INTRODUCTION
Data
logger is an electronics instrument that records measurements of all types at
set intervals over a period of time. Data logger also can record a wide variety
of energy and environmental measurements including temperature, speed, light
intensity, pressure, electric currents and more. The characteristic of a data
logger is the ability to take sensor measurements and store the data for future
used. This is how data logger works, a data logger works with sensors that then
will convert physical phenomena and stimuli into electronic signals such as
voltage or current. These electronics signals are then converted or digitized
into binary data. The binary data is then easily analyzed by software and
stored on a PC hard drive or other form of storage like memory card and CDs.
While
we talking about data logger, data logging is the process of using a computer
to collect data through sensors, analyze the data and save and output the
results of the collection and analysis. Data logging is also implies the
control of how the computer collects and analyzes the data. It is commonly used
in scientific experiments and in monitoring systems where there is the need to
collect the information faster than we do it manually especially when the
experiments need accuracy. Figure below shows the complete data logging
applications elements.
A data logger has an additional
recording and storage facilities. It can store readings from events taking days
or week to unfold. Afterwards, the computer can read the data from it. There
stand alone devices can often record data at high speed for example they can
record the flicker of a lamp and take 100’s of readings in second. The data
logger has buttons to start and stop according as well as an independent power
supply. The buttons allow us to alter the recording speed when the recording
would start. The data logger may have an LCD display to monitor what it is
doing. In nearly every system that find, data logging sensors plug into a box.
The sensor send its ‘readings’ to the box and informs it which type of sensor
it is. The sensor identifies itself using pins on the sensor plug while some
systems place a resistor across the pins and use its value to identify it.
Others sensor have a PIC chip which ‘tells’ the data logger all it needs to
know. Some sensors have their own power supply but the best derive all their
power via the interface. Some devices get all their power through a USB
connection o Parallel port and these tend to be the most reliable. The
interface box has a circuit that converts an analogue sensor signal to a
digital signal. It also has a way communicating with the computer and most
systems use ‘serial’ communication. Serial connections are compatible with
almost every type of computer. While this is not fast communication, they
transfer data fast enough for most purposes. If we want to show sound waves
with these data loggers, we can record the sound at high speed and transfer the
data to the computer afterwards. Data logger can collect readings independently
of the computer, allows results collected in the lab to be downloaded to the lab
computer, can be set to start recording during the night, record very fast, can
be set to start recording at a certain sensor reading and can store the results
of many experiments. Data logger has a rechargeable battery and uses alkaline
batteries.
In every PC data logging and controls system,
there are few basic components which are sensors, connectors, conditioning,
Analog to Digital (A/D) Conversions, Online-Analysis, Logging/Storage, and
Offline-Analysis. A few additional components also required in a dta logging
and Control system including D/A Conversions and actuators.
Sensors
There are many type of sensors that are
used in data logging. Sensors often process data before we can see it. The
types of sensors that have are sensors to measure motion. Sensors that used to
measure motion are accelerometer, light gates and switches, force or dynamic or
mechanic pulley, rotation sensor, shock sensor, sonar distance sensor or ranger
and strain gauge. The sensors that used to measure heat and temperature are
heat flow sensor, full range temperature sensor, low temperature sensor, body
temperature range sensor and thermocouple and high temperature sensors. Sensors
for light and sound, we used light sensor, calorimeter sensor, infra-red
sensor, sound sensor, microphone sensor, sound switch sensor and ultra-violet
sensor. Sensors that used in physiology are pressure sensor, breathing monitor
sensor, heart rate sensor and electrocardiogram sensor.
Any device that is used to convert
physical parameters into electrical signals is called sensors. The sensors must
be calibrated so that electrical output they provide maybe used to take
meaningful measurements. For examples, flow meters, pressure transducers,
accelerometers and microphone. After we
have the sensors, it must be connected to the connectors to transmit its
electrical signal to the systems. There are variety of signal connectors that
each have their own advantages and disadvantages. The simple connectors can be
as simple as tightening a screw around a wire to the more complex like
connectors typically used in NDT shown below.
Conditioning
is the next steps needed for the electrical signal provided by the sensor to be
useful. It is including all actions performed on the signal to improve its
usability before it is digitized. There are few types of conditioning that can
be used. Amplification is used when the voltage levels being measured are very
small. Amplification is used to maximize the effectiveness of the digitizer.
