University of Tennessee at Chattanooga. Stead State Operating Curve Report. Engr 3280L/Week 3. William Disterdick. Brown Team

Transcription

1 1 University of Tennessee at Chattanooga Stead State Operating Curve Report Engr 3280L/Week 3 By Brown Team (Trent, William, William) 09/05/2012

2 2 Introduction: In this laboratory, a percentage of power was loaded on a set of lights and the current that ran through the lights was measured in amperes. The purpose was to know what percent of power was needed in order to get a desired output current of 3.5 to 4.0 amps. However, it s essential to have the current in a steady state operating curve so a true value for the input percent can be known. For a steady state curve to be displayed, the experiment had to run for a substantial amount of time. The report describes the background, theory, procedure, results, and conclusions in detail in order to support the experimental analysis. The results will primarily be represented graphically to provide evidence in the conclusion results and recommendations. The Background and Theory section will explain the technical issues for the experiment using physical and mathematical models that help model the experimental data. Following this section will be the Procedure of the lab. The Procedure will contain enough information to help in understanding how exactly the lab was run. After the Procedure, the Results section of the experiment will be presented though tables, graphs, and specific information relative to the finalization of the lab. The Discussion part of the report builds on the Results and will explain the significance of the experiment. The principles behind the experiment will be expressed in the Conclusions and Recommendations section of the report by summarizing the goals, measurement, and results while providing the reader with certain recommendations. Finally, the Appendix will contain all the extra data and references that help validate the report.

3 3 Background and Theory: The background for light bulbs has a fairly basic concept of how they operate. A source, like a 5HP/3-phase motor with a DC generator in this experiment shown in Figure 1, will supply power to lights that will move electrons through the bulbs. This is done using heat, gas, and metal to produce a steady stream of light. Although the eye cannot quite accurately depict this steady state, values will be obtained that are then graphed using excel in order to better see the steady state operation. The design and shape of a light bulb is shown in Figure 2. The bulb uses the current to produce light when the current comes in contact with the tungsten filament. Figure 1: 5 HP, 3-phase motor on the left, coupling, DC generator on the right

4 4 Figure 2: Light Bulb Components The experiment was setup so that the current would be measured running through the light bulb given a specified percent power input. Figure 3 shows how this was set up. As learned from previous engineering classes, current equals the input voltage divided by the resistance of the blub measure in Ohms (I = E/R). This current is measured in amps. Figure 3: Load lights and power supply

5 5 Figure 4: Block Diagram of System In Figure 4 above, the basic structure for the system is given to represent how the input percent of the motor drives the light bulb system which then outputs a specific current once it reaches steady state. The input and output variables are both a function of time. For this experiment, it is important to note the values recorded are indeed experimental and measured using an amp meter. Therefore, the results can vary and have some error due to the motor not running at its best efficiency all the time.

6 6 Procedure: From a computer, the experiment was run using Labview which sent a signal to a motor in the lab room that would in turn supply the power to the lights. The amount of power sent to the lights depended on the input percent of power. The main concern for the lab was to have an output current that was in the range of amps. In order to get the desired output current range, the input percent was done by a trial and error method. The input and output were directly proportional to each other in the sense that the higher the input percent power was, the higher the current came out to be. It was seen with the Current vs. Time graph that Labview produced concluding the test that it took a while for steady state to be reached. Therefore, the experiment had to be run for 90 seconds. The table below was used as the criteria for the lab to run at. Table 1: Criteria for the Current experiment Current lab Procedure Input 72% Length 90 seconds

7 7 Results: The results to the experiment were quite simple because they were generated automatically. After the lab ran for the desired length and the percent was inputted, Labview automatically generated the table of values and a graph that represented Input Percent and Output Current vs. Time. In figure 4, a line scatter plot was generated in excel using the values obtained from the lab. Input (%) Percent and Current vs. Time Input(%) Average = 3.67 Uncertanty= Output(amps) Time (secs) Output (Amps) 0.5 Figure 4: Percent and Current vs. Time graph. The blue solid line represents the constant input percent that was used to generate the red scatter plot which represents how the current behaved over time. The Average of the results came from the values of current when it was in steady state. This time was from 35 to 90 seconds. In order to verify this, the uncertainty was calculated using twice the value of the standard deviation from the output during steady state. This came to be a value of This means it is about 99% sure that the average for steady state given an input power of 72% is 3.67 Amps.

8 8 Discussion: As mentioned in the Results section, there was only a 1% uncertainty for the steady state current value of 3.67 Amps. This represents how accurate the consistency of the input power was to the lights as well as the current that ran through the bulbs during steady state. For the beginning of the lab up until 35 seconds, the results can be eliminated because that time is needed for the operation of the experiment to become steady. However, from 35 second and on, the value for the current was accepted because it fell in the desired range of amps like mentioned earlier in the report. Another way to prove this was because from the time 35 to 90 seconds, the deviation of the current values was It is important to always note that when running an experiment, it takes some time for a system to have the characteristics of steady state. If this lab was only run for 10, or even 30 second, there would not have been any steady state at all. There wasn t any predicted value for what the input percent need to be, so it was all done by trial and error until a substantial line with slope of zero was generated. This was done in order to maintain an average of 3.67 Amps.

9 9 Conclusions and Recommendations: The results from this lab clearly depict what happens when lights are turned on and how the current behaves as time increases. The experiment was validated when steady state was achieved and the uncertainty was only 1%. As mention before, this only took about 35 seconds and for all time after that, the current should remain very closely to its constant (average) value. All of these results were recorded electronically and through a computer. There is possibility for error and so precaution steps should always be taken when running a lab. It is a good idea to do background reading in order to know how something behaves before supplying power to it. Below in table 2, the essential laboratory values that were recorded and measured are shown. In order to know exactly what factor the input percent relates to the current, many other experiments must be done. Table 2: Display of the lab procedure as well as results obtained and calculated. Current lab Procedure and Results Input 72% Length 90 seconds Average output (For steady state) 3.67 Amps Standard Deviation Uncertainty 0.01

10 10 Appendices: Figure 5: Input Percent and Output Current vs. Time graph. Preliminary graph with 72% input to get the average output current of 3.67 after 35 seconds Table 3: Results table for constant input RESULTS FOR CONSTANT INPUT Time(sec) Input Values (%) Output(Volts)

11 11 Input % Time (sec) S Output (Amps) Figure 6: Input Percent and Output Current vs. time graph. In this figure, a lab partner ran the experiment at approx. 62%. References: Jeanty, Jacquelyn. ( ). How Does a Lightbulb Work? Retrieved September 4, 2012 < Henry, Jim. (1997, October 8). Speed & Voltage Control System. Retrieved September 5, <