means that it measures both air temperature and moisture. Relative humidity, expressed as a percent, is the ratio of actual moisture in the air to the highest amount of moisture air at that temperature can hold. The warmer the air is, the more moisture it can hold, so relative humidity changes with fluctuations in temperature.
The most common type of humidity sensor uses what is called “capacitive measurement.” This system relies on electrical capacitance, or the ability of two nearby electrical conductors to create an electrical field between them. The sensor itself is composed of two metal plates with a non-conductive polymer film between them. The film collects moisture from the air, and the moisture causes minute changes in the voltage between the two plates. The changes in voltage are converted into digital readings showing the amount of moisture in the air. A person with a respiratory illness or certain allergies might use a home humidity sensor because low humidity can exacerbate breathing problems and cause joint pain, while high humidity encourages bacteria, mold, and fungus growth. Home humidors and wine cellars often have a humidity sensor that helps to maintain a consistent relative humidity optimal to safe long-term storage. Humidity sensors can also be used in homes or museums where valuable antiques or artwork are kept, because these items can be damaged or degraded from constant exposure to too much moisture.
CHAPTER 5
5.1 ADVANTAGES OF SCADA SYSTEM
1. SCADA can continue operating even when telecommunication are temporarily lost. 2. SCADA systems allow a smaller number of operators to control a large number of individual assets. 3. SCADA systems were designed to be used on large scale systems with remote assets over a very large geographical area. 4. SCADA system improves operation, maintenance and customer service and provides rapid response to emergencies. 5. It provides a high level of system reliability and availability. 6. The SCADA system can record and store a very large amount of data. 7. The data can be displayed in any way the user require. 8. Thousands of sensors over a wide area can be connected to the system. 9. The data can be viewed from anywhere, not just on site.
5.2 DISADVANTAGES
1. SCADA system works only when there is gsm signal coverage that is when there is no signal the system does not work. 2. This system is more complicated because it has controlling unit. 3. With thousands of sensors there is a lot of wire to deal with the system.
5.3 APPLICATIONS
1. Cold storage application. 2. Industry applications (glass industry). 3. Incubator industries. 4. Food processing. 5. Steel manufacturing.
6. Plant machinery maintenance.
CHAPTER 6
CONCLUSION
The project “GSM BASED SCADA” has been successfully designed and tested. Integrating features of all the hardware components used have developed it. Presence of every module has been reasoned out and placed carefully thus contributing to the best working of the unit. Secondly, using highly advanced IC’s and with the help of growing technology the project has been successfully implemented.
REFERENCES
BOOKS
1 2 3
Mohd. Mazidi,PHI, 8051-Microcontroller and Embedded System.2000 David .E. Simon, Embedded Software Primer, Pearson publishers.2005 Shahin farahani, Gsm Wireless Networks.
WEBSITES www.ref.web.cern.ch/ref/CERN/CNL/2002/003/scada/ www.princeton-indiana.com/wastewater/pages/scada/scada-overview.html www.scadanews.com www.sss-mag.com/scada.html www.scada.com
