Download Lab1: Resistors

Name:
Due date:
Grade:
ECE 2006 LABORATORY 1 – Rev 1.0 Jan, 2004
DIGITAL MULTIMETER
Pre-lab Calculations: None
Objectives
The learning objectives for this laboratory are to give the student the ability to:





use the digital multimeter (DMM) for resistance, voltage, and current measurements.
determine circuit resistance from voltage and current measurements.
determine digital meter accuracy from tolerance specifications.
use the resistor color code chart.
use tables for data.
References
1. Alexander and Sadiku, Fundamentals of Electric Circuits – 2nd Edition, McGrawHill, 2004
2. Color Code Chart, available in Lab.
Background
Figures. Each figure must have a descriptive title and a number. Units must be included
for all numerical values. Figures must be neat and easy to read and understand.
Data. Data is to be taken in ink. It must be clear as to what the data refers to. Do not
forget units. The use of Tables is frequently convenient.
Tables. Tables are used to present information. They must be neat and easy to read and
understand. Each Table requires a number for reference, a descriptive title, and
column headings that describe the data. Units must also be included.
Sample calculations. Sample calculations are used to demonstrate how results were
obtained. Label each sample calculation so that it is clear as to what it refers to.
Each sample calculation should include a symbol equation, a set of numerical
values, a result, and units, such as
R = V/I = 10 Volts/2 Amps = 5 Ohms
-1-
Tolerance. Accuracy is often expressed as a tolerance. A tolerance can be expressed as a
percent or in original units. For example, a 2% tolerance on 50 volts could also
be expressed as 1 volt.
DMM Accuracy. The accuracy is listed on the bottom of the meter. It is given as a
reading percent + number of least significant digits, such as (1% + 1 Digit). To
use this accuracy description, take the following steps:
1. Multiply the reading displayed on the meter by the Percent accuracy.
2. Round the result to the same number of significant digits as the reading
orginally had.
3. Take the result of step 2 and add the Digit value in the least significant
column.
As an example, a meter that reads 0.505 and has a tolerance of (3% + 2 Digits)
actually has a tolerance of:
0.505 * 0.03 = 0.01515  0.015 (after rounding)
(0.015 + .002) = .O17 = 3.4%
the actual value is between .483 and .517.
Whatever the meter displays is a place of accuracy, even if the number displayed
is Zero (e.g. a reading of 2.600 still has 4 places of accuracy, and a Digit value
will be added in the thousandths column). It is always good lab practice to use
the most accurate meter scale when making a measurement. Measuring a 10 Volt
signal on the 20 Volt scale will be more accurate than measuring it on the 200
Volt scale.
Division Tolerances. Assuming the tolerances are less than a few percent,
V  V’
-----I  I’
V
V’
I’ V
= ---  (--- + ---)--I
V
I
I
where V' and 1' are the tolerances on the original measurement and
V’
I’ V
(--- + ---)--V
I
I
is the tolerance on V/I.
Equipment:
Digital Multimeter (DMM)
DC Power Supply
Resistor, 2200 , 4700 , 6800 , 5%
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Procedure
1. Individual resistors.
1.1
Nominal Resistance. Use the color code chart to select three 5% resistor with
nominal values of 2200 ohms, 4700 ohms, and 6800 ohms. Calculate the resistor's
tolerance (5%) and minimum and maximum resistance, and record in Table 1.
Nominal
2200 Ohms
4700 Ohms
6800 Ohms
1.2
Maximum
Ohmmeter Measurements. Measure each of these 3 resistors using the DMM as
an ohmmeter. Record these resistance measurements in Table 2. Calculate the
meter's tolerance for this measurement by following the example shown in DMM
Accuracy above. Record the result in Table 2. Calculate the minimum and
maximum circuit resistance for these ohmmeter measurements and record in
Table 2.
Meter (Measured)
2200 (
)
4700 (
)
6800 (
)
1.3
TABLE 1: Nominal Resistance
All Resistances in Ohms
Minimum

110 Ohms
2090 Ohms
TABLE 2: Measured Resistance
All Resistances in Ohms
Minimum

Maximum
Resistance using Ohm’s Law. Set up the DMM as a voltmeter. Turn on the
power supply and adjust the output to 10 volts, dc. Measure the output with the
DMM and record this voltage in Table 3. Calculate the meter's tolerance for this
voltage and record in Table 3.
Voltage -V
Meter

TABLE 3: Resistance by Ohm’s Law
Current-mA
Resistance - ohms
Meter
V/I
Min.


