Instrumentations Coursework: Strain Gauge Force Measurement

Assignment Part B

(Instrumentations)

Submission date (part B): Wed 13 February 2019

This is an individual course work, any sign of plagiarism will be dealt with severe penalty!

Intended Learning Outcomes: 

- analyse and calculate a force measurement using strain gauge

• analyse and calculate a temperature measurement with platinum resistance sensor
• analyse and calculate temperature measurement with 2 RTDs
• analyse pressure/Force measurement with strain gauges

Please do not re-write the questions. You are NOT supposed to submit the question but only your answer! Please write the question number and your answer only.

Your submission should include as a minimum:

- cover page

- table of contents

- main report with workings and analysis

Your report should be organised into two main sections, part A (Digital control of DC motor) and part B (Instrumentation). This course work should have a general conclusion for each part. A list of references is optional but desirable.

Part A and B has each 50% weightage of the total coursework.

This is supposed to be an INDIVIDUAL coursework. The report, including the descriptive part, all analytical and simulation analysis must be your own individual work written with your own words and clearly referenced when citations are made.

Anyone who is caught to have attempted to copy from someone else will face tough action and get immediately 0 marks for the whole subject course work.

Project Assignment

• Complete Questions 1 ~ 4 as stated in the following pages
• Write your answer in separate paper do not use the question paper!
• Indicate question number and followed by your answer.
• Attached this template as cover page, submission without cover page will not be marked!
• Deadline: 13 February 2019(zero mark if missed this deadline)

Declaration of Originality

I understand that Plagiarism is the act of taking and using the whole or any part of another person’s work and presenting it as my own without proper acknowledgement.

I understand that Plagiarism is an academic offence and if I am found to have committed or abetted the offence of plagiarism in relation to this submitted work, disciplinary action will be enforced.

Refer to Figure Q1 below. Two strain gauges are applied to measure the force applied on the steel bar shown in Figure Q1. All resistance of resistors R₃, R₄ and the unstressed strain gauges R₁ and R₂ are 120 ?. Poisson’s ratio is 0.5. The steel bar has a diameter of 40 mm and the Young modulus of the steel bar is 9.37 x 10¹⁰ N/m².

1. Determine the output voltage V_OUTof the bridge when a load of 50 kN is applied? [4 marks]
2. Determine the sensitivity of the measurement? [2 marks]
3. Determine the output voltage V_OUTwhen the strain gauge R₁is damaged such that R₁ is short-circuited? [2 marks]
4. Determine the output voltage V_OUTwhen the strain gauge R₁is damaged such that R₁ is open circuit? [2 marks]

A Platinum resistance sensor (RTD) has a resistance of 100 ? at ambient temperature of 0⁰ C and a temperature coefficient of resistance ? = 4 x 10^-3 ? / ⁰C. This RTD is incorporated at position R1 in the wheat stone bridge set up in Figure Q2.

The ratio of resistance   100

1. Determine the value of resistance R4 such that the output voltage V_OUTis  0 Volt when ambient temperature is 0⁰ C. [4 marks]

2. Determine the required supply voltage V₁such that the output voltage V_OUT=100 mV when ambient temperature T=100⁰C? [4 marks]

3. Determine the measurement sensitivity?

 

The figure Q3 below show a diagram of wheat-stone bridge with two fixed resistors on the left branch and two temperature sensors (temperature dependant resistors/RTD) on the right branch, R_Therm1 and R_Therm2. Their resistances in Ohms are given as function of temperature T in degree Celsius (⁰C) as stated here:

R_Therm1 = R₁ (1+?₁T) with ?₁ = 0.01/ ⁰C and R₁ = 2 k?

R_Therm2 = R₂ (1+?₂T) with ?₂ = - 0.02/ ⁰C and R₂ = 1 k?

1. Derive the output voltage V_Oas a function of temperature T, meaning determine the output voltage V_O= f(T). [3 marks]
2. At which temperature is the bridge balanced? [2 marks]
3. Determine the output voltage V_Owhen T= -10⁰ C and when T= 25⁰C. [2 marks]

1. Determine the sensitivity of measurement? [1 mark]
2. Assume T=100⁰C, what will be V_O? Define the feasible range and span of temperatures that can be measured by this circuit?

A strain gauge with a gauge factor GF=2, is mounted on a rectangular steel bar (with Young modulus E= 200 x 10⁶ kN/m²) as shown in Figure Q4a below.

The steel bar is 3 cm wide and 1 cm high and it is subjected to a tensile Force of F=30 kN. It is a symmetrical bridge.

1. Determine the resistance change of the strain gauge if the unstressed resistance (no axial load) is 120 ?. [4 marks]

2. Suggest how can the output voltage E_Ocan be increased by factor 2 and even factor 4 with additional strain gauges of the same specifications. Determine E_Owith 1, 2 or 4 strain gauges.

Draw how the strain gauges are being placed on the steel bar and how each strain gauge on the steel bar is connected to various resistor position in the wheat stone bridge

1. To bring the bridge output voltage to the required voltage range, an instrumentation amplifier is being applied (see Figure Q4b). State the advantage of using this IA in this application. [3 marks]