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Unformatted text preview:"12. Experiment Three: Measurement of Resistance Engr. 361 Section 1 9/23/2013 9/30/2013 This lab was centered around the concept of resistance or impedance and the different ways to measure that resistance. Different methods of ﬁnding resistance are presented. The student is then left to their devices and wits to wire, analyze, and understand these different processes. The different methods that can be used are the voltmeter-ammeter, LCR, ohmmeter, and the Wheatstone methods. However, the Wheatstone method was not carried out in this work. Lastly, the output Thevenin resistance is measured also. Tools used in the experiment include: HP model 6212A, DC milli-ampere meter, DC micro-ampere meter, decade resistance box, circuit board, Simpson 260, Tektronix CFGZSO, Tektronix CFC250, low resistance resistor, high resistance resistor, and a LCR meter. Main Parts The ﬁrst part of the lab revolved around the Voltmeter-ammeter method. This was one of the methods to ﬁnd impedance. The experimenter wired the circuit of Figure l and then Figure 2, both using the R(HI) resistor. It would have then been possible to increase the power supply until either the voltage reached ﬁve or the current reach 50microA ﬁrst. The student could then supply the voltage and current to calculate the resistance. Part B of the ﬁrst part is to do the exact same steps as part A, but the R(HI) resistor should be replaced with a R(LO) resistor. The voltage and current would then be there for' resistance calculation. This method is somewhat sound, but there are still some errors that are introduced. Now the experimenter comes to the second part and the second method called the LCR technique. This technique involves using the load, capacitance, and resistance meter. The meter has two metal clamps that are clamped to the resistor metal prongs. The LCR then provides the resistance value of each resistor, and this can be used for comparison with the other methods. Next, the ohmmeter method is visited in the third part of the experiment. The ﬁrst step to doing this is selecting the appropriate range setting on the Simpson 260 multimeter, or the R x 1 setting. The multimeter needs to then be re-calibrated by short circuiting the positive/common plugs; the user must then adjust the zero adjust control to deﬂect the needle to zero. This is done because any time the range setting is changed in ohmmeter mode it must be rectiﬁed. The user needs to only measure the R(HI) and R(LO) now. The experimenter could have also found resistance by doing the Wheatstone method, but it is not realized here. Lastly, the student or person must ﬁnd the output Thevenin resistance. This is accomplished by wiring the network in Figure 11. Therefore, the Tetronix CFG250 and CFC250 must be turned on, and the coaxial cable should be attached to the adapter box. The adapter box will allow the data to be transferred to banana plugs and be used. Vrms value is found to be ﬁve volts with the multimeter hooked up; the circuit is open at this time. The decade resistor box is now plugged into the banana leads, and the generators output voltage is watched until it is half of the original Vrrns; this is all while turning down the decade resistor box resistance, It was 1.25 AC voltage and then brought down to .625 AC voltage to accomplish this. Part VI of the lab is last to be covered, and a few questions have been raised. A is more or less a statement, but the other data resistance reading compare with very little error. B shows that Figure 1 and Figure 2 both have error. Figure one's error is due to the current found being through both the voltmeter and resistor instead of just the resistor. Figure two's error is due to the voltage found being across both the ammeter and resistor instead of just the resistor. C is excluded, and D is answered by saying that Figure 5 is well suited for low resistance because of the current passing through the ammeter being more sensitive to small changes in Rx than that of Figure 4. Part E is satisﬁed because of the fact that most components don't have terminals to the internal resistance. So, this method of output Thevenin resistance was given to thwart this problem. Any error in the data found is minute in this experiment. Data All data is included in the attached appendices at the end of the report. _ R(HI) R(L0) HI 1vs2 181-7k ohms 188k ohms Data Summary Sheets ENGR 361 and ENGR 363 Exneriment Three Name: /I Part I (B): Voltmeter-Ammeter Measurements for Determining Resistances Results for Rm: Magnitude Units Measure Using Figure 1 Circuit a Measure Using —-- -_ Results for Rm : M HI -- FigurelCircuit v _ _ — --— Figure 2 Circuit A Units -_ Exp.'3 Pg. 14 Part II (B): LCR Meter Measurements of Resistances 531" 7 RH]: , -12, - Rm: 45L Part 111 (B): Ohmmeter Measurements of Resistances Rm: I) ; (C): Temperature Measurement Using a Wheatstone Bridge Room Temperature = R2 = at bridge balance Rx = _________ at room temperature Finger Temperature = ; I = at ﬁnger temperature Melting Ice Temperature = 32° F; I= at 32° F Part V (B): Equivalent Internal Resistance Measurement Rx= RDecadeBox = 7n AF Exp. 3, Revision date 9/18/2011. Note: There is no Figure 3 in this revision so that Figures 1 through 7 would be consistent with the previous revision. Exp. 3 Pg. 15 Name: Grading Sheet for Experiment Three Summary: Report Format: Goals and objectives stated? (5) A Organization (5) Experimental concept and procedure (5) Mechanics (punctuation, spelling, etc.) (5) Expressions of ideas and critical analysis (5) 2&1: Voltmeter—ammeter method of measurement of resistance using circuits in Figure 1 and Figure 2 Unknowns using Figure 1 (10) Unknowns using Figure 2 (10) Part II: Resistance measurements using LCR meter Unknown measurements (5) Part III: Ohmmeters Unknowns using ohmmeter (10) Part IV 2 Wheatstone Bridge Unknowns and temperature plot using bridge (10) Part V: Internal (Thevem'n) resistance of a source ___——_. Internal resistance (5) P VI: Analysis and comparison of results to theory _—-—-—-—— (a) Compare resistance values (5) ~ l (b) Error in using Figure 1 and Figure 2: High?—Low? (5) (c) Derive equation for Rx (5) (d) Low resistance in Figure 5 ohmmeter circuit (5) (e) Measurement of intemal resistance (5) Exp. 3 Pg. 13