( KEVIN SONI )DATA ACQUISITION SYSTEM
- 1. GOVERNMENT ENGINEERING COLLEGE – BHUJ ELECTRONICS & COMMUNICATION
- 2. Subject:-ElectronicsMeasurement&Instrumentation NAME ENROLNMENT NO. • NAME • ENDROLLMENT NO. • KEVIN SONI • 160150111097 • PARAG SOLANKI • 160150111096 • SUVA RAMDE • 160150111098
- 3. SINGLE CHANNEL DATA ACQUISITION SYSTEM ◦ The basic single channel data acquisition system consists of a signal conditionercircuit, analog to digital converter, buffer. The analog to digital converter performs theconversions repetitively at a free running internally determined rate ◦ The digital outputs from the buffer are further fed to either digital computer or storage or print signal converter out device. The most popular example of the single channel data acquisition system is the Digital Panel Meter (DPM). • The digital outputs are obtained from the analog to digital converter. The analog to digital converters used for the data acquisition system are designed such that they can accept external commands to convert and hold operations.
- 4. . A/D converters based on dual slope techniques are mostly used for the conversion of low frequency data, generally from thermocouples. The successive approximation technique is most widely used because it gives high resolution and high speed at moderate cost.
- 5. ◦ ◦ Many times it is observed that the signal level is very low compared to the input requirement. In such cases, the amplification of the input signal is done to bring its level to match the input requirement. This is called pre amplification. If the input signals are to be isolated from the system physically, the conductive paths are broken by using mostly optocoupled isolation amplifier. The pre-amplifiers may be coupled with active filters before the processing of data. These filters minimise the effect of noise carrier and interfering high frequency components. Sometimes special purpose filter such as tracking filter may be used to preserve the phase dependent data.
- 6. MULTICHANNELACQUISITIONSYSTEM ◦ The different subsystems of DAS can be time shared by two or more input sources. The number of techniques are employed for time shared measurements. Basically there are three types of multiplexed systems. They are as follows,
- 8. ◦ In this system, there is a single analog to digital converted preceded by a multiplexer The individual analog signals are applied directly. They are amplified and signal conditioned and connected to the multiplexer. Then analog to digital converter converts these analog signals to digital signals. ◦ For the utilization of time, the multiplexer gets or selects new channel to be converted while the previous data stored in the sample and hold circuit is converted into digital form. When this conversion completes, the status line from the converter makes the sample and hold circuit to go back to sample mode. Then it again collects the signal of the next channel. When the data is collected, on proper command, the sample and hold circuit mode changes to the hold mode. The conversion starts again while the multiplexer selects next channel. ◦ This process is comparitively slower but has obvious advantage of low cost due to sharing of more than one channel.
- 9. MULTIPLEXINGOUTPUTS OF SAMPLE/HOLDCIRCUIT When more number of channels are to be monitored at the same time, the multiplexing of the outputs of sample and hold circuit is done. In this case, each sample and hold circuit is attached to each channel.
- 11. ◦ They are synchronously updated by timing circuit. The sample and hold circuit are first multiplexed and then they are connected to the analog to digital converter. This gives the sequential read out of the signals. ◦ The advantage of this multiplexing technique is that this is moderately faster than earlier
- 13. ◦ In this technique, each sample and hold circuit and the analog to digital converter is assigned to the individual channel. The conversion speed is as per the requirement. This technique is exhibiting parallel conversion. In industrial systems, the number of strain guages, thermocouples, LVDTs are distributed over large area. As the analog signal is digitised at the centre, the data transmission provides great immunity against line frequency and other interferences. The data in digital form performs logical operations Based on relative speed at which changes occur in the data, the scanning rate can be increased or decreased. These are also called fast data acquisition systems.
- 14. MODERN DATA ACQUISITION SYSTEM PC BASED DATA ACQUISITIONSYSTEM ◦ Now a days easily available, low cost and wide use of Personal Computer (PC) led the various manufacturers to develop interfaces between PC and the outputs of transducers. The outputs are further processed and analysed by the PC. The advanced techniques allows user to use a PC ADD-ON card which is available in various configurations. By putting this card in PC, the analog signals can be directly interfaced to PC. This gives very powerful communication and analysis of the multiple measurement data.
- 15. The main features of PC based DAS are as follows, 1) The PC based system is used to display the parameters of the system continuously. This helps the operator in monitoring all the parameters instantaneously and conveniently 2) The system parameters are displayed with some display attributes such as blinking, underline, inverse video, extra bright so that the attention of the operator is called. Sometimes colour graphic display is used to indicate normal operation, close to the upper limit and out of the limit. 3) Sometimes some man-machine interfaces called MIMIC displays are used. These are useful in displaying the data measured at any location on the plant near the icon of that location on the screen. This helps operator to take quick action 4) Several parameters are plotted individually or simultaneously on the screen to their characteristics. This helps in pointing out the variations in these parameter measured at two different time.
- 17. ◦ The basic block Physical diagram of PC based phenomena data acquisition system is as shown in the Fig. 9.9.1 These are associated by the software. The software contains the complete programs written for accessing the data, performing calculations with them and display the result on Video Display Unit (VDU). The data analysis hardware is used To speed up the computations and analysis mainly in case of Digital Signal Processing DSP) applications. The data acquisition hardware generally acts as a multipurpose, Fig. 9.9.1 FC based data acquisition system witifunction card. The input signal between the range 10 mV to 10 V is amplified by digitally programmable gain amplifier to a standard level. This amplified input signal is Converted to digital signal vith the help of high speed analog to digital converters interfaced to the PC bus. This signal is recorded, displayed or may be processed further for analysis by the personal computer.