data acquisition system synopsis

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Chapter 1

Introduction


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1.1 INTRODUCTION

A data acquisition system is a collection of software and hardware that lets you measure or

control physical characteristics of something in the real world. A typical system consists of:

Data acquisition (DAQ) hardware

Sensors and actuators

Signal conditioning hardware

A computer runningDAQ software

Fig. 1 Typical data acquisition setup

Data acquisition is the process of sampling signals that measure real world physical conditions

and converting the resulting samples into digital numeric values that can be manipulated by a

computer. Data acquisition systems (abbreviated with the acronym DAS or DAQ) typically

convert analog waveforms into digital values for processing. 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 converted to

digital values.
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Analog-to-digital converters, which convert conditioned sensor signals to digital values.

Data acquisition applications are controlled by software programs developed using various

general purposeprogramming languages such asBASIC,C,Fortran,Java,Lisp,Pascal.

There are also open-source software packages providing all the necessary tools to acquire

data from different hardware equipment. These tools come from the scientific community where

complex experiment requires fast, flexible and adaptable software. Those packages are usually

custom fit but more general DAQ package like theMaximum Integrated Data Acquisition

System can be easily tailored and is used in several physics experiments worldwide.

In 1963, IBM produced computers which specialized in data acquisition. These include

theIBM 7700 Data Acquisition System and its successor, theIBM 1800 Data Acquisition and

Control System. These expensive specialized systems were surpassed in 1974 by general

purposeS-100 computers and data acquisitions cards produced byTecmar/Scientific Solutions

Inc. In 1981 IBM introduced theIBM Personal Computer and Scientific Solutions introduced the

first PC data acquisition products. Data acquisition begins with thephysical

phenomenon orphysical 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 calledsensors. A data acquisition system is a collection of software and

hardware that lets you measure or control physical characteristics of something in the real world.

A complete data acquisition system consists of DAQ hardware, sensors and actuators, signal

conditioning hardware, and a computer running DAQ software.

Asensor,which is a type oftransducer,is a device that converts a physical property into

a corresponding electrical signal (e.g.,strain gauge, thermistor). An acquisition system to

measure different properties depends on the sensors that are suited to detect those properties.

Signal conditioning may be necessary if the signal from the transducer is not suitable for the

DAQ hardware being used. The signal may need to be filtered or amplified in most cases.

Various other examples of signal conditioning might be bridge completion, providing current or

voltage excitation to the sensor, isolation, linearization. For transmission purposes,single
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endedanalog signals, which are more susceptible to noise can be converted todifferential

signals.Once digitized, the signal can be encoded to reduce and correct transmission errors.

1.2DAQ hardware

DAQ hardware is what usually interfaces between the signal and a PC.[6]It could be in the form

of modules that can be connected to the computer's ports (parallel,serial,USB, etc.) or cards

connected to slots (S-100 bus, AppleBus, ISA,MCA, PCI, PCI-E, etc.) in themotherboard.

Usually the space on the back of a PCI card is too small for all the connections needed, so an

externalbreakout box is required. The cable between this box and the PC can be expensive due

to the many wires, and the required shielding.

DAQ cards often contain multiple components (multiplexer, ADC, DAC, TTL-IO, high speed

timers, RAM). These are accessible via abusby amicrocontroller, which can run small

programs. A controller is more flexible than a hard wired logic, yet cheaper than a CPU so that it

is permissible to block it with simple polling loops. For example: Waiting for a trigger, starting

the ADC, looking up the time, waiting for the ADC to finish, move value to RAM, switch

multiplexer, get TTL input, let DAC proceed with voltage ramp.

