Introduction
Technology is the soul of today’s life and with out technology no body can even think of surviving as now everything is dependant over technology. Basically technology is the practical implementation scientific methods and techniques in order to gain any industrial or commercial benefit and purpose. Different electronic components have been introduced and are being used to perform different tasks. Different technologies can be merged to get a new one that will be providing obviously more functionalities and benefits.
Data Acquisition
Data acquisition can simply be defined as the gathering or collection of data by the use of sensors and readers. It is also commonly known as DAQ or DAS. Basically this technology or technique is used in laboratories, factories and in scientific surroundings. It basically refers to the division of real world in to samples and then data is generated that is then used and manipulated by the computer (Data acquisition definition, 1)
Data acquisition is basically used for the collection of data about any process or system. The systems that are used for the collection of information; data acquisition is their basic element. Aim and objective of data acquisition is to collect the physical or electrical properties, measurements or attributes like temperature, current, voltage, pressure, noise, density, height, width and so on. All these data regarding different physical and electrical phenomena are gathered using the sensors. These sensors then use this information and transform it in to the electrical signals. The requirement of number of sensors depends on the systems. Some times only one sensor will be enough and some times the system may require even thousands of sensors. Mostly this is the case when the system is being used in the complex environment. The signals that are received from the sensors are then transformed by the use of different mediums like wires, optical fiber and it can also use some wireless links. These links are then connected to the different instruments that are then used to process, amplify, measure, display, accumulate and level these signals. In recent years with the developments in technology; the instruments of data acquisition has become much simpler than ever. In past it was not that simple; big smoke drums, chart recorders and many other heavy and large mechanical and electrical instruments were used. The work of data acquisition has made easier, faster, more flexible and accurate by involving strong, powerful and robust components like microprocessors, integrated circuits, chips and computers. The use of many sensors has simplified the complex and difficult data processing and it is easy to produce the final result. (What is data acquisition and data logging, 1)
Purpose of Data Acquisition
There are many purposes of data acquisition; and with the improvement in data acquisition these purposes can also be improved. Some of the purposes may include:
- Time saving
- Saving of cost
- Improved efficiency
- Improved performance
- Accurate results
- Reliable processing
- Assurance of quality
These are some of the reasons for which data is collected and for improving these mentioned factors the developments and improvements in the field of data acquisition is almost wanted. (What is data acquisition and data logging, 1)
Data Acquisition Systems
As the name shows the data acquisition systems are the systems and ways that are used to gather the data or information. The information is being gathered for certain reasons and then depending on the purpose only the required information is collected. The data acquisition systems were always present in every field but the nature of work has been changed now. In past the technicians were appointed for logging and noticing the different readings and information but now with the age of developments modern techniques are being used for this. The data acquisition systems contain reliable, flexible and accurate components. The data acquisition systems also use data loggers which are the electronic equipments and are very useful for these kinds of systems. Data loggers are used to integrate with any process, system or entity about which the data is to be collected and then the data is gathered. The data loggers collect the information from the different systems and devices by tracing the temperature sensors, sensors for pressure, sensors of speed, sensors of flow, loop transmitters, sensors indicating weather, and many other components present in the system from which the data is being collected. (What is data acquisition and data logging, 1)
PC Based Data Acquisition
In order to perform data acquisition using pc different types of hard wares as well as application soft wares are used. Obviously it would not be done with out a robust and reliable computer that will be used to collect the information. The requirements and objectives of every data acquisition system are obviously different but the task of collecting, observing, processing and then displaying the result are some of the common goals of every data acquisition system. PC based data acquisition systems also involve sensors, signals, processing of signaling, different modular hard wares and application soft wares. (What is data acquisition, 1)
Classes of Data Acquisition Systems
There are two types of data acquisition systems; these classes are defined on the basis of nature of purpose of gathering the information or data.
- Real Time Data Acquisition: Real time data acquisition is performed when the information that is being received from the sensors has to be used on the immediate basis or there is a little interlude of time after which then information is required. Basically these types of data acquisition systems are used when any system is being controlled.
- Data Logging: Another type of data acquisition system is when the data acquisition is being performed just for the reason of collecting and then storing the data in the data base. This data or information is then used later and it is not of immediate or emergency use. The information of every second and every movement is being stored and this information is saved for the future use.
