Analog Discovery Tutorial: Voltmeter Instrument
Overview
This experiment introduces the Analog Discovery’s Voltmeter instrument. Voltmeters are used
to measure voltage differences in a circuit. Since voltages are a difference in electrical potential
energy at two different points in a circuit, voltmeters generally have two terminals or leads.
When the leads are connected to two different points in a circuit, the voltmeter displays the
voltage difference between the two points.
The Voltmeter instrument can measure both constant and time-varying voltages. Constant
voltages are referred to as DC voltages (DC stands for direct current). Voltages that change
with time are presented in terms of their RMS1 levels.
When you finish this lab, you should be able to:
•
Use the Analog Discovery Voltmeter to measure voltages in a circuit.
•
Explain how the assumed polarity of the voltage corresponds to the sign of the voltage
value.
Lab Procedures:
The circuit for this lab has already been constructed in the Voltage Instrument tutorial, we will
simply add a voltage measurement to the circuit. Before beginning this lab, turn power to your
circuit OFF.
A. Voltage measurement connections
1. Connect 1+ (orange wire) to diode’s
anode
2. Connect 1- (orange wire with white
stripe) to diode’s cathode
3. Open the Voltage Instrument (if it is
not open already) and turn V+ ON.
1
RMS stands for Root-Mean-Square. It is a way of representing a time-varying voltage in terms of a constant
voltage with the same power. It’s kind of tricky, and we won’t worry about it here.
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©2015, Tim Hanshaw
Analog Discovery Tutorial: Voltmeter Instrument
B. Open Voltmeter instrument
1. Open WaveForms to view main
window
2. Click on More Instruments icon
and click on Voltmeter in the
resulting drop-down menu.
C. Voltmeter instrument
1. Channel 1 DC
voltage
1. The voltage across the diode will
displayed under “Channel 1”
Exercises:
1. Reverse the polarity on your voltage measurement and record the measured
voltage. Comment on why the measurement changes as it does.
Hint: “Reversing the polarity” means to just interchange the voltmeter terminals
(connect the 1+ terminal to the cathode and the 1- terminal to the anode). The effect
of this is to reverse the sign convention of your measurement, which simply changes
the sign on the voltage.
2. Use channel 2 of the Voltmeter to measure the voltage across the resistor (the
blue wire and blue with white stripe wire). Set the polarity of your measurement
such that the assumed positive voltage is at the V+ connection, and the assumed
negative voltage is at the diode’s anode. Record the voltage you measure.
3. Add the voltages across the resistor and the voltage across the diode. Comment
on this total voltage relative to the voltage difference being applied to the circuit.
Hint: Use the original polarity of the diode voltage (when the anode is assumed to be
at the higher voltage).
2
©2015, Tim Hanshaw