ENGR201_VoltageMeas_75 - DREXEL UNIVERSITY Engineering...

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Unformatted text preview: DREXEL UNIVERSITY Engineering 201 Voltage Measurement Lab (Lab 4) 05/11/2010 Abstract There were two main purposes for this experiment. First one was measuring the voltage using the NI USB- 6009 DAQ and recording voltage data using LabView software. Second one was again with using LabView software, and it was converting the data to voltage versus time graph and recording the information on data table file. The data table can help to find the mean and standard deviation of the data that was collected during Lab 4. However the aim of this lab was not collecting the right data and using it on the table. It was creating the right LabView program and understanding the concepts behind the creation. As a result, this lab was helpful for seeing that by the help of LabView program, conversions can be made. I Table of Contents Title Page Abstract………………………………………………………. I Introduction…..…………………………………………… 1 Theory………….…………………………………………….. 2 Experimental Program……………………………….. 2 Results………………………………………………………… 6 Uncertainty Analysis…………………………………… 6 Conclusion and Recommendation………………. 6 References………………………………………………….. 8 Appendix…………………………………………………….. 8 Introduction In the engineering field Data Acquisition1 software has huge portion. In this lab, NI- DAQmx Base was used to read data from outside source such as USB- NI 6009 DAQ interface and LABVIEW program was recording the data. In the lab, voltage was measured by HP E3631A DC power supply thorough LabView program that was created special to this lab. Voltage (V)/time (sec) was measured. Voltage is not the only phenomenon that can be found by the Data Acquisition. Using the Data Acquisition current, temperature, pressure and sound could be found. Data Acquisition helps to convert physical and electrical conditions to numerical values. It allows engineers to convert physical phenomenon to numerical values which would help to analyze, study and make improvements. Therefore, every Data Acquisition has three main goals; acquiring, analyzing and presenting information. The purpose of creating this lab was getting familiar with NI- DAQmx and creating new LabView program for different purposes such as measuring voltage. Getting familiar with NI- DAQmx was not just for successfully finishing the lab but it was also for future engineering projects that can occur. In this lab data table was received in Time (seconds) - Voltage form and it proved that LABVIEW program was working right. Creating the LABVIEW program and collecting data through the program was the most important part of the lab. However getting the right number values was not as important as creating the program and proving that it works. By using the data table, mean voltage and standard derivation could be found. This lab was a tutorial for using the NI- DAQmx and creating the right program for collecting the voltage data. Figure 1- National Instruments- USB- 6009 DAQ 1 See Reference 1 1 Theory In this experiment, the general concept was to use the Data Acquisition system from the LabView program to acquire data about the USB- 6009. Using the combination of the LabView program and the external USB- 6009 system, man different forms of data can be measured, calculated, graphed, and recorded. Because of the use of Macintosh computers in the laboratory, the addition of a NI- DAQmx was added to make the system work. Eventually, this will be used for the measurement of temperature. This experiment is preliminary so instead of temperature being measured volts created by the HP E3631A DC power supply. Using the front panel of the LabView, the system should show the same voltage that is being output by the power supply. Recording this data and altering the DC output, the system was tested to show the accuracy of the hardware as well as the programming. If the voltage marked on the HP E3631A DC power supply was the same as the voltage marked by the Front Panel, then the system proved to be accurate. Experimental Program In this lab, two programs were made to measure the voltage produced by a HP E3631A DC power supply using a National Instruments USB- 6009 DAQ interface. The first program measured the voltage and produced a visual output in the form of a meter. Minimum and maximum values were set to 0.00- 6.00, as seen in the Figure 2. Input terminal configuration was set to RSE, physical channel was set to Dev1/ai0 and Unit was set to Volts. 2 Figure 2- Front Panel of Program 1 The purpose of the program was measuring the voltage. Program starts by creating a new task, creating physical channels and starting the task. In the while loop, there is a function to read the task and convert the index array as seen in Figure 3. Index array values are sent to visual display in the form of a meter. Outside of the loop is button to stop the task function and then stop the entire program. 3 Figure 3- Block Diagram of Program 1 The second program used the measured voltage from the first program. In the loop, a five second interval was added, values sent to a graph function and finally data was recorded in the measurement file. Second program started the same way as the first program. Both programs start by creating a new task, creating the physical channels and starting the task. In the while loop the task was placed an index array. This time, time delay was added to the loop in order to make the program measurements in five second intervals. An Elapsed time function was created to find the elapsed time in the measurements. The values for elapsed time and index array were sent to XY graph function to build a graph, as seen on right side of the Figure 4. Last acting that was taken in the loop was sending the values to write to measurement file function in order to record the data. Outside of the loop was the same as first program. There was a stop task function and stop the entire program function. 