The typical sensors that require amplification are the thermocouples and strain
gauges. Attenuation is the reverse of the amplification and necessary for
measuring the high voltages. Filtering is the required to remove unwanted
frequency components from a signal that will prevents the aliasing and reduces
noise.
Excitation
is used to provide the required currents and can be voltage or current source
depending on the sensor type. Linearization is a type of sensors produce
voltage signals that are not linearly related to the physical quantity they
measuring. Isolation is used to in conjunction with attenuation to protect the
system and the user from dangerous voltages or voltage spikes. It also can be
used to when the sensor is on a different electrical ground plane from the
measurement sensor. Lastly, multiplexing. Multiplexing allows you to
automatically route multiple signals into a single digitizer. Most of the
sensors required the combination of two or more of this conditioning technique
like thermocouple.
There
is also other components that build the data logging systems like A/D
conversion that convert analog electrical signal into digital values and
transmit those signal to the computer and these is done by the using the data
acquisition (DAQ) board. Online analysis is used after the analog signal has
been converted to raw binary values. For logging or storage ,PC based data
logging systems generally use the hard drive of the PC to store data, but may
also use tape drivers, network drivers, or RAID drivers. After that, offline
analysis is the performing mathematical analysis on data after it has been
acquired to extract information. There are two forms of control part of the PC
system. The first one is open – loop control which is independent of the
current state of the process and the second one is the closed-loop control in
which the PC measures one or more input variables and uses software to make
decisions about what control signals should be output. Other than that, there
is also D/A converter which the function is to takes the digital values output
by the computer and turns them into analog signals which can be conditioned and
then connected to actuators. Actuators is any device that converts electrical
signals to physical parameters.
People we ask why we use data logging. Data
logging help us do a lot of things. Data logging help us to perform the
experiments in a short time. If we do a manual experiments, we will take time
to construct the apparatus, adjust the parameters, collect the data and to
analysis the data. By using the data logging, we also can perform the
experiments online and also perform the online analysis. For online analysis,
this step will include any analysis that we could like to do before storing the
data. The most basic example is, when converting the voltage measurements to
meaningful scientific units, such as degree Celsius. We can complete these
complex calculations and data compressions before logging the data. Controlling
part of a system based on current measurements. Every data-logging software
applications have to complete the conversions from binary to voltage and the
conversions from voltage to scientific units.
There
is also step in data logging which is log that refers to the storage of
analyzed data including any formatting required for the data files. When doing
the experiment, it is very important to save all the data from the experiment,
therefore by doing data logging, we can save all the data that need to be
analyzed and also the format. Other than that, data logging also help you to do
the offline analysis. Offline analysis is the analysis that we do after storing
the data. For example, we can use the data stored to look for trends in
historical data or data reduction.
Data
logging also will help us by displaying, sharing and reporting the experiment
that had be done. This application can save our time and also the experiment
can be repeated over again to get the result that we need. This does not means
the data logging application will prepare for you the full report of the
experiment like the full writing report but it can help you to create any
reports that need to make present the data. Data logging also can present the
data straight from the online analysis. This means that the monitor able to
display the data you need and also analyzed the data and also viewing the
historical data.
DATA LOGGING
: SPEED OF SOUND
Engage :
Last
weekend, my family decide to go to Gua Kelam in Perlis. As we walk through the
cave there is a lot of nice things to watch. Then, I notice something
interesting, when we talk in the cave, we can hear our voice be reflect. We
hear our own voice echo. Why this happened? I also notice the same phenomena
occur when I talk in empty house or when I shout in the tunnel. How can this
happen and what is the cause?
The speed of sound is the distance travelled during a
unit of time by a sound wave propagating through an elastic medium. In dry air at 20
°C, the speed of sound is 343.2 metres per second. In fluid
dynamics, the speed of sound in a fluid medium either gas or liquid is used
as a relative measure of speed itself. The speed of an object (in distance per
time) divided by the speed of sound in the fluid called the Mach number.
The speed of sound in an ideal gas depends on frequency, but it is weakly
depends on frequency for all real physical situations. Sound speed depends on
pressure only because the air is not quite an ideal gas. For different gases,
the speed of sound is inversely dependent on square root of the mean molecular
weight of the gas, and
affected to a lesser extent by the number of ways in which the molecules of the gas can store heat from compression, since sound in gases is one
type of compression.
