Operational amplifiers
•Notch
•Image credit: http://assets.head-fi.org/6/64/64a5fa3c_14-8DIP.jpg
•Pin 8
•Pin 4
•Image credit:
http://www.facstaff.bucknell.edu/mastascu/elessonsHTML/OpAmps/OpAmp2A0
4.gif
•
•Pin 1
•The golden rules of ―op-amps‖:
•1. The output (6) seeks to make the two input voltages the same (2 and 3).
Another way to say it: For frequencies within the response of the op-amp, pins 2 and 3 will
be the same voltage.
•2. No current flows into the op-amp at the inputs (2 and 3)
Uses are many!
• You will see at least one common use in
your homework and Instrumentation Lab:
Instrumentation Lab
• Understand how instrumentation impacts
what you can (and cannot) measure
• How to use analog and digital
instrumentation
• How to use LabView
Objectives
• Identify uses of lab equipment.
• Be able to use cables and connect equipment.
• Become familiar with using the basic analog
instruments for engineering.
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DC Power Supply
Multi-Meter
Function Generator
Frequency Counter
Oscilloscope
What are analog instruments?
• Instruments that operate using continuous
signals
– ―Analog‖ refers to the fact that the signal
represents some other quantity
• The pressure transducer voltage output is analogous to
the pressure signal on the cylinder.
• Examples:
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–
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Most sensors and transducers
Variable power supplies
Function generators
Voltmeters, ammeters, ohmmeters, multimeters
Benchtop oscilloscopes
Analog instruments in practice
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•
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Power supplies
Multi-meters
Function generators
Frequency counters
Oscilloscopes
Amplifiers
Cables and Connectors
Types of connectors
•Banana: Good for DC
power/signals. Easily ―daisy chain‖.
•BNC (Bayonet Neill-Concelman):
Good for AC signals up to radio
frequencies
•Alligator clip: Temporary
connection for exposed conductors
•Probe tip: Look at points in circuits
using a multi-meter or oscilloscope
•Clipping probe: Clip to circuit
components or exposed wire
conductors for multi-meter or
oscilloscope measurements
•http://cn.digikey.com/1/3/index11.html
Types of cables
•Single conductor
•Photo credit: http://media.digikey.com/photos/General%20Cable%20Photos/HOOKUP%20SOLID%20BLUE.JPG
•Multi-conductor: bundled for cable
management/protection
•Photo credit: http://www.midsouthcable.com/MonthlyWireSpecials.htm
•Shielded: Intended
to reduce radio
frequency
interference (RFI)
•Photo credit:
http://www.computercablestore.com/1000FT_RS_232_Shielded_Ca_PID
30.aspx
•Co-axial: special case of a shielded cable:
Ground connection is woven around an
insulated signal cable. Best for radio
•Photo credit:
http://www.computercablestore.com/1000ft_Precision_Video_RG_PID1402.as
Electronics terminology
• “Short”: A short circuit—a conductive bridge between the
high and low voltages of a circuit. We wish to avoid shorts!
• Open circuit: No path between the high and low voltages of a
supply
• Continuity: the ability for current to flow through a circuit—a
continuous current path.
• Ground: The voltage of earth. A safe reference voltage when
used properly.
• “Bias”: Applying a DC voltage to an AC signal. Equivalent to
mean or ―DC‖ voltage
• Polarity: Distinguishing positive and negative voltage leads.
The greater voltage is positive; the lesser, negative
• “Gain”: The amplification factor of an active electronics
component: Vout/Vin
• Jumper: A short piece of conductive wire used to connect
points in circuits
DC Power Supply
• Produces
positive,
negative and
multiple voltages
for test
conditions.
• Can be regulated
for constant
current or
constant voltage
Uses for DC Power
•
•
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•
Battery Charging
Computer Power
Attitude Indicator
Others?
Uses for DC Power
• Pressure Sensors
• Others?
7 hole probe transducer (+/- 15 VDC)
7 hole probe transducer (24 VDC)
Gas Injection Pressure (18-30 VDC)
DC Power Supply Types
• Several industry standard DC
voltage sources
– Cell phone chargers (Droid
X takes 5.1V)
– 6V sealed lead acid
Batteries.
– 12V is common in cars and
small airplanes.
– 24V for newer light
airplanes, industrial control
system voltage, electric
boat motors.
– Other examples?
• More that 50 volts requires
special safety consideration
like personal protective
equipment and special
training.
(Space Systems Simulation Laboratory)
DC Power Supply
•―Benchtop‖ power supply
•Easily adapts to applications
•Provides DC voltage source.
• Tektronix CPS250 has one fixed 5 V and
• Two variable 0-20 V outputs.
Fixed 5V, Ground Referenced
•Absolute
voltage will
―float‖ when
not
referenced.
•A floating
condition
should be
avoided in
most cases
Variable Output
• Analog meters indicate the voltage and current output of
each variable supply (A or B individually). Use the
switch to select the desired source to monitor.
Variable Output
• Variable outputs are controlled by the
voltage and current knobs.
• Voltage is maintained until the current
draw in the load reaches the set-point
of the current control.
• The current control appears to do
nothing until a load is present.
Variable Output, Ground
Referenced
Multi-Meter
•
•
•
•
Used to make measurements
Voltage across components (RMS or AC)
Current through components (RMS or AC)
Caution:
• Disconnect power to the circuit before measuring resistance!
• Beware connecting high voltage/current signals to the multi-meter
Multi-Meter
• Measures
– Resistance
– Voltage (AC and DC)
– Current (AC and DC)
• AC voltage is often
called RMS.