4 Figure 4- Front Panel of Program 2 In the Write to Measurement File, data was recorded as seen in right side of Figure 6. The incoming signals, the names of the lab partners, as well as the title were exported using this part of the program. 5 Figure 5- Block Diagram of Program 2 Figure 7 is the data that was collected for one volt. It shows the time interval in seconds and the recorded volts. Figure 6- Resulting Data from Program 2 (1 Volt) 6 Results and Discussion For the first section of the lab the VI created was in place merely to test that the apparatus was working and was able to collect viable results for the voltage being generated. The VI generated no data points which could be analyzed or graphed; however, it contained a meter which displayed on the front panel the current voltage being generated. On the block diagram for the first VI the meter was placed within a while loop so that it would display continuous results and not just the first reading given, this allowed to group to ascertain that the National Instruments USB- 6009 DAQ was fully operational and giving accurate readings. In the second VI the meter was removed and a graphing function was added to the block diagram with a “Write to File” output at the end. This allowed the group to begin collecting the required information for the lab for each of the voltage measurements of 0, 1, 2,3,4,5, and 6 volts. The parameters for the measurement were set to - 5.00 Volts and +5.00 volts in the front panel of the VI, despite this, when recording the data for 5 and 6 volts the output file returned information that had values about +5.00 Volts. In addition even though the machine generating the voltage was not touched at all during the recording of data the values in the output file still varied above and below the target reading. This was a consistent trend for each of the values tested, even the “0” value which one might assume would not deviate from itself during data acquisition. This program created in the VI could be used to track the voltage generated by many machines that do not display the voltage on their interface. It could also be used in other types of circuits which have resistors to measure their resistive capabilities or to discover if some parts of a circuit system have begun to malfunction. Uncertainty Analysis The system that is created allows for very little uncertainty. This is because all the measurements taken are recorded very accurately and accounted for. The time interval is recorded very accurately, to the sixth decimal place. The volts are also recorded to a large decimal amount. The variance recorded is due to the wire system itself. Conclusion From the results generated during each of the seven tests only the first five (0, 1, 2, 3, and 4 volts) can be analyzed properly for their accuracy and worth. The parameters were supposed to limit the test of 5 volts and 6 volts so that the reading would not be taken if the value exceeded 5 volts. Contrary to this the file generated from the VI displayed results identical to the first five tests with numbers very close above and below the predicted reading. Each of the seven tests showed that the voltage will never be a consistent number to more than one significant figure, and instead shows that the values will fluctuate as seen in Figure 6 where the values for the zero readings range from; - 0.0067 to +0.008591 which is a very accurate measurement; however it proves that even though the output from the 7 machine reads at 0.000 the actual reading will vary because of instrument error or fluctuations in the output. A way to improve the accuracy of the measurements is to have values recorded every 1 second instead of every 5 seconds, this would allow for more precise calculations of how much the voltage fluctuates from the chosen value to record. In addition the values tested could range from more than just 0 volts to 6 volts, and instead go up to values such as 10 or 50 or 100 volts. This would provide a broader spectrum for how much the reading fluctuates, because while the variance of the predicted reading to the actual reading at just a couple volts is very small, the number could grow to possibly 0.1 or even 1.0 volts of the value being tested is high enough. In everyday life systems like the VI created are used, Electricians use voltmeters almost daily in their jobs in order to test outlets or the ends of lines which lead to light fixtures or fans. These voltmeters allow the Electricians to know if the line they are testing is giving the proper output for the switch or fixture being installed. Overall this lab produced meaningful results because it showed that even when human error can be removed almost entirely from an experimental procedure, it still proves that error can occur because of possible faulty wiring or just how machines can be inaccurate just like humans can be. If the 5 volts and 6 volts readings are discounted from the analysis than the results produced are perfect, but even with them the same trend is seen in fluctuation of data. 8 References 1) http://sine.ni.com/np/app/culdesac/p/ap/daq/lang/en/pg/1/sn/n17:daq/docid/tut- 8734 Appendix DATAQ Instruments This is a reference that displays data acquisition software that is common in the engineering field. It describes the hardware and software available from DATAQ as well as a basic introduction to the corresponding applications. http://www.dataq.com/applicat/index.htm What Is Data Acquisition? This is a reliable source for the definition of data acquisition. National Instruments, a major leader in the data acquisition industry, defines the purpose of data acquisition “is to measure an electrical or physical phenomenon such as voltage, current, temperature, pressure, or sound”. To do this, the created “systems incorporate signals, sensors, actuators, signal conditioning, data acquisition devices, and application software.” http://www.ni.com/dataacquisition/whatis.htm 9 ...
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This note was uploaded on 10/07/2011 for the course ENGR 201 taught by Professor Miller during the Fall '08 term at Drexel.

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