Name
Section
The Proper Use of the Digital Multi-meter in the Measurement of DC Volts
Warning: Failure to follow instructions may lead to injury or equipment damage.
No Drinks or Water Bottles Permitted on any Lab Tables during these activities.
Activity I A digital multi-meter and a variety of batteries of various size and
voltage values will be made available for student groups to measure.
Practice the measurement of DC voltage of different batteries using the DC
voltage settings on the multi-meter.
Measure and record the value for at least six different batteries according to
the directions below.
Identify a battery with about 1.5 volt DC output and set it aside for later use.
Record your results in table A.
Activity II Hook up the variable DC power supply in the lab table using the red
and black cables provided. Be sure to use the correct DC inputs on the power
panel. Before turning on the dc power switch, carefully turn the variable power
dial completely to the left and set it to zero. Turn the power switch on and
determine if the power supply is at zero volts to begin. Gently turn the dial one
full turn and measure the voltage at one full turn and record this in table B. Using
the multi-meter as a DC voltmeter measure the voltage output of the variable
power supply in increments of “full turns” of the dial up to 10 full turns.
Record the results in the table B below.
Use care when turning the dial of the variable voltage supply.
The power units need to be used in future labs and can be replaced quickly.
Be careful not to injure the power units. Turn the dial slowly for best results.
Activity III Use a battery with no more than 1.5 volts dc and the single wire and the
flashlight bulb provided to create the simplest circuit needed to “light a bulb”.
Once this has been achieved, draw a diagram of the circuit using the symbols found
in the Physics Reference Table of a battery, a bulb and conducting wire. Be sure your
illustration of the circuit shows the voltage of the battery used and the bulb lit up.
Questions
1. What is the meaning of a negative sign when measuring a DC voltage
when using the multi-meter? What is the plus sign an indication of?
2. Explain what occurs when a light bulb burns out. What MUST occur for
the flashlight bulb to light up?
Table A batteries
V 1 = __________________ v
V 2 = __________________ v
V 3 = __________________ v
V 4 = __________________ v
V 5 = __________________ v
V 6 = __________________ v
Table B Variable “10 turn” DC power supply
lab table # _____ power unit position ________ Room 2 E ____
0 turn
V0 = ___________ v
1 turn
V1 = ___________ v
2 turns
V2 = ___________ v
3 turns
V3 = ___________ v
4 turns
V4 = ___________ v
5 turns
V5 = ___________ v
6 turns
V6 = ___________ v
7 turns
V7 = ___________ v
8 turns
V8 = ___________ v
9 turns
V9 = ___________ v
10 turns
V10 = ___________ v
Maximum output voltage = ___________ v
Make a graph of the voltage output per number of full turns of the table
power supply output.
Determine the slope of the best fit line using proper units.
Name
section
Lab on Electricity: The Proper Use of the Digital Multi-meter
The multi-meter is a versatile tool and can be used to measure DC voltages
and DC currents over a wide range of values. To become familiar with this
useful electrical device, look at the inputs for the measurement probes. The
probes are color coded for easy use. The multi-meter is also labeled for
correct use. Look at the various setting and functions of the multi-meter.
The black probe lead is inserted into the common COM input.
To begin insert the red probe lead to measure DC voltage into the VΩ input.
Determination of DC voltages using the multi-meter.
To measure the output voltage of an unknown battery, begin by setting up a
multi-meter to perform a DC voltage measurement.
1. Connect red test lead to VΩ input connector and black test lead to COM
input connector.
2. Set Function/Range switch to the desired DC and V position.
* If the voltage to be measured is NOT known, set the range switch to the
highest value to begin. Reset voltage range downward until a reading is
obtained.
3. Turn off power to the device or circuit being tested for safety.
4. Connect test leads to the device or circuit to be measured.
5. Turn on power to the device or circuit being measured.
The voltage value will appear on the digital display (plus or minus polarity).
6. Turn off power to the device or circuit being tested prior to disconnecting
the test leads.
Measure and label the DC voltages of the batteries provided.
Determine which battery has a voltage output of no more than 1.6 V and no
less than 1.3 V.
With the wire and bulb provided, using a battery with a voltage of no more
than 1.5 V, light the flashlight bulb.
After the bulb lights, draw a circuit diagram of this simple circuit using the
symbols given in the reference table.
II Determination of DC current using the multi-meter.
The instructions that follow prepare the multi-meter to measure DC current.
1. Connect red test lead to the mA input connector for current measurements
up to 200mA. Connect the red test lead to the 10A input connector for
currents greater than 200mA.
Connect black lead to the COM input connector.
2. Set Function/Range switch to desired DC and A position. If the current is
NOT known, set the range switch to the highest range to begin.
3. Turn off power to the device or circuit to be tested and discharge all
capacitors for safety.
4. Make a break to open the circuit in which the current is to be measured.
Now securely connect the test leads in series with the load in which the
current is to be measured. Current passes through the ammeter and the load
when the current is measured.
5. Turn on the power to the circuit being tested.
6. Read the value of the DC current on the digital display.
Reset the range if necessary until an accurate reading is obtained.
7. Turn off all power to the circuit being tested and discharge all capacitors
for safety.
8. Disconnect the test leads of the ammeter from the circuit and reconnect
the break in the circuit where current was being tested.
Measure the current used by the bulb when lit.
Record the DC current measured here. I = ___________________ A
Now set up and measure the power output of the DC power supply.
Plug in the power leads to the proper connections and set up a multi-meter to
measure DC voltage and the other multi-meter to measure DC current.
Record the power output of the table voltage and current here.
Voltage = ________________ V
Current = __________________ A