1.3 DAQ device drivers

DAQ device drivers are needed in order for the DAQ hardware to work with a PC. The device

driver performs low-level register writes and reads on the hardware, while exposing API for

developing user applications in a variety of programming environments.
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Chapter 2

Block Diagram, Working & hardware

details


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2.1 Block diagram

MATLAB SOFTWARE

8051 MICROCONTROLLER

SENSOR

1

SENSOR

2

SENSOR

3

SENSOR

4

ADC 0808

MAX

232 IC

RELAY 1 RELAY 2


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2.2 Description:

The above fig is the block diagram of data acquisition and logging system depicts the

total blue print of the proposed project. The total essence and the functioning of the project is

represented in a single block diagram. The block diagram mainly consists of 8 parts. They

include

Power supply

LM35 Temperature sensor

ADC0808

AT89C51 Microcontroller

MAX 232

PC Relay

Relay driver

2.3 Power Supply:

The input to the circuit is applied from the regulated power supply. The a.c. input

i.e., 230V from the mains supply is step down by the transformer to 12V and is fed to a

rectifier. The output obtained from the rectifier is a pulsating d.c voltage. So in order to get a

pure d.c voltage, the output voltage from the rectifier is fed to a filter to remove any a.c

components present even after rectification. Now, this voltage is given to a voltage regulator

to obtain a pure constant dc voltage.

2.4 LM35 temperature sensor:

The LM35 series are precision integrated-circuit temperature sensors, whose output

voltage is linearly proportional to the Celsius (Centigrade) temperature. The LM35 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 does not require any external calibration or trimming to provide typical accuracies of

14Cat room temperature and 34C over a full 55 to +150Ctemperature range. Low cost is

assured by trimming and calibration at the wafer level.


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2.5 Analog to digital converter:

Analog-to-digital converters are among the most widely used devices for data

acquisition. Digital systems use binary values, but in the physical world everything is

continuous i.e., analog values. Temperature, pressure (wind or liquid), humidity and velocityare the physical analog quantities. These physical quantities are to be converted into digital

values for further processing. One such device to convert these physical quantities into

electrical signals is sensor.

2.6 AT89C51 Microcontroller:

Microprocessors and microcontrollers are widely used in embedded systems products.

Microcontroller is a programmable device. A microcontroller has a CPU in addition to a fixed

amount of RAM, ROM, I/O ports and a timer embedded all on a single chip. The fixed

amount of on-chip ROM, RAM and number of I/O ports in microcontrollers makes them ideal

for many applications in which cost and space are critical. The CPU can work on only 8 bits

of data at a time. Data larger than 8 bits has to be broken into 8-bit pieces to be processed by

the CPU. 8051 is available in different memory types such as UV-EPROM, Flash and NV-

RAM.

2.7 Max 232:

Max232 IC is a specialized circuit which makes standard voltages as required by RS232

standards. This IC provides best noise rejection and very reliable against discharges and short

circuits. MAX232 IC chips are commonly referred to as line drivers. To ensure data transfer

between PC and microcontroller, the baud rate and voltage levels of Microcontroller and PC

should be the same.

2.8 Relay:

A relay is anelectrically operatedswitch.Many relays use an electromagnet to operate a

switching mechanism mechanically, but other operating principles are also used. Relays are

used where it is necessary to control a circuit by a low-power signal (with complete electrical

isolation between control and controlled circuits), or where several circuits must be controlled

by one signal. The first relays were used in long distance telegraph circuits, repeating the
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signal coming in from one circuit and re-transmitting it to another. Relays were used

extensively in telephone exchanges and early computers to perform logical operations.

2.9 Relay driver:

The ULN2803 current driver is a high voltage, high current Darlington arrays each

containing seven open collector Darlington pairs with common emitters. Each channel is rated at

500mA and can withstand peak currents of 600mA. Suppression diodes are included for

inductive load driving and the inputs are pinned opposite the outputs to simplify board layout.

2.9 Working of Project:

This is a temperature logging System .The idea of this project is to retrieve the real

time data from the high temperature furnaces on computer. Four heat Sensors i.e., LM35 are

used to sense the heat and an IC ADC0808 is used to convert the data into digital.LM35

digital sensor has got 3 pins i.e., VCC, GND and output pins when LM35 is heated the

voltage at output pin increases, it is connected to the analog to digital convertor IC

(ADC).Then the values of all the sensors are sent serially by MC through Max 32 IC to the

Computer.