Actually it should be kept in mind that there is a range of devices that are used for the real time data acquisition and data logging systems and all these devices have characteristics that can be set according to the type of system and then all the devices can be used for both of the purposes. The devices can be any simpler recorder or it can be complex and complicated computer system. The data acquisition system is the center point of any system and it can also be said that this system is also responsible for keeping all the other equipments in the system together. (What is data acquisition and data logging, 1)
Understanding of ADC
ADC is a terminology that is very much closely related to data acquisition and it stands for Analog to Digital converters. It is a device that is used to transform the analog signals that are being received from the wires or sensors to the digital format that is equal to the analog format. The electronic device can be said as the soul of the data acquisition systems and with out this device data acquisition will not be possible. An analog signal can be defined as any signal that is continuous. In analog signals any variable feature or the feature that changes with some passage of time of the signal is showing some other feature that is also changing with the time. Analog signals are known to be the electrical quantities. It can be said as the copy of any feature that is varying with time and analog signals are just copying and representing one time varying quantity by means of another time varying feature. But the analog signals are not used for displaying the information as there are some of the lack nesses in the analog systems like these signals contain a lot of noise that is obviously unwanted. Where as the digital signals can also be known as the discrete signals and these signals are divided in to samples. An analog signal is a property that keeps on changing with the passage of time but the digital signal is the sampled form of the analog signal. In analog signals the time will be the independent variable where as the signal will be the dependant variable over time where as in digital signal the value is being collected after a predefined passage of time not in the continuous manner. Quantization is being done in the digital signals as if the value will not be sampled then the time values of digital signal will need to have an infinite limit of number of digits and the system will not be simple but it will become more complex. So in digital signals a fixed precision has been decided and the values are then approximated over that precision. The approximation of précised values with in some specified limit of digits is the process of quantization which is the specialty of digital signals. (Staller, 1)
Why to Convert Analog Signals in to Digital Signals
The analog signals are always converted in to the digital signals before they are displayed over the personal computers as a result. This conversion is done because the analog signals contain much noise and degraded quality so for improving the quality of the signal the signals are converted in to the digital format and for displaying the information over the personal computer it is necessary that the format should be digital. The analog signals are used to display the information in the numbers where as the digital signals represented in bits and when the analog signals are converted in to the digital format then for displaying the information on the computers it is necessary that the information is converted in to the bits format as the computers understand the language of bits and bytes not the language of numbers. Digital signals are best in quality and they can even be used for pictures and music as well. Digital signals spread more clearly and efficiently as compared to the analog signals. The reason may be that the pulses of digital signals are very much clearly defined and are also presented in orderly manner so it is easier for the electronic devices or analog to digital converters to understand these pulses and can distinguish between the real signal and noise in the signal. (Analog and Digital, 1)
Method of Converting Analog in to Digital Format
The conversion of analog signals in to the digital ones is being done by using the technique of sampling. In sampling the analog signals are being measured after certain passage of time that is pre determined. In sampling the physical quantities will be measured and they will be measured at this time in numbers. Hence a stream of numbers is obtained which is then converted in to the bits. The conversion of numbers in to bits is very much necessary for representing the data over the computers using the ADC as computers understand the language of binary digital data not the numbers and other languages. The simplest digital signals have two states of operation that is on and off or 1 and 0. The input that is being provided to the analog to digital converters is consisting of voltages that tend to vary in between infinite quantity of values. Where as the out put generated by the analog to digital converters has some predefined levels or states. This number of states or levels can be judged by placing a power of two 2, 4, 6 and so on. There can be difference in the result when different ADCs are being used.(What is analog to digital conversion, 1)
ADC and Data Acquisition
