# 2. Basic Electrical Measurements

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Resistor Color Code
To determine the value of a given resistor look for the gold or silver tolerance
band and rotate the resistor as in the photo at Right. (Tolerance band to the
right). Look at the 1st color band and determine its color. This maybe difficult
on small or oddly colored resistors. Now look at the chart and match the &quot;1st &amp;
2nd color band&quot; color to the &quot;Digit it represents&quot;. Write this number down
Now look at the 2nd color band and match that color to the same chart. Write this number next to the 1st Digit. The Last
color band is the number you will multiply the result by. Match the 3rd color band with the chart under multiplier. This is
the number you will multiple the other 2 numbers by. Write it next to the other 2 numbers with a multiplication sign
before it. Example : 2 2 x 1,000.
To pull it all together now, simply multiply the first 2 numbers (1st number in the tens column and 2nd in the ones
column) by the Multiplier.
Example:




First color is red which is 2
Second color is black which is 0
third color is yellow which is 104 = 10,000
Tolerance is silver which is 10%
Therefore the equation is:
2 0 x 10,000 = 200,000 Ohms = 200 kΩ
Specified Range within which the actual resistance value must lie = [200 kΩ]•[&plusmn;10%] = 180kΩ  Ractual  220 kΩ
ENGR 12L
Experiment 2 Basic Electrical Measurements
Names______________________________________________
Part 1 Measuring Resistance
Figure 1. DMM and connection to measure resistance.
DMM dial should be turned to OHM position
Directions
1. Check out a Digital MultiMeter (DMM)
2. From the lead-rack, select a set of “banana Jack” lead wires; one BLACK and ONE RED. These
will serve as the input connection to the DMM and VOM.
3. From your kit pick any 4 resistors.
4. Read the color code and enter the values in the “coded” columns of Table-1. Also calculate minmax range based on the tolerance of the resistor as “coded”.
Table I – Resistors Measurements
Nominal Value
(coded)
Min-Max Range
(coded)
DMM Value
Within Spec
(Yes/No)
5. Switch the DMM dial to the OHM symbol, wire the banana leads as shown in figure 1.
6. Use the DMM to MEASURE the Values of each resistance. Record these values in Table 1,
column 3.
7. Use your measurements to make an assessment of whether the resistors are within specification
8. Place all three resistors back in their container.
Part 2 Verifying Ohm’s Law
Figure 2. Circuit for verifying Ohm’s Law.
DMM1 in DC V mode. DMM2 in DC A mode.
Directions
1. You’ll need a second DMM to measure current. Check out a Scope DVM 630 for more precise
current measurement. And another set of alligator leads
2. Take out the “bread board” from your kit, and a “load” resistor, RL, required to construct the circuit
shown in Error! Reference source not found.2. The load resistor should be between 200 Ω 500Ω
3. Vary the supply voltage as shown in Table II. At each voltage, measure the voltage across and the
current through the resistor.
4. Reduce the Data by completing the power calculations in Table III
Table III – V/I Measurements, Power Calculations – RL
5. DMM Measured Resistance of RL = _______________________
Vs,Nominal
(Volt)
Vs,Actual
IL
P = IV
P = I2R
P = V2/R
1
2
3
4
5
5. Plot the Voltage vs Current data in Matlab/Freemat. Type:
V=[ 1, 2, 3, 4, 5];
I = [ your 5 current measurements];
plot(V,I);
[Copy and Insert your plot here]
6. Calculate the “in circuit” resistance from your voltage/current curve: In Matlab type
fit = polyfit(I, V)
The resistance will be the first number in the result.
Calculated “in circuit” resistance RL = _____________________
% difference from DMM _______
Part 3 Verifying KCL and KVL
Figure 3. Circuit for measuring KCL and KVL
1. The instructor will hand you a packet of resistors, all of the same value, between 300 and 500
ohms. Pick out four of these. Verify but don’t record their value.
2. Build the circuit shown WITHOUT THE DMM at A inserted.
3. Measure the values of Vs, V1, V2, V3, V4 and enter them below
Vs
V1
4. Verify KVL by calculating:
Left Loop
Right Loop
Outer Loop
V2
V3
V4
-Vs + V1 + V2 =
-V2 – V3 + V4 =
-Vs + V1 – V3 + V4 =
5. If you are more than 0.1 V away from 0 you probably have a measurement error. Recheck your
readings and redo the calculations.
6. TURN OFF THE VOLTAGE SUPPLY and attach the COMM clip of the Scope 360 DMM to the
node marked A. Move the A end of resistor R1 to another (unoccupied) row of the breadboard.
Attach the RED V/A/Ω Lead to the R1 resistor to complete the circuit through the ammeter.
7. Measure the value of I1 and record. I1 =______________
8. TURN OFF THE SUPPLY and rewire the DVM V/A/Ω lead as shown (you do not need to move
the COM lead:
9. Measure the value of I2 and record. I2 =______________
10. TURN OFF and rewire once more in similar fashion to measure I3. I3 = _________________
11. Compute I1 + I2 + I3 = ____________________________
TURN IN PROCEDURES
Complete the tables, insert the Matlab plot, put the name of both Students doing this lab in the
indicated place. Save the lab and upload to the ENGR12L file uploader.