Download Lab 6

David Gitz
23-July-07
ECE 235-Lab 6
Introduction: To examine the properties of First Order R-L and R-C Circuits. 2
Experimental Methods are used, Method 1 with a Oscilloscope and Function Generator,
and Method 2 using PSPICE.
7a. R-C Circuit Results (See Graphs marked Page 1 and 2)
The step response of a R-C Circuit is given by the Discharge portion of the curve, i.e.
the negative slope; and the natural response is given by the Charging portion of the curve,
the positive slope.
7b. For the 500 Ohm CircuitTheoretically:
RC   RC  510 1F  .051mS
Experimentally (Method 1):
Time / Div  .5
Volts / Div  .5
VMAX  2.4V
(1  .6623) VMAX  .8V
t  t0  RC    .07mS
Experimentally (Method 2):
  .056mS
For the 250 Ohm CircuitTheoretically:
RC  250 1F  .025mS
Experimentally (Method 1):
Time / Div  .5
Volts / Div  .5
VMAX  2.4V
(1  .6623) VMAX  .8V
t  t0  RC    .02mS
7c.
The meaning of the time constant is how long the circuit takes to respond to the stimulus
voltage. The lower the time constant, the steeper the curve and the faster the time
response. The higher the time constant, the shallower the curve and the slower the
response time.
7d. For the 250 Ohm Circuit-
Theoretically:
RC  250 1F  .025mS
Experimentally (Method 1):
Time / Div  .5
Volts / Div  .5
VMAX  2.4V
(1  .6623) VMAX  .8V
t  t0  RC    .02mS
Experimentally (Method 2):
  .032mS
8a. R-L Circuit Results (See Graphs marked Page 3 and 4)
The step response of a R-L Circuit is given by the Charging portion of the curve, the
positive slope.; and the natural response is given by the Discharge portion of the curve,
i.e. the negative slope
8b. For the 500 Ohm CircuitTheoretically:
L
100mH
 t  t0   
 .2mS
R
500
Experimentally (Method 1):
V MAX  2.0V
V MAX  (1  .6623)  .675V
  .25mS
Experimentally (Method 2):
  .21mS
8c. The time constant for Resistor-Inductor Circuits has the same effect as the ResistorCapacitor Circuit. The higher the time constant the longer it takes to reach a discharge
state and the shallower the curve. The lower the time constant the steeper the curve and it
takes circuit less time to reach a discharge state.
8d. For the 250 Ohm CircuitL
100mH
 t  t0   
 .4mS
R
250
Experimentally (Method 1):
VMAX  1.8V
VMAX  (1  .6623)  .607V
  .3mS
Experimentally (Method 2):
  .413mS
9. An increase in either circuit yields a lower time constant for R-L Circuits and a higher
time constant for R-L Circuits, and vice versa respectively.
Conclusion: From this Lab, it was seen that either a R-L or a R-C Circuit, when excited
with a periodic voltage, will result in a periodic response given by the circuit’s
parameters. Also, the natural response and the step response are opposite for R-L and
R-C circuits.