The readings taken from different ADCs can vary a bit and can move away from the original or real answer; the reason for this problem is that the manufacturing of integrated circuits used in different ADCs are different and this is the reason why the analog to digital converters have some inaccuracies. The performance of these analog to digital converters can be divided in to two groups generally. One group will be the DC accuracy and the other will be the dynamic performance. The converter is then selected according to the nature of input; if the input is static like temperature, pressure sensor and so on then the best choice will be a converter that is being used to measure the accuracy and if the input is dynamic like noise or tone then obviously the accuracy is difficult to achieve but the achievement of performance will be the better option over here. So when the analog to digital conversion is being made then the specialists should be experienced enough that they are going to choose the right equipment so that the correct or most appropriate result is obtained. By using the same technique and procedure the data acquisition is used for generating the results over personal computers. When data acquisition system is applied to any thing whose data is to be collected then that data acquisition system should also include analog to digital converters in to it and only then the results are possible to be displayed over the computer screen. It can be said that ADCs are the important part of data acquisition system just because analog to digital converters will help the data acquisition system to understand the data properly and it will allow the system to eliminate the noise and any un wanted element so the result will be refined and the result will also be able to be displayed over the computer screens. (Staller, 1)
Types and Operations of Different ADCs
There are many different types of analog to digital converters that are then used by the designers and technicians according to the need of the system. Few of the analog to digital converters are being described below:
Direct Conversion ADCs
The direct conversion analog to digital converters are also known as the flash converters as the infrastructure over which the direct ADCs are designed shows that they have got very high speed and the sampling rate associated with the direct ADCs is up to 1 GHz. The direct conversion ADCs need a very large number of comparators which makes the resolution inadequate or restricted. The input signal is required by all the comparators at a time and the comparators should be similar because if there is any difference in the comparators then error will be generated. In direct conversion ADCs the time that is taken when the out put is being latched is very short or aperture interval is short. The output is produced by the priority encoder; the out put is digital and is corresponded with the highest active comparator used in the system.
Successive Approximation ADCs
The successive approximation converters use a technique for the conversion which is depending over the successive approximation register (SAR). Bit weighing conversion is the other name of successive approximation conversion. It involves a comparator that is used to measure the applied input voltage against the output. The output is N bit digital to analog converter. By applying the digital to analog converter at the out put; the final result that is produced will be the sum of N weighting steps. At the start all the bits of successive approximation register are set to 0 and after that starting with the most significant bit all the bits will be set to 1. If the output is not more than the voltage of the input signal then that will be set to 1 and will not be changed. But if the out put is more than the voltage of the input signal then it will be changed to 0. The sampling rate of successive approximation converters is 1 Msps. These are not used in many cases because they give the lowest production cost among all the other converters and also depict low supply current.
Integrating ADCs
It can be termed as a classical converter. It involves an integrator at the input, apart from the integrator it also includes a comparator, capacitor, counter and control logic. A capacitor is charged for a fixed time interval of time by a current that is equal as well as proportional to the voltage that has been input. When the time interval ends the counter of the device is reset and opposite polarity voltage is applied to the integrator input. The opposite polarity that is applied to the integrator input will allow the capacitor to discharge by a current that is constant and it will remain discharged until the voltage at the integrator output is again zero. The time interval for which the capacitor is charged will be proportional to the input voltage and it will be used to enable the counter. The last count will be the result or the out put. These types of converters are mostly used in the multi meters. These are very much slow devices and their input bandwidth is also very low but they are still useful as these devices have strong ability to understand the high frequency noises and these can also recognize the low frequency noises; so these devices are very much useful for the industrial applications where there is too much noise around.
Sigma Delta ADCs
Another name for sigma delta converters is over sampling converters. These converters contain two parts; one is modulator and the other is digital filter. The modulator part consists of an integrator, a comparator and also a feedback loop containing a digital to analog converter. This part is very much similar to the integrating analog to digital converters. This part is used to over sample the signal that is applied over the input and a serial bit stream is produced whose frequency is more than the needed sampling rate. The other part of digital filter acts as the output part and it will convert the bit stream in to the digital words. These converters have high speed and using the filters these can eliminate the noise to the large extent. These are best for the audio purposes and the applications where the bandwidth is up to 1 MHz. These converters are very much accurate and they are also not very much expensive. (ADC most popular types, 1) PCI 922I card uses multifunctional integrating ADC having 16 single ended or 8 differential inputs. The sampling rate is 250 kS/s.
Works Cited
ADC- most popular types (2008) Web.
Analog and digital (2008) Web.
Data acquisition definition- PC magazine (2008) Web.
Len Staller, Embedded.com- Understanding analog to digital convertors specifications (2005). Web.
What is analog to digital conversion? (2008) Web.
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What is data acquisition Products and services (2008) Web.