Transcript Experiment8_9

Week 5
Experiments 8 and 9
Lecture Schedule
• Next week (9/29/2011)
– Topics of lectures are:
• Design a Voltmeter
– You have two weeks to perform this lab
• Make-up Lab #1
– Pre-Lab Report due 10/4/2011
– Validation due 10/5/2011
– Post-Validation Report due 10/7/2011
• Following week (10/6/2011)
– No lab lecture
Same Circuit: Experiment 8 and 9
You should use the +5V and
+9V supplies on the ANDY
board.
You should use red wire to
bring the +5V and +9V from
the block terminals to the
breadboard.
Shared and Distributed Nodes
X and Y are distributed nodes.
The voltage is the same at all
points along the wires.
Since there is a dot where
the horizontal wire crosses
the vertical wire between
the +5V supply and R3,
the wires are connected.
Redrawing the Circuit
Labeling Nodes
Left click on the wire
attached to the node that
you want to label.
Go to Edit/Label and enter
the name of the node in the
Set Attribute Value pop-up
window and click OK.
Alternatively, just double
click on the wire and the Set
Attribute Value window will
open.
Setting Resistor Tolerance - Schematics
• Double click on the resistor
• In the pop-up window entitled Part Name,
click on the part attribute called Tolerance.
– In the window below VALUE, enter 5% and then
click Save Attr and then click OK.
• 5% will appear next to the resistor symbol.
Setting Resistor Tolerance - Capture
• Double click on a resistor, which launched a
pop-up window entitled Property Editor.
– Change the entry after Filtered by: to <Current
Properties> if not already set to this.
– Scroll across the properties until you find
TOLERANCE.
• Type 5% into the window below TOLERANCE and then
close the pop-up window.
For all Pspice Programs
• If you make the change to the TOLERANCE on
the first resistor that you place in the circuit
and then copy the resistor to place the other
resistors into the circuit, you only need to
modify the TOLERANCE of the resistors once.
• If you place all of the resistors into the circuit
before changing the properties, you will need
to click on each resistor and enter ‘5%’ into
TOLERANCE.
To Find How PSpice has Labeled Nodes
• Open a Netlist
– This is created automatically when you run a
simulation. You can generate it before running a
simulation by:
– In Capture
• Select PSpice/Create Netlist
• Then select PSpice/View Netlist
– In Schematics
• Select Analysis/Create Netlist
• Then select Analysis/Examine Netlist
Netlist
• Listed are all of the
components in the circuit
• The strings starting with
an N are the number of
the nodes that the
component is attached to.
– For example, R3 is
connected to nodes
N00043 and 0 (ground).
The node N00043 is
shared with R4 and R5.
– Note that the list also
shows which of the
resistors have had the
tolerance changed.
Setting up a Monte Carlo Simulation
• Monte Carlo simulations in PSpice can be run
as either:
– a worst case analysis where the maximum
deviation from the nominal values of each
component are used in the calculations
– a statistically-driven variation from the nominal
values of the components using a bell shaped
curve for the distribution of deviations.
Monte Carlo
• Set up a Simulation Run
– You must select one of the other types of analysis first
• Click on DC Sweep
– Pick either of the voltage sources to sweep
» Make both the start and end values equal to the value of the
voltage source, pick any value for the increment, and click OK.
– Then, select Monte Carlo/Worst Case
• Enter V(node name) or V(component:node)
– Note that you will also have to put a voltage marker on to the circuit
schematic no matter what you put as the output variable
• Enter the number of runs (500 is recommended)
• In Capture, pick a random number between 1 and 32767 and
select uniform for the distribution.
– Do not unselect the Bias Point Detail
Output Plot
Finding the Thevenin Equivalent
Resistance
• There are several methods that can be used to
determine the Thevenin equivalent resistance,
RTH, of a circuit.
1. Find the open circuit voltage and short circuit
current: RTH = VOC/ISC
Also used in calculating the Load Line of a circuit,
which will be used frequently in ECE 2204 and 3204.
2. Source transformation
Norton/Thevenin Conversions - emphasized in the
lecture portion of the course.
Determine VOC
Replace R5 with an open circuit
and determine the voltage
across the nodes where R5 had
been attached (Nodes X and Y).
The polarity of VOC is not
important when calculating RTH.
However, the way you orient the
+/_ signs for VOC will determine
the direction of the short circuit
current, which will be calculated
next.
The value of VOC is the final
Thevenin equivalent voltage
source for the circuit.
Determine ISC
Replace R5 with a short circuit
and determine the current that
flows through the short circuit
between the nodes where R5
had been attached (Nodes X
and Y).
The short circuit current
should flow out of the – side
of the open circuit voltage.
RTH = VOC /ISC
The value of ISC is the final
Norton equivalent current
source for circuit.
Thevenin Equivalent Circuit
For this week’s experiment, we
will use the function generator
with constant.lib to create a d.c.
voltage for Vth, which is equal to
the open circuit voltage Voc.
Rth is:
(a) the equivalent resistance of
the circuit without the 680 W
resistor in it and with the two
voltage supplies replaced
with short circuits.
(b) equal to Voc/ Isc.
Creating Vth
• One technique is to use a voltage divider.
Source Transformations
By choosing appropriate values for R1 and R2,
the Thevenin resistor, Rth, in the final
transformation will have the same value as Rth
calculated for the circuit in Experiment 8 and 9.