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.
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
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:
Air(0º C )
Air (20º C )
Carbon dioxide (0ºC )
Oxygen (0º C )
Helium (0º C )
Chloroform (20º C )
Ethyl alcohol (20º C )
Mercury (20 º C )
Fresh water (20º C )
Seawater (20º C )
Glass (Pyrex )
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.
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.
· 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.
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.