Lab Report2 by nuhman10

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									 University of Southern Mississippi
EET 110 Introductory Circuit Analysis
 Lab 2: Resistors and the Color Code




     Lab Instructor: Dan Garcia




      Date Performed: 2/2/2006
      Date Submitted: 2/9/2006
      Submitted by: Chris Mills
                   Akio Lofton
                   Latara Hudson
                   Cortez Davis
                   Matt Landry
                   Elizabeth Buckley
                   Bonnie Williams
                   Domingo Megia Planet
Abstract
        In this lab the group validated the nominal value of various ¼ watt resistors by
direct measurement. In addition to these measurements, the participants in the lab
measured their skin resistance and used Ohm’s Law to predict the value of a lethal
voltage. Next the effect of a meter’s connection to an energized circuit was noted.
Finally, the power rating of a resistor was related to its size as ability to release heat and
survive the resultant rise in temperature due to its power dissipation.


Introduction
        Common commercial resistors are marked with color-coded bands that represent
digits in the nominal value of the resistor and specify accuracy with an additional band if
applicable. In addition to variations in resistors there are two major types of meters,
analog and digital, which must be investigated to uncover their specific relative strengths
and weaknesses.


Materials
        Archer Kit Volt-Ohm-Milliameter Model 14A
        Hewlett Packard Digital Multimeter Model 114z
        220, 3.3k, 10k, 470k, and 1M ¼ watt resistors
        A resistor placard indicating sample values of carbon resistors at ¼, watt ½ watt,
1 watt, 2 watt, and higher power ratings


Methods
        In parts 1 and 2 the color code table [Table 1] was used to predict te resistance in
ohms of the ¼ watt carbon resistors supplied. The color bands are read from left to right,
where the band closest to the end of the resistor’s body is the first significant digit; the
next is the second significant digit and the third is the power of ten of the multiplier. A
band succeeding these is an indication of accuracy where a gold band signifies 5%
tolerance, a silver band indicates 10% tolerance and no band signifies 20% tolerance.
         Thus, based on the bands present on the body of a resistor its nominal specification can
         be calculated.


           Color     Black Brown      Red Orange        Yellow   Green Blue Violet Grey White
           Value 0           1        2      3          4        5          6       7        8    9
         Table 1. The Resistor Color Code.


                   In parts 3 the digital multimeter was used to measure the skin and body resistance
         from one hand to the other. In part 4 the digital multimeter was used to measure the
         resistances of the various scales of voltage and current of another meter.


         Results
                   Part 1 of the lab was completed through the observation of a placard displaying
         resistors of various sizes and wattages. It was observed that as the size of the resistor
         increased it would be able to handle more power traveling through it. Instructor Garcia
         pointed out this observation at the close of the lab, and said that though we were not
         required to sketch the different wattages, the fundamental ideas of an increase in wattage
         for a resistor were the important things to note for this portion of the lab.
                   Part 2 consisted of determining the nominal resistance of the resistors based on
         the color code and verifying this value through testing with the digital multimeter. The
         expected values based on the color code are dispayed in Table 2.
Resistor               Color Bands - Color                       Color Bands – Numerical Value
(Nominal               1         2    3      4                   1      2       3        4
Value)
220                   Red    Red    Brown       Gold            2      2       1        5%


3.3k                  Orange Orange Red     Gold                3      3       2        5%


10k                   Brown Black Orange Gold                   1      0       3        5%
470k                Yellow Violet Yellow Gold               4       7       4      5%

1M                  Brown Black Green Gold                  1       0       5      5%


        Table 2. Expected Values of Resistors Based on Color Code


        In order to verify the nominal values of the resistors, the accuracy band was considered
        and a range of acceptable resistances was calculated using Equation 1.
          Equation 1:
               (Value of Accuracy Band)(Nominal Value) =
                            Acceptable Deviation


        The number achieved through this equation is added to the end of the nominal value in
        order to achieve the acceptable range, for example, in the 220 resistor the acceptable
        deviation is 11. Thus the acceptable range for the 220 resistor would be written as:
        220 +/- 11. From this range a set of minimum and maximum acceptable values were
        calculated and these are shown in Table 3.
               As a side note, the lab did not have any 1M resistors and because of this even
        though they appear in the materials list and in the nominal value calculation table [Table
        2], they were not tested in the lab.


