from IPython.core.display import HTML
def set_width(width):
display(HTML(f"""<style>
.container {{ width:{width}% !important;
min-width:800px !important; margin: 0 auto}}
.jp-Cell {{ width:{width}% !important;
min-width:800px !important; margin: 0 auto}} </style>"""))
# Set container width to X% of the fullscreen
set_width(50)
1A: Digital multimeter + voltage divider#
Learning goal: understand how to use the DMM, how it behaves as part of a (voltage divider) circuit, and what its limitations are.
In each assignment the estimated time you will spend per part is given. If you spend much more time than that, it is a clear sign to ask for help sooner.
Structure + Timing of this experiment:
30 (10+10+10+0) min Background+Anticipate+Simulate : per person. This is homework: finish it before the 4 hours practicum session
55 (10+30+15) min implement & investigate: with partner (group of 2)
10 min compare&conclude : with group of 4 (per table)
Background#
⏳ Estimated time: 10 min
During this practical session, you will use a power supply, testboard, and two digital multimeters: a handheld one, and one in the caddie (do not take this Agilent DMM out of the caddie!!). Spend some time getting familiar with these devices. Ask the TAs if you have doubts.
Have a look at the individual intros:
Anticipate 1: Which voltage will the DMM measure over R2?#
⏳ Estimated time: 10 min
If the DMM measures the voltage over R2 in the image below, with R1=R2, predict:
which voltage over R2 will be measured, for increasing resistor values (both resistors being either 10 Ω, or 1 kΩ, 10 MΩ)?
Watch the following movie clip for an explanation on the voltage divider
https://www.youtube.com/watch?v=RSAVxhfckII
### TO DO ="your answer to predict 1&2"
Anticipate 2: Which setting to use on the DMM for max accuracy#
⏳ Estimated time: 10 min
The formula for the accuracy of the 5½ digit DMM is specified as ±(0.025% + 0.005%) = ±(reading%+ range%) by the manufacturer.
Calculate the accuracy for a measurement of 1.2 V on a 2V and 20 V range
Explain which range is prefered for optimally measuring 1.2V.
Note: the 1.2V is the reading, which is smaller than the 2 or 20 V range.
For a 2V range measured with a 3½ digit DMM, the maximum is 1.999 V, the minimum is 0.001 V.
For a 20 V range measured with a 3½ digit DMM, the maximum is 19.99 V, the minimum is 0.01 V.
For each range with the same number of digits, you have a different number of digits behind the decimal point.
ℹ️ Hint
You’ll find these hints throughout the practicals. You can use them to check whether you are on the right track, and for troubleshooting the more common issues.
For 1.2V, the accuracy is 0.4 mV. (± 0.025% * 1.2+0.005% * 2V)
Please note:
not all exercises will be checked/evaluated with the TA, only a selection
the TA will only check you off after all questions are evaluated (see the section EVALUATE at the end of the notebook)
you can always ask help from a TA, but before you do, discuss with your direct neighbor (groups of 4); learn from each other.
## accuracy 1.2V in 2V range is
# accuracy 1.2V in 20V range is
# better to measure in the .... range because ....
### TO DO: 'explain which range gives you a better accuracy'
Simulate#
⏳ Estimated time: 0 min
You will have to learn how to simulate in LTSpice, and will learn this in a later assignment.
Implement 1: Discuss predictions#
⏳ Estimated time: 10 min
Discuss your predictions with your partner.
If they don’t agree: find differences, and try to resolve. You may ask your TA for help, always.
Below we continue with the detailed steps for building and measuring the voltage divider. If you want a quick overview, feel free to watch the following movie clip.
Implement&investigate 2: Build a voltage divider with R1&R2#
⏳ Estimated time: 30 min
The goal is to find out how voltage meters can influence their own measurement. To do this you have to build the following circuit on test board 1.
Person1: Connect the power supply with the resistors on the testboard#
Try to think by yourself which connections have to be made.
ℹ️ Dropdown Hint: If you are not sure what to do click here
Place testboard 1 at your table.