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Max.
1.4
Connect the circuit in Figure 1 for each resistor using the DMM as the ammeter
(AM). Record the current in Table 3. Calculate the meter's tolerance for this
current measurement and record in Table 3. From these voltage and current
measurements and their tolerances, calculate the circuit's resistance as V/I. Also,
using the formula from Division Tolerances, calculate the tolerance on this
calculated resistance and the minimum and maximum circuit resistance for these
meter readings and record in Table 3.
FIGURE 1. Current Measurement
2. Series Resistance Circuit
2.1
Connect the circuit in Figure 2.
FIGURE 2: Series Resistors
2.2
From the color code on the resistors, calculate the circuit's nominal equivalent
resistance, Req. Also calculate its tolerance at (5%), minimum and maximum
circuit resistance and record in Table 4.
Nominal - Req
Measured - Req
TABLE 4: Series Resistance
All Resistances in Ohms
Minimum


Minimum
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Maximum
Maximum
2.3
Measure the circuit's equivalent resistance using the DMM as an ohmmeter.
Record this resistance measurement in Table 4. Calculate the meter's tolerance for
this measurement and record in Table 4. Calculate the minimum and maximum
circuit resistance for this ohmmeter measurements and record in Table 4.
2.4
Using the DMM as a voltmeter, adjust the DC power supply to approximately 10
volts, measure the output and record this voltage in Table 5. Calculate the meter's
tolerance for this voltage and record in Table 5.
2.5
Connect the circuit in Figure 1, BUT substitute the series circuit in Figure 2 for R.
Use the DMM as the ammeter. Record the current in Table 5. Calculate the
meter's tolerance for this current measurement and record in Table 5. From these
voltage and current measurements and their tolerances, calculate the circuit's
resistance, the tolerance on this calculated resistance, and the minimum and
maximum circuit resistance for these meter readings and record in Table 5.
TABLE 5: Series Resistance by Ohm’s Law
Voltage -V
Meter

Current-mA
Meter

V/I
Resistance - ohms
Min.

Max.
3. Parallel Resistance Circuit
3.1
Connect the circuit in Figure 3.
FIGURE 3: Parallel Resistors
3.2
From the color code on the resistors, calculate the circuit's nominal equivalent
resistance, tolerance (5%), minimum and maximum circuit resistance, and record
in Table 6.
-5-
Nominal - Req
Measured - Req
TABLE 6: Parallel Resistance
All Resistances in Ohms
Minimum


Minimum
Maximum
Maximum
3.3
Measure the circuit's equivalent resistance using the DMM as an ohmmeter.
Record this resistance measurement in Table 6. Calculate the meter's tolerance for
this measurement and record in Table 6. Calculate the minimum and maximum
circuit resistance for this ohmmeter measurements and record in Table 6.
3.4
Using the DMM as a voltmeter, adjust the DC power supply to approximately 10
volts, measure and record this voltage in Table 7. Calculate the meter's tolerance
for this voltage and record in Table 7.
Voltage -V
Meter

3.5
TABLE 7: Parallel Resistance by Ohm’s Law
Current-mA
Resistance - ohms
Meter
V/I
Min.


Max.
Connect the circuit in Figure 1, BUT substitute the parallel circuit in Figure 3 for
R and use the DMM as the ammeter. Record the current in Table 7. Calculate the
meter's tolerance for this current measurement and record in Table 7. From these
voltage and current measurements and their tolerances, calculate the circuit's
resistance, the tolerance on this calculated resistance, and the minimum and
maximum circuit resistance for these meter readings and record in Table 7.
Conclusions
Which measurement technique is most accurate? (Answer in one or more complete
sentences at the end of your Lab Report.)
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SAMPLE CALCULATIONS
**Include tolerance calculations for the 4700 resistor in your Report**
TABLE 1 - NOMINAL RESISTANCE:
Nominal resistance = 4700
R
tolerance ± =
R
min =
R
max =
TABLE 2 - OHMMETER MEASUREMENTS:
Ohmmeter reading =
R
tolerance = (±)
R
min =
R
max =
TABLE 3 - RESISTANCE BY OHM’S LAW:
Voltmeter (VM) reading =
VM tolerance ± =
Ammeter (AM) reading =
AM tolerance ± =
R = V/I =
R
tolerance ± =
R
min =
R
max =
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