          Resistor      Minimum Value                    Maximum Value
          220          209                             231

          3.3k         3.135k                          3.46k


          10k         9.5k                            10.5k



          470k         446.5                           493.5


        Table 3. Minimum and Maximum Acceptable Values for Resistors
           Using the above calculated acceptable range the resistors were tested, their
 percent difference was calculated, and their nominal values were either confirmed or
 rejected. The results of this part of the experiment are shown in Table 4.
Meter        VOM                                             DMM

Normal       Measured      Nominal         % Difference      Measured Nominal Value            % Difference
Resistor     Value         Value                             Value        Confirmed?
Value                      Confirmed?
220         215          Yes             2.27%             214         Yes                  2.7%




3.3k        3.2k         Yes             3.03%             3.27k       Yes                  .9%



10k         9.9k         Yes             1.00%             9.97k       Yes                  .3%


470k        480k         Yes             2.13%             466k        Yes                  .85%



 Table 4. Results of the Digital Multimeter Analysis of the Nominal Values of the
 Resistors

           As can be seen through this graphical display of the data gathered in part 2, the
 nominal values of all the resistors used in the experiment were verified. This verification
 can be issued through the use of either the calculated % difference or the measured value
 because they are both measurements of the deviation in the nominal value from the actual
 measured value.

           In part 3 of the lab each member of the group measured their body/skin resistance
 from one hand to the other. By using this value and an assumed constant 10mA as a lethal
 current in Ohm’s Law the members of the group calculated the amount of voltage that
 would be lethal. The results of these calculations are shown in Table 5.
  Group Member Name             Measured Resistance       Calculated Voltage
                                                          (in V)
                                (in )

Akio Lofton                     880000                    880
Latara Hudson                   ?                         ?
Cortez Davis                    530000                    530
Matt Landry                     340000                    340
Elizabeth Buckley               ?                         ?
Bonnie Williams                 1701000                   1701
Chris Mills                     340000                    340
Domingo Megia Planet            246700                    246.7



 Table 5. Measured Body Resistance and Calculated Lethal Voltages

           From these measurements and calculations it can be seen that Ohm’s Law can be
 used to calculate a lethal voltage and that any voltages exceeding those calculations
 shown in the second column of Table 5 for any specific member of the group would be
 lethal.

           In part 4 the group measured the internal resistance of the voltmeters when the
 meter was shorted out (by connecting the negative and positive leads). Only the VOMs
 (Volt-Ohm Meters, analog) were tested in this part because the equipment required for
 testing DMMs was not available in the lab. The results of the measurements are shown in
 Table 6.
 VOM
                 /V Rating         Calculated      Measured         % Difference
                                    Resistance      Resistance

10V              20000 /V          .200M          .201M           .5%




1000V            20000 /V          20M            20.08M          .4%


Table 6. Measurements of the Internal Resistance of Laboratory Owned VOMs

Conclusions
           In part one it was acknowledged that the size of a resistor is directly proportional
to both its ability to dissipate heat, and its power rating.
           The conclusions derived from part 2 are that the nominal values of resistors in the
laboratory are well within the expected acceptable range, and that through the calculation
of an expected range the validity of an accuracy band of any resistor can be tested.
           In part 3 Ohm’s Law was shown to be useful in calculating voltages given a
resistance and current measurement, and it was concluded that a lethal voltage can be
calculated through the measurement of skin resistance and the assumption that 10mA is a
sufficiently deadly current.
           Through part 4 it was concluded that the internal resistance of a VOM could be
calculated by shorting the leads and measuring the resultant ohms. This serves also as a
means of compensating for errors introduced by the connection of a meter to an energized
circuit.

								
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