Connect a red wire in the red socket, and a black wire in the black socket
Place R1&R2 in series, by connecting the right pins with a small red wire.
Connect to the power supply:
without power on, adapt the source to output 5V
put the red and black wire in the correct ports
turn on the power output, just before measuring
Person2: Connect the caddies’ DMM as current meter#
After reading the intro notebook on DMM’s you know how to connect a current meter:
ℹ️ Dropdown Hint
replace the small red wire between R1 and R2 with the DMM in current meter mode.
Switch on the DMM, set the measurement to Idc (DC current)
Measuring current should be done carefully since the DMM is part of the circuit.
A common mistake is to leave the cables or test leads in the current input terminals and measure voltage.
Remember that the current terminals are connected to a very low resistance (Shunt resistance).
When connected in parallel to your circuit, high current will flow through the DMM.
This can damage both the multimeter and the circuit.
If you are not sure about how to connect your multimeter, please ask one of the TAs.
ℹ️ Hint You can touch the metal part of the resistor to measure above R2 as metal is conductive. The exposed part of pin already in U1 is also metal.
Person2: Connect the handheld DMM as voltage meter.#
Now use the handheld DMM to measure the voltage across R2
ℹ️ Dropdown Hint
Find another set of wires with testpins.
Place the handheld DMM as voltage meter, parallel to R2
Turn the knob of the handheld to Vdc (or V with a horizontal flat line)
Upload your drawing of the meters (or photograph of your circuit+measurement pins) below
To upload the picture, run the first cell of code. Below it, “Upload” button will appear.
Click on it and choose the right file. Then run the second cell of code
from ipywidgets import FileUpload
from IPython.display import Image
import os
upload=FileUpload()
upload
file_name="1A_1_VImeters.jpg"
if upload.value!={}:
with open(file_name,"wb") as f:
try: f.write(upload.data[-1]) # python 3.7 Kernel code, not working on Vocareum
except: f.write(upload.value[-1]["content"]) # python 3.8 Kernel code, works on Vocareum if you change the kernel
Image(filename=file_name, width="50%")
Implement&investigate 3: Measure current and voltage of the voltage divider#
⏳ Estimated time: 15 min
Time to measure the voltage and current using appropiate settings on the DMM(think of your answer to Anticipate 2)
You can use the table below to keep track of your measurements
Resistor |
Voltage (V) |
Current (mA) |
|---|---|---|
R2 |
- |
- |
R4 |
- |
- |
R6 |
- |
- |
What do you notice about resistors R1 and R2?
ℹ️ Hint do they dissipate energy in some way?
ℹ️ Hint holding your hand closeby is enough. Make sure to only touch the casing, not the metal
In the cell below:
Is the current through the resistor dangerous? Look it up!
## TO DO= what do you notice about R1 and R2?
Compare & Conclude: per group of 4#
⏳ Estimated time: 10 min
Wait till all (4) group members finish their measurements, please help each other!
Compare your results with your other group members.
If your results do not agree, or your results are not in line with your predictions, then work with your group members to find out likely sources of discrepancies. Ask a TA for assistance to help you identify your problem.
If your results agree, and are in line with all predictions, then talk to a TA and get checked off
to be checked off by a TA:
Which setting of the DMM is most accurate (PREDICT2)
Explain the odd measured voltage, both qualitatively and quantitatively?
exit card:
Write a brief abstract on what you learned (conclusion, useful graph),
Which troubleshooting skills do you want to remember for next sessions,
Which code do you copy for use in next sessions,
How do you think this notebook could be improved
# 1A digital multimeter
### TO DO="1.which setting is most accurate (predict2) "
### TO DO="2.explain the odd measured voltage"
### TO DO="3a. abstract"
### TO DO="3b. troubleshooting"
### TO DO="3c. code?"
### TO DO="4. what changes would you suggest?"
If you got stuck during the measurement, at the end of the lab assignment we offer you a movie clip with our recorded efforts in the lab. If you were successfull with measuring, then skip this movie clip