Multi-meter Range settings
• When measuring voltage, start with a range known
higher than the voltage to be measured and lower the
scale until the best precision is obtained without going
over range.
Start Here,
Then try lower.
Measuring resistance
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•
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Continuity Tests
To measure lead resistance, connect test leads together.
Resistance measurements must be out of circuit.
Google ―resistor color codes‖ for calculators.
– http://www.dannyg.com/examples/res2/resistor.htm
– http://samengstrom.com/elec/resistor/
Measuring resistance
Resistance Color Code
Measuring resistance
Blue
Gray
Brown
680Ω 5%
Gold
Measuring resistance
• Notice the operation of the range switches.
– The number for the switch is the maximum that
setting can display.
– The multiplier is added to the result in the display.
Example: 20K setting with 8.20 in the display
indicates an 8.2K Ohm or 8200 Ohm resistor.
Resistance Ranges
DC Voltage Measurements
• Now set up the
power supply to
give 12V.
• Select a range
higher than
expected.
• Measuring a
higher voltage
on a low setting
can damage a
meter!
DC Voltage Measurements
• Use the multi-meter
to measure the
voltage.
• How do the multimeter results
compare to the
indication of the
power supply
meters?
– Some can be pretty
accurate and some
off several volts.
– Which one is
accurate?
DC Voltage Measurements
• Calculate the
value of the
resistor based
on the voltage
and current of
the power
supply.
• Calculate the
power being
consumed by
the resistor.
DC Current Measurements
• The setting on the meter for current is A, for
Amps, the standard unit for current.
• Current measurements are possible, but not
common.
– Since all the current must pass through the
measuring device, the meter or input device will
influence the circuit more than making voltage
measurements.
– An alternative would be to measure the voltage of a
known resistance and calculate current.
DC Current Measurements
• Most DAQ inputs are voltage only. Current input devices
are available but mainly for industrial control
applications.
• Don’t try to measure current unless you have calculated
the approximate current at the point of measurement.
• Calculate the power requirement of the component in the
circuit to ensure it is suitable for the test procedure.
DC Current Measurements
Power Supply Modes
• Connect power supplies A and B in parallel using the
cables, then do the same using the mode switch.
• Try the same for series. Set up a 30 Volt source using
the multi-meter to measure the voltage.
• Understand the connection of the independent power
supplies before using the mode switch.
Series Voltage Connection
Parallel Voltage Connection
Negative DC Voltage
Multiple voltages
• Often signal amplifiers require +15 and -15 volt sources.
• Do this by connecting two variable supplies together and
referencing the center to ground.
• Voltage measurements are usually made relative to
ground.
• Connect the common (black) lead of the meter to
ground and measure the other two voltages.
Multiple voltages, +/- 15
Oscilloscope
Oscilloscope for DC
Objectives
• Oscilloscope
– Hook up and obtain a visual representation of
a signal.
– Measure DC Voltages
– Use scaling properly
Oscilloscope
Y
X
• Tektronix TDS 2002B has features common to most all
scopes.
• The two most important controls are amplitude
corresponding to the Y value and,
• Time base which corresponds to the X value.
Oscilloscope
Position Controls
• Once the scope is on and some part of the trace is
visible, adjust the amplitude and position until the trace is
in the screen, then adjust the time base to get the best
representation of the signal.
• For DC measurement, time base is irrelative, so set it to
1 or 2 mSec/div.
• Then adjust the amplitude so the measured signal will fit
on the screen.
Oscilloscope (6.1)
Y
X
• Basic Setup
– Locate the trace using the position control, the amplitude and the
time base. Beam find may be helpful here also.
– The mode should be in auto most of the time. Once the scope is
set up, other modes may be useful.
• The trace plots the voltage like an X-Y plot with time on
the X position.
Oscilloscope (6.1)
One Division
=1cm
• The division lines do not indicate the origin of the plot.
The origin is adjustable using the position controls.
• The divisions and corresponding settings determine the
values of the plotted signal.
Set up the Scope
• Vertical
– Select CH1.
– VOLTS/DIV to 2
– Coupling to DC,
– Attenuation to 1x
Set up the Scope
• Settings:
– Trigger
• Slope in upper setting
• Mode to Auto
– Horizontal
• SECS/DIV to 5ms/div
Set up the Scope
• Settings:
– Adjust Contrast as required DISPLAY MENU.
– Position trace using Horizontal and Vertical Position
controls.
Connect Signals (6.2)
• Using a double banana
connector and BNC
cable, connect power
supply to the CH1 BNC
input below the
VOLTS/DIV control.
• For now do not use a
ground reference
jumper on the power
supply.
Connect Signals (6.2)
• Set supply to around 6
volts.
• Be certain of the
connection using the
double banana plug.
The shield of the BNC
cable will be connected
to ground through the
scope, so only connect
it to the common point
on the power supply, in
this case, the negative
terminal.
DC Scope Measurements
• Coupling switch
– Use the GND position to find a reference zero.
– Set to DC to measure the mean and fluctuating parts.
(Fluctuating part of the power supply should be
extremely minimal.)
Vertical Scale (6.3)
• With the coupling switch set to GND, the position control
sets the origin by moving the trace up and down on the
screen. Set it on the center line of the graph.
• Place the coupling switch back to DC to read the
voltage.
• The trace should move 3 div up the display.
• With the VOLTS/DIV on 2.0, that would indicate 6 volts.
• Now vary the voltage and watch the trace move.
• We will use this technique to set up the dynamic Beam
experiment.