Now MC processes this data and communicates with computer via RS232

communication and simultaneously switches ON & OFF the relays. One can set by interactive

way some parameters like set point, low limit, and high limit on the computer screen. When

temperature of some sensors increases beyond set point, the MC sends commands to relay

driver IC ULN2803.The Max232 IC is used for RS232 communication and ULN2803 IC is

used for relay control. The heaters (lamps in the test board) connected through relay contacts

are (specific for that sensor) turned OFF (or ON in opposite case).When temperature goes

above high limit or below low limit the alarm will be turned on. Software is used for keeping

the real time records of heat sensors in computer. This software has a provision for eight

sensors but only four have been used here.


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Fig. Circuit Diagram, of the system


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2.10 SOFTWARE TOOLS

2.11 Keil Software:

Keil compiler is software used where the machine language code is written and

compiled. After compilation, the machine source code is converted into hex code which is to

be dumped into the microcontroller for further processing. Keil compiler also supports C

language code.

2.12 Proload:

Proload is software which accepts only hex files. Once the machine code is converted

into hex code, that hex code has to be dumped into the microcontroller and this is done by the

Proload. Proload is a programmer which itself contains a microcontroller in it other than the

one which is to be programmed. This microcontroller has a program in it written in such a

way that it accepts the hex file from the keil compiler and dumps this hex file into the

microcontroller which is to be programmed.

As the proload programmer kit requires power supply to be operated, this power supply is

given from the power supply circuit designed above. It should be noted that this programmer

kit contains a power supply section in the board itself but in order to switch on that power

supply, a source is required. Thus this is accomplished from the power supply board with an

output of 12volts.

2.13 Keil Compiler:

With the Keil tools, you can generate embedded applications for virtually every 8051

derivative. The supported microcontrollers are listed in the VisionDevice Database.The Keil

Software 8051 development tools are designed for the professional software developer, but any

level of programmer can use them to get the most out of the 8051 microcontroller

architecture.We are constantly adding new devices and simulation support for on-chip

peripherals so be sure to check web-basedDevice Databaseif your plan to use a device that is

currently not listed in your local Vision installation.

The Keil Software 8051 development tools listed below are programs you use to compile

your C code, assemble your assembly source files, link and locate object modules and libraries,

create HEX files, and debug your target program.
http://www.keil.com/ddhttp://www.keil.com/ddhttp://www.keil.com/ddhttp://www.keil.com/ddhttp://www.keil.com/ddhttp://www.keil.com/ddhttp://www.keil.com/ddhttp://www.keil.com/dd


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Vision is an Integrated Development Environment that combines project

management, source code editing, and program debugging in one single, powerful

environment.

The Cx51 ANSI Optimizing C Cross Compiler creates relocatable object modules

from


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Chapter 3

Conclusion and Future enhancement:


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3.1 Conclusion:

In this work, an attempt has been done to design a data logger, which is of less cost,

portable, very low power consumption, self contained. It is an efficient data logger, which

works in real time mode. The reduced number of channels also makes the system simple. Thelogger can use up to 8 channels of analog to digital converter in performing its task but that will

result in increased number of channels. The programming and interfacing of microcontroller

has been mastered during the implementation. This work includes the study of PC .Hence by

3.2 Future enhancement:

This system can be connected to communication devices such as modems, cellular phones,

or satellite terminal to enable the remote collection of recorded data or alarming of certain

parameters. The new system will email information based upon a regular schedule of based

upon alarms


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Chapter 4

REFERENCES


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REFERENCES

Andrew J Thompson, John L Bahr and Neil R Thomson, Low power data logger,

proceedings of conference department of physics, university of otago, Dunedin.

Peter Roberson, Using data loggers, science teachers workshop, 2004, north Sydney.

Muhammad Ali Mazidi and Janice Gillispe Mazidi, The 8051 microcontroller and

embedded systems, Pearson education ltd., India, 2004.

National Semiconductor Corporation, LM35 datasheet, precision centigrade

temperature sensors, Atmel data book, November 2000 update.

National Semiconductor Corporation, ADC0808/ADC 0809 data sheet, 8-bit

Microprocessor compatible A/D converters with 8-channel multiplexer, national

Semiconductor data book, October 2002 update

H S kalsi, Electronic instrumentation, Tata McGraw-Hill Ltd., New Delhi, 1999.

data acquisition system synopsis

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