Speed of sound refers
to the speed of sound waves in air and the speed of sound varies from substance
to substance. Sound travels faster in liquids and non-porous solids compared in air. It travels about 4.3
times as fast in water, and nearly 15
times as fast in iron. Sound waves in solids are composed of compression waves
just as in gases and liquids, but also exhibit a different type of sound wave
called a shear wave, which occurs only in solids. The different types of waves
in solids usually travel at different speeds. The speed of a compression sound
wave in solids is determined by the medium's compressibility, shear
modulus and density.
Sound
is a longitudinal wave that is created by a vibrating object, such as a guitar
string, the human vocal cords or the diaphragm of a loudspeaker. Moreover,
sound can be created or transmitted only in a medium, such as a gas, liquid and
solid. To see how sound waves are produced and why they are longitudinal,
consider the vibrating diaphragm of a loudspeaker. When the diaphragm moves
outward, it compresses the air directly in front of it. The compression causes
the air pressure to rise slightly. The region of increased pressure is called
condensation, and it travels away from the speaker at a speed of sound. The
condensation is analogous to the compressed region of coils in a longitudinal
wave.
Sound
travels through gases, liquids and solids at considerably different speeds as
shown in the table below:
Substance
|
Speed (m/s)
|
Gases
Air(0º C )
Air (20º C )
Carbon dioxide (0ºC )
Oxygen (0º C )
Helium (0º C )
|
331
343
259
316
965
|
liquids
Chloroform (20º C )
Ethyl alcohol (20º C )
Mercury (20 º C )
Fresh water (20º C )
Seawater (20º C )
|
1004
1162
1450
1482
1522
|
Solids
Copper
Glass (Pyrex )
Lead
Steel
|
5010
5640
1960
5960
|
Near
room temperature, the speed of sound in air is 343 m/s and is markedly greater
in liquids and solid. For example, sound travels more than four times faster in
water and more than seventeen times faster in steel than it does in air. In
general, sound travels slowest in gases, faster in liquids and fastest in
solids. Like the speed of a wave on a guitar string, the speed of sound depends
on the properties of the medium. In a gas, it is only when the molecules
collide that the condensations and rarefactions of a sound wave can move from
the place to other place. It is reasonable, then, to expect the speed of sound
in a gas to have the same order of magnitude as the average molecular speed
between collisions. Sonar is a technique for determining water depth and
locating underwater objects, such as reefs, submarines, and schools of fish.
The core of a sonar unit consists of an ultrasonic sound, and at a later time
the reflected pulse returns and is detected by the receiver. The water depth is
determined from the electronically measured round-trip time of the pulse and a
knowledge of the speed of sound in water. In a liquid, the speed of sound
depends on the density and the adiabatic bulk modulus. For the speed of sound
in liquid for example in seawater, the speed is 1522 m/s, which is more than
four times as great as the speed in air. The speed of sound is an important
parameter in the measurement of
distance. Accurate distance measurements using ultrasonic sound also play an
important role in medicine where the sound often travels through liquid-like
materials in the body. A routine preoperative procedure in cataract surgery,
for example, uses an ultrasonic probe called an A-scan to measure length of the
eyeball between the lens of the eye and the retina. When sound travels through
a long, slender, solid bar, the speed of the sound depends on the properties of
the medium.
Empower :
Ø
Equipment required
v 2 microphones-crystal Mics were used since they are cheap and give a large
output
v 1 metre wooden rule
v Fast digital storage oscilloscope-the ADC-212 was used
v
A balloon-to burst for a
sudden loud sound source
Ø
Experiment set up
v
The experiment was set up as
shown below with two crystal microphones placed 1 metre apart.
· Result
·
The balloon was burst
approximately 2 m away from the foremost Mic. The plot below shows the results
clearly.
The lefthand “BLUE” trace is from the foremost Mic
(Mic1) and the righthand “red” trace is from Mic (Mic2)
The waveform from Mic1 between -164µs and 500 s is
clearly visible in the trace from Mic2 delayed by 2929 µs. There is second variation
, in the waveform from Mic1, around 1.5 ms caused by an echo from one
wall or ceiling.
Enhance :
Telling how far away a person with a starter’s gun, at
a running race, is by comparing the time difference from when you can see the
gun’s smoke to when you hear the sound.
Telling how far away a cliff is by making a sound and
measuring how long it takes for the echo to return
Telling where an enemies gun was fired.
Telling how far
away a lighting strike.