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MultiSIM – Lab #7
Student Name ______________________
Circuit A
The resistance of a Voltage Controlled Resistor (VCR) changes linearly as a function of the
voltage. Its resistance is dependent on a pre-determined voltage. Dependent sources are used
for circuit analysis but are not physical devices, thus are not available to be purchased in an
electronics parts catalogue. They are used with other resistive components to simulate active
device models.
1. The Voltage Controlled Resistor is adjusted to 10 ohms/Volt. This means that for every volt
measured across R3, the VCR will exhibit 10 ohms. Run the simulation by pressing the Run
Simulation switch or selecting Simulate/Run from the menu.
2. The current through the VCR is shown by the I2 indicator. The voltage across the VCR is
measured by the V1 meter and is dependent on the voltage across R3. Calculate the resistance
of the VCR. Record your result.
VCR resistance = _____________
3. Double-click on the VCR to change its setting to 60 ohms/volt. Run the simulation again and
note the difference in the voltages and currents around the circuit. Calculate the resistance of the
VCR. Record your result.
VCR resistance = _____________
4. Comment on your results.
Circuit B
Circuit B makes use of two different transducers. Transducers convert energy from one form to
another. As you will determine, the sensing and control resistor will alter its resistance with
changes in temperature. You can alter the temperature by depressing the letter "T" on your
keyboard. The lower case "t" will increase the temperature of the component and upper case "T"
will decrease its temperature.
5. Observing Circuit B, run the simulation by pressing the switch in the upper right corner of the
task bar or selecting Simulate/Run from the menu. Note the behavior of the Infrared Emitting
Diode.
Explain your results.
_____________________________________________________________________________
________
Note the voltage reading on the voltage indicator. Highlight the sensing and control resistor by
left-clicking on it and increase its temperature by pressing "T" a few times.
What happens to the voltage across the resistor?
___________________________________________
Explain what is happening in terms of the resistance.
________________________________________
Decrease its temperature below 35 degrees celsius.
What happens to the voltage?
___________________________________________________________
Explain your results.
___________________________________________________________________
_____________________________________________________________________________
+
0.000
V
1kohm
R1
I2
+
0.000
A
-
+
50V
-
0.000
V
V1
10 Ohms/V
+
200ohm
R3
-
1kohm
R2
0.000
+
A
Circuit A
42.000
1kOhm
120 V
60 Hz
0Deg
Key = T
Circuit B
+
-
0.000
V
0.000
V