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EE4001 Electrical Engineering 1

Lab 02: Wheatstone Bridge

Mark Halton

Objective:

Introduce students to the operation of the Wheatstone Bridge.

Lab Prep Checklist:

In advance of the lab:

Read the lab document-focus on the circuits, formulae, procedure, and photos.

Draw circuits and write out the formulae in your dedicated lab book.

Attempt theory calculations for Circuit 1 and Circuit 2.

Run and edit the SIMetrix file for Circuit 1.

Create your own SIMetrix file for Circuit 2.

Reference the support documentation for Tinkercad and build Circuit 1 and Circuit 2.

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Equipment:

Power Supply; Breadboard; Resistors; 1k0 Potentiometer; Multimeter; Leads.

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V

V

V

V

The lab prep tasks must be completed by each student in a dedicated lab book.

There will be penalties applied to lab report grades if lab prep is not completed or insufficient.

Lab prep will provide insight into the experimental measurements you expect to record.

You must take photos of each circuit (& readings) to provide evidence of your experimental practice.

Ensure to include your Student ID in each photo./n4.

Rx

Procedure:

Using the lab equipment provided, build Circuits 1 and 2 in turn.

For each circuit, use the Multimeter to measure (set) the resistance of the potentiometer (Rx) to 1k

(as close as possible). Ensure to select the resistance (2) button on the Multimeter.

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When the resistance Rx is set, use the Multimeter to measure the voltage at point A (VA) and point

B (VB). Determine the voltage VAB = VA-VB. For Circuit 2, ensure to measure the voltage Vx.

For each circuit, also measure the currents (I, 11, 12).

Repeat these same measurements for Rx set to 7500 and then to 10500 (as close as possible).

Lastly, twist the dial of the potentiometer to set Rx to an unknown resistance value and leave it at

this value for both circuits. For each circuit, take the same voltage & current measurements as before.

Ensure all results are presented clearly in tabular format for each circuit as shown. Ensure to add an

extra column for voltage Vx for Circuit 2.

1k0

7500

10500

VA

Table: Calculated and Measured Results [Circuit_].

Theory Measured

VB

VAB

11

Theory Measured Theory Measured Theory Measured Theory

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Measured

2 of 5/nCircuit 1:

Circuit 2:

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10V

Vin

10V

OV

if VA = 0,

if R₁ R₂ R₂ = R₁

OV

1k0

RD

VAB=VA-V₂

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then

R1

VA

R₂

R₂

h

R1

VA -

1k0

RI

1k0

R₂

then Van = Vin (RR)

R+R₂

1k0

Rx

1k0

R2

1k0

Rx

Lo VB

Vx

1k0

to Va

3 of 5/nul.ie

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3 of 5

Analysis & Discussion:

With reference to Circuit 1, comment on your observations when Rx is nominally set to 1k0.

Describe what happens when the value of Rx is changed to 7500.

Describe what happens when the value of Rx is changed to 10500.

For the unknown value of Rx, describe and demonstrate how the voltage readings you take can

determine Rx.

Repeat the same steps for Circuit 2. Record and explain the different results that you obtain. In

particular, you should explain why changing the value of Rx will have an effect on the voltage Vx.

Further Considerations:

Where have Kirchoff's current and voltage laws been demonstrated?

Where have the voltage divider law and current division law been demonstrated?

How does the Wheatstone Bridge allow you to determine an unknown value of resistance?

Conclusions:

The conclusions should complete your report and should state if the objectives for the lab have been

achieved or otherwise.

Lab Reports:

All lab reports should be written in the third person.

Your lab report should be submitted as a .pdf document (not a MS Word.docx) in Brightspace.

Submission deadline is usually one week after the final group have completed this lab.